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 x 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 x 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.