Meckel's Cave Meningiomas: New Classification System Focalized on Dumbbell Lesions Deriving from the Morphometric Analysis of the Posterior Petrous Apicectomy on Fresh Non-Formalin-Fixed Specimens. A Correlative Anatomoclinical Study

BACKGROUND: The Meckel's cave (MC) is commonly affected by neoplastic lesions that often require neurosurgical treatment. We simulated the posterior petrous apicectomy (PPA) on fresh cadavers to verify the in vivo feasibility of the approach. We proposed a new classification system of MC meningioma based on the extent of middle cranial fossa (MCF) involvement. METHODS: Ten fresh, noneformalin-fixed specimens were used in this study. Through a retrosigmoid approach, 20 PPAs were performed. Subsequently, the cerebral hemispheres were removed to quantify the MCF exposure and dimensions of the suprameatal tubercle. Twenty-four patients operated on for MC meningioma were classified as follows: group 1, tumor <3 cm; group 2, tumor >3 cm. Group 2 was subdivided into to 5 subtypes: 2A, tumor of the MCF; 2B, tumor of the posterior cranial fossa; 2C, tumor of MCF and posterior cranial fossa; 2C type I, MCF <15 mm; and 2C type II, MCF >15 mm. RESULTS: The extent of MCF exposure through the PPA is 13 mm. Mean suprameatal tubercle dimensions were 10.4 mm x 3.8 mm. Mean extent of bony removal for the PPA was 10.2 mm. PPA was successfully performed in 3 patients without major neurologic sequelae. CONCLUSIONS: Preliminary results obtained with the PPA in 2C type I meningiomas are encouraging. The new classification system proposed can be useful in clinical practice, especially in the choice of the most suitable surgical approach for dumbbell meningiomas.