Pathological classification and molecular genetics of meningiomas

Meningiomas are extremely common adult brain tumors originating from meningeal coverings of the brain and spinal cord. While most are slowly growing Word Health organization (WHO) grade I tumors, rare variants (clear cell, chordoid, papillary, and rhabdoid), as well as brain invasive (WHO grade II), atypical (WHO grade II), and anaplastic (WHO grade III) meningiomas are considerably more aggressive. This review summarizes the histopathological and genetic features of meningiomas, including differential diagnosis, pitfalls, and grading challenges. Early stages of meningioma tumorigenesis are closely linked to inactivation of one or more members of the 4.1 superfamily, including the neurofibromatosis type 2 (NF2) and 4.1B (DAL-1) genes, which interact with the 14-3-3 protein family. Other chromosome 22q genes implicated include BAM22, BCR (breakpoint cluster region), and TIMP-1, the last of which is implicated in higher-grade meningiomas. Atypical meningiomas also commonly show chromosomal losses of 1p, 6q, 10, 14q, and 18q, as well as multiple chromosomal gains. While most relevant genes remain unknown, two chromosome 14q candidates (MEG3 and NDRG2) have recently been identified. In addition to alterations of CDKN2A, p14(ARF), and CDKN2B tumor suppressor genes on 9p21, a contribution of the wingless (wnt) pathway with alterations of the E-cadherin and beta-catenin proteins, as well as alterations of the hedgehog signaling pathway have been implicated in anaplastic meningiomas. The integration of histopathological appearance, complex genetic/genomic data, and outcome will likely result in the identification of clinically distinct meningioma subgroups, which in turn can facilitate the development of targeted therapeutic strategies.