Hemangiopericytoma: collision with meningioma and recurrence.

Intracranial hemangiopericytomas are a rare type of primary brain tumor, representing only about 0.5% of all primary brain tumors. Even more rare is the co-existence of two juxtaposed primary brain tumors, termed a "collision" tumor. This report provides the first documentation in the literature of a hemangiopericytoma colliding with a meningioma, and recurring after treatment with gross total resection. Surgical samples were fully evaluated with hematoxylin and eosin and reticulin staining, as well as immunohistochemical analysis. Results were classically representative of a hemangiopericytoma (World Health Organization grade II) and of a meningioma (World Health Organization grade I). This report of a unique collision tumor not only augments the repertoire of collision tumor combinations described in literature but also provides follow-up on the clinical outcome of the patient, thereby raising clinically relevant issues ranging from presentation to treatment paradigms.