Hemangiopericytoma of the cerebello-pontine angle. Diagnostic pitfalls and the diagnostic value of the subunit A of factor XIII as a tumor marker.

The authors report on a case that during its 9-year-long history has repeatedly been misdiagnosed due to the misleading clinical and histopathological findings. The patient has been treated, in chronological order, for cerebrovascular disease, acoustic Schwannoma, glomus tympanicum tumor (chemodectoma) and finally turned out to have an intracranial hemangiopericytoma that originated from the area of the glomus tympanicum and eventually widely metastatized within and outside the intracranial compartment. The proper diagnosis was reached with the help of detailed immunohistochemical analysis. The subunit A of Factor XIII (FXIIIa) can be demonstrated on formaldehyde-fixed paraffin embedded sections. It has recently been shown that FXIIIa reactivity is characteristic and hence diagnostic of a subpopulation of cells within systemic and intracranial (central) hemangiopericytomas (HPCs). Since it is consistently missing from all cell components of ordinary meningiomas, glomus tumors (chemodectomas) and a host of other soft tissue tumors, its presence or absence is a helpful sign in various differential diagnostic dilemmas.