Mucinous meningioma. Report of an unusual variant of meningioma that may mimic metastatic mucin-producing carcinoma.

An unusual variant of meningioma is described that was characterized by small clusters and strands of meningothelial cells surrounded by abundant mucinous stroma. The unusual appearance of the lesion prompted an initial diagnosis of metastatic mucin-secreting carcinoma (so-called colloid carcinoma) resulting in extensive clinical evaluation in search for a primary. Histochemical studies showed the mucinous material to be composed of strongly sulfated acid mucopolysaccharides rich in hyaluronic acid. Immunohistochemical studies showed strong membrane staining of the tumor cells with epithelial membrane antigen and positive cytoplasmic staining with vimentin antibodies. Ultrastructural examination revealed the characteristic features of meningothelial cells (i.e., abundant long, interdigitating cytoplasmic processes joined by well-developed cell junctions) but failed to demonstrate secretory activity within the neoplastic cells. The prominent mucinous stroma in this case most probably represents a nonspecific reaction of stromal cells to an undetermined stimulus. Mucinous meningioma should be added to the list of morphologic variants of meningioma and should be considered in the differential diagnosis of mucinous lesions in intracranial locations.