Deep sylvian fissure meningioma without dural attachment in an adult: case report.

Meningiomas are thought to arise from arachnoid cap or meningothelial cells that not only cluster on the surface of pacchionian granulations but also can cover the arachnoid membrane in other locations. This frequent apposition to the dura mater probably accounts for the usual attachment of the neoplasm to this layer. We report a deep sylvian fissure meningioma without dural attachments in the right hemisphere of an adult patient. The patient initially presented with simple partial seizures. Magnetic resonance imaging revealed a contrast-enhancing circular mass in the superior aspect of the insular region, deep to the inferior parietal lobule. Surgical exploration confirmed the absence of dural attachments. Microscopically, the tumor was found to be a sparsely cellular meningioma with an extensive collagenous matrix. A survey of the literature reveals that the majority of cases of meningiomas without dural attachments occur either in children or below the tentorium. Extremely rare cases of supratentorial meningiomas without dural attachment have been described in adults. The uncommon locations of these tumors at sites distant from the dura mater is postulated to reflect the rare occurrence of arachnoidal cap cells in the Virchow-Robin spaces along the cerebral vasculature or in pial layers distant from the dura mater.