Sinoscopic Treatment of Rostral Maxillary and Ventral Conchal Sinusitis in 60 Horses

Objective— To evaluate the use of sinoscopy for detection and treatment of ventral conchal sinus (VCS) and/or rostral maxillary sinus (RMS) disease in horses.
Study Design— Case series
Animals— Horses (n=60) with suspected paranasal sinus disease.
Methods— Horses were evaluated by sinoscopy through a conchofrontal sinus (CFS) portal with ventral conchal bulla (VCB) fenestration. Other endoscopic sinus approaches and adjunctive diagnostic tests; oral examination, computed tomography, radiography, scintigraphy and endoscopic examination of the upper portion of the respiratory tract were used in some horses.
Results— The CFS approach permitted adequate observation of the RMS and VCS in 53 horses (88%). Hemorrhage caused by VCB fenestration prevented examination of the RMS and/or VCS in 12 horses (21%). Observation of lesions was possible in all horses diagnosed with neoplasia, sinus cysts, and progressive ethmoidal hematomas. Endoscopy of the paranasal sinuses was useful diagnostically in 82% of horses with primary sinusitis. Other diagnostic modalities were usually required to confirm a diagnosis of dental sinusitis.
Conclusions— Trephination into the CFS with VCB fenestration is a minimally invasive technique that provides consistent access to the RMS and VCS. It facilitates diagnosis of many sinus disorders and endoscopically guided treatment of many horses with sinus cysts and primary sinusitis, in combination with sinus lavage.
Clinical Relevance— Many diseases affecting the RMS and VCS can be diagnosed and resolved endoscopically using a CFS approach with VCB fenestration, thus avoiding the need for osteoplastic sinus surgery and its associated risks and complications.     

Radiographic identification of the equine ventral conchal bulla

Involvement of the ventral conchal sinus (VCS) is an important diagnostic and prognostic feature in cases of the equine sinus disease. The authors aimed to ascertain if the caudo-dorsal extension of the VCS, the ventral conchal bulla (VCB) is identifiable on plain radiographs of cadaver skulls without sinus disease. Bilateral frontonasal sinus flaps were made in 10 equine cadaver skulls. Plain lateral, lateral oblique and dorso-ventral radiographs were then obtained followed by the same views taken with stainless steel wire outlining the caudal border of the VCB. Plain radiographs were randomised and blindly evaluated by two observers who marked where they believed the VCB to be positioned. This was then correlated with the true position of the VCB using radiographs with wires in place. The ease of identification of the VCB was classified as 'easy' or 'difficult'. The VCB was correctly identified in 70 per cent of lateral radiographs, but only 45 per cent of lateral oblique radiographs and 17 per cent of dorso-ventral radiographs. If a clinician was confident that he or she could identify the VCB, they were usually correct. Conversely if the clinician judged VCB identification as 'difficult', they usually identified it incorrectly. In the authors' clinical experience, the VCB of horses with sinusitis involving this compartment is more radiologically evident than in clinically normal horses. Knowledge of the normal radiographic anatomy of this structure should aid clinicians in identifying horses with sinusitis affecting the VCS.     

Equine paranasal sinus disease: a long-term study of 200 cases (1997-2009): ancillary diagnostic findings and involvement of the various sinus compartments

Reasons for performing study: There is a lack of objective information on the value of ancillary diagnostic techniques used to investigate equine sinus disease, and also on which sinus compartments are commonly affected in this disorder. Objectives: To record the ancillary diagnostic findings used to investigate equine sinus disease and to document which compartments are affected. Materials and methods: The clinical case records of 200 consecutive cases of sinus disease, including subacute (<2 months' duration) primary (n = 52); chronic (>2 months' duration) primary (n = 37); dental (n = 40); traumatic (n = 13); sinus cyst (n = 26); sinus neoplasia (n = 10); dental related oromaxillary fistula (n = 8); mycotic sinusitis (n = 7) and intra‐sinus progressive ethmoid haematoma (n = 7) were retrospectively examined. Results: Nasal endoscopy showed exudate draining from the sino‐nasal ostia in 88% of cases and a sino‐nasal fistula was present in 15% of cases. Sinoscopy was performed in 79% of cases and was of great diagnostic value. More recently, 22% of cases had fenestration of the ventral conchal bulla performed to allow sinoscopy of the rostral sinus compartments. Radiography was performed in 97% of cases and showed intra‐sinus fluid lines to be common (69% prevalence) in subacute primary sinusitis. Radiographic dental apical changes were not specific to dental sinusitis, e.g. 29% of chronic primary sinusitis cases had radiographic dental changes. Scintigraphy was performed in 20% of cases and was helpful in identifying dental apical changes when radiography was inconclusive. Overall, the caudal maxillary (78% involvement) and rostral maxillary (61%) sinuses were most commonly affected, with the ventral conchal sinus (VCS) (54% involvement) and conchofrontal sinuses (48%) less so. The VCS showed the greatest tendency to contain inspissated pus (present in 46% of all affected VCS). Conclusions: Nasal endoscopy, sinoscopy and skull radiography are of great value in diagnosing the presence and causes of equine sinus disease.     

