Sacral hemangiopericytoma involving the retrorectal space: report of a case.

A primary hemangiopericytoma (HP) of the bone is rare, because the vast majority of these tumors arise in soft tissue. This report presents a case of a hemangiopericytoma in the sacrum (S1-S2) with extension to the retrorectal space. Only a few cases of osseous hemangiopericytomas in the sacrum and involving the retrorectal space have so far been reported.