External auditory canal cholesteatoma: a rare entity.

Cholesteatomas are cystic masses lined with stratified keratinizing squamous epithelium. Most are found in the epitympanum of the middle ear cavity; only rarely do they occur in the external auditory canal. (1) The differential diagnosis of an external auditory canal cholesteatoma (EACC) includes keratosis obturans, postinflammatory medial canal fibrosis, malignant otitis externa, and squamous cell carcinoma.

EACC can occur spontaneously following trauma or surgery as a result of the entrapment of squamous epithelial debris during the healing process. Normally, epithelial migration carries debris outward from the tympanic membrane. However, when debris has accumulated in the external auditory canal, changes in cellular proliferation may occur, and they can evolve into an EACC. (1)

Clinically, patients tend to present with otorrhea and a chronic, dull pain. The otorrhea is believed to be linked to an associated localized infection, usually a Pseudomonas aeruginosa infection. (1,2) Less commonly, patients present with a conductive hearing loss that is caused by occlusion of the external canal by the debris or the cholesteatoma. (3)

On otoscopic examination, EACC can be difficult to distinguish from other inflammatory, infectious, or neoplastic processes. Keratosis obturans is the most difficult to distinguish, and since EACC may require surgical intervention and keratosis obturans is managed medically, distinguishing between these entities is important.

The characteristic imaging features of an EACC are the appearance of a soft-tissue mass and associated erosion of the inferior portion of the external canal with a localized periostitis and sequestration of bone (figure). (2) Bone fragments are often present within the mass, but the tympanic membrane is typically spared. Occasionally, an EACC extends into the middle ear cavity, facial nerve canal, mastoid cavity, or tegmen tympani. (4) It is believed that the bone erosion, periostitis, and sequestration are the results of a weakening of the bone by proteolytic enzymes within the cyst lining. (l) In addition, the erosion might also be partly related to the accumulation of keratin debris, which traps moisture and results in a bacterial infection that can cause ulceration of the epithelial layer and the formation of granulation tissue.

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Treatment options include conservative medical therapy with frequent cleaning and debridement of the keratin debris and sequestered bone. If the mastoid air cells are invaded, a modified radical mastoidectomy may be indicated, with the tympanic membrane and ossicles left intact. (1)

References

(1.) Heilbrun ME, Salzman KL, Glastonbury CM, et al. External auditory canal cholesteatoma: Clinical and imaging spectrum. AJNR Am J Neuroradiol 2003;24:751-6.

(2.) Malcolm PN, Francis IS, Wareing MJ, Cox TC. CT appearances of external ear canal cholesteatoma. Br J Radiol 1997;70:959-60.

(3.) Naim R, Linthicum FH Jr. External auditory canal cholesteatoma. Otol Neurotol 2004;25:412-13.

(4.) Chakeres DW, Kapila A, LaMasters D. Soft-tissue abnormalities of the external auditory canal: Subject review of CT findings. Radiology 1985; 156:105-9.

Matthew Dang, MD; Enrique Palacios, MD