Lymphoplasmacyte-Rich Meningioma: Possible Formation of Intratumoral "Tertiary Lymphoid Structures"

A surgical case of lymphoplasmacyte-rich (LPR) meningioma that arose in the region of the clivus of an 81-year-old woman is reported. The tumor consisted largely of a dense and diffuse infiltration of mature lymphocytes and a smaller number of plasma cells. Mainly in the peripheral region of the tumor, small sheets or clusters of large polygonal cells having vesicular nuclei and palely eosinophilic cytoplasm were observed. Some of these cells formed cellular whorls. These cells showed immunoreactivity for progesterone receptor, epithelial membrane antigen, somatostatin receptor type 2A, epithelial cadherin, and podoplanin, thus confirming the diagnosis of LPR meningioma. Although lymph follicles having germinal centers were not evident, the distributions of lymphocytes and plasma cells were heterogeneous, and plasma cells occasionally appeared to surround lymphocytic aggregates. Some intratumoral venules showed features of "high endothelial venules." These findings suggested that a dense accumulation of lymphocytes and plasma cells in LPR meningioma was not a simple inflammatory cell infiltration but might represent formation of "tertiary lymphoid structures." Whereas some inflammatory cells showed cytoplasmic immunoreactivity for programmed cell death ligand-1, meningioma cells did not express it.