Sinus disease

      The diagnosis and treatment of diseases of the paranasal sinuses and conchae of horses are complicated by the large size of these structures, their complex anatomy, difficulties of access to them, and the advanced state of many diseases before diagnosis is made. In horses under 5 years of age, the maxillary sinuses are largely filled with embedded parts of the third to sixth cheek teeth (fourth premolar, first through third molars, or 108–111 and 208–211). As the reserve crowns of cheek teeth become shorter with age, the maxillary sinus enlarges and its rostral limit approaches the infraorbital foramen [
      • Hillmann D.J.
      Skull.
      ]. The position of the bony septum that divides the maxillary sinus into rostral and caudal parts is variable, but it is usually directed obliquely across the roots of the fourth and fifth cheek teeth (109,110 and 209,210) approximately 5 cm from the end of the facial crest [

      McCann JL, Dixon PM, Mayhew JG. A clinical study of the anatomy of sphenopalatine sinus. In: Proceedings of the 38th Congress of the British Equine Veterinary Association. 1999. p. 178.

      ]. The dorsal part of the septum is formed by the bulla of the ventral conchal sinus and is delicate and cribriform (Fig. 1). The rostral maxillary sinus opens into the middle nasal meatus through a slit-like passageway to the nasomaxillary opening. It communicates with the ventral conchal sinus through the conchomaxillary opening dorsal to the infraorbital canal (see Fig. 1).
      Figure thumbnail gr1
      Fig. 1Anatomy of the right paranasal sinuses and nasal passage in a transverse section through the second molar (110) as viewed from the front. 1 = frontal sinus; 2 = dorsal conchal sinus; 3 = rostral maxillary sinus; 4 = ventral conchal sinus; 5 = dorsal meatus; 6 = middle meatus; 7 = nasolacrimal duct; 8 = ventral meatus. Arrow points to opening from the rostral maxillary sinus to the middle meatus.
      The caudal maxillary sinus has a large opening caudally and medially over the infraorbital canal into the sphenopalatine sinus [
      • Hillmann D.J.
      Skull.
      ]. Because of its close relation with the brain, pituitary gland, optic chiasma, and a variety of nerves and arteries, disease in the sphenopalatine sinus could create signs referable to these structures [

      McCann JL, Dixon PM, Mayhew JG. A clinical study of the anatomy of sphenopalatine sinus. In: Proceedings of the 38th Congress of the British Equine Veterinary Association. 1999. p. 178.

      ,
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ]. The caudal maxillary sinus has a small opening medially into the middle conchal sinus; dorsally, it communicates with the frontal sinus through the large frontomaxillary opening (approximately 3 cm×4 cm oval). A slit-like passageway between the rostral edge of the frontomaxillary opening and the conchal bulla leads from the caudal maxillary sinus through the nasomaxillary opening and into the middle nasal meatus.
      The right and left frontal sinuses are separated along the midline by a complete septum. The frontal sinus has a large communication at its rostral end with the dorsal conchal sinus and thereby forms the conchofrontal sinus (see Fig. 1). The conchae (or turbinates) are delicate scrolls of bone that are attached laterally in the nasal passage and contain the conchal sinuses (see Fig. 1). The paranasal sinuses are lined by respiratory mucous membrane composed largely of pseudostratified columnar ciliated epithelium and goblet cells [
      • Hare W.C.D.
      Equine respiratory system.
      ]. Blood flow to the frontal sinus is provided largely by the ethmoidal artery, and the maxillary sinus is supplied by branches of the sphenopalatine artery. The major blood supply to the ethmoidal area is the arterial ethmoidal rete, formed from anastomosis of the internal and external ethmoidal arteries, and a minor source is the caudal nasal branch of the sphenopalatine artery [
      • Bell B.T.L.
      • Baker G.J.
      • Abbott L.C.
      • et al.
      The macroscopic vascular anatomy of the equine ethmoidal area.
      ].

      Diagnosis of sinus disease

      Most sinus diseases cause a unilateral nasal discharge, and facial distortion is the second most common clinical sign [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 1: details of horses, historical, clinical and ancillary diagnostic findings.
      ]. A bilateral discharge is rare in unilateral cases [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 1: details of horses, historical, clinical and ancillary diagnostic findings.
      ], because the source of fluid is usually rostral to the most caudal end of the nasal septum, a feature that can help to distinguish between diseases of the sinuses and those of the guttural pouches, lungs, and pharynx. Diseases of the sinuses can cause abnormal respiratory noise by impingement of medial walls of the conchae into the nasal passage, and even displacement of the nasal septum, or by extension of sinus masses into the nasal passage and pharynx. Exophthalmos may be seen with a fungal granuloma and neoplasia, and epiphora can develop in some diseases by compression of the osseous nasolacrimal duct.
      Percussion can be used to detect space-occupying material within the sinuses but is not always reliable. To percuss the sinuses, the fingers of one hand are tapped sharply against the overlying bones of the sinuses and the corresponding area on the normal side is percussed immediately afterward for comparison. An oral examination should be performed to detect dental abnormalities in horses with a suspected sinus neoplasm. Changes in peripheral blood samples are uncommon, except that the packed cell volume may be decreased in horses with chronic infections or neoplasia.

       Endoscopy of nasal passages

      Endoscopy is used to detect sinus abnormalities extending into the nasal passages and to rule out other diseases of the upper respiratory tract and guttural pouches with similar clinical signs. Special attention must be paid to the ethmoturbinates and the caudal end of the middle meatus, because blood, pus, and masses can be seen at these sites in horses with sinus disease.

       Radiography

      Diagnostic-quality radiographs of the sinuses can be taken with a portable X-ray tube, because the facial bones are thin and air within the sinuses acts as a natural contrast agent for soft tissue densities and fluid. An imaging system with a wide range of exposure latitude and photographic contrast is desirable [
      • Gibbs C.
      Dental imaging.
      ]. Rare-earth screens are now available in a wide range of speeds and details, and medium-speed and medium-detail screens are useful for most equine dental radiographs [
      • Gibbs C.
      Dental imaging.
      ]. Grids are rarely needed for equine dental radiography, because the amount of scattered radiation is relatively small, they require more exposure, and alignment can be difficult [
      • Gibbs C.
      Dental imaging.
      ].
      Lateral radiographs of the skull can be limited by image distortion caused by beam divergence, magnification, and superimposition [
      • Gibbs C.
      Dental imaging.
      ]. To improve views of tooth roots, the cassette can be held at an angle beneath the jaw on the affected side, and the beam can be directed obliquely approximately 30° to 60° in a dorsal-to-ventral direction. Sinus cavities are difficult to evaluate on dorsoventral views, because the cheek teeth and the overlying masseter muscles obscure much of the field. This view does demonstrate nasal passage involvement and impingement on or distortion of the septum, however. The ventrodorsal projection with offset mandible can be used to demonstrate low-grade periapical infection, alveolar disease, and chronic osteitis if standard oblique radiographs yield inconclusive findings [
      • Gibbs C.
      Dental imaging.
      ]. Recommended settings for lateral or lateral oblique radiographs of the equine skull are 80 kVp and 10 mA for 0.1 seconds or 20 mA for 0.06 seconds. For the dorsoventral projection, 80 kVp and 10 mA for 0.13 to 0.4 seconds or 20 mA for 0.16 to 0.2 seconds are recommended [
      • Rosenstein D.S.
      • Stick J.A.
      Diagnostic techniques in equine upper respiratory tract disease.
      ].

       Computed tomography

      The major advantage of computed tomography (CT) compared with conventional radiographs is lack of superimposition and enhanced demonstration of individual components of the skull (Fig. 2). Also, the regions of interest have high inherent radiographic contrast, and CT provides clear unobstructed images of the teeth [
      • Gibbs C.
      Dental imaging.
      ]. Disadvantages are the need for general anesthesia, specialized equipment, tables adapted for equine use, and proper positioning.
      Figure thumbnail gr2
      Fig. 2Image of the head of an American Miniature Horse obtained by computed tomography. The extent of the abscess in the frontal sinus and the dental distortion could not be seen on standard radiographs.

       Nuclear scintigraphy

      The advantages of nuclear scintigraphy compared with CT are that it can be performed in conscious animals and the equipment tends to be less expensive and more widely available [
      • Weller R.
      • Livesy L.
      • Maierl J.
      • et al.
      Comparison of radiography and scintigraphy in the diagnosis of dental disorders in the horse.
      ]. The disadvantage is potential radiation hazard, necessitating strict control of radioisotope and patient handling [
      • Weller R.
      • Livesy L.
      • Maierl J.
      • et al.
      Comparison of radiography and scintigraphy in the diagnosis of dental disorders in the horse.
      ]. In a recent study, the sensitivity of scintigraphy for dental disease was excellent and the specificity was moderate, which was the opposite of results obtained with radiography [
      • Weller R.
      • Livesy L.
      • Maierl J.
      • et al.
      Comparison of radiography and scintigraphy in the diagnosis of dental disorders in the horse.
      ]. The sensitivity and specificity were enhanced when both techniques were combined [
      • Weller R.
      • Livesy L.
      • Maierl J.
      • et al.
      Comparison of radiography and scintigraphy in the diagnosis of dental disorders in the horse.
      ].

       Centesis

      This procedure is used to sample fluid or to flush the sinuses and can be performed with the horse standing and mildly sedated. If a generalized sinus problem is suspected, a suitable site is 2.5 to 3 cm dorsal to the facial crest and the same distance rostral to the medial canthus; another site is midway between the dorsal midline and medial canthus. If only the rostral maxillary sinus is involved, the area chosen for centesis is 3 cm dorsal to the facial crest and approximately 3 cm caudal to the infraorbital foramen. The site is clipped of hair, prepared for aseptic surgery, and infiltrated with local anesthetic. A 1-cm long incision is then made through the skin and subcutaneous tissues, and a 2- to 4-mm diameter Steinmann pin attached to a Jacob's chuck is used to drill a hole through the bone. In some cases, a 16-gauge needle alone can be used to penetrate the bone. Sinus fluid is aspirated, with or without lavage, and submitted for Gram staining, cytologic examination, culture, and sensitivity testing. A large volume of fluid is then delivered by gravity into the sinus cavity, and this fluid and exudate should flow freely from the nasal passage if the nasomaxillary opening is patent. Complications of centesis are rare but include local cellulitis.

