Endoscopic Examination of Normal Paranasal Sinuses in Horses

Veterinary Surgery, 20, 6, 418-423, 1991

Endoscopic Examination of Normal Paranasal Sinuses in Horses ALAN J. RUGGLES, DVM, MICHAEL W. ROSS, DVM, Diplomate ACVS, and DAVID E. FREEMAN, MVB, PhD, Diplomate ACVS

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.

sinuses the horse-frontal, T dorsal conchal, ventral conchal, rostral maxillary, caudal maxillary, and sphenopalatine-are lined with reH E SIX PARANASAL

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spiratory epithelium and communicate directly or indirectly with the nasal cavity through the nasomaxillary apertures. Paranasal sinus disorders in horses may be caused by dental disease, cyst formation, neoplasia, ethmoid hematomas, traumatic injury, bacterial or fungal infection, or primary inflammation. Clinical signs of sinus disease include nasal discharge, epistaxis, epiphora, facial deformity, stertor, dyspnea, and exophthalmos.2 Techniques for diagnosis of sinus disorders include evaluation of clinical signs, radiography, endoscopic examination of the upper airway, and aspiration of sinus contents for cytologic and bacteriologic examination.2-6 Although these techniques are useful, information yielded by them may be difficult to interpret.6 Surgical

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exploration through bone flaps may produce a definitive diagnosis, but it requires general anesthesia and additional expen~e.~.’ Examination of the equine paranasal sinuses by arthroscope has been described, but detailed descriptions of the preferred portal placement, the anatomy of the sinus as viewed through the arthroscope, and the risk of complications are lacking.’ Endoscopy can be a valuable diagnostic tool, especially when noninvasive techniques yield inconclusive results. It may allow the diagnosis of and treatment for sinus disease in conscious horses without the need for general anesthesia and exploratory flap sinusotomy. The objectives of this study were to refine and evaluate endoscopic methods for the frontal and caudal maxillary sinuses, develop a method to examine the rostral maxillary sinus, describe the anatomy of the sinuses as seen from

From the Department of Clinical Studies, University of Pennsylvania, School of Veterinary Medicine, New Bolton Center, Kennett Square, Pennsylvania. Reprint requests: A. J. Ruggles, DVM, New Bolton Center, 382 West Street Road, Kennett Square, PA 19348.

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RUGGLES, ROSS, AND FREEMAN each portal. and identify any postoperative complications in normal. conscious horses. Materials and Methods Cadaver SpPcitnenJ

Left and right paranasal sinuses of 10 horses euthanatized for reasons other than upper airway disorders were examined endoscopically. The horses were 2 to 10 years of age and weighed 3 5 0 kg to 5 0 0 kg. Endoscopic portals were made with a 6.35 mm ( 1 / 4 ) Steinmann pin in a hand-held chuck through a 1.5 cm skin incision. In the frontal sinus. the portal was placed 60% ofthe distance from the midline to the medial canthus and 0.5 cm caudal to a line joining both medial canthi (20 examinations) (Fig. IA). In the caudal maxillary sinus, the portal was placed 2 cm rostral and 2 cm ventral to the medial canthus (20 examinations) (Fig. IB). In the rostral maxillary sinus, two portals were evaluated. A rostral portal 3 cm caudal to the infraorbital canal and 1 cm ventral to a line joining the infraorbital foramen and medial canthus was used in 20 examinations. A caudal portal placed 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 medial canthus was used in 12 examinations. For portals in the rostral maxillary sinus, the levator nasolabialis muscle was pushed dorsally with the Steinmann pin to prevent damage to the muscle and reduce hemorrhage. The holes were enlarged by gently rotating the sharp edges of the pin at the margins of the holes to allow greater mobility of the arthroscope. A 4.0-mm, 30" arthroscope.* a fiberoptic light cable, and a 150-watt light sourcet were used. The sinuses were examined directly through the arthroscope without a camera or monitor. Each portal was evaluated for ease of identification of structures in the frontal and maxillary sinuses. With the arthroscope placed in the frontal sinus portal, structures in the frontal and caudal maxillary sinuses were marked with colored map pins placed with Ferris-Smith rongeurs. The rongeurs were inserted through the caudal maxillary sinus portal and guided with the arthroscope in the frontal sinus portal. When the structures had been marked, maxillary and frontal sinusotomies were made and the exact locations of the colored pins were determined. The structures identified were the ethmoid turbinate, frontomaxillary aperture, dorsal conchal sinus, infraorbital canal, ventral conchal bulla, sphenopalatine sinus, conchal maxillary aperture, nasomaxillary aperture, fourth upper premolar (PM,), first (MI), second (M2), and third (M,)

* Scanlon Instruments. Englewood. Colorado t Richard Wolf Medical Instruments Co., Rosemont. Illinois

upper molars, and the maxillary sinus septum. The marking pins were left in the roots of the caudal cheek teeth and a dorsal 60" lateral-ventrolateral oblique radiograph was made of each side of the heads to confirm the location of the pins relative to each tooth root.

