Meningioma pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Haytham Allaham, M.D. [2]

Overview

Pathogenesis

Meningioma arises from arachnoid "cap" cells that compose the meninges, which are normally involved in the protection of the central nervous system by forming a thick envelope around the brain and spinal cord. Meningiomas are usually benign; however, a small percentage can develop a malignant nature. The exact pathophysiology of meningioma depends on the histological subtype of the tumor.^[1] Meningiomas are frequently found attached to the dura surrounding the brain tissue in several locations that include:^[1]

Genetics

Development of meningioma is the result of multiple genetic mutations.^[1]
The most common gene involved in the pathogenesis of meningioma is the neurofibromatosis 2 gene located on chromosome 22.^[1]
Other genes involved in the pathogenesis of meningioma include:^[1]

Protein kinase (AKT1) gene located on human chromosome 14
Meningioma 1 (MN1) gene located on human chromosome 22
Phosphatase and tensin homolog (PTEN) gene located on both human chromosomes 10 and 19
SMO gene located on human chromosome 6 and 7

Gross Pathology

On gross pathology, a gray, well-circumscribed, dome-shaped mass is a characteristic finding of meningioma.^[1]

Microscopic Pathology

On microscopic histopathological analysis, whorled appearance, calcification, and psammoma bodies are characteristic findings of of meningioma.^[2]
The table below differentiates between the three main groups of meningioma according to WHO histological classification:^[2]^[3]^[4]


Grade	Histologic features	Image

Benign (Grade I) meningioma	Less then 4 mitosis/10 HPF, no atypia	Grade 1 Meningioma
Atypical (Grade II) meningioma	Brain invasion, 4 or more mitosis/10 HPF, necrosis, increased cell count, high nucleus:cytoplasm ratio, increased nucleoli size, presence of sheeting	Grade 2 menigioma
Anaplastic (Grade III) meningioma	20 or more mitoses/10 HPF, histology similar to carcinoma or sarcoma	Grade 3 menigioma

Shown below is a series of microscopic images featuring specific findings seen in each subtype of meningioma:^[2]

A smear showing meningothelial meningioma with syncytial appearance and whorl formation
A smear showing meningothelial meningioma with onion bulb formation
A smear showing meningothelial meningioma HPS stain
A smear showing fibrous meningioma with spindle cells in parallel bundles
A smear showing fibrous meingioma on EMA stain
A smear showing transitional meningioma with coexisting lobular and fasicular growth patterns
A smear showing psammomatous meningioma with numerous psammoma bodies
A smear showing angiomatous meningioma with hyalinized vessels
A smear showing microcystic meningioma with cystic appearance and increased pleomorphism of the elongated cells
A smear showing secretory meningioma with secretory granules
A smear showing secretory meningioma with PAS stain positive secretory granules
A smear showing chordoid meningioma with myxoid appearance
A smear showing papillary meningioma with discohesive meningothelial tumor cells around a fibrovascular core
A smear showing rhabdoid meningiomao with abundant cytoplasm and cross-striations