       Direct endoscopic examination

      Direct endoscopic examination is used when results of radiography and nasal endoscopy are inconclusive [
      • Ruggles A.J.
      • Ross M.W.
      • Freeman D.E.
      Endoscopic examination of normal paranasal sinuses in horses.
      ]. Sedation and local anesthesia can be used to insert an arthroscope or preferably a flexible endoscope into the sinuses to examine them directly or with a camera and monitor. The following portals are used: for the frontal sinus, 60% of the distance from midline toward the medial canthus and 0.5 cm caudal to the medial canthus; for the caudal maxillary sinus, 2 cm rostral and 2 cm ventral to the medial canthus; and for the rostral maxillary sinus, 50% of the distance from the rostral end of the facial crest to the level of the medial canthus and 1 cm ventral to a line joining the infraorbital foramen and the medial canthus [
      • Ruggles A.J.
      • Ross M.W.
      • Freeman D.E.
      Endoscopic examination of normal paranasal sinuses in horses.
      ]. Direct endoscopic examination is more useful for examining the tooth roots of the second and third upper molars in horses older than 5 years of age than it is for examining rostral teeth in younger horses. If surgery is indicated, portals should be made away from the proposed bone flap or the portal should be allowed to heal before surgery because it can predispose to fracture or necrosis of the bone flap.
      The flexible endoscope is sterilized by immersion in glutaraldehyde beforehand and then is rinsed in sterile water or saline. To make the portal, a 2.5-cm long vertical skin incision is made, the underlying periosteum is reflected, and a hole is made in the bone with a 14-mm Michele trephine. The skin can be closed, or if the sinus is infected, it can be left open to accommodate a lavage tube or allowed to heal by second intention. Rare complications are temporary periosteal reaction, cellulitis, and subcutaneous emphysema. Lesions diagnosed in this way include ethmoid hematomas in unusual sites (eg, sphenopalatine sinus) (Fig. 3, Fig. 4), sinus cysts, neoplasia, tooth root abnormalities, orbital floor fractures, neoplasia, sinusitis, and fungal infections [
      • Ruggles A.J.
      • Ross M.W.
      • Freeman D.E.
      Endoscopic examination and treatment of paranasal sinus disease in 16 horses.
      ,
      • Worster A.A.
      • Hackett R.P.
      Equine sinus endoscopy using a flexible endoscope: diagnosis and treatment of sinus disease in the standing sedated horse.
      ]. Biopsy instruments or probes (see Fig. 4) can be inserted through a second portal under endoscopic guidance, or the same portal can be enlarged with rongeurs to allow insertion of a Ferris-Smith or intervertebral rongeur alongside the endoscope. The rongeurs can then be used to remove biopsies and bone fragments or to break down the caudal bulla of the ventral conchal sinus to create a portal for insertion of the scope into the rostral maxillary sinus or ventral conchal sinus.
      Figure thumbnail gr3
      Fig. 3View of the left caudal maxillary sinus and sphenopalatine sinus obtained by direct endoscopy. Rostral is to the bottom of the view. SPS = sphenopalatine sinus; CMS = caudal maxillary sinus; IOC = infraorbital canal. Arrowheads point to the caudal edge of the frontomaxillary opening.
      Figure thumbnail gr4
      Fig. 4View of an ethmoid hematoma in the left sphenopalatine sinus obtained by direct endoscopy. The probe was inserted through a separate portal in the caudal maxillary sinus. Rostral is to the bottom of the view. CB = caudal bulla of the ventral conchal sinus. Arrowheads point to the caudal medial edge of the frontomaxillary opening.

      Diseases of the sinuses

       Sinusitis

      Primary sinusitis is caused by an upper respiratory tract infection of the paranasal sinuses, and secondary sinusitis is caused by a tooth root infection. Primary sinusitis can be seen in horses over a wide age range [
      • Lane J.G.
      • Gibbs C.
      • Meynink S.E.
      • et al.
      Radiographic examination of the facial, nasal and paranasal sinus regions of the horse: I. Indications and procedures in 235 cases.
      ], although the highest incidence is in 6-year-old horses [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 1: details of horses, historical, clinical and ancillary diagnostic findings.
      ]. Dental disease is less common in horses under 4 years of age [
      • Lane J.G.
      • Gibbs C.
      • Meynink S.E.
      • et al.
      Radiographic examination of the facial, nasal and paranasal sinus regions of the horse: I. Indications and procedures in 235 cases.
      ]. The organisms most commonly involved in primary sinusitis are Streptococcus equi and Streptococcus zooepidemicus [
      • Schumacher J.
      • Honnas C.
      • Smith B.
      Paranasal sinusitis complicated by inspissated exudate in the ventral conchal sinus.
      ], and staphylococcal granuloma (botryomycosis) is a rare cause [
      • Blackford J.T.
      • Goble D.O.
      • Henry R.W.
      • et al.
      Triangulated flap technique for nasofrontal surgery: results in 5 horses.
      ]. Inflammation and swelling in the nasal mucosa from a viral or bacterial infection could obstruct the nasomaxillary opening, block sinus drainage, and thereby predispose to or exacerbate sinusitis. Occlusion of the nasomaxillary aperture has been reported as a cause of sinusitis in young horses [
      • Schumacher J.
      • Dutton D.M.
      • Murphy D.J.
      • et al.
      Paranasal sinus surgery through a frontonasal flap in sedated, standing horses.
      ,
      • Henninger W.
      • Reifinger M.
      Einseitige Auftreibung des Gesichtsschädels durch ein okklusives Kieferhöhlenempyem bei einem Jungpferd.
      ]. Horses with Cushing's disease and glucocorticoid-producing adrenal tumors also seem predisposed to sinusitis [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 1: details of horses, historical, clinical and ancillary diagnostic findings.
      ,
      • Freeman D.E.
      • Orsini P.G.
      • Ross M.W.
      • et al.
      A large frontonasal bone flap for sinus surgery in the horse.
      ]. Primary sinusitis usually involves all the sinus cavities but can be confined to the ventral conchal sinus, where it forms an abscess that is difficult to detect on radiographs and is not readily accessible at surgery [
      • Schumacher J.
      • Honnas C.
      • Smith B.
      Paranasal sinusitis complicated by inspissated exudate in the ventral conchal sinus.
      ]. In secondary sinusitis, the teeth involved in decreasing order of frequency are the first molar (109, 209), fourth premolar (108, 208), and third premolar (107, 207); sometimes, more than one tooth may be involved. Open wounds and any destructive diseases of the sinuses can also cause secondary sinusitis.

       Clinical signs

      The most common clinical sign of primary sinusitis is a unilateral mucopurulent nasal discharge [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 1: details of horses, historical, clinical and ancillary diagnostic findings.
      ]. Bilateral nasal discharge could indicate bilateral sinusitis [
      • Coumbe K.M.
      • Jones R.D.
      • Kenward J.H.
      Bilateral sinus empyema in a 6-year-old mare.
      ]. Stertorous breathing may be evident during work or at rest. Facial distortion is less common with primary sinusitis than with secondary sinusitis, neoplasia, and sinus cysts [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 1: details of horses, historical, clinical and ancillary diagnostic findings.
      ] but can develop in the more chronic stages, especially in young horses. Epiphora may be evident with or without facial distortion [
      • Coumbe K.M.
      • Jones R.D.
      • Kenward J.H.
      Bilateral sinus empyema in a 6-year-old mare.
      ,
      • Mason B.J.E.
      Empyema of the equine paranasal sinuses.
      ]. Clinical signs of secondary sinusitis closely resemble those of primary sinusitis, except the nasal discharge may be fetid and sinus tracts can extend from the cheek teeth to the skin. Maxillary swelling and sinus tracts are more common with apical infections of the first three cheek teeth, whereas nasal discharge is more common with apical infections of caudal rather than rostral cheek teeth [
      • Dixon P.M.
      • Tremaine W.H.
      • Pickles K.
      • et al.
      Equine dental disease Part 4: a long-term study of 400 cases: apical infections of cheek teeth.
      ]. Erosion of the cribriform plate with subsequent purulent meningoencephalitis and neurologic signs is a rare complication of severe and chronic sinusitis.

