Ectopic dural osteolytic meningiomas.

Intracranial meningiomas usually originate from the arachnoidal cells of the internal dural layer: meningiomas that originate from different sites are ectopic. The authors describe the case of a small meningioma adhering to the external dural layer without involvement of the internal layer, accompanied by osteolysis of the internal surface of the skull. A review of the literature on cranial ectopic meningiomas yielded only four cases described as originating from the external dural layer. Osteolysis of the skull was always present and was not found to have prognostic significance. The authors suggest that these four primary ectopic meningiomas originating from the external dural layer should be differentiated from intraosseous meningiomas of the skull.