The external auditory canal (EAC) is a curved channel approximately 2.5 cm long leading from the auricle to the tympanic membrane. The lateral one-third is cartilaginous (continuous with the auricle) and the medial two-thirds is bony (from the tympanic plate of the temporal bone). The skin of the EAC contains cerumen-secreting modified sweat glands (ceruminous glands) in the outer cartilaginous portion only.
The EAC is the site of otitis externa (swimmer's ear), exostoses from cold water exposure (surfer's ear), keratosis obturans, and EAC carcinoma. Exostoses are bony overgrowths of the bony EAC from repetitive cold water exposure, narrowing the canal and trapping water and cerumen. Canalplasty (drilling back the exostoses) restores canal width. The posterior EAC wall is thinned in posterior tympanotomy for cochlear implant surgery. Malignant otitis externa from Pseudomonas aeruginosa in diabetic patients invades the bony EAC and skull base, requiring prolonged IV antibiotics and sometimes surgery.
Bilateral bony exostoses narrowing the external auditory canal from repetitive cold seawater exposure cause cerumen impaction, recurrent otitis externa, and conductive hearing loss; canalplasty by drilling the exostoses under microscopic magnification through a transcanal or post-auricular approach restores canal diameter with low recurrence using protective ear plugs for future cold water exposure.
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