Conscious Hor.w.y Exploratory endoscopy of the left frontal, caudal maxillary, and rostral maxillary sinuses was performed in five adult horses. The frontal sinus portal, caudal maxillary sinus portal. and caudal portal of the rostral maxillary sinus were used. Before and 1 day after surgery, packedcell volume and total protein values were determined. A dorsal 60" lateral-ventrolateral oblique radiograph of the left paranasal sinuses was made before and 30 days after endoscopic examination. The horses were sedated with detomidinet (0.02 mg/kg intravenously [IV]), and the sites were prepared for aseptic surgery. Portal sites were infiltrated with mepivacaine.4 During examination, balanced polyionic sterile fluid (500 mL) was lavaged through each of the rostral maxillary and caudal maxillary sinuses. The skin incisions were closed with 2-0 nylon in a simple interrupted pattern. Phenylbutazone 11 was administered after surgery (4.4 mg/kg, orally BID on day 1, and 2.2 mg/ kg, BID on days 2 and 3). The horses were examined for evidence of discomfort. nasal discharge or bleeding, incisional complications, and cosmetic appearance daily for the first 4 days, and then on days 7, 14, 30, and 60. Skin sutures were removed on day 14. Results Cudaver Spt crmens

The frontal sinus portal was 5.0 cm (range, 4.4 cm to 5.4 cm) lateral to midline (Fig. 1A) and consistently provided access to the frontal and caudal maxillary sinuses. Sinus structures were not damaged by the Steinmann pin. The portal was positioned directly over the frontomaxillary aperture. and the arthroscope could be directed easily through this aperture to examine the caudal maxillary sinus. On both sides of the head in all 10 horses, the ethmoid turbinate, dorsal conchal sinus, frontomaxillary aperture, infraorbital canal. ventral conchal bulla. and nasomaxillary aperture were identified correctly and evaluated (Fig. 2). The entrance to the sphenopalatine sinus was observed in all examinations, and the sphenopalatine sinus could be entered in nine examinations by directing $ Dormosedan. Norden Laboratories, Lincoln. Nebraska 5 Carbocaine-V. Winthrop Veterinary Products. New York. New York I( Phenylbutazone. Burns Veterinary Supply, Anthony Products, Arcadia, California

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ENDOSCOPY OF PARANASAL SINUSES

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A

Fig. 1. Portal locations for endoscopic examination of the equine paranasal sinuses. (A) Dorsal view. The solid circle marks the location of the frontal sinus portal, and the dotted circle marks the location of the frontomaxillary aperture, ventral to the portal. (B) Lateral view. (a) Rostra1portal of the rostral maxillary sinus; (b) caudal portal of the rostral maxillary sinus; (c) caudal maxillary sinus portal.

the arthroscope medial and caudal to infraorbital canal. The maxillary sinus septum was seen in eight examinations. The caudal maxillary sinus portal provided access to the caudal maxillary sinus. Sinus structures were not damaged by the Steinmann pin. The portal was just dorsal to the level ofthe caudal cheek teeth and infraorbital canal. On both sides of the head in all 10 horses, the ethmoid turbinate, frontomaxillary aperture, infraorbital canal, ventral conchal bulla, and nasomaxillary aperture could be identified correctly and evaluated (Fig. 3 ) . The sphenopalatine sinus could be entered by directing the arthroscope dorsal to the infraorbital canal. The entrance to the dorsal conchal sinus could be seen by directing the arthroscope dorsally and medially through the frontomaxillary aperture in three examinations (Fig. 4). The maxillary sinus septum could be seen in 12 examinations. The rostral portal of the rostral maxillary sinus provided access to the rostral maxillary sinus in 18 examinations. In two examinations, the maxillary sinus septum was penetrated and the arthroscope was inserted into the caudal maxillary sinus. In two examinations, the roots of PM4were damaged by the Steinmann pin. The infraorbital canal was seen in 15 examinations, the conchomaxillary

