Pilomatrix carcinoma presenting as an extra axial mass: clinicopathological features.

Pilomatrix carcinoma is the rare malignant counterpart of pilomatrixoma, a skin adnexal tumour originating from hair matrix cells. Pilomatrix carcinoma can arise as a solitary lesion de novo, or through transformation of a pilomatrixoma. Pilomatrixoma was first described erroneously as being of sebaceous gland origin but was later discovered to be derived from hair matrix cells. They are rare, slow growing tumours of the skin found in the lower dermis and subcutaneous fat and are predominantly found in the neck and the scalp. While known to be locally aggressive, no malignant form was thought to exist until it was described relatively recently. Since then, approximately ninety cases of pilomatrix carcinoma have been reported.We report the case of a 41 year old mentally retarded male who had a longstanding lesion in the left neck for approximately fifteen years previously diagnosed as a pilomatrixoma. He presented with severe headache, falls and visual disturbance and a biopsy showed pilomatrix carcinoma of the occipital region which, on computed tomography ( CT ) invaded the occipital bone, the cerebellum and the left temporal lobe. At his initial presentation he had a craniotomy and subtotal excision of the lesion but received no adjuvant therapy. After an early intracranial recurrence he had further debulking and adjuvant external beam radiotherapy. He has had no further intracranial recurrence after three and a half years of follow-up. Here we present the pathological features of this uncommon tumour.