The great majority of malignant epithelial neoplasms of the pinna are basal cell carcinomas, a small number only being squamous cell carcinomas. The few basal cell carcinomas that occur in the ear canal arise near the external opening. Their preference for the exposed part of the external ear is in keeping with the accepted view that sunlight is in most cases the causal factor in skin insufficiently protected by melanin pigment.
The gross appearance of basal cell carcinoma is usually one of a pearly wax-like nodule that eventually ulcerates. Twenty-five per cent of basal cell carcinomas of the pinna are of the morphea type (see below). The importance of this variety is that although the edge of the tumour tends to infiltrate subcutaneously, this cannot be recognised clinically or on gross pathological examination. The classical and most frequent form of basal cell carcinoma is composed of solid masses of cells, which are seen to be arising from the basal layers of the epidermis or the outer layers of the hair follicles. The cells are uniform with basophilic nuclei and little cy-
toplasm. At the periphery of the neoplastic lobules the cells tend to be palisaded. Mitoses are frequent as are alveolar or cystic spaces. Squamous cell differentiation is also common.
The splitting up of cell groups by much hyaline fibrous tissue, so that the carcinoma appears compressed into thin strands, is referred to as the morphea type of basal cell carcinoma (Fig. 8.7). The suggestion that tumours with this histology have a worse outlook is probably related to their tendency towards insidious infiltration (see above). There is otherwise no convincing evidence of the relationship of a particular histologi-cal appearance to prognosis in basal cell carcinoma. However, when immunohistochemical assessment for Ki-67 antigen (MIB1 in paraffin sections), a proliferation-associated antigen, is performed on basal cell carcinomas, those tumours that recur have been shown to possess a higher proportion of cells positive for that antigen than those that do not . The degree of tumour angiogenesis is another histologic factor that shows promise in judging the prognosis of basal cell carcinoma .
This is not an aggressive neoplasm and in at least 90% of cases a 3-year cure can be easily achieved by surgical excision. In a few cases repeated recurrences with deep extension to the middle ear, mastoid and even cranial cavity may, however, take place. Metastasis is rare.
Pinna lesions in a prominent position are identified early. A serious problem with the canal lesions is the delay in diagnosis because of the minimal symptoms that may be present. Pain, hearing loss and drainage of blood or pus are the main features in that group. A plaque-like or even polypoid mass may be felt or even seen.
Squamous carcinomas arising on the pinna grossly resemble those seen elsewhere on the skin. The appearances of the canal lesions are those of a mass, sometimes warty, occluding the lumen and invading deeply into the surrounding tissues. There may be dissolution of the tympanic membrane with invasion of the middle ear.
Squamous cell carcinoma of the external ear usually shows significant degrees of keratinisation. In the cases with a canal origin evidence of origin from canal epidermis is usually present. In cases arising deep within the ear canal there is usually a concomitant origin from middle ear epithelium and dissolution of the tympanic membrane (see below). The neoplasm may be so well differentiated that it can be confused with benign papilloma. The association of a well-differentiated squamous carcinoma with marked desmoplasia may also delay the correct diagnosis. The verrucous form of squamous cell carcinoma has been seen in the external ear . Metastatic spread of squamous carcinoma of the pinna and external auditory meatus to lymph nodes is unusual. Squamous carcinoma of the external canal is an aggressive disease with a high propensity towards local recurrence. The outcome of the disease following surgical excision is related to the clinical stage at presentation; the higher the stage the worse the outcome .
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