USING SEMI‐AUTOMATED SEGMENTATION OF COMPUTED TOMOGRAPHY DATASETS FOR THREE‐DIMENSIONAL VISUALIZATION AND VOLUME MEASUREMENTS OF EQUINE PARANASAL SINUSES

The system of the paranasal sinuses morphologically represents one of the most complex parts of the equine body. A clear understanding of spatial relationships is needed for correct diagnosis and treatment. The purpose of this study was to describe the anatomy and volume of equine paranasal sinuses using three‐dimensional (3D) reformatted renderings of computed tomography (CT) slices. Heads of 18 cadaver horses, aged 2–25 years, were analyzed by the use of separate semi‐automated segmentation of the following bilateral paranasal sinus compartments: rostral maxillary sinus (Sinus maxillaris rostralis), ventral conchal sinus (Sinus conchae ventralis), caudal maxillary sinus (Sinus maxillaris caudalis), dorsal conchal sinus (Sinus conchae dorsalis), frontal sinus (Sinus frontalis), sphenopalatine sinus (Sinus sphenopalatinus), and middle conchal sinus (Sinus conchae mediae). Reconstructed structures were displayed separately, grouped, or altogether as transparent or solid elements to visualize individual paranasal sinus morphology. The paranasal sinuses appeared to be divided into two systems by the maxillary septum (Septum sinuum maxillarium). The first or rostral system included the rostral maxillary and ventral conchal sinus. The second or caudal system included the caudal maxillary, dorsal conchal, frontal, sphenopalatine, and middle conchal sinuses. These two systems overlapped and were interlocked due to the oblique orientation of the maxillary septum. Total volumes of the paranasal sinuses ranged from 911.50 to 1502.00 ml (mean ± SD, 1151.00 ± 186.30 ml). 3D renderings of equine paranasal sinuses by use of semi‐automated segmentation of CT‐datasets improved understanding of this anatomically challenging region.     

Transnasal endoscopic treatment of equine sinus disease in 14 clinical cases

Transnasal endoscopic sinus treatment was used in four horses diagnosed with primary sinusitis and 10 horses with dental sinusitis. Pre-existing (n = 5) or surgically created (n = 9) sinonasal fistulae were used as portals for transnasal endoscopic exploration, debridement and lavage of the inflamed sinus cavities. Endoscopic sinonasal fistulation was performed using either trans-endoscopic diode laser fibre (four cases) or an electrocautery instrument under endoscopic control (five cases). All procedures were performed on standing sedated horses with the use of local anaesthesia. In six cases, the ventral concha was fenestrated in order to gain a portal into the ventral conchal and rostral maxillary sinus. In two cases the dorsal concha was fenestrated to access the caudal group of the paranasal sinuses. One case required fenestration of the ventral conchal bulla due to its empyema. Post-operative bleeding was controlled with a nasal cavity tamponade for 24 h. Endoscopic lavage and debridement of the inflamed sinuses were performed every 2–3 days. Medical treatment consisted of antibiotic and anti-inflammatory drugs. In the cases of dental sinusitis, the underlying dental pathology was addressed. Median hospitalisation time was 10 days (range 5–25 days) and the median number of endoscopic procedures (including the initial procedure) was 4 (range 3–7). Cases were followed-up by telephone consultations with their owners. Intervals between discharge and last follow-up ranged from 4 to 22 months (median 9.5 months). Complete recovery was reported in 10 cases, clinical improvement (occasional nonpurulent discharge) in two cases. Two cases were readmitted due to recurrence of the purulent nasal discharge; both subsequently underwent trephination of the affected sinuses and made a full recovery after removal of the remaining pathological sinus content.     