aperture was seen in 12 examinations, and the maxillary sinus septum was seen in 11 examinations. In one examination, the nasomaxillary aperture of the rostral maxillary sinus was identified. Positive identification of cheek teeth roots in the rostral maxillary sinus was difficult. The caudal portal of the rostral maxillary sinus was made for 12 examinations. The portal was positioned 4.0 cm (range, 3.3 cm to 4.5 cm) caudal to the rostral end of the facial crest and provided access to the rostral maxillary sinus in eight examinations. In four examinations, the caudal maxillary sinus was entered. When the arthroscope was placed properly in the rostral maxillary sinus, identification of the infraorbital canal, maxillary sinus septum, and conchomaxillary aperture was possible (Fig. 5). Identification of the roots of the cheek teeth was difficult. The roots of M2 and M3 were identified correctly in 16 examinations and could be seen equally well from the frontal sinus and caudal maxillary sinus portals. Root identification was difficult through the arthroscope and after flap sinusotomy in horses younger than 5 years. The roots of the caudal cheek teeth blended into the structure of the infraorbital canal, which made positive identification difficult, especially for PM4 and M I . In older horses, the roots of the caudal cheek teeth were

RUGGLES, ROSS, AND FREEMAN

Fig 2 Left frontal and caudal maxillary sinuses, viewed through the frontal sinus portal in a cadaver specimen Rostral is to the left caudal is to the right, and medial is uppermost (A) Ventral conchal bulla, (B) ethrnoid turbinate, (C) infraorbital canal, (D)roots of the second molar, (E) roots of third molar, (F) caudal border of frontornaxillary aperture, (G)dorsal conchal sinus Short arrow points to nasomaxillary aperture, curved arrow points to entrance to sphenopalatine sinus, medial to infraorbital canal

ventral to the infraorbital canal and were more easily identified. The maxillary sinus septum passed over the roots of MZin 14 specimens and between M , and Mzin six specimens. In all specimens. Mi was located in the rostral maxillary sinus.

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Fig 3 Left caudal maxillary sinus, viewed through the caudal maxillary sinus portal in a cadaver specimen Rostral is to the left, caudal is to the right, and dorsal is uppermost (A) ventral conchal bulla, (B) ethmoid turbinate, (C) infraorbital canal, (D) roots of the second molar, (E) roots of the third molar, (F) maxillary sinus septum, black arrow points to medial aspect of the frontomaxillary aperture, white arrow points to entrance to the sphenopalatine sinus, medial to infraorbital canal

was noted when mucosa was probed with surgical instruments and during lavage. Lavage fluid tended to fog the view through the arthroscope. but this was diminished if the fluid was warmed to 37°C. All incisions healed primarily. The horses did not resent palpation of the portal sites. Fever. nasal discharge, and

Conscious Horses The frontal sinus portal consistently provided access to the frontal and caudal maxillary sinuses. The caudal maxillary sinus portal provided access to the caudal maxillary sinus in four horses. In one horse. the rostral maxillary sinus was entered inadvertently, so a second portal was created caudal to the first portal. Use of either the frontal or the caudal maxillary sinus portals allowed identification of sinus structures in all five horses. The caudal portal of the rostral maxillary sinus provided access to the rostral maxillary sinus in three horses and to the caudal maxillary sinus in two horses. When the arthroscope was placed in the rostral maxillary sinus, identification of the maxillary sinus septum, infraorbital canal, and conchomaxillary aperture was possible. Sinus structures were not damaged while making the portals. Detomidine provided excellent chemical restraint in four horses; one horse required administration of xylazine7 (0.37 mg/kg IV) during endoscopy. Some reaction T Rompun. Mobay Corporation, Shawnee, Kansas

Fig. 4. Left caudal maxillary sinus viewed through the caudal maxillary sinus portal in a cadaver specimen. Rostral is to the left, caudal is to the right, and dorsal is uppermost. The arthroscope is positioned to examine the dorsocaudal aspect of the sinus. (A) roof of the frontal sinus; (8)ventral conchal bulla; (C) ethmoid turbinate; (D)infraorbital canal; small black arrow points to medial aspect of the frontomaxillary aperture; arrowhead points to nasomaxillary aperture; white arrow points to entrance to sphenopalatine sinus, medial to infraorbital canal.

