Mixed pilocytic and pilomyxoid astrocytoma

The predominantly cystic lesion within the posterior aspect of the right temporal lobe along the cortical margin of the middle temporal gyrus measures approximately 11 x 12 mm. A small enhancing anterior mural nodule is demonstrated.

No surrounding vasogenic edema. No increase in regional perfusion (not shown). The MRS is non-specific (not shown). The remainder of the brain is unremarkable.

Conclusion:

The differential diagnosis of the isolated right temporal lobe lesion is that of a ganglioglioma or pleomorphic xanthoastrocytoma, DNET and low grade glioma.

MICROSCOPIC DESCRIPTION:

The sections show features of a moderately cellular glial tumor. In some areas (50%), the appearances are typical for those of pilocytic astrocytoma. Scattered bipolar astrocytes are seen in fibrillary background. These cells have elongated and hyperchromatic nuclei. There are many associated Rosenthal fibers. In specimen 4 (50%), the tumor forms perivascular pseudorosettes, in which the bipolar cells radiate from the central blood vessels. The background is prominently myxomatous. Tumor is also present in the subarachnoid space. The features here resemble those of pilomyxoid astrocytoma. Overall, mitoses are inconspicuous. No endothelial cell hyperplasia or necrosis is present. Cerebral cortex is present in specimens 2 and 3. The neurons appear to show normal lamination and orientation. No dysmorphic or balloon cells are present. Neoplastic ganglion cell component, as in ganglioglioma, is not seen. The tumor cells in the pilomyxoid areas are GFAP, synaptophysin, p53 and MGMT immunostains positive. The Ki-67 index is up to 3%. EMA and IDH-1 immunostains are negative.

DIAGNOSIS: Low grade astrocytoma with mixed features of pilocytic and pilomyxoid astrocytoma.

Comment: The behavior of these intermediate tumors is unclear and cannot be predicted on histology. It is not known whether they behave more like pilocytic (grade I) or pilomyxoid (grade II) astrocytoma.