Posterior Petrous Meningiomas: Surgical Classification and Postoperative Outcomes in a Case Series of 130 Patients Operated via the Retrosigmoid Approach.

OBJECTIVE:A standardized definition and classification of primary posterior petrous meningiomas (PPMs) is lacking, with consequent challenges in comparing different case series. This study aimed to provide an anatomical description and classification of PPMs analyzing a homogeneous series of patients operated via the retrosigmoid approach. METHODS:PPMs originate laterally to the petro-occipital fissure within the venous ring composed of the superior petrosal, sigmoid, inferior petrosal, and cavernous sinuses. We proposed a classification based on tumor site of origin, direction of growth relative to the internal acoustic meatus, and cranial nerves' displacement. Four types of PPMs were defined: retromeatal (type A), meatal (type B), premeatal (type C), and broad-based (type D). We performed a retrospective analysis of 130 consecutive patients with PPMs who underwent surgery as first-line treatment. RESULTS:The PPM classification predicted clinical presentation, postoperative morbidity, and resection rates. Headache, hydrocephalus, and cerebellar deficits were more common in type A (59.0%, 37.7%, 49.2%) and type D (66.7%, 66.7%, 33.3%). Hypoacusia/anacusia was more common in type B (87.5%), while trigeminal hypoesthesia/anesthesia was more common in type C (85.0%). After surgery, patients with type A and D PPMs were at higher risk to develop cerebellar deficits (11.5%-22.2%), whereas patients with type B and C PPMs presented with hypoacusia/anacusia (12.5%) and trigeminal deficits (10.0%), respectively. The near-total resection rate was higher in type A (91.8%), followed by types B (82.5%), C (80.0%), and D (77.8%) PPMs. CONCLUSIONS:The PPM surgical classification has an operative and prognostic relevance. In expert hands, the retrosigmoid approach represents a safe and effective approach to remove PPMs.