9 Cholesteatoma of the External Auditory Canal
Cholesteatoma of the external auditory canal is a rare entity, comprising 1 out of 1,000 cases of all otologic patients. A typical appearance is accumulated debris with bone erosion covered by inflamed skin with spotty exposure of necrotic bone. The patient usually suffered from repetitive otorrhea with dull pain in the affected ear. The lesion usually affects the inferior wall of the external auditory canal, that is, the tympanic bone, and progression of the disease involves posterior wall to open the mastoid, and anterior wall to expose the capsule of the temporomandibular joint. In advanced cases, the mastoid may be filled with debris similar to middle ear cholesteatoma. Pathogenesis of this primary idiopathic lesion is not known. It is speculated that ischemic process of the affected region plays key role, and factors that impair microcirculation of the external auditory canal, such as hemodialysis, diabetes mellitus, smoking habit, and irradiation of the head or the epipharynx, have been reported to increase incidence. Early lesions can be managed conservatively, but in advanced lesions, surgical correction is required. The eroded bone is drilled and covered with multiple layers using materials such as bone paste, cartilage, fascia, and soft tissue flaps. The mastoid should be either opened applying canal wall down technique or closed by reconstruction of the posterior wall.
Secondary cholesteatoma in the external auditory canal may arise after tympanoplasty due to various reasons. An involved vascular strip in the lateral part of the meatus, reabsorption of the posterior canal wall that is thinned too much in canal wall up technique, incorrect arrangement of the skin flap that allows it falling down to the cavity, and an excessively lowered posterior canal wall can be the cause of iatrogenic cholesteatoma in this location. The secondary cholesteatoma can also be formed medially to the stenotic lesions in the external auditory canal. Iatrogenic stenosis after tympanoplasty, congenital anomaly, exostosis, fibrous dysplasia of the temporal bone, temporal bone fracture, and scar formation after overuse of cotton swabs can be the cause of such stenosis. Accumulated debris medially to the stenosis causes destructive process in the external auditory canal. Once such lesion is inflamed, the stenosis usually gets narrower, and severe pain with facilitated destructive process may compel an early surgery.