       Diagnosis

      On endoscopic examination, pus may be seen draining from the nasomaxillary opening into the middle meatus (Fig. 5). On radiographs, fluid lines should be evident, and in more severe cases, contents appear mineralized [
      • Gibbs C.
      Dental imaging.
      ]. If primary sinusitis is confined to the ventral conchal sinus, radiographs may demonstrate a soft tissue density dorsal to the third to fifth cheek teeth and within the ventral conchal sinus [
      • Schumacher J.
      • Honnas C.
      • Smith B.
      Paranasal sinusitis complicated by inspissated exudate in the ventral conchal sinus.
      ,
      • De Moor Von A.
      • Verschooten F.
      Empyem und Nekrose der Nasenmuscheln beim Pferd.
      ].
      Figure thumbnail gr5
      Fig. 5Purulent material draining from the middle meatus.
      In young horses, the root apices of cheek teeth are smooth and round, but they become progressively more narrow and spicular in older horses, and the reserve crowns become progressively shorter. Eruption of a tooth is accompanied by an increase in vascularity of the tooth pulp, which is evident on radiographs as a cystic distention of the lamina dura with a smooth and regular outline [
      • Gibbs C.
      Dental imaging.
      ]. The lamina dura is a radiodense line that represents the alveolar bone and periodontal ligament interface, and the periodontal ligament appears as a radiolucent line around the tooth root.
      Signs of dental infections on lateral films are proliferative changes of osteitis characterized by localized and ill-defined areas of increased radiopacity and coarseness of bone texture overlying the affected tooth root [
      • Gibbs C.
      Dental imaging.
      ]. The radiographic signs of periapical granuloma vary, but the most consistent is an area of increased lucency around the affected apex or apices, referred to as a halo [
      • Gibbs C.
      Dental imaging.
      ,
      • Mason B.J.E.
      Empyema of the equine paranasal sinuses.
      ]. The zone of osteolysis is usually surrounded by sclerotic bone. Loss of the lamina dura is a less reliable indicator of pathologic change, because this structure is an inconsistent feature on radiographs of normal horses [
      • Gibbs C.
      Dental imaging.
      ]. In many cases, the roots may be partly destroyed or distorted, increased in density, and “clubbed” (cement deposition) [
      • Gibbs C.
      Dental imaging.
      ,
      • Baker G.J.
      Some aspects of equine dental radiology.
      ]. A granular pattern around a root can be caused by food material and gas bubbles, and fluid lines and gas-fluid interfaces can indicate anaerobic abscesses [
      • Gibbs C.
      Dental imaging.
      ]. An intraoral examination should be used to detect inflammation around the mucosa, fractures of teeth, patent infundibulum, or malocclusion, which would suggest secondary sinusitis; however, the absence of dental lesions does not rule out an apical granuloma [
      • Mason B.J.E.
      Empyema of the equine paranasal sinuses.
      ].
      By identifying changes in adjacent bone, nuclear scintigraphy may provide useful information regarding the exact tooth or teeth involved and at an earlier stage than can be achieved with radiography [
      • Weller R.
      • Livesy L.
      • Maierl J.
      • et al.
      Comparison of radiography and scintigraphy in the diagnosis of dental disorders in the horse.
      ,
      • Boswell J.C.
      • Schramme M.C.
      • Livesy L.C.
      • et al.
      Use of scintigraphy in the diagnosis of dental disease in four horses.
      ]. Scintigraphy with 99mTc-HMPAO–labeled leukocytes may prove to be a useful adjunctive method for identifying the location of a periapical abscess [
      • Boswell J.C.
      • Schramme M.C.
      • Livesy L.C.
      • et al.
      Use of scintigraphy in the diagnosis of dental disease in four horses.
      ].

       Treatment

      Treatment of primary sinusitis involves sinus lavage with large volumes of warm sterile physiologic saline (see section on centesis for technique), with repeated treatments in many cases. Choice of systemic antibiotics is based on culture and sensitivity testing of aspirates collected by centesis, but response can be poor in chronic cases [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 2: treatments and results of treatments.
      ]. Delayed or ineffective treatment allows primary sinusitis to progress to chronic osteitis, advanced necrosis and destruction of soft tissue and bone, and deep-seated abscesses. Such cases can be treated successfully by surgical debridement and curettage through a bone flap. The time-honored technique of establishing drainage through a surgically created sinonasal opening has been questioned because of a possible lack of efficacy [
      • Schumacher J.
      • Dutton D.M.
      • Murphy D.J.
      • et al.
      Paranasal sinus surgery through a frontonasal flap in sedated, standing horses.
      ,
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 2: treatments and results of treatments.
      ]. The surgical opening could alter mucociliary clearance and diminish production of endogenous nitric oxide, which could be bactericidal [
      • Schumacher J.
      • Dutton D.M.
      • Murphy D.J.
      • et al.
      Paranasal sinus surgery through a frontonasal flap in sedated, standing horses.
      ,
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 2: treatments and results of treatments.
      ]. Surgical treatment of inspissated pus in the ventral conchal sinus can be done effectively under general anesthesia or as a standing procedure [
      • Schumacher J.
      • Honnas C.
      • Smith B.
      Paranasal sinusitis complicated by inspissated exudate in the ventral conchal sinus.
      ,
      • Schumacher J.
      • Dutton D.M.
      • Murphy D.J.
      • et al.
      Paranasal sinus surgery through a frontonasal flap in sedated, standing horses.
      ].
      Secondary sinusitis is treated by removal of the diseased tooth (see below) or other primary problem and removal of abnormal mucosa, irrigation of the sinus cavity, and systemic antibiotics. Unsuccessful treatment can be attributed to persistent osteitis, abscesses, failure to remove all the involved root and infected bone, and failure to treat obligate anaerobes with metronidazole [
      • De Moor Von A.
      • Verschooten F.
      Empyem und Nekrose der Nasenmuscheln beim Pferd.
      ,
      • Mackintosh M.E.
      • Colles C.M.
      Anaerobic bacteria associated with dental abscesses in the horse and donkey.
      ]. In one study, oral extraction combined with sinus irrigation through a trephine hole was effective in the treatment of periapical infections in maxillary cheek teeth [
      • Dixon P.M.
      • Tremaine W.H.
      • Pickles K.
      • et al.
      Equine dental disease Part 4: a long-term study of 400 cases: apical infections of cheek teeth.
      ].

       Ethmoid hematoma

      An ethmoid hematoma is a nonneoplastic, progressive, and locally destructive growth in the paranasal sinuses that resembles a tumor in appearance and development. The largest hematomas arise from the ethmoidal labyrinth, and smaller and less common lesions originate from the floor and walls of the maxillary sinuses [
      • Cook W.R.
      • Littlewort M.C.G.
      Progressive haematoma of the ethmoid region in the horse.
      ,
      • Sullivan M.
      • Burrell M.H.
      • McCandlish I.A.P.
      Progressive haematoma of the maxillary sinus in a horse.
      ] and rarely invade the nasal passages. As an ethmoid hematoma expands, the surface of its capsule ulcerates, and this causes epistaxis. The expanding hematoma also causes pressure necrosis of surrounding bone [
      • Cook W.R.
      • Littlewort M.C.G.
      Progressive haematoma of the ethmoid region in the horse.
      ,
      • Sullivan M.
      • Burrell M.H.
      • McCandlish I.A.P.
      Progressive haematoma of the maxillary sinus in a horse.
      ] and spreads into the frontal sinus, sphenopalatine sinus, nasal passages, and nasopharynx [
      • Cook W.R.
      • Littlewort M.C.G.
      Progressive haematoma of the ethmoid region in the horse.
      ]. An expanding hematoma rarely causes facial distortion, except possibly in foals [
      • Colbourne C.M.
      • Rosenstein D.S.
      • Steficek B.A.
      • et al.
      Surgical treatment of progressive ethmoidal hematoma aided by computed tomography in a foal.
      ]. It is most commonly seen in horses older than 6 years of age (most often in horses 10–12 years of age) but has been described in a foal [
      • Colbourne C.M.
      • Rosenstein D.S.
      • Steficek B.A.
      • et al.
      Surgical treatment of progressive ethmoidal hematoma aided by computed tomography in a foal.
      ]. The disease seems to be less common in Standardbreds than in other breeds, and bilateral disease is more common in mares [
      • Rothaug P.G.
      • Tulleners E.P.
      Neodymium:yttrium-aluminum-garnet laser-assisted excision of progressive ethmoid hematomas in horses: 20 cases (1986–1996).
      ].

       Clinical signs

      Mild, persistent, spontaneous intermittent and unilateral epistaxis is the most common clinical sign. A stertorous respiratory noise may be heard at rest but is more pronounced during exercise, and airflow may be reduced through the nostril on the affected side. The sinuses are usually normal on percussion. Some horses have a mild mucopurulent discharge in conjunction with epistaxis, and rarer signs are coughing, malodorous breath, and head shaking [
      • Cook W.R.
      • Littlewort M.C.G.
      Progressive haematoma of the ethmoid region in the horse.
      ]. Bilateral cases have been reported [
      • Cook W.R.
      • Littlewort M.C.G.
      Progressive haematoma of the ethmoid region in the horse.
      ,
      • Rothaug P.G.
      • Tulleners E.P.
      Neodymium:yttrium-aluminum-garnet laser-assisted excision of progressive ethmoid hematomas in horses: 20 cases (1986–1996).
      ,
      • Schumacher J.
      • Yarbrough T.
      • Pascoe J.
      • et al.
      Transendoscopic chemical ablation of progressive ethmoidal hematomas in standing horses.
      ].

       Diagnosis

      The lesion can be seen extending into the nasal passages on endoscopic examination, but the absence of a mass in the nasal passage does not rule out a lesion contained within the sinuses [
      • Sullivan M.
      • Burrell M.H.
      • McCandlish I.A.P.
      Progressive haematoma of the maxillary sinus in a horse.
      ]. When the mass is large, its caudal edge can be seen extending around the vomer bone on endoscopy of the contralateral nasal passage. The hematoma can be seen on radiographs as a smooth-walled and well-circumscribed density that contrasts well with air in the sinus cavity (Fig. 6). On a dorsoventral projection of the head, the mass may be seen in the nasal passages, where it impinges on but rarely displaces the nasal septum.
      Figure thumbnail gr6
      Fig. 6Radiographic appearance of an ethmoid hematoma in the right sinuses of a 28-year-old Thoroughbred gelding. An ethmoid hematoma had been removed from the left sinus when the horse was 12 years old (arrow indicates wire sutures used for flap repair). Fluid lines are also evident.

