Novel eosinophilic intracytoplasmic inclusions in a meningioma

Two forms of inclusion, extracellular and intracytoplasmic, have been reported in meningiomas. The authors recently encountered a case of meningothelial meningioma with unusual round eosinophilic intracytoplasmic inclusions.

Ultrastructural and immunohistochemical studies were performed on the surgically removed tissue.

Ultrastructurally, the inclusions were found in the cytoplasm and processes of the tumor cells. Each inclusion consisted of a dense central mass of filaments with a looser, less dense periphery of radiating filaments. At the periphery, crystalloid lamellar structures and granules were intermingled frequently. No limiting membrane was observed. Immunohistochemically, the inclusions were unreactive for five classes of intermediate filaments, actin, ubiquitin, and amyloid.

The intracytoplasmic inclusions were ultrastructurally distinct from those reported previously. The molecular aspect of these novel eosinophilic intracytoplasmic inclusions remained uncertain.