External auditory canal cholesteatomas are a rare subtype of acquired cholesteatoma.
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Epidemiology
The external acoustic canal is a rare location for a cholesteatoma with an estimated incidence of around 1.2 per 1,000 new otological patients ref. The overall incidence rate in one large study was 0.30 per year per 100,000 inhabitants 1. For comparison, the annual incidence of middle ear cholesteatoma is around 9.2 per 100,000 ref.
Clinical presentation
Patients often present with chronic dull otalgia and otorrhea. A less common presentation is conductive hearing loss due to canal occlusion 2.
Pathology
A distinction from keratosis obturans has been introduced only in the last few decades. Both mainly consist of epithelial debris in the external acoustic canal. The most useful findings confirming an external auditory canal cholesteatoma are focal osteonecrosis with or without sequestration and lack of epithelial covering of the bony surface 2. The distinction between keratosis obturans and cholesteatomas is not merely one of pedantry but also impacts the treatment strategy 3.
Etiology
External auditory canal cholesteatoma can be divided into ref:
-
primary (idiopathic/spontaneous)
rare
no antecedent cause identified
-
secondary
more common
postoperative, postinflammatory, posttraumatic, radiation-induced
A special type of secondary cholesteatoma of the external auditory canal are those associated with congenital atresia of the external auditory canal.
Radiographic features
Plain radiograph
The Schüller, Stenvers, and Mayer views of the petrous bone have been largely replaced by CT ref.
CT
High-resolution bone window temporal bone CT is the method of choice to localize the cholesteatoma, which appear as soft tissue density lesions, and to demonstrate bony erosion ref.
MRI
MRI cannot show the early involvement of compact bone. Its role in external acoustic cana cholesteatoma is not defined ref.
Treatment and prognosis
Small lesions can be treated endoscopically under local anesthesia, whereas larger lesions need surgery to remove the cholesteatoma and affected bone areas ref. Grafting of defects may be necessary. Prognosis depends on the extent at the time of diagnosis.
History and etymology
External auditory canal cholesteatomas were first reported by Toynbee in 1850 ref.
Differential diagnosis
General imaging differential considerations include ref
squamous cell carcinoma of the external auditory canal
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