Carcinoma cuniculatum of the sacral skin: a case report

A 49-year-old woman presented with a non-healing perianal abscess following a 13 year history of chronic abscesses and discharging sacral/buttock sinuses. On examination, the skin in the right gluteal area was oedematous and erythematous. Multiple intercommunicating fistulous openings in the skin discharged puslike material. Macroscopic examination showed an extensive infiltrating cystic and deeply penetrating dermal and subcutaneous tumour with fistulous tracts extending to the skin surface. Histology revealed normal skin overlying an extensive, cystic, well differentiated verrucous carcinoma. The tumour was characterised by papillo-matous projections of squamous epithelium into a central cystic cavity, consistent with a carcinoma cuniculatum. The patient has been well with no recurrence in follow-up over 2 years. Carcinoma cuniculatum is a subtype of well differentiated squa-mous cell carcinoma, which may be considered an inverted form of verrucous carcinoma. It is characterised by extensive formation of crypts and sinuses and the absence of cytological atypia. The word cuniculatum is used to refer to the similarity of the crypts and sinuses to rabbit burrows. Other lesions to be considered in the differential diagnosis include carcinoma ex hidradenitis suppurative, giant keratoacanthoma, verrucous carcinoma, and pseudoepithe-liomatous hyperplasia.