Sign Up for a Free Account
  • Updated 12.18.2020
  • Released 06.27.1997
  • Expires For CME 12.18.2023

Meningiomas

Introduction

Overview

Meningiomas are the most common primary intracranial tumors. Although most are benign, morbidity can be high, and in some cases the tumor is fatal. The author reviews the pathophysiology, presentation, and treatment of this tumor, including new prognostic indicators in atypical and malignant meningiomas.

Key points

• Surgery and radiation form the cornerstones of therapeutic management of meningiomas.

• There are several pathways that are involved in meningioma formation and progression, Notch signaling pathway, and overexpression of SPARC protein.

• AKT1 and SMO pathways are involved in the pathogenesis of non-NF2 associated skull base meningiomas, which may serve as potential therapeutic targets in the medical management of these challenging tumors.

• Therapies targeting pathways involved in meningioma development and progression are actively undergoing evaluation.

Historical note and terminology

The word "meningioma" was first used by Cushing in 1922 to describe a tumor originating from the meninges (18). In 1938 Cushing and Eisenhardt, in a classic monograph, described a classification system for these tumors (19). Meningiomas originate from the arachnoidal cap cell, a meningothelial cell in the arachnoidal membrane. They generally arise where arachnoidal villi are numerous (41). Meningiomas were classified by their site of origin, and this system is still used and is augmented by the neuroanatomically specific incidence of specific mutations within subtypes of meningiomas. The common sites of origin and incidence rates are shown in Table 1 (19; 49; 69).

Meningiomas are classified as benign (WHO grade I), atypical (grade II), or malignant (grade III). All grades may invade bone producing both an osteoblastic and a lytic reaction (41). There are numerous histologic subtypes, most of which do not influence the natural history. Some specific exceptions exist. WHO grade II meningiomas, also known as atypical meningiomas, include chordoid and clear cell subtypes (10). These tumors make up 5% to 7% of all meningiomas (54). Grade II meningiomas are diagnosed based on increased mitotic index of equal to or greater than 4 mitoses per 10 high-power fields or 3 or more of the following features: increased cellularity, small cells with high nuclear:cytoplasmic ratio, prominent nucleoli, uninterrupted patternless or sheet-like growth, and foci of "spontaneous" or "geographic necrosis" (14). The updated WHO classification system from 2016 includes “brain invasion” as criteria for WHO grade II meningiomas (48).

WHO grade III meningiomas make up 1.0% to 2.8% of all meningiomas. Grade III meningiomas are also known as anaplastic meningiomas or malignant meningiomas. These include anaplastic, rhabdoid, and papillary histologic types (10). Grade III meningiomas have further increase in mitoses and cellularity with conspicuous necrosis (52). Grade III meningiomas by definition must have equal to or greater than 20 mitoses per 10 high-power fields (14).

This is an article preview.
Start a Free Account
to access the full version.

  • Nearly 3,000 illustrations, 
including video clips of 
neurologic disorders.

  • Every article is reviewed by our esteemed Editorial Board for accuracy and currency.

  • Full spectrum of 
neurology in 1,200 
comprehensive articles.

Questions or Comment?

MedLink, LLC

10393 San Diego Mission Rd, Suite 120

San Diego, CA 92108-2134

Toll Free (U.S. + Canada): 800-452-2400

US Number: +1-619-640-4660

Support: service@medlink.com

Editor: editor@medlink.com