Intraoperative depression of the bulla of the maxillary septum as a method of improving sinus drainage without epistaxis in horses

Current methods of creating sinus drainage and allowing egress of a sinus pack at the end of surgery create significant haemorrhage. Given that haemorrhage is already a concern in some sinus surgeries, the method described allows for a significant reduction in blood loss. The objective was to describe a method of enlarging the nasomaxillary aperture in horses to allow egress of a sinus pack, and subsequent endonasal treatment, without incurring significant haemorrhage. The bulla of the maxillary septum is depressed using a gloved finger (through a sinus flap or trephine hole) or using a long curved Peine instrument under sinoscopic control before fenestration. No major operative or post-operative complications have been encountered. Satisfactory widening of the nasomaxillary aperture has been accomplished in all cases, although at times, when the bulla is under the floor of the dorsal conchal sinus, it can be difficult to compress. It is imperative that this procedure be performed before fenestration. If performed after fenestration, the most rostral edge of the fenestration can be difficult to identify, and this becomes an impediment to widening the nasomaxillary aperture. Enlarging the nasomaxillary aperture with a finger or blunt instrument allows improvements in sinus drainage without the complication of severe epistaxis. Depression of the bulla of the maxillary septum, before surgical fenestration into the rostral maxillary and ventral conchal sinuses, allows opening of the nasomaxillary aperture with minimal haemorrhage. Thereafter, the sinus pack can be egressed via this route, which is also large enough to perform sinus lavage and post-operative treatments endonasally without the risk of disturbing the external surgical site.     

Laser Vaporization of the Dorsal Turbinate as an Alternative Method of Accessing and Evaluating the Paranasal Sinuses

Objective: To report a technique for stoma creation into the conchofrontal sinus (CFS) through the dorsal turbinate and to evaluate stoma as a site for sinoscopy. Study Design: Prospective experimental study. Animals: Cadaveric equine heads (n=2) and normal adult horses (5). Methods: Technique feasibility was established on 2 cadaver heads. A diode laser fiber with a contact probe was passed into the nasal passage through a custom built, laser introducer rod (LIR). A videoendoscope was passed ventral to the LIR. A site on the caudal, medial aspect of the turbinate overlying the dorsal conchal sinus (DCS) was identified. A stoma to facilitate endoscope passage was created through the turbinate and sinoscopy performed to identify structures within the CFS and caudal maxillary sinus (CMS) and to evaluate the quality of the approach. The procedure was then performed in standing, sedated horses. Time required, laser energy used and complications were recorded. Endoscopy was performed ≥5 weeks postoperatively to assess stoma size and long‐term effects of the procedure. Results: A stoma was successfully created through the turbinate in both cadaveric skulls and in 4 horses; the stoma persisted for ≥5 weeks. The location of the stoma in 1 horse precluded sinoscopy. Conclusions: Laser vaporization of the dorsal turbinate through the nasal passage creates a stoma that lasts for at least 5 weeks providing a portal to the paranasal sinuses. Based on experience in 1 horse stoma location is critical to ensure adequate endoscope manipulation and sinoscopy. Clinical Relevance: Standing endoscopic sinusotomy within the nasal cavity through the DCS is an alternative to more invasive sinusotomy techniques with fewer potential complications and a cosmetic result.     

Use of serial standing computed tomography for diagnosis,treatment and monitoring of a horse with acute myonecrosis of the head

An 11-year-old American Quarter Horse gelding was referred to the JT Vaughan Large Animal Teaching Hospital at Auburn University, College of Veterinary Medicine, for investigation of acute and severe right-sided facial swelling and nasal discharge. Standing computed tomographic (CT) examination of the head identified severe soft tissue swelling surrounding the right mandible, emphysema within the soft tissues tracking along fascial planes and right-sided caudal and rostral maxillary sinusitis. Using CT identification and ultrasound guidance, several targeted fasciotomies were created into the right masseter, cranial cervical musculature, supraorbital space and caudo-medial aspect of the mandible. The right-sided sinusitis was treated by right conchofrontal sinus trephination and lavage. Aerobic and anaerobic cultures obtained from the fasciotomy sites and conchofrontal sinus both yielded Prevotella intermedia and Peptostreptococcus asaccharolyticus. During hospitalisation, serial, standing CT examinations were performed for monitoring case progression and guiding further fasciotomies in the face of continued myonecrosis. Follow-up CT performed at 1 month showed resolution of the emphysema and presence of chronic right ventral conchal sinusitis. The sinusitis was treated by fenestration of the right ventral concha with a diode laser via the nasal passage.     

