Indications

Ventral bulla osteotomy (VBO) is indicated for diseases of the middle ear, including chronic otitis media that cannot be resolved medically, inflammatory polyps, cholesteatomas, granulomas, and, rarely, neoplasia.¹ To ensure appropriate case selection, signalment, presenting signs, results of diagnostic testing/imaging, and response to therapy should all be taken into consideration.

Clinical signs of middle ear disease can include head shaking, pain on deep palpation of the ear, head tilt (pain or vestibular), and other signs of vestibular dysfunction if the inner ear is also affected (circling, loss of balance, and nystagmus). Horner’s signs and facial nerve paralysis may also be present. Signs of nasopharyngeal polyps can include dysphagia, gagging, dyspnea, sneezing, stridor, and nasal discharge based on location; signs are often unilateral but may be bilateral depending on the size and origin of the polyp. If the polyp extends into the external ear canal, aural discharge may also be present.

Sedation may be required for a complete oral and otoscopic exam to evaluate the nasopharynx and external ear canal for the presence or absence of masses or infection. Otoscopic examination is often used to evaluate the external ear canals and determine if the tympanic membrane is intact. Video otoscopy under anesthesia can be used for evaluation of the horizontal canal, and endoscopy can be used to fully assess the nasopharynx.

Preoperative Imaging

No matter the diagnosis (polyp, otitis media, or mass lesions), preoperative imaging is recommended to confirm the location and extent of disease and better guide treatment. Computed tomography (CT) is the gold standard for identifying masses, presence of fluid in the middle ear, laterality of polyps, bony changes, and extent of disease.^2,3 If access to CT is not available, skull radiography may be performed, though it is often not sensitive for detection of middle ear disease. Radiography may show fluid opacity within the bulla and/or thickening of the bone. Lysis of bone is not expected with nonneoplastic disease, though may be present with malignancy (Figure 11.1).^4,5

Polyps

Inflammatory polyps are benign, pedunculated masses originating from the mucosa of the nasopharynx, oropharynx, middle ear, or auditory (eustachian) tube and can be found in the pharynx, external ear canal, or confined to the middle ear. They are also referred to as nasopharyngeal or aural polyps depending on location. They are the most common nasopharyngeal disease of younger cats¹³ and the most common nonneoplastic aural mass in cats (Figure 11.2).¹⁴ They are usually found in young cats but have been reported in older cats and, rarely, in dogs.^15–18

Although inflammation is present histopathologically, it is unknown whether inflammation is the cause or result of polyps. The cause of polyps is unknown despite their frequency; congenital and viral causes have been suggested.^19–21

Nasopharyngeal inflammatory polyps may be treated with traction‐avulsion, traction and corticosteroids, or traction with VBO. One study suggested that post‐traction treatment with steroids decreased recurrence from 64% to 0%, though case numbers were small (22 cats).²² Other studies showed a higher rate of recurrence with traction‐avulsion of aural inflammatory polyps (50% with middle ear involvement or growing into the external ear canal) compared to those of nasopharyngeal origin (11%).^21–23 Endoscopic‐guided transtympanic excision has also been described for the removal of polyps in two cats.²⁴ If recurrence is noted, or if there is failure of clinical signs to improve post‐traction, VBO becomes indicated.

To perform removal by traction, the animal is placed under general anesthesia or deep sedation. The polyp should then be easily identified at the caudal border of the soft palate (or, less frequently, in the ear canal). The palate can be retracted rostrally (a spay hook is often helpful for this purpose), or the polyp manipulated caudally. The polyp is grasped with Allis tissue forceps or hemostats, as close to the base as possible. Gentle rostroventral tension, with or without a gentle rotation/twisting motion, is placed on the instrument. If necessary, a second instrument is used to grasp the polyp further dorsally as more of the stalk becomes visible. Ideally, the stalk associated with the polyp will also be removed from the auditory tube. In some patients, blood will be evident beneath the tympanic membrane on otoscopic examination, and there is frequently mild pharyngeal bleeding with the removal of nasopharyngeal polyps. Retraction may result in Horner’s syndrome or vestibular signs. Rarely, an approach to the nasopharynx via a midline incision in the soft palate is required to facilitate polyp exposure and removal (Figures 11.3 and 11.4).^21,25 One tip to reduce the risk of bleeding into the lower airways and to provide adequate control of the anesthetic depth is to intubate the patient prior to attempting polyp removal.

Steatoma/Cholesteatoma

Found in dogs and rarely in cats, aural cholesteatomas are congenital or acquired epidermoid cysts (keratin debris surrounded by keratinizing stratified squamous epithelium) in the middle ear.^26,27 They represent the presence of squamous epithelium within the middle ear; in the congenital presentation, the tympanic membrane is intact; however, the formation of acquired cholesteatomas requires inflammation (chronic otitis media/externa) as well as a defect in the tympanic membrane to allow squamous epithelium entry into the middle ear.

Congenital cholesteatoma is a developmental defect that occurs when a squamous epithelial cyst forms within the middle ear behind an intact tympanic membrane. Acquired cholesteatomas occur when retraction of the tympanic membrane into the middle ear or migration of squamous epithelium through a perforated tympanic membrane leads to cyst formation. Despite their nonneoplastic etiology, severe cholesteatoma may expand rapidly and cause destruction of surrounding structures, including bone (Figure 11.5). Diagnosis is made via a combination of history, clinical signs, changes in imaging (CT), appearance of keratin within a cystic structure at surgery, and histopathology.^26,27

Small, noninvasive cholesteatomas may be treated with long‐term antibiotics based on culture and bacterial sensitivity, and vitamin A therapy may also be helpful.²⁸ When the patient is experiencing clinical signs, such as the development of a head tilt, the author also treats with the occasional course of prednisolone (anti‐inflammatory dose) or nonsteroidal anti‐inflammatory, if not otherwise contraindicated. Depending on the extent of involvement of the external ear canal in the presence of chronic otitis, VBO or total ear canal ablation with lateral bulla osteotomy may be indicated. Prognosis depends on severity of disease (size, invasiveness, tissue destruction); in one study, 52% of dogs undergoing surgery for cholesteatoma removal via VBO or total ear canal ablation with lateral bulla osteotomy had recurrent signs post‐operatively.²⁷

Clinical signs associated with cholesteatoma are those of chronic otitis externa (discharge, swelling, redness), as well as an inability to fully open the mouth, head tilt, facial nerve paralysis, ataxia, nystagmus, circling, and unilateral atrophy of the temporalis and masseter muscles. If bulla expansion into the nasopharynx and oropharynx occurs, respiratory signs may also be present.^26,27

Cholesterol Granuloma

Cholesterol granuloma, predominantly found in dogs but also noted in cats, is also the result of chronic inflammation and may be present in the same ear or patient as cholesteatoma. In this disease process, the granulomatous tissue contains cholesterol crystals.^29–31 Cholesterol granulomas may be seen as a complication following total ear canal ablation with lateral bulla osteotomy.³²

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