Primary extradural meningiomas: a report on nine cases and review of the literature from the era of computerized tomography scanning

Object. Primary meningiomas arising outside the intracranial compartment (p rimary extradural meningiomas [PEMs]) are rare tumors. To develop a better understanding of these tumors and to establish a comprehensive classificati on scheme for them, the authors analyzed a series of patients treated at th e M. D. Anderson Cancer Center (MDACC) and reviewed all cases reported in t he English-language literature since the inception of the use of computeriz ed tomography (CT) scanning. Methods. Clinical records, results of radiographic studies, and histologica l slides were reviewed for all cases of PEM at MDACC. Demographic features, symptoms, tumor location, histological grade, and patient outcome were ass essed in all cases. A comprehensive literature search identified 168 PEMs i n 142 patients reported during the CT era. These reports were also analyzed for common features. Tumors for both data sets were classified as purely e xtracalvarial (Type I), purely calvarial (Type II), and calvarial with extr acalvarial extension (Type III). Type II and Type III tumors were further c ategorized as convexity (C) or skull base (B) lesions. The incidence of PEMs at MDACC was 1.6%, which was consistent with the rate reported in the literature. In both data sets, the male/female ratio was n early 1:1. The most common presenting symptom was a gradually expanding mas s. The age of patients at diagnosis of PEM was bimodal, peaking during the second decade and during the fifth to seventh decades. In all MDACC cases a nd in 90% of those reported in the literature the PEMs were located in the head and neck. The majority of tumors originated in the skull (70%). In the MDACC series and in the literature review, the majority (67% and 89% , respectively) of tumors were histologically benign. Although fewer PEMs w ere malignant or atypical (33% at MDACC and 11% in the literature), their i ncidence was higher than that observed for primary intracranial meningiomas . Distant metastasis was not a common feature reported for patients with PE Ms (6% in the literature). Outcome data were available in 96 of the cases culled from the CT-era liter ature. The combination of the MDACC data and the data obtained from the lit erature demonstrated that patients with benign Type IIB or Type IIIB lesion s were more likely to experience recurrence than patients with benign Type IIC or Type IIIC tumors (26% compared with 0%, p < 0.05). The more aggressi ve atypical and malignant tumors were associated with a statistically signi ficant higher death rate (29%) relative to benign tumors (4.8% death rate, p < 0.004). Conclusions. Defining a tumor as a PEM is dependent on the tumor's relation to the dura mater and the extent and direction of its growth. Classificati on of PEMs as calvarial or extracalvarial and as convexity or skull base le sions correlates well with clinical outcome.