Ultrastructural profile of microcystic meningioma

Microcystic meningioma was originally classified as a subtype of meningioma by the World Health Organization classification of brain tumours in 1993, and accounts for 1.6% of intracranial meningiomas. This subtype is a variety of meningioma in which micro- and macro-cysts are diffuse. The morphologic characteristics are well defined, while the histogenetic mechanism that give rise to these patterns remain unclear. The authors present an electron microscopic study of an unusual case of fronto-temporal microcystic meningioma, manifesting as history of headache, right paresis and dysphasia in a 73-year-old female. Computer tomography revealed a large hypodense mass in the left fronto-temporal region, with slight contrast enhancement. Ultrastructural observation showed complex alterations among small vessels and intratumoral capillaries in a background of severe modification in vessel permeability. This electronic microscopy study documented that growth of the cyst was due not only to accumulation of in extracellular fluid, but also to cytolysis consequent to ingravescent hydropic degeneration.