       Treatment

      Ablation of the intranasal portion of the hematoma with a neodymium:yttrium (Nd:YAG) laser and intralesional injection of 10% formalin can be performed as standing procedures through the endoscope. Surgical treatment for lesions that fail to respond to formalin involves removal of the entire lesion through a frontonasal bone flap [
      • Freeman D.E.
      • Orsini P.G.
      • Ross M.W.
      • et al.
      A large frontonasal bone flap for sinus surgery in the horse.
      ], with or without ablation by the Nd:YAG laser [
      • Rothaug P.G.
      • Tulleners E.P.
      Neodymium:yttrium-aluminum-garnet laser-assisted excision of progressive ethmoid hematomas in horses: 20 cases (1986–1996).
      ]. This approach allows greater access to the lesion than would be predicted based on radiographs, and it is not unusual to find the hematoma encased in a shell of bone that must be removed to improve exposure (Fig. 7). The origin must be removed but may be difficult to approach within the ethmoidal labyrinth or sphenopalatine sinuses (Fig. 8), or it may be obscured by copious hemorrhage during surgery. Usually, a large opening from the sinus cavity into the nasal passage is created by surgical removal of the hematoma. The recurrence rate after surgical removal of ethmoid hematomas has been estimated at 0% [
      • Bonfig H.
      Diagnose und Therapie des progressiven Hämatoms der Siebbereinregion—dargestellt an 13 klinischen Fällen.
      ], 8% [
      • Rothaug P.G.
      • Tulleners E.P.
      Neodymium:yttrium-aluminum-garnet laser-assisted excision of progressive ethmoid hematomas in horses: 20 cases (1986–1996).
      ], 14.4% [
      • Greet T.R.C.
      Outcome and treatment in 23 horses with progressive ethmoidal hematoma.
      ], 41.6% [
      • Cook W.R.
      • Littlewort M.C.G.
      Progressive haematoma of the ethmoid region in the horse.
      ], and 44.4% [
      • Specht T.E.
      • Colahan P.T.
      • Nixon A.J.
      • et al.
      Ethmoidal hematoma in nine horses.
      ], and long-term remission of clinical signs was reported as 33% in one study [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 2: treatments and results of treatments.
      ]. A recurrence rate of 43% has been reported for bilateral lesions compared with 8% for unilateral lesions in one study [
      • Rothaug P.G.
      • Tulleners E.P.
      Neodymium:yttrium-aluminum-garnet laser-assisted excision of progressive ethmoid hematomas in horses: 20 cases (1986–1996).
      ]. Recurrence may be recognized within the first 6 to 12 months after surgery, and repeat endoscopic examination is recommended every 6 months. Improved methods of treatment, especially with improved access through large bone flaps, can facilitate removal of the entire lesion and reduce recurrence. Recurrence should be documented by endoscopy and not clinical signs, because remission of clinical signs does not rule out recurrence [
      • Schumacher J.
      • Yarbrough T.
      • Pascoe J.
      • et al.
      Transendoscopic chemical ablation of progressive ethmoidal hematomas in standing horses.
      ] and isolated recurrence of epistaxis does not always indicate recurrence of the lesion (personal observation) [
      • Rothaug P.G.
      • Tulleners E.P.
      Neodymium:yttrium-aluminum-garnet laser-assisted excision of progressive ethmoid hematomas in horses: 20 cases (1986–1996).
      ]. Also, horses that had a lesion on one side can develop a lesion on the other years after successful treatment (see Fig. 6).
      Figure thumbnail gr7
      Fig. 7Intraoperative view of the left sinuses (rostral to the right) through a large frontonasal bone flap in a horse with an ethmoid hematoma (2). The hematoma was covered by a shell of bone that was removed to reveal the lesion. 1 = reflection of dorsal nasal concha; 3 = ethmoidal labyrinth; 4 = caudal maxillary sinus seen through the frontomaxillary opening; 5 = rostral maxillary sinus and infraorbital canal.
      Figure thumbnail gr8
      Fig. 8Longitudinal section of the head of a horse that had an ethmoid hematoma removed years previously (note deformed sinus architecture rostrally to the right). Arrowheads indicate lesion remaining in the sphenopalatine sinus that caused persistent clinical signs.

       Intralesional formalin

      Intralesional formalin treatment has the advantage that it is an inexpensive standing procedure and usually free of complications, although chemical destruction of the cribriform plate with subsequent brain damage has been reported as a rare complication [
      • Frees K.E.
      • Gaughan E.M.
      • Lillich J.D.
      • et al.
      Severe complication after administration of formalin for treatment of progressive ethmoidal hematoma in a horse.
      ]. The mechanism of action is protein hydrolysis, which desiccates and coagulates the tissue [
      • Schumacher J.
      • Yarbrough T.
      • Pascoe J.
      • et al.
      Transendoscopic chemical ablation of progressive ethmoidal hematomas in standing horses.
      ]. Butorphanol is not recommended for sedation because it causes involuntary jerky head movements, and xylazine or detomidine is satisfactory. Although a special tubing and needle system is available (Cook Veterinary Products, Spencer, IN) (Fig. 9), homemade systems work well (Fig. 10), provided that the needle/tubing connection is secure. An 18-gauge needle (broken off the hub) is inserted in the end of the tubing, which is then passed in retrograde fashion into the biopsy channel of the endoscope until the needle is no longer exposed when the scope is passed up the nostril, and a sufficient length of tubing is available at the other end to attach to a needle and syringe. If the needle is passed normograde, it could damage the lining of the biopsy channel. Alternatively, to avoid problems with the needle, a beveled point can be cut on the end of the catheter to penetrate the lesion, provided that the catheter is rigid (see Fig. 10) and the capsule is not too thick. When the endoscope is properly positioned, the needle or tubing is advanced into the nasal portion of the hematoma, and approximately 50 mL of 10% neutral buffered formalin (4% formaldehyde solution) is injected. There is some loss by drainage around the injection site. If there is a large component of the lesion within the sinus, this can be injected through an 18-gauge needle inserted alongside the endoscope (Fig. 11), although this procedure carries the risk of severe sinusitis and even conchal necrosis. With time, the hematoma treated by formalin becomes “shriveled” and black as well as considerably smaller (Fig. 12), although it can recur from that point. Some lesions need to be reinjected with formalin repeatedly, and a period of 3 to 4 weeks is recommended as the injection interval [
      • Schumacher J.
      • Yarbrough T.
      • Pascoe J.
      • et al.
      Transendoscopic chemical ablation of progressive ethmoidal hematomas in standing horses.
      ]. Also, the intranasal portion of the lesion might constitute too small a component of the entire mass to allow a satisfactory response to treatment by this method (Fig. 13). Recheck endoscopy is recommended at least every 6 months so that recurrent lesions can be treated when they are small.
      Figure thumbnail gr9
      Fig. 9Commercially available catheter for injection of intralesional formalin of ethmoid hematomas (Cook Veterinary Products, Spencer, IN).
      Figure thumbnail gr10
      Fig. 10Different homemade catheters for injection of intralesional formalin of ethmoid hematomas with 18-gauge needles secured in thick-walled tubing and part of the needle and hub used for the injection port (top). For one system, a sharp bevel has been cut in the thick-walled catheter for injection of the mass. Bar = 1 cm.
      Figure thumbnail gr11
      Fig. 11Method of injecting formalin into an ethmoid hematoma (black arrowheads) in the right sinuses. The 18-gauge needle was inserted through the trephine hole beside the scope, and some formalin droplets can be seen escaping from the mass. White arrowheads indicate the frontomaxillary opening.
      Figure thumbnail gr12
      Fig. 12Endoscopic appearance of an ethmoid hematoma in the left nasal passage (arrowhead) at 1 month after injection with intralesional formalin. Note the shriveled appearance of the lesion and the large size of the ethmoturbinate region. This lesion recurred 12 months later and responded to a single injection then.
      Figure thumbnail gr13
      Fig. 13Longitudinal section of a horse's head to show part of an ethmoid hematoma in the right nasal passage (1) connected by a stalk (white arrowheads) that passed through a slit in the dorsal conchal sinus to the larger part of the lesion in the sinuses (2). 3 = dorsal conchal sinus cut to expose the sinus cavity; 4 = ethmoidal labyrinth. Any treatment directed at the nasal portion of the lesion might fail to destroy the sinus portion.

       Sinus cysts

      Sinus cysts are single or loculated fluid-filled cavities (Fig. 14) with an epithelial lining, and they contain yellow acellular fluid [
      • Lane J.G.
      • Longstaffe J.A.
      • Gibbs C.
      Equine paranasal sinus cysts: a report of 15 cases.
      ]. They develop in the maxillary sinuses and ventral conchae and can extend into the frontal sinus. A congenital form has been reported in foals as a cause of facial swelling and dyspnea since birth [
      • Sanders-Shamis M.
      • Robertson J.T.
      Congenital sinus cyst in a foal.
      ,
      • Beard W.L.
      • Robertson J.T.
      • Leeth B.
      Bilateral congenital cysts in the frontal sinuses of a horse.
      ]. Sinus cysts have been reported in horses less than 1 year of age and in horses older than 9 years of age in one study [
      • Lane J.G.
      • Longstaffe J.A.
      • Gibbs C.
      Equine paranasal sinus cysts: a report of 15 cases.
      ] but without any apparent age distribution in a larger study [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 1: details of horses, historical, clinical and ancillary diagnostic findings.
      ]. The condition has been attributed to a tooth root abnormality [
      • Leyland A.
      • Baker J.R.
      Lesions of the nasal and paranasal sinuses of the horse causing dyspnoea.
      ], but most cysts do not have dental involvement. Lane et al [
      • Lane J.G.
      • Longstaffe J.A.
      • Gibbs C.
      Equine paranasal sinus cysts: a report of 15 cases.
      ] proposed that paranasal sinus cysts have the same underlying pathogenesis as ethmoid hematomas, but this was not substantiated in another study [
      • Tremaine W.H.
      • Clarke C.J.
      • Dixon P.M.
      Histopathological findings in equine sinonasal disorders.
      ].
      Figure thumbnail gr14
      Fig. 14Fragments of a sinus cyst with typical loculations encased in bone and sinus lining. Bar = 1 cm.

