When a cyst is not a cyst

Case 1

A 75 year old man presented to his general practitioner with a lump on his scalp. His medical history included aplastic anaemia but he was otherwise well. The GP examined the lump and diagnosed a loculated epidermoid cyst. During excision he found that it adhered to the underlying tissues and so removed it piecemeal. Histological examination of the specimen was difficult because the sample was fragmented, but the lesion was clearly malignant. Plastic surgeons performed a wide excision, and histology showed a tumour with features of a poorly differentiated sebaceous carcinoma.

The differential diagnosis included a metastatic tumour, so extensive investigations were carried out to identify a primary malignancy, but none was found. The patient continued under close follow-up and showed no sign of recurrence 12 months after initial surgery.

Case 2

An 11 year old girl presented to her GP with a three month history of a lump on the back of her head, which was painful and growing larger. The GP made a clinical diagnosis of an epidermoid cyst and referred her non-urgently to the general surgeons. The lesion was thought to be benign, …