Malignant primary pulmonary tumor with hemangiopericytoma-like features: conventional hemangiopericytoma versus solitary fibrous tumor

Although extremely rare, the primitive lung hemangiopericytoma in adults is similar to hemangiopericytomas with other soft tissue localizations. Although generally benign and curable after radical surgery, it might also have a malignant clinical course with dissemination in both lungs, infiltration of vital organs (heart, pulmonary artery), extension to the adjacent tissues, and even pulmonary metastases. The treatment of choice is the complete tumor resection with negative surgical margins after excision. Certain histologic features might indicate a malignant potential. The clinical outcome of patients is variable: some are cured after radical surgery and others might present relapse and recurrences that necessitate a second intervention, radiation therapy, and/or chemotherapy. Over the years, the conventionally-defined hemangiopericytoma concept has evolved because of the nonspecific histologic growth pattern (characteristic monotonous appearance, moderate or high cellularity, and a well-developed branching vascular pattern) shared by numerous, unrelated benign or malignant lesions. Hemangiopericytoma is no longer considered a specific entity but rather as a characteristic growth pattern; in the heterogeneous group of hemangiopericytoma-like neoplasms, many lesion categories have been individualized and defined. We report an uncommon case of primitive lung tumor exhibiting hemangiopericytoma-like features, with an aggressive, fatal clinical course. Because of the major histologic overlap between solitary fibrous tumor and hemangiopericytoma and lack of clear classification criteria, we encountered difficulty in including this case in a known clinical entity; primitive solitary fibrous tumor of the lung, which mimics lung hemangiopericytoma, seemed to be the most plausible diagnosis. We discuss the case particularities and the radiologic and pathologic correlations.