HEMANGIOPERICYTOMA - HISTOPATHOLOGICAL PATTERN OR CLINICOPATHOLOGICALENTITY

The tumor designated by Stout and Murray as ''hemangiopericytoma'' (HP C) more than 50 years ago continues to represent a source of uncertain ty and disagreement among pathologists, In particular, questions exist regarding the synonymity of a hemangiopericytomatous growth pattern-d efined by a monomorphic population of compact polygonal or bluntly fus iform cells and a branching stromal vascular pattern with a ''staghorn '' configuration-and the presence of a reproducible biological entity, It has been shown repeatedly that these same histologic features may be observed at least focally in a diversity of neoplasms, including '' true'' hemangiopericytomas, synovial sarcomas, mesenchymal chondrosarc omas, infantile fibrosarcomas, malignant fibrous histiocytomas, malign ant peripheral nerve sheath tumors, leiomyosarcomas, endometrial strom al sarcomas, solitary fibrous tumors, myofibromas, malignant mesotheli omas, thymomas, sarcomatoid carcinomas, malignant melanomas, and ''pho sphaturic mesenchymal tumors.'' Despite their potential sharing of the microscopic attributes in question, such neoplasms have individualist ic clinical features and can also be distinguished from one another by specialized pathologic analyses. HPC is ''defined'' in that context b y reactivity for vimentin, with or without CD34 and CD57, but it lacks other immunodeterminants of epithelial, neural, and myogenous differe ntiation, Paradoxically, this phenotype is indeed associated with the presence of myogenous-type cytoplasmic filaments in ultrastructural ev aluations of HPC, Other lesions that may resemble ''true'' HPC-but whi ch possess dissimilar subcellular and clinical characteristics-include solitary fibrous tumors, hemangiopericytomalike tumors of the sinonas al tract, and ''infantile (congenital) hemangiopericytomas.'' Such obs ervations suggest that the hemangiopericytoma is both a pathologic ent ity and a morphological pattern, and they emphasize the utility of adj uvant pathologic studies in this diagnostic context. Copyright (C) 199 5 by W.B. Saunders Company