Primary Malignant Melanoma of the External Auditory Canal: CT Features

Abstract

Malignant melanoma (MM) is a malignancy with poor prognosis. Between 25% and 30% of primary cutaneous MM occur in the head and neck, and of these, 5%-10% arise on the external ear. [1][2][3][4] The helix is the most common site, followed by the lobule, the tragus-preauricular skin, and the concha.3 Primary melanoma of the external auditory canal (EAC) is rare. We report a case of a primary malignant melanoma of the external auditory canal and describe its computed tomographic (CT) features. Case ReportA 65-year-old man presented with a two-year history of painful mass in the left ear, with recent increase in size and ipsilateral hearing loss. There was no previous history of ear problem, trauma or surgery. On physical examination, the EAC was obliterated by an ulcerated red brownish mass. The pinna was intact with no evidence of regional lymphnode enlargement. The facial nerve function was normal. The endoscopic biopsy microscopically showed malignant epithelioid melanocytes with pigmented granular cytoplasm, large nuclei and prominent eosinophilic nucleoli expanding in the dermis. Mitoses were present and there was brisk lymphoid infiltrate at the base. On plain skull x-ray, no obvious bony changes were observed. Temporal bone CT scan in transverse and coronal planes demonstrated a soft tissue mass obliterating the EAC and eroding its inferior margin as well as the roof of the temporo-mandibular joint (TMJ). The mass was invading the hypotympanic cavity through the tympanic membrane. The inferior tympanic bony margin was partially eroded. The tumor had involved the ossicular chain with erosion of the malleus and the long process of the uncus. The mass was moderately and homogeneously enhancing after intravenous contrast injection. The epitympanic cavity, the mastoid cells and the internal ear were preserved. No intracranial extensions or metastases were detected. Magnetic resonance imaging (MRI) examination was not done due to lack of facilities. The patient underwent a subtotal tumor excision with regional lymph node dissection. The surgical treatment was followed by multiple sessions of radiotherapy. Six months later, the patient presented with a large local recurrence, intracranial and lymphnode metastases, and died one month later.