FILAMENTOUS AGGREGATES IN A MENINGIOMA

The light microscopic and ultrastructural appearances of unusual filam entous aggregates in a right parietal meningioma in a 14-year-old boy are described. The tumor showed prominent meningothelial as well as fi broblastic components and was graded as an atypical meningioma. By lig ht microscopy, eosinophilic, PAS-positive, granular, irregularly shape d Rosenthal fiber-like structures were widespread within the tumor, in both an intra- and an extracellular location. By immunohistochemical staining, similar location of positivity was obtained for vimentin, la minin, and collagen type IV. The inclusions were nonreactive for kerat in, lysozyme, alpha-1-antitrypsin, and ubiquitin. Ultrastructurally, t hese aggregates were composed of an irregular tangle of filaments with electron dense condensations, sometimes with a lattice pattern. The i ntracellular aggregates were membrane-bound, and some were found withi n dilated rough endoplasmic reticulum, while extracellularly, they fil led up spaces between adjacent tumor cells. Less prominently, floccule nt osmiophilic nonfilamentous material was also seen within the inclus ions. These observations suggest that these novel inclusions in a meni ngioma are composed of intermediate filaments (vimentin) and extracell ular matrix proteins, with active synthesis in the rough endoplasmic r eticulum and subsequent extrusion from the tumor cells into the extrac ellular spaces.