CD34 and dural fibroblasts: the relationship to solitary fibrous tumor and meningioma.

Intracranial solitary fibrous tumors (SFTs) are typically dural-based, CD34-positive neoplasms of uncertain histogenesis. We examined ten cases of meninges obtained at autopsy from patients with no history of neurological illness, head trauma, or neurosurgical intervention, and ten cases of typical meningiomas with attached dural margins not involved by tumor. All cases were immunostained with CD34. CD34 reactivity was noted in the long, thin delicate processes of dural fibroblasts preferentially located in the meningeal portion of the dura rather than the periosteal portion. No CD34 reactivity was identified in the arachnoid or pia mater, except in some endothelial cells. One supratentorial dural-based fibrous nodule and one SFT within the confines of the fourth ventricle showed strong and diffuse reactivity to CD34, bcl-2, and vimentin, and were negative for epithelial membrane antigen (EMA), S-100 protein, glial fibrillary acidic protein, smooth muscle actin, and desmin. We also describe a meningothelial meningioma within which a well circumscribed SFT-like nodule was embedded. The SFT-like nodule was strongly CD34 positive and EMA negative, and the meningioma was strongly EMA positive and CD34 negative. Fibroblasts of the dural border cell layer are attached to the underlying arachnoid, and their inclusion with arachnoidal stromal elements and pial-based tela choroidea during formation of choroid plexus interstitium may account for intraventricular SFTs. Our results suggest that SFTs and dural-based fibrous nodules derive from CD34-positive dural-based fibroblasts, and that CD34 reactivity in meningiomas may result from inclusion of dural fibroblasts within the neoplasm.