Microscopic Appearance

The granulomas are composed of numerous central epithelioid macrophages with abundant eosinophilic cytoplasm and vesicular nuclei. Multinucleated giant cells representing a fusion of these macrophages may be seen, but are not always present (Figs. 5.2 and 5.3). Although not common, giant cells may contain asteroid bodies or calcified nodular Schaumann bodies. The central cluster of epithelioid macrophages is surrounded by a cuff of benign lymphocytes and plasma cells. Necrosis is uncommon but rarely may be seen. Although blood vessels may be seen within rare granulomas, this is not common. With age progressively more fibrosis is seen in the meninges.

The tissue surrounding parenchymal granulomas contains gemistocytic astrocytes and may exhibit edema or loss of neuropil. Small perivascular cuffs of benign lymphocytes are frequently seen in the tissue surrounding the parenchymal granulomas. Microglial nodules are usually absent. Special stains for mycobacteria, fungi, and amyloid are negative.

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