6/20/2006 Case 1: Hemangiopericytoma encompassing meningioma

Clinical History:

A 37 year-old man with a "right frontal tumor, probable meningioma." No systemic disease or familial syndrome.

Diagnostic Notes:

This was an H&E stained slide of a right frontal mass from a 37 year old man, thought pre-operatively to most likely be a meningioma. There was no significant medical history or familial history. The mass was a neoplasm of mostly moderate to high cellularity, attached to dura. The majority of the mass was a spindle cell lesion with rather small cells which was moderately vascular. The cells were not whorled nor were they arranged in lobules, and the pattern was that of a fairly cellular variant of
hemangiopericytoma and similar tumors, although staghorn vessels were not obvious. In addition there was a nodule of lower cell density which was pale on the H&E stain, and which had cells with a different character with a more epithelioid appearance and a suggestion of some poorly-formed whorls. This resembled a meningioma, and was wholly surrounded by the larger mass. Mitotic figures could be found in the large mass but not in the small pale nodule embedded in the larger mass.

Special stains showed that the main portion of the mass had some reticulin around individual cells, mostly close to vessels, whereas the paler nodule had none at all except around vessels themselves. The cells in the small pale nodule were strongly vimentin and EMA immunopositive, whereas those in the larger mass were mostly negative for both of these markers. A trichrome stain showed extensive collagen deposition in the larger mass but not much in the small nodule. A CD34 stain was negative in tumor cells in both parts of the tumor, but did mark endothelial cells appropriately throughout the section. A MIB1 stain showed a proliferation index of about 10% in the main portion of the tumor but a much lower level in the small pale nodule.

The case was signed out by Dr Wolfe as a Hemangiopericytoma encomassing a Meningioma. The membership generally agreed; there was some discussion about
arachnoidal cell hyperplasia in reaction to a hemangiopericytoma but most felt that the nodule embedded in the larger mass was too large and not sufficiently like an arachnoid granulation to be just reactive. There was also the usual discussion of the differential diagnosis of hemangiopericytoma in the cranial cavity and elsewhere, including synovial sarcoma in other body sites based in part on typical chromosomal translocations, and solitary fibrous tumor. As noted, however, the consensus agreed with Dr Wolfe's original diagnosis.

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