       Clinical signs and diagnosis

      The major clinical signs are facial swelling, nasal discharge, dullness on percussion, and partial airway obstruction. The nasal discharge is rarely malodorous or bloody [
      • Lane J.G.
      • Longstaffe J.A.
      • Gibbs C.
      Equine paranasal sinus cysts: a report of 15 cases.
      ]. On endoscopic examination, the nasal passage appears narrow and the ventral conchae can appear enlarged. Radiographs are more diagnostic than endoscopic examination, and they can demonstrate multiloculated densities and fluid lines in the sinuses, occasionally with dental distortion and displacement, flattening of tooth roots, soft tissue mineralization, and considerable deviation of the nasal septum and vomer bone.

       Treatment

      Radical surgical removal of the cyst and the involved conchal lining carries a good prognosis for complete recovery, and the recurrence rate is low [
      • Lane J.G.
      • Longstaffe J.A.
      • Gibbs C.
      Equine paranasal sinus cysts: a report of 15 cases.
      ]. The associated dental abnormalities usually do not need to be addressed. The sinuses are frequently so disrupted by the cyst that a large communication is established into the nasal passages after surgery, and some horses have a recurrent mucous discharge after surgery that is of little clinical importance.

       Wounds and fractures

      Blunt injuries to the frontal sinus and nasal bones caused by kicks from other horses or collisions with fixed objects cause open or closed wounds to the sinuses. Many can go unnoticed, because the fracture fragments are forced into the sinus cavity and the overlying skin detaches from the bone to maintain a normal facial contour. As healing progresses, the hematoma and fracture callous produce a firm subcutaneous swelling along the fracture line and the depressed bone forms a facial concavity.

       Clinical signs

      Epistaxis and subcutaneous emphysema are common clinical signs of sinus trauma, and less common signs are dyspnea and epiphora. In acute cases, it may be possible to feel a hematoma and fracture fragments. Severe trauma to the head and sinuses can cause ocular and central nervous system abnormalities.

       Diagnosis

      A history of direct trauma to the head is sometimes available. On radiographs, fracture fragments and fluid lines from blood can be seen within the involved sinuses, but several oblique views may be required to demonstrate the injury (Fig. 15). Depression fractures around the orbit cause the globe to collapse into the sinuses and the third eyelid to prolapse (Fig. 16). In many cases, the fracture is more extensive than the external soft tissue injury and radiographic findings would suggest [
      • Turner A.S.
      Surgical management of depression fractures of the equine skull.
      ].
      Figure thumbnail gr15
      Fig. 15Oblique radiograph of a depression fracture into the frontal sinuses.
      Figure thumbnail gr16a
      Fig. 16(A) Open fracture of the sinuses with collapse of the floor of the orbit into the sinus cavity and prolapse of the third eyelid. (B) Same fracture 2 weeks after repair. Note that the wound had to be extended to gain access to the floor of the orbit and fracture fragments.
      Figure thumbnail gr16b
      Fig. 16(A) Open fracture of the sinuses with collapse of the floor of the orbit into the sinus cavity and prolapse of the third eyelid. (B) Same fracture 2 weeks after repair. Note that the wound had to be extended to gain access to the floor of the orbit and fracture fragments.

       Treatment

      The fracture fragments can be exposed through a large curvilinear skin flap (Fig. 17). Blood clots are removed, and the sinus cavity is flushed liberally with saline solution. To facilitate elevation of the fracture fragments, holes can be drilled in adjacent bone and a periosteal elevator, Steinmann pins, or Langenbeck retractors can be passed through these to pry up depressed fragments. If the fragments wedge firmly together in their normal position and form a stable union, it may be unnecessary to wire them [
      • Turner A.S.
      Surgical management of depression fractures of the equine skull.
      ], but large fragments should be wired to parent bone (Fig. 18). All small fragments without periosteal attachments should be removed [
      • Turner A.S.
      Surgical management of depression fractures of the equine skull.
      ]. The head should be bandaged so as to cover the wound if possible, and the horse should recover from general anesthesia either with assistance or wearing a padded head guard. Healing after repair of acute wounds is usually excellent and cosmetically acceptable.
      Figure thumbnail gr17
      Fig. 17A fracture into the frontal sinus extending the width of the face between the orbits and depressed into the sinus cavity (same horse as in ). Arrows indicate the fracture line that is intact to form a hinge for the depressed segment (rostral is to the right). Note the skin flap used to expose the fracture.
      Figure thumbnail gr18
      Fig. 18Same fracture as in repaired by wires after the depressed bone was pried into position by Steinmann pins inserted in the nasal passages. Final cosmetic appearance was good.
      In horses with long-standing healed depression fractures, fluorocarbon polymer and carbon fiber can be used to restore facial contour [
      • Valdez H.
      • Rook J.S.
      Use of fluorocarbon polymer and carbon fiber for restoration of facial contour in a horse.
      ], or the healed fracture fragments can be cut with a saw and elevated into position. A better cosmetic appearance can be obtained by primary open reduction shortly after injury rather than by facial reconstruction later, however. If severe fractures are not treated, complications can be expected, such as sinusitis, sequestra formation, facial deformity, abnormal bone growth in young horses, and nasal obstruction.

       Neoplasia and neoplasia-like lesions

      In horses, sinonasal tumors are more common in the sinuses than in the nasal passages in contrast to other species [
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ,
      • Head K.W.
      • Dixon P.M.
      Equine nasal and paranasal sinus tumours Part 1: review of the literature and tumour classification.
      ]. The most common type of neoplasm of the paranasal sinuses of the horse is squamous cell carcinoma [
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ,
      • Head K.W.
      • Dixon P.M.
      Equine nasal and paranasal sinus tumours Part 1: review of the literature and tumour classification.
      ], which may arise from the buccal mucosa [
      • Head K.W.
      • Dixon P.M.
      Equine nasal and paranasal sinus tumours Part 1: review of the literature and tumour classification.
      ]. Other tumors of the paranasal sinuses are adenocarcinoma, bone and dental tumors, fibrosarcomas, and hemangiosarcomas [
      • Head K.W.
      • Dixon P.M.
      Equine nasal and paranasal sinus tumours Part 1: review of the literature and tumour classification.
      ]. The predilection site for squamous cell carcinoma, unspecified carcinomas, and sarcomas is the caudal maxillary sinus, whereas adenocarcinomas are found in the nasal and ethmoidal regions [
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ,
      • Head K.W.
      • Dixon P.M.
      Equine nasal and paranasal sinus tumours Part 1: review of the literature and tumour classification.
      ]. Although most sinonasal tumors are locally aggressive, metastases are rare [
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ,
      • Head K.W.
      • Dixon P.M.
      Equine nasal and paranasal sinus tumours Part 1: review of the literature and tumour classification.
      ,
      • Walker M.A.
      • Schumacher J.
      • Schmitz D.G.
      • et al.
      Cobalt 60 radiotherapy for treatment of squamous cell carcinoma of the nasal cavity and paranasal sinuses in three horses.
      ].
      Adamantinomas are seen usually in young horses but are more common in the mandible than in the upper jaw [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Complex odontomas originate from dental follicles and have been described in the horse [
      • Freeman D.E.
      Paranasal sinuses.
      ]. An odontoma is not a true neoplasm but a tumor-like malformation or hamartoma composed of dentin, enamel, and cementum [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Cementomas are rare irritative hyperplastic lesions of cementum of the root apex [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Fibrous dysplasia, which is a dysplastic focal proliferation of stroma and bone different from osteodystrophia fibrosa, has been described in the maxillary sinus of a horse [
      • Freeman D.E.
      Paranasal sinuses.
      ].
      Although most tumors of the paranasal sinuses develop in older horses, osteoma, osteosarcoma, fibrosarcoma, angiosarcoma, and lymphosarcoma have been reported in horses from 6 weeks to 2 years of age [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Congenital tumors in the maxillary sinuses of horses are rare and include ethmoid carcinoma, fibrosarcoma, and possible spindle cell sarcoma [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Congenital ameloblastic odontomas have been described in the maxillary sinus of foals [
      • Freeman D.E.
      Paranasal sinuses.
      ].

       Clinical signs and diagnosis

      The most common presenting signs of sinonasal tumors are unilateral purulent or mucopurulent nasal discharge and facial swelling (81%–82% of cases) [
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ]. Epistaxis has been reported in 23% of cases, and ocular swelling, periocular swelling, ocular discharge, epiphora, enlarged local lymph nodes, weight loss, head shaking, and neurologic signs are less common [
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ,
      • Freeman D.E.
      Paranasal sinuses.
      ]. Because nasal invasion is uncommon, biopsies must be taken directly from the lesion within the sinus to make a definitive diagnosis [
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ]. Specimens from deep within the tumor are more likely to be diagnostic than those taken from more superficial areas [
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ].

       Treatment and prognosis

      Surgical treatment is generally unsuccessful, because the tumor is usually too extensive and tissue destruction is too great by the time of diagnosis, and many sinus tumors, especially carcinomas, are locally invasive and likely to recur [
      • Dixon P.M.
      • Head K.W.
      Equine nasal and paranasal sinus tumours Part 2: a contribution of 28 case reports.
      ,
      • Head K.W.
      • Dixon P.M.
      Equine nasal and paranasal sinus tumours Part 1: review of the literature and tumour classification.
      ]. In one report, results of aggressive radiotherapy of advanced squamous cell carcinomas in three horses were encouraging, because radiation-induced complications were mild and survival duration and quality of life were good [
      • Walker M.A.
      • Schumacher J.
      • Schmitz D.G.
      • et al.
      Cobalt 60 radiotherapy for treatment of squamous cell carcinoma of the nasal cavity and paranasal sinuses in three horses.
      ]. Osteomas are usually amenable to treatment because they are benign, grow slowly, have pedunculated or sessile attachments over a small base, and tend to form well-circumscribed lesions rather than infiltrate [
      • Freeman D.E.
      Paranasal sinuses.
      ].

