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Case of the Week #250

5 September 2012 - Case of the Week #250

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Thanks to Dr. Bassma Mohamed El Sabaa, Alexandria School of Medicine (Egypt), for contributing this case and the discussion. To contribute a Case of the Week, follow the guidelines on our Case of the Week page.

November 10, 2012
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Case of the Week #250

Clinical History:

A 4 month old boy had a two month history of manifestations of increased intracranial pressure. MRI showed a 1.5 x 1.5 cm solid mass in the hypothalamic area, which was biopsied.

Gross examination revealed a few tiny soft slimy tissue fragments collectively measuring 1.5 x 1.0 cm.

Micro images:


GFAP staining

What is your diagnosis?


Pilomyxoid Astrocytoma [PMA], WHO Grade II; ICD-O 9425/3


This hypothalamic tumor in a 4 month old is composed of monomorphic, spindled, bipolar, GFAP+ glial cells in a loose fibrillar and strikingly myxoid background, in a somewhat angiocentric pattern.

The differential diagnosis is based on patient age and tumor site, and includes pilocytic astrocytoma, pilomyxoid astrocytoma, low-grade diffuse astrocytoma and ependymoma.

Pilocytic astrocytoma:
Features in this case that support this diagnosis:
● Age: children
● MRI: enhancing cyst with a mural nodule
● Histology: elongated, bipolar cells; glomeruloids of thin walled blood vessels

Features of pilocytic astrocytoma not present in this case:
● Rosenthal fibers and eosinophilic granular bodies
● Myxoid changes are only FOCAL

Diffuse infiltrating astrocytomas:
Features in this case that support this diagnosis:
● Myxoid change can be seen in low-grade astrocytoma (WHO grade II)

Features of diffuse infiltrating astrocytoma not present in this case:
● Usually adults
● Myxoid stroma with perivascular bipolar cells is unusual

Features of ependymoma not present in this case:
● Regular perivascular rosettes, true rosettes
● Extensive myxoid background unusual

This case has characteristic features of pilomyxoid astrocytoma, including a prominent myxoid matrix, monomorphous bipolar spindle cells, a prominent angiocentric arrangement, some glomeruloid vessels, and no mitotic figures / significant pleomorphism. The spindle cells are GFAP and vimentin positive, and negative for synaptophysin, neuron specific nuclear protein (Neu-N), chromogranin, neruofilament and epithelial membrane antigen (EMA). The MIB1 (Ki-67) labeling index varies between 0.9-6.1% with marked regional variations.

Pilomyxoid astrocytoma is an aggressive variant of pilocytic astrocytoma, with more local recurrence (55-76%) and CSF spread (11-14%). Up to 33% of patients die of disease within 2 years after diagnosis (J Neuropathol Exp Neurol 1999;58:1061, J MedGenMed 2004;6:42). To date, no specific cytogenetic or molecular pathologic findings or associated syndromes have been identified.

Nat Pernick, M.D., President
and Palak Thakore, Associate Medical Editor
PathologyOutlines.com, Inc.
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