Primary pulmonary hemangiopericytoma.

Hemangiopericytoma is a potentially malignant tumor of vascular origin. It usually is a solitary lesion and may arise in the chest or in extrathoracic areas. It is usually encapsulated. Microscopic features vary with the degree of differentiation of the individual tumor. The more differentiated variety exhibits abundant capillaries with open lumina surrounded by ovoid tumor cells; in the less differentiated tumors, the capillaries lack lumina and the tumor cells are spindle shaped. The prognostic significance of the microscopic pattern is controversial. However, prominent mitotic activity, necrosis, hemorrhage, and increased cellularity are ominous signs and are usually noticed in tumors that later exhibit malignant behavior. The larger the lesion, the more likely that it will be symptomatic. Treatment of choice is ample surgical resection.