Endoscopic Examination of Normal Paranasal Sinuses in Horses

The frontal, caudal maxillary, and rostral maxillary sinuses of 10 equine cadavers were examined endoscopically, and the findings were confirmed by sinusotomy. Similar endoscopic examinations were performed in five conscious, adult horses by using sedation and local anesthesia. Useful portals of entry for the arthroscope in adult horses were: for the frontal sinus, 60% of the distance in a lateral direction from midline to 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. The frontal sinus portal was most useful for examination of the frontal and caudal maxillary sinuses. The caudal maxillary sinus portal was most useful for examining the sphenopalatine sinus. Structures in the frontal and caudal maxillary sinuses could be approached surgically by viewing them through the frontal sinus portal and guiding an instrument to them through the caudal maxillary sinus portal. Tooth root identification was reliable for the second and third upper molars in animals older than 5 years, but was more difficult for the rostral teeth and in younger animals. Endoscopy was not difficult to perform and was well tolerated in standing, sedated horses. The only complication of this procedure was mild, local subcutaneous emphysema that resolved spontaneously within 14 days.     

Surgical anatomy of the nasal and paranasal sinuses in Egyptian native sheep (Ovis aries) using computed tomography and cross sectioning

The present work aimed to describe the normal computed tomography (CT) and cross‐sectional anatomy of the nasal and paranasal sinuses in sheep and to correlate these features with the relevant clinical practices. Twenty apparent healthy heads of Egyptian native breed of sheep (Baladi sheep) of both sexes were used for studying these sinuses. CT images and their closely identical cross sections of the same head were selected and serially labelled in a progression from the rostral nasal region to the caudal aspect of the head using cheek teeth as landmarks. The current investigation reported seven sinuses in sheep, including maxillary, frontal, lacrimal and sphenoidal as paranasal, as well as dorsal and middle conchal and ethmoidal as nasal with unnoticeable palatine and ventral nasal conchal sinuses. The boundaries, extension, structure and communications of these sinuses were fully described. The current study provided anatomical guidelines for surgical interference in the frontal and maxillary sinuses during trephination, dehorning and sinuscopy. Also, an acceptable anatomical explanation was reported in this study for the high incidence of maxillary sinusitis than other sinuses. CT and cross‐sectional anatomy could be used as helpful database for diagnosis and clinical interference of the nasal and paranasal sinuses in sheep.     

Extra-nasal approach to access the dorsal and ventral conchal bullae in horses

Nasal conchal bulla empyema can be found in up to 20% of horses with paranasal sinus disease but remains difficult to diagnose and can result in persistent unilateral discharge before presentation. Our aim in this experimental ex vivo study was to describe two extra-nasal approaches to access the nasal conchal bullae. Six cadaveric heads were used to determine the ideal landmarks to access the dorsal and ventral conchal bullae through two rhinocenteses performed with the aid of a 14G needle and a mallet through the maxillary bone, and to access both bullae simultaneously through a 13-mm diameter trephination. Both techniques were performed bilaterally. To assess correct placement of the rhinocenteses and trephination, each bulla was injected with a coloured insulating foam before performing a maxillary bone flap to inspect the bullae. Both bullae were successfully entered with the 14G needle in all instances. The nasolacrimal duct was damaged while entering the ventral conchal bulla in 3/12 approaches. Trephination of the maxillary bone allowed access to both nasal conchal bullae in all cases but one, where the portal was placed too dorsally and did not allow access to the ventral conchal bulla. The opening created with the trephine could allow the use of a small instrument such as a rongeur which could have diagnostic and therapeutic benefits. The limitations are that this was an ex vivo study and nasolacrimal duct damage could have clinical repercussions if the duct becomes obstructed after accessing the ventral conchal bulla. It was concluded that the techniques described are simple, minimally invasive and provide access to the conchal bullae for diagnostic and therapeutic purposes. Additionally, they may reduce the need for CT or laser for the diagnosis and treatment of bulla empyema.     