       Fungal infections

      Fungal infections of the sinuses are rare and sporadic and difficult to treat. Many of the organisms involved are saprophytes that can be found in barnyard soil and manure [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Granulomas caused by Cryptococcus neoformans, Coccidioides immitis, Allescheria boydii (Maduromycosis), and Pseudallescheria boydii have been reported in the nasal passages, frontal and maxillary sinuses, cribriform plate, nasopharynx, conchae, conchal sinuses, and sphenopalatine sinus of horses [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Granulomas usually distort and destroy bone in a progressive fashion and can produce a retrobulbar mass and displace the cerebral hemisphere [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Spread to distant organs, such as the lungs and jejunum, is unusual [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Discrete lesions caused by Aspergillus and Penicillium spp can be focal or cause diffuse sinusitis and bone erosion [
      • Freeman D.E.
      Paranasal sinuses.
      ,
      • Arnauld des Lions J.
      • Guillot J.
      • Legrand E.
      • et al.
      Aspergillosis involving the frontal sinus in a horse.
      ]. Transient mycotic infections can develop after sinus surgery [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 1: details of horses, historical, clinical and ancillary diagnostic findings.
      ].

       Clinical signs

      Clinical signs closely resemble those of sinus neoplasia and can include nasal discharge, severe facial distortion, swollen periorbital region and exophthalmos, blindness with postorbital lesions, epistaxis, and weight loss [
      • Freeman D.E.
      Paranasal sinuses.
      ].

       Diagnosis

      Information about the horse's origin may be valuable in making a diagnosis, because some infections, such as coccidioidomycosis, are considered to be endemic in arid parts of the United States [
      • Freeman D.E.
      Paranasal sinuses.
      ]. On endoscopic examination, fungal granulomas are usually evident as large, firm, lobulated or nonlobulated masses covered by intact, smooth, and glistening mucosa in the nasal passages [
      • Freeman D.E.
      Paranasal sinuses.
      ]. On radiographs, fungal granulomas can be recognized as smooth-walled and well-demarcated soft tissue densities in the nasal passages and sinuses [
      • Freeman D.E.
      Paranasal sinuses.
      ]. The most definitive diagnosis can be made by biopsy of representative samples.

       Treatment

      Public health concerns apply to some fungal infections in horses [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Surgery through large bone flaps can be effective, but recurrence is possible, and humane destruction is recommended when the disease has become too extensive [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Antifungal agents, such as amphotericin B and ketoconazole, have variable effects against large fungal granulomas but could be used after surgical bulking of the lesion [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Sinus infection by Aspergillus fumigatus can be treated successfully by debridement through a bone flap, followed by topical application of enilconazole through an indwelling catheter for several days after surgery [
      • Arnauld des Lions J.
      • Guillot J.
      • Legrand E.
      • et al.
      Aspergillosis involving the frontal sinus in a horse.
      ]. A favorable outcome has been reported for treatment of Aspergillus infections in sinuses and nasal passages with topical natamycin [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 2: treatments and results of treatments.
      ].

       Halicephalobus gingivalis infection

      Halicephalobus gingivalis is a saprophytic nematode found in decaying humus, and infection through an unknown route involves the sinuses, central nervous system, and, to a lesser extent, kidneys [
      • Pearce S.G.
      • Bouré L.P.
      • Taylor J.A.
      • Peregrine A.S.
      Treatment of a granuloma caused by Halicephalobus gingivalis in a horse.
      ]. Infection of the sinuses produces a mass of grayish yellow fibrous tissue that obliterates the sinuses and their walls, loosens teeth, and distorts sinus architecture [
      • Freeman D.E.
      Paranasal sinuses.
      ,
      • Pearce S.G.
      • Bouré L.P.
      • Taylor J.A.
      • Peregrine A.S.
      Treatment of a granuloma caused by Halicephalobus gingivalis in a horse.
      ]. Infection can be unilateral or bilateral, involve both the upper and lower jaws, and spread from there to the kidneys and cerebellum [
      • Freeman D.E.
      Paranasal sinuses.
      ,
      • Pearce S.G.
      • Bouré L.P.
      • Taylor J.A.
      • Peregrine A.S.
      Treatment of a granuloma caused by Halicephalobus gingivalis in a horse.
      ].
      Predominant clinical signs are facial distortion with firm swellings in the maxilla, unilateral or bilateral nasal discharge, marked dyspnea and stridor, difficulty in eating, and weight loss [
      • Freeman D.E.
      Paranasal sinuses.
      ]. The condition can be confused with squamous cell carcinoma, but the female rhabditiform nematodes as well as their larvae and eggs can be seen in clusters or scattered throughout a biopsy specimen [
      • Freeman D.E.
      Paranasal sinuses.
      ,
      • Pearce S.G.
      • Bouré L.P.
      • Taylor J.A.
      • Peregrine A.S.
      Treatment of a granuloma caused by Halicephalobus gingivalis in a horse.
      ]. Surgical debulking, intraoperative lavage with ivermectin, and subsequent oral ivermectin were successful in one horse with a periorbital granuloma [
      • Pearce S.G.
      • Bouré L.P.
      • Taylor J.A.
      • Peregrine A.S.
      Treatment of a granuloma caused by Halicephalobus gingivalis in a horse.
      ]; however, the response to ivermectin is not always favorable, and the prognosis seems to be poor, especially because of risk of spread to other organs [
      • Freeman D.E.
      Paranasal sinuses.
      ].

       Miscellaneous

      Frontal sinus eversion forms a hard and slow-growing protuberance over the frontal sinus and probably is a congenital defect [
      • Martin G.S.
      • McIlwraith C.W.
      Repair of a frontal sinus eversion in a horse.
      ]. The bony protuberance can be removed through a large elliptic incision, and the resulting defect in the frontal bone can be repaired with synthetic polypropylene mesh (Marlex) and skin [
      • Martin G.S.
      • McIlwraith C.W.
      Repair of a frontal sinus eversion in a horse.
      ]. Osteodystrophia fibrosa or secondary nutritional hyperparathyroidism can develop in horses on a high-phosphorus diet, such as bran, and can be attributed to calcium deficiency [
      • Freeman D.E.
      Paranasal sinuses.
      ]. It is rare under modern management conditions, however [
      • Freeman D.E.
      Paranasal sinuses.
      ]. Conchal necrosis [
      • De Moor Von A.
      • Verschooten F.
      Empyem und Nekrose der Nasenmuscheln beim Pferd.
      ] might be caused by advanced mycotic rhinitis [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 1: details of horses, historical, clinical and ancillary diagnostic findings.
      ] and usually responds to removal of the affected concha by intranasal curettage and lavage.
      The reserve tooth crowns of young Welsh ponies and smaller breeds can project a considerable distance into the sinus cavities and cause firm, painless, bilateral swellings in the nasal bones that should not be confused with injuries or disease. Facial lumps or “horns” can be seen in horses as symmetric painless prominences of the nasal and frontal bones and possibly are caused by an embryologic fault [
      • Freeman D.E.
      Paranasal sinuses.
      ].

