Fibrillary Astrocytoma

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Fibrillary astrocytoma is the most frequent histology variant of LGG. These lesions are predominantly composed of fibrillary neoplastic astrocytes.


The presence of nuclear atypia is necessary for diagnosis, but these lesions lack mitotic activity, necrosis or microvascular proliferation. Cell density is low to moderate. Fibrillary neoplastic astrocytes are marked by scant and barely discernible cytoplasm, creating the appearance of “naked nuclei.” Neoplastic cells are characterized by enlarged, irregularly shaped, or irregularly hyperchromatic nuclei. Microcysts containing mucinous fluid are characteristic. GFAP, vimentin, and S-100 are consistently expressed, though not by all tumor cells.


Treatment is controversial. Some tumors may be observed with serial MRI with the assumption that almost all of these tumors will at some point undergo malignant degeneration to a higher grade tumor. Biopsy or attempted resection is advocated when diagnosis is in doubt. Anaplastic astrocytomas may appear similar on MRI and often require treatment with adjuvant radiation post surgery.

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