Meningiomas

1. Meningiomas • Usually considered benign tumors • Comprise 15% of primary intracranial tumors • More common in women – F:M 2:1 • Highest incidence in the sixth and seventh decades • Found along external surfaces of the brain and occasionally within the ventricular system • Grossly, they are well-circumscribed and firm • Radiologically, they exhibit homogeneous contrast enhancement on CT and MRI; calcification is common

2. Meningiomas • Microscopically, the cells are relatively uniform, with round or elongated nuclei, and tend to form whorls and psammoma bodies (laminated calcific concretions) • Most frequent genetic defect – mutations in the neurofibromatosis 2 gene (merlin) on chromosome 22q • Some meningiomas contain estrogen and progesterone receptors • Ultrastructurally, they form complex interdigitations between cells

3. Meningioma Subtypes • Syncytial - whorled clusters of cells in tight groups • Fibroblastic – elongated cells and abundant collagen deposition • Transitional – features of syncytial and fibroblastic types • Psammomatous – numerous psammoma bodies • Secretory – PAS + intracytoplasmic droplets and intracellular lumens by electron microscopy • Microcystic – loose, spongy appearance Most are considered grade I/IV by the WHO, with a relatively low risk of recurrence; the various histologic appearances carry no prognostic significance