The patient went on to have a resection. 

Histology

Paraffin sections show a densely hypercellular spindle cell tumor. Tumor cells have mildly pleomorphic elongated vesicular nuclei and coarse bipolar processes and are arranged in intersecting fasciculi. A very occasional mitotic figure is identified. No necrosis is seen. No brain parenchymal tissue is included.

Very weak immunostaining for epithelial membrane antigen (EMA) is noted in tumor cells in some areas. Approximately 2-3% of tumor cells show strong nuclear staining for Ki-67.

No immunostaining for cytokeratins (AE1/AE3, CAM 5.2; CK 7, CK 20), S-100 protein, GFAP, neurofilament protein, CD34, tyrosinase or smooth muscle actin (SMA) is seen in tumor cells.

FINAL DIAGNOSIS. Undifferentiated spindle cell tumor of uncertain malignant potential, probably a meningioma. 

Comment: Although the regional weak immunostaining for epithelial membrane antigen (EMA) in this tumor is consistent with meningioma, the histological appearances of tumor cells and their architectural arrangement are unusual for meningioma and a mesenchymal tumor (metastasis from a low-grade sarcoma or gastrointestinal stromal tumor) cannot be excluded.

Discussion

Additionally, the possibility of this representing a chordoid glioma or a subependymal giant cell astrocytoma should be considered based on location and appearance, however, immunohistochemistry is very helpful. 

Although the histology is unusual for meningioma, the patient has remained well 5 years after resection without evidence of a systemic malignancy. The imaging appearances are also in keeping with an intraventricular meningioma.