Intraventricular meningioma - third ventricle

The patient went on to have a resection. 

Histology

Paraffin sections show a densely hypercellular spindle cell tumour. Tumour 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 tumour cells in some areas. Approximately 2-3% of tumour 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 tumour cells.

Final diagnosis:

Third ventricle tumour:FINAL DIAGNOSIS. Undifferentiated spindle cell tumour of uncertain malignant potential, probably a meningioma. 

Comment:

Although Although the regional weak immunostaining for epithelial membrane antigen (EMA) in this tumour is consistent with meningioma, the histological appearances of tumour cells and their architectural arrangement are unusual for meningioma and a mesenchymal tumour (metastasis from a low-grade sarcoma or gastrointestinal stromal tumour) 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.