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Cholesteatoma is an epidermoid cyst that forms within the middle ear cavity. Contrary to what the name suggests, it is non-neoplastic and has nothing to do with cholesterol or fat. Rather, it is charaterised by a cornifying stratified squamous epithelium which produces keratin leading to a slowly expansile lesion within the tympanic bulla. The aetiology is incompletely understood but, although congenital forms are possible, they are most likely a result of chronic otitis externa in which keratinizing stratified epithelium has had the opportunity to seed and establish within the middle ear chamber. Although in theory the cyst is benign, it can cause a range of signs relating to its position and size. Symptoms therefore include signs of otitis media – head tilt, nystagmus, circling etc but animals can also present as dogs who are reluctant to fully open their mouths and/or are reluctant to eat and this is due to encroachment of the cholesteatoma on the temperomandibular joint (TMJ). We have also seen some dogs which presented with dysphagia due to orpharyngeal compression from ventral outgrowth from the bulla. The lesions can also extend medially and erosion of the cranial vault can lead to otitis interna and even meningoencephalitis. The treatment of choice is surgical removal of the keratin contents together with the secretory lining responsible for the lesion and this involves either total ear canal ablation and lateral bulla osteotomy or ventral bulla osteotomy (or both!). Surgery can be challenging as the distorted anatomy makes it hard to remove all of the responsible epithelium and this leads to recurrence which is reported in approximately 50% of cases (Hardie et al 2008). Recurrence is most likely in dogs with either neurological signs, bone lysis or inability to open the mouth. Cholesteatomas are cystic tumors that can expand in the middle ear (most commonly in dogs). They can be locally destructive, lead to secondary inflammation, and may induce a secondary otitis externa/media. Although the pathogenesis of these tumors isn’t completely understood, they may be associated with eustachian tube dysfunction (leading to tympanic membrane invagination), may occur secondary to chronic otitis media, or may be secondary to surgery of the ear canal and middle ear. There is no significant breed predilection, and the age of affected patients varies. Clinical signs often include those associated with otitis externa/media (head shaking, pain on palpation of ear/bulla or opening of mouth, exudate in the external ear canal, facial nerve palsy). In chronic cases, the cholesteatoma may not be visible on otic examination due to stenosis, exudate, and chronic changes. When visible, the tumor is frequently pearly white and protrudes from the middle ear to the external ear canal, with the tympanic membrane no longer intact. A complete neurologic examination is warranted, focusing on dysfunction of the facial nerve. Diagnosis involves advanced imaging to assess the changes to the middle ear. Bulla radiographs can be performed if CT or MRI are not available, but they do not provide as much information. Cholesteatomas will cause lysis, sclerosis, and proliferation of the bulla. The bulla may also expand and be filled with soft tissue. Otitis externa may also be evident. Samples for cytology and histology should be submitted when possible to confirm the type of lesion present. Culture of the middle or external ear should also be considered based on cytology because of the potential for secondary infection. Surgical treatment may be curative in 50% of cases and, if possible, should be done early in the disease to limit tumor expansion. However, surgery even in later-stage disease may be palliative. Bulla osteotomy or total ear canal ablation with bulla osteotomy should be considered. As much diseased tissue as possible should be removed. Medical management may include treating secondary infections and use of corticosteroids (systemic and topical) to reduce inflammation.