Endoscope-Guided Balloon Sinuplasty of the Equine Nasomaxillary Opening

Objective— To describe and evaluate an endoscope-guided balloon sinuplasty technique for dilation of the equine nasomaxillary opening (NMO).
Study Design— Experimental study.
Animals— Equine cadaver heads (n=5); Quarter Horses (n=4).
Methods— A custom rigid balloon introducer was passed into position within the NMO at the caudal recess of the middle meatus. Under endoscopic guidance, a balloon catheter was passed via the introducer into the NMO and inflated to 6 atmospheres, for 30 seconds 3 times, to dilate the NMO. Drainage rates after sinuplasty were evaluated for the caudal maxillary sinus in 5 cadaver heads and balloon sinuplasty was performed in 4 live horses. All skulls were examined to assess the efficacy of NMO dilation.
Results— Positioning of the balloon catheter was readily achieved in all heads. Dilation was observed endoscopically and confirmed on necropsy in all heads. Drainage rates from the caudal maxillary sinus increased significantly (∼1.5 ×) in all 5 cadaver heads after sinuplasty ( P =.001).
Conclusions— Dilation of the NMO improved sinus drainage in all 5 cadaver heads. Endoscopic evaluation of the ostium revealed marked dilation of the NMO in live horses and indicates potential clinical use in standing horses.
Clinical Relevance— Balloon sinuplasty of the NMO opening is an easily performed, clinically applicable technique for use in standing horses. Clinical studies will be necessary to evaluate the efficacy of this technique in diseased sinuses.     

Equine dental disease part 4: a long-term study of 400 cases: apical infections of cheek teeth

Of 400 horses referred because of equine dental disease, 162 suffered from primary apical infections of their cheek teeth (CT), including 92 with maxillary CT infections and 70 with mandibular CT infections. Maxillary swellings and sinus tracts were more common (82 and 26% incidence, respectively) with infections of the rostral 3 maxillary CT, than with infections of the caudal 3 maxillary CT (39 and 5% incidence, respectively). Nasal discharge was more commonly present with caudal (95%) than rostral (23%) maxillary CT infections. Mandibular CT apical infections commonly had mandibular swellings (91%) and mandibular sinus tracts (59%) and these infections were closely related to eruption of the affected CT. A variety of treatments, including medical treatment, apical curettage, repulsion and oral extraction of affected teeth were utilised in these cases, with oral extraction appearing to be most satisfactory. Infections of caudal maxillary CT with a secondary paranasal sinusitis were most refractory to treatment, with a complete response to the initial treatment achieved in just 33% of these cases. Most other cases responded fully to their initial treatment. The long-term response to treatment was good in most cases.     

Sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty for treatment of dorsal displacement of the soft palate in 102 thoroughbred racehorses

Objective— To compare racing performance before and after sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty in Thoroughbred racehorses with intermittent dorsal displacement of the soft palate (DDSP).
Study Design— Retrospective study.
Animals— Thoroughbred racehorses (n=102) with DDSP.
Methods— Retrieved data included signalment, primary complaint, and upper respiratory tract endoscopic finding. Lifetime race records were compared for earnings per start before and after surgery, days to 1st start, and races won postoperatively.
Results— Comparing mean earnings per start for 3 races before ($2792) and after ($3806) surgery, racing performance improved significantly after surgery in 63% (46/73) of horses that competed in at least 1 race before and after surgery ( P =.02). Mean and median days to 1st start after surgery were 109 and 69 days, respectively. Of horses that raced postoperatively 65% (60/92) won at least 1 race, and 77% (71/92) raced in >5 races after surgery.
Conclusions— Sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty significantly improved racing performance in experienced Thoroughbred racehorses with performance limiting DDSP, and overall had a similar outcome to other reported surgical techniques for treatment of DDSP.
Clinical Relevance— Sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty should be considered as a surgical approach to correction of DDSP in Thoroughbred racehorses; however, it is possible that staphylectomy may not be necessary to achieve a desirable outcome.     

