DO SPINAL MENINGIOMAS PENETRATE THE PIAL LAYER - CORRELATION BETWEEN MAGNETIC-RESONANCE-IMAGING AND MICROSURGICAL FINDINGS AND INTRACRANIALTUMOR INTERFACES

OBJECTIVE: To study the relationships between spinal dura-arachnoid an d tumor-cord interfaces in spinal meningiomas and to investigate wheth er a disruption of the pial layer and penetration of the tumor in the spinal cord occurs. METHODS: Fifteen patients with histologically prov en meningiomas underwent magnetic resonance imaging (MRI) preoperative ly. All patients underwent microsurgery. The histological characterist ics of the tumors were compared with MRI and microsurgical findings. R ESULTS: At surgery, the peritumoral hypointense rim revealed by MRI in 10 of 15 patients corresponded to a well-defined cerebrospinal fluid- containing space confined between the outer arachnoidal layer and the inner leptomeningeal layer. In those patients in whom the hypointense peritumoral rim was absent, the inner layer was either difficult to id entify or clearly absent, and the blood vessels were extremely adheren t to the tumor, requiring a more cautious dissection. Penetration of t he tumors through disruption of the pial surface was not documented. C ONCLUSION: Previous anatomic and electron microscopy studies demonstra ted, in human spinal meninges, the presence of an intermediate layer a ttached to the inner aspect of the arachnoid, extending laterally over the dorsal surface of the spinal cord and arborizing over the nerve r oots and blood vessels. The intermediate layer is not present in human cerebral leptomeninges. The presence/absence of this layer might expl ain the hypointense rim detected by MRI and might also explain why no penetration and no peritumoral edema is observed in spinal meningiomas as compared with intracranial meningiomas.