LAUSR

displaying marked mass effect on the adjacent temporal lobe and moderate vasogenic edema. Surgical resection revealed multiple irregular, pink-tan soft tissue fragments measuring 2 x 2 x 1.1 cm in aggregate. Microscopically, the specimen showed blood vessel proliferation with typical “stag horn” patterns. The vessels were surrounded by proliferating neoplastic round to oval cells with moderate pleomorphism, occasional nuclear atypia and high cellularity. Rare mitotic figures were seen (<5 per 10 hpf). Invasion of skeletal muscle and bone can be seen in some sections. Immunohistochemical analysis revealed the tumor cells were positive for STAT6 and CD34, with a low Ki67 mitotic index (1%-3%). This case is noteworthy for the rarity, atypically aggressive nature and presentation of this entity.