Sinonasal hemangiopericytoma-like tumor with true pericytic myoid differentiation: A clinicopathologic and immunohistochemical study of five cases

Background. Sinonasal hemangiopericytoma-like tumor (SHPCL) is an uncommon vascular tumor that is sometimes difficult to diagnose. Method. We report five cases arising from the nasal cavity. The tumors were subdivided into two types, prototype and soft tissue type, by the difference in histologiC features. Results. The prototype, made up of three tumors, is characterized by uniform, spindle-shaped myoid cells that have eosinophilic cytoplasm and uniform nuclei and lay down in an orderly fashion. The soft tissue type, made up of two tumors, is similar to the hemangiopericytoma of soft tissue. Immunohistochemically, the tumors were positive for vimentin (100%), smooth muscle actin (80%), muscle-specific actin (100%), fibroblast growth factor-2 (100%), and vascular endothelial growth factor (100%). All were negative for cytokeratin, desmin, CD34, and factor VIII-related antigen. These histopathologic features suggest myoid differentiation and angiogenic activity of the tumors. All the tumors were treated with wide surgical excision. Only one case of soft tissue-type tumor with active mitoses received additional postoperative radiotherapy. No recurrence was found during 13 to 120 months of follow-up. Conclusions. Our data suggest that SHPCL with convincing myoid differentiation may have a more favorable clinical course than its soft tissue counterpart.