Figure 2. Transmission electron microscopy (TEM) demonstrates microvilli-containing lumens and microlumens in secretory meningioma.

(A) Low magnification view of secretory meningioma showing a cluster of intracytoplasmic lumens with various compaction of the content. (B) H&E cytologic preparation of secretory meningioma showing a cell with an intracytoplasmic lumen/inclusion pushing the nucleus. Note the clear space between the content and the periphery of the inclusion. (C) High magnification of the boxed area in (A) showing that the clear space from (B) contains microvilli (arrow). (D) Intracytoplasmic lumen/inclusion with blunted microvilli-devoid surrounding membrane. (E) High magnification of the lamellar content of inclusions containing compacted material. (F) Cell with intracytoplasmic inclusion and tightly apposed mitochondria and rough endoplasmic reticulum (inset) and microvilli (arrows) on the plasma membrane. (G–H) Ultrastructural and H&E cytologic appearance of intracytoplasmic multiloculated inclusions compartmentalized by long microvilli (arrow in G). (I) Microlumen with dense, thick microvilli containing an actin filament core. Blue arrows indicate surrounding desmosomes. (J) Comparative view of a microlumen from ependymoma showing abundant microvilli within a lumen delimited by adherens junctions (arrows).