34th Annual Scientific Meeting proceedings

Cholesteatoma (more accurately referred to as tympanokeratoma) is an invasive, non-cancerous epidermal cyst of the bulla causing expansion and destruction of surrounding bone defined by the presence of keratinized stratified squamous epithelium within the cavity, which typically contrasts with the pseudostratified ciliated columnar epithelium found around the Eustachian tube.  Cholesteatoma are reported in a number of species including dogs, humans and gerbils.  Annual incidence in humans has been reported to be approximately 1.5–3 cases per million individuals in Europe.  Risk factors for acquired cholesteatoma in the UK population include the male sex, a history of deprivation/poverty and an inconclusive link with smoking.

Congenital cholesteatoma arises from residual embryonic epidermal cells within the bulla.  Acquired cholesteatoma are further divided into primary-acquired and secondary acquired cholesteatomas.  The former develop due to pressure changes in the middle ear that cause tympanic membrane retraction, often as a result of eustachian tube dysfunction following chronic otitis media. This retraction can damage the ossicles and cause erosion of the mastoid bone.  Secondary-acquired cholesteatomas arise from direct injury to the tympanic membrane, typically caused by infection or trauma.

A number of theories exist in human medicine as to the aetiology of cholesteatoma but none are unequivocally proven:

Immigration theory – involves squamous epithelium progressing from the margin of a tympanic membrane perforation into the middle ear and then forming a cholesteatoma.

Basal hyperplasia theory - chronic inflammation may lead to transformation of the normal, thin, mature epidermis of the tympanic membrane and adjacent canal into a thicker form resembling that of the foetus.

Retraction pocket theory - part of the tympanic membrane, usually the pars flaccida, invaginates towards the middle ear prior to cholesteatoma formation.  The main precipitating factor is functional obstruction of the eustachian tube, resulting in poor middle-ear and mastoid ventilation.

In dogs, the assumption has always been that cholesteatoma occur secondary to chronic otitis externa and rupture of the tympanic membrane.  However given the rise in popularity of brachycephalic breeds and subjectively in our clinic, the proportion of brachycephalic dogs represented in our cholesteatoma population, is it possible that Eustachian tube dysfunction in brachycephalic breeds predisposes them to cholesteatoma development.   An alternative theorem is the use of propylene glycol in ear cleaners as this has been shown experimentally to induce cholesteatoma formation. 

Clinical signs of cholesteatoma include aural discharge and pain, head shaking, pain on opening the mouth and neurological abnormalities, including peripheral vestibular signs, facial paralysis and Horner’s syndrome.  Key CT features include expansion of the bulla, hyperostosis of the bulla wall, lysis of the bulla wall, osteosclerosis, ring contrast or non-contrasting enhancing material filling the bulla and bony changes within the temporomandibular joint and/or paracondylar process.   However, Botelho et al found that advanced imaging findings could not propose a presumptive diagnosis of tympanokeratoma in 60% of their study population (100 dogs).   In humans non-echo planar (non-EP) diffusion-weighted (DW) MRI is more commonly used and has been reported for use in dogs by Coeuriot et al.

There are multiple surgical approaches described in human medicine depending on the anatomical extension of the cholesteatoma and involvement of the mastoid bone but there has been a move to trans-endoscopic surgery in recent years for cholesteatomas which are confined to the bulla as this appears to give more favourable outcomes.  In dogs, treatment is still broadly centred around total ear canal ablation and lateral bulla osteotomy given the high incidence of concurrent chronic otitis externa in this population although trans-canal endoscopic debridement has been reported with some success in a small case population by Imai et al.

Recurrence rates in veterinary medicine are reported to be up to 50%.  However in humans it is much lower (depending on the extent of the lesion) and this is likely due to the stage at which the diagnosis is made and also the use of magnification to allow more thorough debridement.  There remains much debate in human medicine about recidivistic disease (which occurs due to incomplete excision) versus recurrent disease (due to a failure to manage underlying predisposing factors) and the author would propose that there is a role for the use of intra-operative endoscopy of the bulla to reduce the incidence of the former given the likelihood of leaving epithelial remnants in situ reported by Watt et al. 

References

1. Botelho CB,  Tortoriello R,  Koch SN,  Fernandes JI.  Clinical aspects of middle ear tympanokeratoma in dogs diagnosed through advanced imaging, otoendoscopy and histopathological evaluation. Vet Dermatol.  2025; 00: 1–7.
2. Coeuriot C, Gaillot H, Agoulon A, Madec S, Michel G, Prelaud P, Briand A, Bensignor E, Bruet V, Abadie J, Ruel Y, Fusellier M. Characteristics and diagnostic performance of nonechoplanar diffusion-weighted imaging in detecting canine tympanokeratoma (cholesteatoma). Vet Radiol Ultrasound. 2024 Nov;65(6):836-843.
3. Giffoni, Rodolfo Baptista^∗; dos Santos, Gabriele^∗; Aguiar, Ricardo Santos^∗; Lins, Lucas Costa^∗; Cruz, Marcelo Leandro Santana^∗; Lima, Adriano Damasceno^†. Endoscopic-Guided Resection of Middle Ear Cholesteatoma: A Systematic Review and Meta-Analysis. Otology & Neurotology  2025 46(4):p 418-424
4. Greci V, Travetti O, Di Giancamillo M, Lombardo R, Giudice C, Banco B, Mortellaro CM. Middle ear cholesteatoma in 11 dogs. Can Vet J. 2011 Jun;52(6):631-6
5. Hardie EM, Linder KE, Pease AP. Aural cholesteatoma in twenty dogs. Vet Surg. 2008 Dec;37(8):763-70
6. Imai, A., Kondo, H., Suganuma, T. and Nagata, M.  Clinical analysis and non-surgical management of 11 dogs with aural cholesteatoma. Vet Dermatol. 2019 30: 42-e12
7. Masaki M, Wright CG, Lee DH, Meyerhoff WL. Experimental cholesteatoma. Epidermal ingrowth through tympanic membrane following middle ear application of propylene glycol. Acta Otolaryngol. 1989 Jul-Aug;108(1-2):113-21.
8. Watt MM, Regier PJ, Ferrigno CRA, McConkey MJ, Fox-Alvarez WA, Bertran J. Otoscopic evaluation of epithelial remnants in the tympanic cavity after total ear canal ablation and lateral bulla osteotomy. Vet Surg. 2020 Oct;49(7):1406-1411