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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?































Diagnosis:

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

Discussion:

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

Ependymoma:
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.
30100 Telegraph Road, Suite 408
Bingham Farms, Michigan (USA) 48025
Telephone: 248/646-0325
Email: NatPernick@Hotmail.com
Alternate email: NatPernick@gmail.com