True hemangiopericytoma of the nasal cavity - Immunohistochemical and electron microscopic study of 2 cases and a review of the literature on sinonasal hemangiopericytomas

Two cases of nasal tumors with pericytic myoid differentiation are reported . The tumors occurred in a 77-year-old woman and a 60-year-old man as polyp oid lesions covered by normal mucosa. Histologically, the tumors were compo sed of uniform short spindle or stellate cells with indistinct cell borders arranged in narrow and short fascicles. Numerous blood vessels of various sizes were common in both cases. The tumor cells of both cases stained inte nsely with anti-vimentin and anti-actin antibodies, but not with anti-desmi n, CD34, or anti-high-molecular-weight caldesmon antibodies. Ultrastructura l examination revealed well-developed actin thin filaments with dense bodie s, subplasmalemmal plaques, intercellular junctions, and irregular disconti nuous basement membranes. These histopathologic features suggest true peric ytic differentiation of the tumors (true hemangiopericytoma), unlike soft t issue-type hemangiopericytoma. Generally, sinonasal hemangiopericytomas are subdivided into soft tissue-type hemangiopericytomas and true hemangioperi cytomas identical to the cases presented here. Soft tissue-type hemangioper icytomas are frequently highly aggressive, whereas true hemangiopericytomas show localized benign behavior. Sinonasal true hemangiopericytomas should be strictly differentiated from soft tissue-type hemangiopericytomas.