Cytologic and Histological Features Distinguishing Myxoid Meningioma From Chordoid Meningioma: A Case Report.

Meningiomas are the most common primary brain tumors worldwide and are classified into 15 subtypes in the 5th edition of the WHO classification. Myxoid meningioma, characterized by the presence of a mucinous matrix within the tumor, is a rare metaplastic meningioma subtype classified as WHO grade 1. Chordoid meningiomas similarly contain a mucinous matrix, but are WHO grade 2. Accurate distinction between these subtypes is essential for determining appropriate treatment and predicting prognosis. Herein, we present a case of myxoid meningioma requiring differential diagnosis from chordoid meningioma. A man in his 60s presented with falls, depression, and urinary incontinence. Imaging revealed a tumor 6 cm in diameter in the right frontal region. Tumor resection with rapid intraoperative diagnosis was performed. Cytology revealed epithelioid cells with oval nuclei, intranuclear cytoplasmic inclusions, and mucinous matrix. Squash cytology confirmed tumor cell clusters with a vascular network. Histological examination revealed tumor cells forming cord-like structures within an Alcian blue-positive, Periodic acid-Schiff-negative mucinous matrix, along with an abundant vascular architecture. Myxoid and chordoid meningiomas share many cytological similarities, and mucin staining patterns are diagnostically unclear. However, the latter tend to show lymphocytic and plasma cell infiltration. This case lacked such infiltration, and the vascular stroma aided differentiation. For rapid intraoperative diagnosis, a combination of frozen sections and cytology, less susceptible to freezing artifacts, is considered beneficial for accurate diagnosis. In meningiomas with a mucinous matrix, careful evaluation of cellular appearance and tumor stroma findings is essential for distinguishing between subtypes with different WHO grades.