      Surgery of the paranasal sinuses

       Frontonasal flap technique

      A frontonasal flap approach can be used to enter the conchofrontal and caudal maxillary sinuses and, by additional steps, the rostral maxillary and ventral conchal sinuses (see Fig. 1) [
      • Freeman D.E.
      • Orsini P.G.
      • Ross M.W.
      • et al.
      A large frontonasal bone flap for sinus surgery in the horse.
      ]. It can be used also for removal of fifth and sixth cheek teeth, but access to the fourth cheek tooth and rostral part of the rostral maxillary sinus is usually limited. The size and position of the flap can be designed to suit the lesion. Before sinus surgery, a potential blood donor should be identified by cross-matching.
      The caudal edge of the bone flap is at a right angle to the dorsal midline and midway between the supraorbital foramen and the medial canthus of the eye (Fig. 19). The lateral edge starts 2 to 2.5 cm medial to the medial canthus of the eye, then runs slightly dorsal to a line from the medial canthus to the nasoincisive notch, and is approximately 10 cm long. The rostral edge, which is at a right angle to the dorsal midline, should be at or caudal to the point at which the nasal bones become parallel (Fig. 19, Fig. 20). A cut more rostral to this can enter the nasal passages and cause severe hemorrhage and can heal with a permanent nasal blemish. The flap should be as wide as possible without involving the nasolacrimal duct. The skin is incised to overlap the bone incision by 5 mm (Fig. 21), and the corners are curved. Underlying periosteum is incised and elevated along the proposed line of the bone cut so as to expose a 3- to 5-mm wide strip of bone. The bone flap should not be detached from its soft tissue attachments anymore than this, or it may become necrotic. The exposed bone is cut with an oscillating bone saw to create a three-sided flap (see Fig. 19), or the flap can be cut with an osteotome along lines that join drill holes at the corners. Small bony attachments between the underside of the flap and floor of the frontal sinus are cut with a 9-mm osteotome, elevating the osteotome at the same time until three sides of the flap are completely free (Fig. 22). Wide periosteal elevators or osteotomes are placed under the flap at each end to start to pry it open and fracture it along the midline (Fig. 23). As the fracture starts, the bone edges are elevated with fingers while downward pressure is applied along the proposed fracture line with the thumbs to force the fracture along that line (Fig. 24). By fracturing the bone to form a “hinge” on the midline, the fracture is more stable than when flapped in the other direction (ie, lateral base). Also, the flap based on the midline falls away from the surgical field and does not interfere with access.
      Figure thumbnail gr19
      Fig. 19Approaches to the sinuses through a frontonasal bone flap (broken line in A) and maxillary bone flap (broken line in B). 1 = rostral maxillary sinus; 2 = caudal maxillary sinus; 3 = ventral conchal sinus; 4 = sphenopalatine sinus; 5 = frontal sinus; 6 = ethmoidal labyrinth; 7 = frontomaxillary opening; 8 = dorsal conchal sinus. The conchofrontal sinus (5 and 8 combined) is outlined with a solid line.
      Figure thumbnail gr20
      Fig. 20Typical large frontonasal flap. In this case, the packing was brought out through the trephine hole, which was also used for flushing the sinus.
      Figure thumbnail gr21
      Fig. 21Method of placing incisions in the skin (solid line) and periosteum (broken line) so that the soft tissues overlap the bone incision.
      Figure thumbnail gr22
      Fig. 22Use of a chisel or osteotome to cut bony attachments to the underside of the bone flap.
      Figure thumbnail gr23
      Fig. 23Method of prying up the edges of the flap with osteotomes or periosteal elevators to start the elevation.
      Figure thumbnail gr24
      Fig. 24Method of using the fingers to pry up the edge of the flap to complete its elevation while using the thumbs to force the fracture at the desired point on the dorsal midline. If the flap is not freed adequately, resistance to elevation can be sensed more easily through the fingers and thumbs than if it were elevated to the point of fracture with instruments.
      This approach allows direct access to the conchofrontal sinus and the caudal maxillary sinus. The bulla of the ventral conchal sinus and the rostral edge of the frontomaxillary opening can be removed to allow access to the rostral maxillary sinus and ventral conchal sinus (see Fig. 7). Disruption of conchal walls can cause profuse hemorrhage and therefore should be the last step.
      To control hemorrhage after surgery, a 3-in stockinet is placed into the sinus and nasal passages and is tied or folded at the end inserted into the most caudal part of the sinus (Fig. 25). To do this, an assistant passes a Chambers mare catheter up the nasal passage until it can be digitally directed into the sinus. A length of umbilical tape is tied to the end of the catheter in the sinus, and one end is drawn out of the nostril and the other remains in the sinus. Saline-soaked gauze is then placed within the “sock” of stockinet in accordion fashion until the sinuses are packed. The umbilical tape is tied around the redundant portion of stockinet and the gauze within and is then used to draw them through the nostrils (see Fig. 25). The free end of stockinet and the gauze within it are sutured to the roof of the false nostril with a heavy mattress suture over a butterfly of gauze sponge, and any excess packing is trimmed flush with the nostril. Alternatively, packing can be brought out through a trephine hole in adjacent intact bone (see Fig. 20). The purpose of the stockinet sock is to prevent migration of the packing into the pharynx, from where it can be swallowed. The bone flap is repaired by suturing only the subcutaneous tissues and skin, without sutures in the bone (see Fig. 20). Alternatively, the bone flap can be discarded and soft tissues only used in the repair, but this can deform the face (Fig. 26). A gauze pad is applied over the incision and secured in place with a figure-of-eight Elastikon wrap (Johnson & Johnson, division of Ethicon, Arlington, TX) around the head and over and under the eyes. At 48 to 72 hours after surgery, the packing is removed by first removing the inner gauze and then the outer sock. The hemorrhage that follows over the next 15 to 20 minutes can be reduced by elevating the horse's head. Antibiotics, such as penicillin and gentamicin, can be given on the morning of surgery and continued for 3 to 5 days afterward.
      Figure thumbnail gr25
      Fig. 25Method of packing the paranasal sinuses. Stockinet with the closed end placed in the sinuses and nasal passages as described. This “sock” is then packed with gauze in accordion fashion until it is filled.
      Figure thumbnail gr26
      Fig. 26Depression medial to the eye on a horse that had a sinus flap in which the bone was discarded.
      The cosmetic appearance of the healed bone flap is usually excellent, although white hairs can grow on the face along parts of the healed incision. Complications are transient and uncommon; they include infection around buried sutures that can drain until the suture is absorbed and epiphora caused by fracture and thickening of the lacrimal bone at a point distant to the flap. As with any sinus surgery, the large opening created between the sinus and nasal passage (Fig. 27) could interfere with normal sinus drainage and defense mechanisms, thereby predisposing to recurrent nasal discharge [
      • Tremaine W.H.
      • Dixon P.M.
      A long-term study of 277 cases of equine sinonasal disease Part 2: treatments and results of treatments.
      ,
      • Schumacher J.
      • Yarbrough T.
      • Pascoe J.
      • et al.
      Transendoscopic chemical ablation of progressive ethmoidal hematomas in standing horses.
      ]. A fungal-like plaque can form on the sinus side of the healed incision, and this can contain hair, dermal elements, fungi, and bacteria, presumably formed by seeding the raw sinus surface with skin from the face (see Fig. 27). This might cause some mild discharge but does not warrant treatment.
      Figure thumbnail gr27
      Fig. 27Endoscopic view of the right nasal cavity of a horse that had a frontal flap 2 years previously to remove an ethmoid hematoma. Note the large communication with the sinus cavity and the fungal-like plaque of diphtheritic membrane on the underside of the healed flap.
      Temporary bilateral carotid artery occlusion can be used to reduce intraoperative hemorrhage during sinus surgery [
      • Wyn-Jones G.
      • Jones R.S.
      • Church S.
      Temporary bilateral carotid artery occlusion as an aid to nasal surgery in the horse.
      ], and both arteries can be approached through an 8-cm long incision in the uppermost jugular groove. The risk of damage to the recurrent laryngeal nerve should be considered in athletic horses before using this technique, and it might be safer for more sedentary horses. The effects of this on bleeding can be marked, variable, or negligible.

       Maxillary sinus flap

      This flap is useful for diseases of the rostral part of the sinuses, particularly the rostral maxillary sinus and the premolar teeth (see Fig. 19). It is a smaller flap than the frontonasal flap, allows little access to large parts of the sinuses (especially in a young horse with large reserve crowns) (Fig. 28), and does involve more soft tissue dissection Therefore, it is not recommended for most diseases.
      Figure thumbnail gr28
      Fig. 28Limited access to the ventral conchal sinus through the maxillary flap (broken line) in a young horse (top) compared with an old horse (bottom). Arrow indicates route over infraorbital canal and cheek teeth into the ventral conchal sinus, which can be the site of infection and cyst formation.

       Standing sinus surgery

      A frontonasal flap approach has been described as a standing procedure after sedation, local anesthetic infiltration of the skin, and local anesthetic injection through a small hole into the sinus cavity [
      • Schumacher J.
      • Dutton D.M.
      • Murphy D.J.
      • et al.
      Paranasal sinus surgery through a frontonasal flap in sedated, standing horses.
      ]. Diseases treated successfully by this approach include ethmoid hematoma, osteoma, inspissated exudate in the ventral conchal sinus, sinusitis, and a polyp [
      • Schumacher J.
      • Dutton D.M.
      • Murphy D.J.
      • et al.
      Paranasal sinus surgery through a frontonasal flap in sedated, standing horses.
      ]. Hemorrhage is less than expected compared with the same surgery on the anesthetized horse, presumably because the head is elevated in the standing horse, which might reduce blood pressure in the sinuses [
      • Schumacher J.
      • Dutton D.M.
      • Murphy D.J.
      • et al.
      Paranasal sinus surgery through a frontonasal flap in sedated, standing horses.
      ]. Although a nasosinus ostium was not created in all horses with sepsis, the favorable outcome that followed was attributed to preservation of normal sinus defense mechanisms and a patent nasomaxillary opening [
      • Schumacher J.
      • Dutton D.M.
      • Murphy D.J.
      • et al.
      Paranasal sinus surgery through a frontonasal flap in sedated, standing horses.
      ].

       Tooth repulsion

      Diseased teeth that have caused secondary sinusitis can be repelled with a dental punch inserted through a bone flap or trephine hole. For the third to sixth cheek teeth, which have considerable caudal curvature in horses less than 8 years old, the roots are on a vertical line from the caudal edge of the occlusal surface. After removal, the tooth is checked to confirm that it is abnormal, the alveolar socket is palpated for fragments, and intraoperative radiographs are taken to ensure that all fragments of teeth and bone have been removed. The alveolar socket is then packed with gauze, polymethyl methacrylate, or dental acrylic to prevent migration of food from the oral cavity into the maxillary sinus. Polymethyl methacrylate forms a more secure packing than dental wax and can remain in place for several years without apparent adverse effects, possibly for the life of the horse. It can cause thermal necrosis of soft tissue and bone as it cures, however. Packing must not be inserted deeply in the socket; it can “mushroom” into the sinus and become difficult to extract if removal becomes necessary or can interfere with healing of the sinus.
      The rate of serious postoperative complications after repulsion of maxillary cheek teeth can be as high as 47%, and such complications include infection of a second tooth, bone sequestration, chronic sinusitis, draining tracts, retained dental packing, feed impaction of the alveolus or sinus, suture line dehiscence, or sloughed skin flaps [
      • Pritchard M.A.
      • Hackett R.P.
      • Erb H.N.
      Long-term outcome of tooth repulsion in horses: a retrospective study of 61 cases.
      ]. If an orosinus fistula forms after tooth removal, the alveolar defect can be sealed by suturing the transposed ventral edge of the levator nasolabialis to its sinus opening [
      • Orsini P.G.
      • Ross M.W.
      • Hamir A.N.
      Levator nasolabialis muscle transposition to prevent an orosinus fistula after tooth extraction in horses.
      ].

      References

        • Hillmann D.J.
        Skull.
        in: Getty R. Sisson and Grossman's the anatomy of the domestic animals. 5th edition. WB Saunders, Philadelphia1975: 318-348
      1. McCann JL, Dixon PM, Mayhew JG. A clinical study of the anatomy of sphenopalatine sinus. In: Proceedings of the 38th Congress of the British Equine Veterinary Association. 1999. p. 178.

