Grossly, a well-circumscribed whorled tan-yellow mass is seen; note the attached dura.
At low power, fascicles of spindled cells whorl around vessels.
The cells are monotonous and this regions is rather hypocellular
A hypocellular area blends into an atypical focus (bottom left) with increased cellularity and pleomorphism. However, these features alone are not enough to trigger a diagnosis of atypical meningioma. A mitotic rate of greater than 4 mf/10 hpf must also be present.
The cells are embedded in a collagen-rich matrix.
Meningiomas show dual epithelial and mesenchymal differentiation, and thus are immunohistochemically reactive with both epithelial and mesenchymal markers. The fibrous, angiomatous and metaplastic subtypes can be considered the "mesenchymal variants" (Fletcher).
The fibrous variant is composed of spindled cells arranged in fascicles. Whorling of cells around vessels and psammoma bodies are common as well. Mitotic figures should be minimal (less than 4 mits per 10 HPF).
The main differential diagnosis is a schwannoma, which can also arise in the cerebello-pontine angle. Like fibrous meningiomas, schwannomas are composed of fascicles of spindled cells, however, schwannomas exhibit the characteristic Antoni A and Antoni B regions with Verocay bodies. These features are absent in meningiomas and furthermore, schwannomas do not exhibit whorling of cells around vessels or psammoma bodies (Prayson).
Can occur at any age, and there is a clear female predominance. Interestingly, there is an association with certain malignancies, especially breast cancer and a history of previous radiation (Prayson).
This variant is classified as a WHO Grade I tumor.
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Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 1707-1710.
Kumar V, Abbas AK, Fausto N. Robbins and Cotran Pathologic Basis of Disease. 7th Ed. Philadelphia, PA: Elsevier; 2005: 1409-1410
Prayson, RA. Neuropathology: Foundations in Diagnostic Pathology. Philadelphia, PA: Elvesier; 2005: 489-494.
Prayson R, Kleinschmidt-Demasters BK, Cohen ML. Brain Tumors. Consultant Pathology Series New York, NY: Demos Publishing: 2010: 190-2.