MUCINOUS MENINGIOMA - REPORT OF AN UNUSUAL VARIANT OF MENINGIOMA THATMAY MIMIC METASTATIC MUCIN-PRODUCING CARCINOMA

An unusual variant of meningioma is described that was characterized b y small clusters and strands of meningothelial cells surrounded by abu ndant mucinous stroma. The unusual appearance of the lesion prompted a n initial diagnosis of metastatic mucin-secreting carcinoma (so-called colloid carcinoma) resulting in extensive clinical evaluation in sear ch for a primary. Histochemical studies showed the mucinous material t o be composed of strongly sulfated acid mucopolysaccharides rich in hy aluronic acid. Immunohistochemical studies showed strong membrane stai ning of the tumor cells with epithelial membrane antigen and positive cytoplasmic staining with vimentin antibodies. Ultrastructural examina tion 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 activit y within the neoplastic cells. The prominent mucinous stroma in this c ase most probably represents a nonspecific reaction of stromal cells t o an undetermined stimulus. Mucinous meningioma should be added to the list of morphologic variants of meningioma and should be considered i n the differential diagnosis of mucinous lesions in intracranial locat ions.