Lipomatous hemangiopericytoma - A morphologically distinct soft tissue tumor

Hemangiopericytoma of soft tissue is a controversial pathologic entity. The relative nonspecificity of the characteristic branching capillary pattern and cytologic features of the constituent cells, in addition to the lack of a distinct immunohistochemical staining profile, has resulted in uncertain ty and a lack of consensus regarding this subgroup of tumors. Notwithstandi ng the doubt surrounding this entity, a morphologically unique variant, des ignated lipomatous hemangiopericytoma, was reported in 1995. To our knowled ge, there have been no further reports of these tumors since the original d escription. We describe a lipomatous hemangiopericytoma that arose within t he thigh of a 41-year-old woman. The tumor presented as a slowly enlarging, minimally tender, pulsatile mass. The tumor was completely excised and was found to be composed of an admixture of typical hemangiopericytoma and pre dominantly mature adipose tissue. Unlike previous descriptions of this enti ty, the current example exhibited a full range of adipocyte differentiation , including many multivacuolated adipocytes of variable size with character istic nuclear scalloping (lipoblast-like cells). The mitotic count was less than 2 per 10 high-power fields examined. The clinical course has been ben ign during the short follow-up period. We discuss the pathologic features, including the immunohistochemical staining profile and ultrastructural appe arance of this distinctive tumor, and briefly discuss the relationship betw een hemangiopericytoma and solitary fibrous tumor of soft tissue, a neoplas m with many clinical and pathologic similarities.