Solitary Fibrous Tumor of the Meninges: A Lesion Distinct From Fibrous Meningioma:A Clinicopathologic and Immunohistochemical Study

Seven solitary fibrous tumors (SFTs) of the meninges are presented and their clinicopathologic features are compared with those of 64 fibrous meningiomas (FM). Patients with SFT included 5 females and 2 males age 47 to 73 years. The dura-based tumors involved the parasagittal region (1), tentorium (2), cerebellopontine angle (2), and spinal region (2). One each showed invasion of brain and of a spinal nerve root. Of four SFTs with at least 1-year follow-up, one subtotally resected example recurred. No tumors metastasized. All consisted of spindle cells disposed in fascicles between prominent, eosinophilic bands of collagen. Whorls and storiform cell arrangements were lacking. Mitoses ranged from 1 to 7/10 400 × fields. MIB-1 labeling indices ranged from 1% to 18% (mean 4%). All were PAS negative and showed strong immunoreactivity for vimentin and CD34. Of cases studied, half were estrogen and all were progesterone receptor immunopositive. The majority (72%) of FMs occurred in females and most (72%) were supratentorial. Recurrence was noted in 15%. Mitotic activity varied from 0 to 3 mitoses per 10 400 × fields (mean <1). MIB-1 labeling indices ranged from 1% to 5% (mean 1.5%). Unlike SFT, FMs were glycogen-containing and variously exhibited a storiform pattern (13 of 20), psammoma body formation (9 of 20), and calcification of collagen (4 of 20). Immunoreactivities included vimentin (100%), focal to patchy EMA (80%), S-100 protein (80%), collagen IV (25%), and patchy, mild-to-moderate CD34 staining (60%). Of cases studied, nearly half were estrogen and all were progesterone receptor staining positive. Meningeal SFTs represent a distinct morphologic entity, the morphologic and immunohistochemical features of which differ from those of FM and suggest a histogenetic relationship to pleural SFT. Although a minority histologically appear to be low grade malignant, our limited experience suggests that they behave in a benign fashion. The classification of mesenchymal tumors affecting the central nervous system must be expanded to include SFT.