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ENDOSCOPY OF PARANASAL SINUSES

Fig. 5. Left rostral maxillary sinus viewed through the caudal portal of the rostral maxillary sinus in a cadaver specimen. Rostra1 is to the left, caudal is to the right, and dorsal is uppermost. (A) infraorbital canal; (B) roots of first molar; (C) maxillary sinus septum; curved arrow points to location of the conchomaxillary aperture, which leads into the ventral concha1 sinus.

changes in appetite, attitude, packed-cell volume, or total protein did not develop. Subcutaneous emphysema developed around the maxillary sinus portals in all horses. Emphysema was considered mild in four horses, and resolved completely within 4 days in these horses. In one horse, subcutaneous emphysema was more extensive and was present from the caudal maxillary sinus portal to the nasoincisive notch. This remained nonpainful and cool and resolved by day 14. In two horses. there was soft tissue swelling 1 cm in diameter around the caudal maxillary sinus portal. The swelling was cool and nonpainful, and it was most prominent between days 14 and 30. By day 30, swelling had resolved completely in one horse and remained 0.5 cm in diameter in another. At day 60, small fibrous enlargements ( < 0.3 cm) could be palpated over one frontal and one caudal maxillary portal. All hair had regrown and scars were difficult to detect. Cosmetic results at day 60 were judged to be excellent. Radiographs made on day 30 revealed no evidence of sinusitis, dental disease, or fluid accumulation.

Discussion Endoscopic examination of the equine paranasal sinuses provided a useful, detailed evaluation of sinus structures. Sinus structures were identified consistently and accurately, with the exception PM4 and M , . An instrument in the caudal maxillary sinus portal could have been used to obtain tissue for biopsy under guidance of an arthroscope placed in the frontal sinus portal. A separate portal for instrument placement was not attempted

in the rostral maxillary sinus. Endoscopy was not difficult to perform and was well tolerated. Periodic cleansing of the arthroscope was necessary because debris and blood obscured the view. A video camera was not used because it reduced light intensity even when a 1000-watt light source was used. The portals used for the frontal and caudal maxillary sinuses consistently provided an excellent view of these sinuses. The rostral maxillary sinus was difficult to examine consistently through the portals used for it. The caudal portal of the rostral maxillary sinus was judged to be superior to the rostral portal because sinus structures were avoided and the sinus could be evaluated more completely. The frontal sinus portal is recommended for general examination of the frontal and caudal maxillary sinuses in standing horses. This is in agreement with a previous report.' The frontomaxillary aperture tends to be located laterally in the frontal sinus, and a portal placed approximately 5 cm lateral to midline in adult horses (450 kg) will be centered above it. Since the location of the maxillary sinus septum is variable, we recommend that the caudal maxillary sinus portal be placed 2 cm rostral to the level of the medial canthus. Manipulation of the arthroscope through the caudal maxillary sinus and both rostral maxillary portals was more difficult and less comfortable for the surgeon than through the frontal sinus portal. The caudal maxillary sinus portal allowed more consistent examination of the sphenopalatine sinus than the frontal sinus portal. The frontal sinus and caudal maxillary sinus portals should be used concurrently if surgical manipulation is necessary in the frontal or caudal maxillary sinuses. The variable location of the maxillary sinus septum precluded accurate identification of the correct site for the rostral maxillary sinus portal. The septum is usually located 5 cm caudal to the rostral end ofthe facial crest."") In one horse, it was 2 cm rostral to the medial canthus. Radiographs obtained before surgery may be useful in locating the maxillary sinus septum. In this study, the maxillary sinus septum was most commonly found at the rostral portion of Mz. We recommend entering the rostral maxillary sinus immediately rostral to the maxillary sinus septum. There were no serious complications associated with the procedure. and cosmetic results were judged to be excellent at day 60. Owners should be warned of the risk of subcutaneous emphysema and the potential for the production of excessive callus or fibrous tissue at the portal sites. The potential for hairless or white-haired regions at portal sites exists, but the condition was not seen in this study.

RUGGLES, ROSS, AND FREEMAN Endoscopy proved a reliable method of evaluating sinus structures in normal. conscious horses, and the information gained from this study may be applied clinically. As a diagnostic tool, its value may be greatest when standard. noninvasive methods yield inconclusive results. Endoscopy may be most useful for the examination of horses with primary sinusitis, sinus hemorrhage. or neoplastic lesions if fluid or masses associated with these abnormalities do not restrict the field of view. Lavage of the sinus with large volumes of tluid through the arthroscope cannula may improve visibility when disease is present. Sedatives and topical application of local anesthetic agents may be necessary when obtaining tissue for biopsy from within the sinus structures. Hemorrhage was slight and did not complicate endoscopic evaluation in normal horses, but it may be a risk when disease is present and during biopsy or surgical procedures.

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