Malignant haemangiopericytoma: case report and ultrastructural study.

A case of a rapidly fatal malignant haemangiopericytoma arising in the deep tissues of the face is recorded. The histology of the tumour was anaplastic but otherwise typical. Ultrastructural study confirmed the diagnosis by revealing tumour cells with delicate interdigitating cytoplasmic processes and basement membrane formation resembling pericytes. A feature of the tumour not previously recorded in haemangiopericytoma was ciliogenesis.