Cholesteatoma of the external ear canal

A cholesteatoma may sometimes occur lateral to the tympanic membrane, in which case it is called a cholesteatoma of the external ear canal (EECC).

Epidemiology

The EEC is a rare location for a cholesteatoma with an estimated incidence around 1.2 per 1,000 new otological patients. The overall incidence rate in one large study was 0.30 per year per 100,000 inhabitants¹. For comparison, the annual incidence of middle ear cholesteatoma is around 9.2 per 100.000.

Pathology

EECC has been first reported by Toynbee in 1850. A distinction from keratosis obliterans has been introduced only in the last few decades. Both mainly consist of epithelial debris in the EEC. The most useful findings confirming an EECC are focal osteonecrosis with or without sequestration and lack of epithelial covering of the bony surface². The treatment strategies differ with both conditions³.

Classification

• primary or spontaneous EECC : idiopathic form : the pathogenetic events are unclear
• secondary EECC : postoperative- postinflammatory - posttraumatic - radiation-induced
• EECC with congenital atresia of the external auditory canal

Radiographic features

Plain film

Schüller, Stenvers, Mayer views of the petrous bone have been largely replaced by CT.

CT

High-resolution bone window CT is the method of choice to localise the lesion and to demonstrate bony erosions.

MRI

Can't show early involvement of compact bone. Its role in EECC is unknown.

Treatment and prognosis

Small lesions can be treated endoscopically under local anaesthesia, whereas larger lesions need surgery to remove the cholesteatoma and affected bone areas. Grafting of defects may be necessary. Prognosis depends on the extent at the time of diagnosis.

Differential diagnosis

General imaging differential considerations include

• keratosis obliterans