The spectrum of histologic growth patterns in benign and malignant fibrous tumors of the pleura.

A review of the histologic growth patterns in 50 cases of benign and malignant fibrous tumors of the pleura (localized or solitary fibrous tumor, fibrous mesothelioma) is presented. Two major histologic growth patterns were observed admixed in various proportions: solid spindle and diffuse sclerosing. The solid spindle growth pattern assumed various configurations, including fascicular areas, storiform and herringbone formations, angiofibroma and hemangiopericytoma-like areas, synovial sarcoma-like areas, and neural-type palisading, thus simulating a variety of soft-tissue neoplasms. The diffuse sclerosing pattern, although rarely assuming a dominant role, was present in varying proportions in virtually all cases. In areas with extensive sclerosis, focal degeneration of collagen simulating tumor necrosis was often present. Other less frequently observed features were the formation of "amianthoid" fibers, multinucleated giant cells, and foci of metaplastic ossification. On ultrastructural and immunohistochemical examination, the tumor cells showed nondistinct features. Due to the extreme variability in morphologic appearances and the lack of distinctive ultrastructural or immunohistochemical characteristics, these tumors can pose a significant diagnostic problem. Familiarity with their histologic appearances and correlation with the gross findings and clinical setting are essential for arriving at the correct diagnosis.