        • Dixon P.M.
        • Head K.W.
        Equine nasal and paranasal sinus tumours.
        Vet J. 1999; 157: 279-294
        • Hare W.C.D.
        Equine respiratory system.
        in: Getty R. Sisson and Grossman's the anatomy of the domestic animals. 5th edition. WB Saunders, Philadelphia1975: 498-523
        • Bell B.T.L.
        • Baker G.J.
        • Abbott L.C.
        • et al.
        The macroscopic vascular anatomy of the equine ethmoidal area.
        Anat Histol Embryol. 1995; 24: 39-45
        • Tremaine W.H.
        • Dixon P.M.
        A long-term study of 277 cases of equine sinonasal disease.
        Equine Vet J. 2001; 33: 274-282
        • Gibbs C.
        Dental imaging.
        in: Baker G.J. Easley J. Equine dentistry. WB Saunders, Philadelphia1999: 139-169
        • Rosenstein D.S.
        • Stick J.A.
        Diagnostic techniques in equine upper respiratory tract disease.
        in: Auer J.A. Stick J.A. Equine surgery. 2nd edition. WB Saunders, Philadelphia1999: 314-326
        • Weller R.
        • Livesy L.
        • Maierl J.
        • et al.
        Comparison of radiography and scintigraphy in the diagnosis of dental disorders in the horse.
        Equine Vet J. 2001; 33: 49-58
        • Ruggles A.J.
        • Ross M.W.
        • Freeman D.E.
        Endoscopic examination of normal paranasal sinuses in horses.
        Vet Surg. 1991; 20: 418-423
        • Ruggles A.J.
        • Ross M.W.
        • Freeman D.E.
        Endoscopic examination and treatment of paranasal sinus disease in 16 horses.
        Vet Surg. 1993; 22: 508-514
        • Worster A.A.
        • Hackett R.P.
        Equine sinus endoscopy using a flexible endoscope: diagnosis and treatment of sinus disease in the standing sedated horse.
        Proc Am Assoc Equine Pract. 1999; 45: 128-130
        • Lane J.G.
        • Gibbs C.
        • Meynink S.E.
        • et al.
        Radiographic examination of the facial, nasal and paranasal sinus regions of the horse:.
        Equine Vet J. 1987; 19: 466-473
        • Schumacher J.
        • Honnas C.
        • Smith B.
        Paranasal sinusitis complicated by inspissated exudate in the ventral conchal sinus.
        Vet Surg. 1987; 16: 373-377
        • Blackford J.T.
        • Goble D.O.
        • Henry R.W.
        • et al.
        Triangulated flap technique for nasofrontal surgery: results in 5 horses.
        Vet Surg. 1985; 4: 287-294
        • Schumacher J.
        • Dutton D.M.
        • Murphy D.J.
        • et al.
        Paranasal sinus surgery through a frontonasal flap in sedated, standing horses.
        Vet Surg. 2000; 29: 173-177
        • Henninger W.
        • Reifinger M.
        Einseitige Auftreibung des Gesichtsschädels durch ein okklusives Kieferhöhlenempyem bei einem Jungpferd.
        Wien Tierarztl Monatsschr. 1998; 85: 59-63
        • Freeman D.E.
        • Orsini P.G.
        • Ross M.W.
        • et al.
        A large frontonasal bone flap for sinus surgery in the horse.
        Vet Surg. 1990; 19: 122-130
        • Coumbe K.M.
        • Jones R.D.
        • Kenward J.H.
        Bilateral sinus empyema in a 6-year-old mare.
        Equine Vet J. 1987; 19: 559-560
        • Mason B.J.E.
        Empyema of the equine paranasal sinuses.
        JAVMA. 1975; 167: 727-731
        • Dixon P.M.
        • Tremaine W.H.
        • Pickles K.
        • et al.
        Equine dental disease.
        Equine Vet J. 2000; 32: 182-194
        • De Moor Von A.
        • Verschooten F.
        Empyem und Nekrose der Nasenmuscheln beim Pferd.
        Dtsch Tierarztl Wochenschr. 1982; 89 ([Empyema and necrosis of the nasal conchae in a horse]): 275-281
        • Baker G.J.
        Some aspects of equine dental radiology.
        Equine Vet J. 1971; 3: 46-51
        • Boswell J.C.
        • Schramme M.C.
        • Livesy L.C.
        • et al.
        Use of scintigraphy in the diagnosis of dental disease in four horses.
        Equine Vet Educ. 1999; 11: 165-169
        • Tremaine W.H.
        • Dixon P.M.
        A long-term study of 277 cases of equine sinonasal disease.
        Equine Vet J. 2001; 33: 283-289
        • Mackintosh M.E.
        • Colles C.M.
        Anaerobic bacteria associated with dental abscesses in the horse and donkey.
        Equine Vet J. 1987; 19: 360-362
        • Cook W.R.
        • Littlewort M.C.G.
        Progressive haematoma of the ethmoid region in the horse.
        Equine Vet J. 1974; 6: 101-108
        • Sullivan M.
        • Burrell M.H.
        • McCandlish I.A.P.
        Progressive haematoma of the maxillary sinus in a horse.
        Vet Rec. 1984; 114: 191-192
        • Colbourne C.M.
        • Rosenstein D.S.
        • Steficek B.A.
        • et al.
        Surgical treatment of progressive ethmoidal hematoma aided by computed tomography in a foal.
        JAVMA. 1997; 211: 335-338
        • Rothaug P.G.
        • Tulleners E.P.
        Neodymium:yttrium-aluminum-garnet laser-assisted excision of progressive ethmoid hematomas in horses: 20 cases (1986–1996).
        JAVMA. 1999; 214: 1037-1041
        • Schumacher J.
        • Yarbrough T.
        • Pascoe J.
        • et al.
        Transendoscopic chemical ablation of progressive ethmoidal hematomas in standing horses.
        Vet Surg. 1998; 27: 175-181
        • Bonfig H.
        Diagnose und Therapie des progressiven Hämatoms der Siebbereinregion—dargestellt an 13 klinischen Fällen.
        Pferdeheilkunde. 1989; 5: 71-79
        • Greet T.R.C.
        Outcome and treatment in 23 horses with progressive ethmoidal hematoma.
        Equine Vet J. 1992; 24: 468-471
        • Specht T.E.
        • Colahan P.T.
        • Nixon A.J.
        • et al.
        Ethmoidal hematoma in nine horses.
        JAVMA. 1990; 197: 613-616
        • Frees K.E.
        • Gaughan E.M.
        • Lillich J.D.
        • et al.
        Severe complication after administration of formalin for treatment of progressive ethmoidal hematoma in a horse.
        JAVMA. 2001; 219: 950-952
        • Lane J.G.
        • Longstaffe J.A.
        • Gibbs C.
        Equine paranasal sinus cysts: a report of 15 cases.
        Equine Vet J. 1987; 19: 537-544
        • Sanders-Shamis M.
        • Robertson J.T.
        Congenital sinus cyst in a foal.
        JAVMA. 1987; 190: 1011-1012
        • Beard W.L.
        • Robertson J.T.
        • Leeth B.
        Bilateral congenital cysts in the frontal sinuses of a horse.
        JAVMA. 1990; 196: 453-454
        • Leyland A.
        • Baker J.R.
        Lesions of the nasal and paranasal sinuses of the horse causing dyspnoea.
        Br Vet J. 1975; 131: 339-346
        • Tremaine W.H.
        • Clarke C.J.
        • Dixon P.M.
        Histopathological findings in equine sinonasal disorders.
        Equine Vet J. 1999; 31: 296-303
        • Turner A.S.
        Surgical management of depression fractures of the equine skull.
        Vet Surg. 1979; 8: 29-33
        • Valdez H.
        • Rook J.S.
        Use of fluorocarbon polymer and carbon fiber for restoration of facial contour in a horse.
        JAVMA. 1981; 178: 249-252
        • Head K.W.
        • Dixon P.M.
        Equine nasal and paranasal sinus tumours.
        Vet J. 1999; 157: 261-278
        • Walker M.A.
        • Schumacher J.
        • Schmitz D.G.
        • et al.
        Cobalt 60 radiotherapy for treatment of squamous cell carcinoma of the nasal cavity and paranasal sinuses in three horses.
        JAVMA. 1998; 212: 848-851
        • Freeman D.E.
        Paranasal sinuses.
        in: Beech J. Equine respiratory disorders. Lea & Febiger, Philadelphia1991: 275-303
        • Arnauld des Lions J.
        • Guillot J.
        • Legrand E.
        • et al.
        Aspergillosis involving the frontal sinus in a horse.
        Equine Vet Educ. 2000; 12: 326-328
        • Pearce S.G.
        • Bouré L.P.
        • Taylor J.A.
        • Peregrine A.S.
        Treatment of a granuloma caused by Halicephalobus gingivalis in a horse.
        JAVMA. 2001; 219: 1735-1738
        • Martin G.S.
        • McIlwraith C.W.
        Repair of a frontal sinus eversion in a horse.
        Vet Surg. 1981; 10: 149-153
        • Wyn-Jones G.
        • Jones R.S.
        • Church S.
        Temporary bilateral carotid artery occlusion as an aid to nasal surgery in the horse.
        Equine Vet J. 1986; 18: 125-128
        • Pritchard M.A.
        • Hackett R.P.
        • Erb H.N.
        Long-term outcome of tooth repulsion in horses: a retrospective study of 61 cases.
        Vet Surg. 1992; 21: 145-149
        • Orsini P.G.
        • Ross M.W.
        • Hamir A.N.
        Levator nasolabialis muscle transposition to prevent an orosinus fistula after tooth extraction in horses.
        Vet Surg. 1992; 31: 150-156