Transarterial coil embolization of the internal and external carotid and maxillary arteries for prevention of hemorrhage from guttural pouch mycosis in horses

OBJECTIVES: To develop a transarterial coil embolization technique for occlusion of the internal carotid artery (ICA), external carotid artery (ECA), and maxillary arteries (MA) in normal horses and to evaluate this technique for prevention of hemorrhage in horses affected with guttural pouch mycosis. ANIMALS: Ten adult, normal horses and 4 horses with guttural pouch mycosis. METHODS: All horses had transarterial coil embolization of the rostral and caudal ICA, caudal MA, and rostral ECA. In 1 affected horse, an aberrant actively bleeding branch of the ECA was also occluded. Normal horses had a premortem angiogram, and were killed either at 1 or 2 weeks or 1, 2, or 3 months after the procedure. Specimens from the ICA, ECA and MA were evaluated by light microscopy. RESULTS: No surgical complications were observed, except 1 horse that developed laryngeal hemiplegia and 1 pilot horse that had embolization of the cerebral arterial circle. In normal horses, premortem angiography confirmed complete occlusion of all vessels, and coils were positioned as intended. All normal horses had partially maturing to mature, continuous thrombi occluding at the coils. In affected horses, no further episodes of epistaxis were observed. By day 60, all mycotic plaques had resolved without further treatment. Ophthalmic complications were not observed. CONCLUSION: Transarterial embolization provided a safe, rapid, and effective method for ICA, ECA, and MA occlusion in normal and affected horses. In affected horses, the technique was possible despite active bleeding, allowing adequate identification and occlusion of all sources of hemorrhage.     

A Large Frontonasal Bone Flap for Sinus Surgery in the Horse

A large frontonasal bone flap was created to treat diseases of the paranasal sinuses in 14 horses. The bone flap was made as wide as possible within the confines of the nasolacrimal duct so the floor of the frontal sinus and the dorsal and ventral conchae could be opened. These openings exposed the nasal passages, maxillary sinuses, and ventral conchal sinus thereby facilitating removal of diffuse and localized lesions from these sites. Diseases treated were ethmoid hematomas (4 horses), sinus cysts (5 horses), cryptococcal granuloma, osteoma, hemangiosarcoma, pus in the ventral conchal sinus, and periapical infection of a second molar. Four horses were euthanatized during or after surgery, one because of postsurgical pleuritis and pneumonia (horse with osteoma) and three because of their primary problems (cryptococcal granuloma, hemangiosarcoma, pus in the ventral conchal sinus). Skin suture abscesses that responded to treatment developed in four horses. Ten horses returned to their intended uses, the sinus flaps healed without blemish, and the original problems did not recur. The frontonasal flap technique provided greater access to all paranasal sinuses than methods described previously.     

Arthroscopic Anatomy of the Equine Temporomandibular Joint

OBJECTIVE: To develop an arthroscopic approach to, and describe the arthroscopic anatomy of, the equine temporomandibular joint (TMJ). STUDY DESIGN: Cadaveric study, after which the technique was tested in horses. ANIMALS OR SAMPLE POPULATION: Ten cadaveric equine heads and 5 normal horses (age, 5-13 years; weight, 425-545 kg). METHODS: Specimens or horses were positioned in right lateral recumbency. After fluid distention of the TMJ, arthroscopic portals were made in the dorsal compartment over the most prominent portion of the joint outpouching (caudodorsal approach) and in rostral and intermediate locations. The joint was explored and photographed. Positional changes in the mandible were made to determine if observation of the joint could be improved. Instrument portals were created to assess the feasibility of surgical arthroscopy. Cadaveric heads were dissected to assess iatrogenic damage, whereas experimental horses were observed for postoperative complications for 30 days. RESULTS: A caudodorsal arthroscopic approach provided the best evaluation of the dorsal compartment of the TMJ. The approach allowed observation of the rostral and caudal synovial pouches and the lateral aspect of the joint including the articular disc. Examination of the medial aspect of the joint was limited to the most rostral and caudal aspects. Access to the lateral aspect of the ventral compartment of the TMJ was precluded by the position of the transverse facial artery and vein. In specimens, iatrogenic damage was minimal and limited to the articular fibrocartilage, articular disc, and penetration of the parotid salivary gland. If the latter also occurred in horses, no adverse effects were noted. In horses, mild fluid extravasation occurred and resolved within 1 day. All horses ate normally after surgery but had periarticular swelling and mild pain upon palpation of the TMJ for 2 days. CONCLUSIONS: A caudodorsal arthroscopic approach to the TMJ allowed adequate observation of the lateral aspect of the dorsal compartment of the joint. Access to the ventral compartment was precluded by the location of the transverse facial artery and vein. CLINICAL RELEVANCE: Conditions affecting the lateral and caudal aspects of the dorsal compartment of the TMJ should be visible by arthroscopy.