GROSS AND MICROSCOPIC DESCRIPTIONS:
The patient underwent surgical resection of tumor. The surgical specimen consisted of multiple fragments of whitish red slightly firm soft tissue that measured approximately 2.0x1.5x1.0 cm in aggregate. Serial sections revealed whitish red cut surfaces without evidence of focal necrosis, cystic changes or hemorrhages. Hematoxylin and eosin stained sections showed haphazardly arranged spindle cells alternating with collagenous, hypocellular areas in a richly vascular background without necrosis (Fig. 2A). Focal areas were suggestive of a hemangiopericytoma (HPC); however, true staghorn blood vessels and pericyte proliferation were not prominent (Fig. 2B). No evidence of significant nuclear atypia or mitosis was present. With immunohistochemical studies, spindled cells exhibited diffuse extensive CD34 (Fig. 2C) and vimentin immunoreactivity (Fig. 2D) but were negative for S-100 (Fig. 2E), CD31, glial fibrillary acidic protein and Leu-7 (not shown). Endothelial cells were immunoreactive with antibodies to both CD31 and CD 34.
Electron microscopy revealed spindle cells which were widely separated from each other in an abundant extracellular matrix that consisted predominantly of collagen fibrils (Fig. 3A). There were no cell junctions or surface microvilli. Nuclei were moderately irregular, with clumped and dispersed chromatin. The cytoplasm contained polysomes, rough and smooth endoplasmic reticulum, mitochondria, intermediate filaments, secondary lysosomes, and rare lipid droplets (Fig. 3B).