Harry W. Boothe, DVM, MS, DACVS
The primary indications for middle ear surgery in small animals include unresponsive otitis media (with or without otitis externa), removal of inflammatory polyps (cats), and exploration of the tympanic cavity. Pain is the primary clinical sign associated with otitis media; however, head shaking, ear scratching, otic discharge, head tilt, vestibular signs, and Horner's syndrome may be observed.
Physical examination, including otoscopic evaluation and radiologic (including computerized tomography [CT]) evaluation confirms the diagnosis. Otoscopically, attempt to visualize the tympanic membrane prior to irrigating the external ear canal. Exudate or masses within the external ear canal may obliterate the tympanic membrane. The tympanic membrane may be reddened, bulge into the ear canal, or be ruptured. Radiographs of the skull should be made to evaluate the tympanic bullae. Lateral, ventrodorsal, oblique, and open-mouth projections of the skull can be made. Radiographic views which consistently provide helpful information are the oblique and open-mouth projections. Computerized tomographic evaluation of the tympanic bulla is particularly helpful at distinguishing fluid density from that caused by tissue. The anatomy of the tympanic bullae in dogs and cats differ. Both species have the tympanic cavity connected to the pharynx by the auditory tube. The tympanic bullae of both dogs and cats appear normally as a very thin shell of bone with an intraluminal air density. With disease and chronicity, the tympanic bullae become sclerotic and thickened, and the tympanic cavity may contain a fluid or tissue density.
The feline tympanic bulla is divided into ventromedial and dorsolateral compartments by an incomplete transverse septum. Both compartments are accessed via a ventral bulla osteotomy, with the larger ventromedial compartment entered first. Only the smaller dorsolateral compartment is visualized via a lateral bulla osteotomy; however, flushing of the ventromedial compartment is possible. The sympathetic fibers in the middle ear are present on the dorsal aspect of the bulla and are rather readily traumatized in the cat compared to the dog.
Otitis media is a relatively common disease that often goes unrecognized. It frequently accompanies chronic otitis externa, particularly in dogs, and it may be seen as a primary condition in cats. Otitis media may be diagnosed on otoscopic exam by visualizing changes in the tympanic membrane. Such changes may include loss of integrity, change in color (becoming more opaque and grey), and change in shape (becoming more convex and bulging). Radiographic (including CT) assessment of the tympanic bullae can be helpful in diagnosing otitis media. It is easier to distinguish changes in the tympanic cavity on CT than with radiographs. Radiographs are most helpful in assessing duration of middle ear disease, because the tympanic bullae become sclerotic with chronicity.
Inflammatory polyps are benign, pedunculated growths that may occur in the nasopharynx, middle ear, or external ear canal in cats. Site of origin is believed to be the mucosa of the auditory canal or the tympanic cavity. Inflammatory polyps may extend from the tympanic cavity through the tympanic membrane into the external ear canal or via the auditory tube into the nasopharynx, or both. Histologically, inflammatory polyps are composed of a core of vascularized fibrous connective tissue covered by squamous of columnar epithelium. Inflammatory polyps occur most commonly in cats < 2 years of age, but they can occur in cats of any ages. There appears to be no gender or breed predilection. Otitis media accompanies inflammatory polyps within the tympanic bulla, but it is unclear whether the infection initiated the polyp growth or is secondary to its presence.
Clinical signs observed depend of the size and location of the polyp. Nasopharyngeal polyps often result in signs of upper respiratory tract infection, upper airway obstruction, and possibly dysphagia. Otic polyps result in signs of otitis externa, otitis media, and possibly otitis interna. Thoroughly evaluate the external ear canal otoscopically and the nasopharynx visually and by palpation. Visualize the area dorsal to the soft palate by retracting the soft palate rostrally with a spay hook, and use a dental mirror to facilitate evaluation of the area, or use a flexible endoscope with its end retroflexed above the soft palate. Careful digital palpation through the soft palate may also reveal masses.
Treatment of otitis media often involves a combination of medical and surgical techniques. Accurate microbiologic assessment of the tympanic cavity is critical to success. If otitis media accompanies chronic otitis externa, then a total ear canal ablation with bulla osteotomy is frequently recommended. If primary otitis media is present, then a myringotomy may be indicated. Myringotomy may be considered both a diagnostic and a therapeutic procedure. Puncture the pars tensa portion of the tympanic membrane at the five or seven o'clock position using a spinal needle or a small Steinmann pin. Use a 3.5 F polypropylene catheter to aspirate fluid from the tympanic cavity for culture and susceptibility testing. Flush the tympanic cavity with warm saline until the escaping fluid is clear. Choose an appropriate systemic antimicrobial agent based on susceptibility testing results. Continue therapy for 4 to 6 weeks.
Surgical treatment of otitis media usually involves performing a bulla osteotomy. The tympanic bulla may be approached surgically through two approaches: lateral and ventral. The lateral bulla osteotomy is usually reserved for cases with concurrent otitis externa that require a total ear canal ablation. Ventral bulla osteotomy is performed as a separate procedure. Ventral bulla osteotomy provides better visualization and exposure of the ventral aspect of the tympanic cavity than the lateral approach. Position the paramedian skin incision midway between the angular process of the mandible and the level of the wings of the atlas. Dissect between the digastricus muscle and the hypoglossal and styloglossal muscles. Identify the tympanic bulla as a raised, rounded structure between the angular process of the mandible and jugular (paracondylar) process of the skull. Penetrate the tympanic bulla with a Steinmann pin and enlarge the opening with rongeurs. Obtain microbiologic and histologic samples from the tympanic cavity. Flush the tympanic cavity with warm saline solution, and carefully remove tissue and exudate by gentle curettage. Close the incision routinely.
Surgical removal of the polyp combined with ventral bulla osteotomy is the treatment of choice for inflammatory polyps. Remove the nasopharyngeal and/or otic portion of the inflammatory polyp using traction. With the cat secured in dorsal recumbency with the head slightly elevated, perform a ventral bulla osteotomy Enter the ventromedial compartment and collect samples for culture and susceptibility testing as well as biopsy. Carefully remove remnants of the polyp from the ventromedial compartment by gentle curettage. Avoid the dorsal aspect of the ventromedial compartment and the dorsolateral compartment when curetting Repeatedly and thoroughly flush the tympanic bulla. Close the incision routinely.
Monitor the cat closely during anesthetic recovery for respiratory distress. If observed, administer corticosteroids. Administer analgesics for 1 to 2 days. Administer antimicrobials based on culture and susceptibility testing results. Amoxicillin/clavulanic acid seems to be a good empirical choice for cats with inflammatory polyps before culture results are known. Horner's syndrome is a common complication after bulla osteotomy in cats. Most signs of Horner's syndrome will resolve within a few days to a few weeks postoperatively. Head tilt toward the affected side may be evident postoperatively. Postoperative persistence of an existing head tilt is often permanent.
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