Dysembryoplastic neuroepithelial tumor (atypical)

Case Discussion

The patient went on to have a craniotomy and resection. 

Histology

MICROSCOPIC DESCRIPTION:

Paraffin sections show cerebral cortex and white matter. Within the cortex and extending for a short distance into white matter are relatively circumscribed hypercellular areas composed of cells with round and oval hyperchromatic nuclei, many with peri-nuclear clearing.

Formation of glioneuronal element-like structures and occasional mature neurons within spaces between these structures are noted. No mitotic figures, microvascular proliferation or necrosis are seen. The cells show strong immunostaining for synaptophysin and Nogo A and weaker staining for GFAP. There is patchy, moderate nuclear staining for p53. No staining for IDH-1 is seen. The topoisomerase labeling  index is approximately 1%. Mild dysplastic features in the form of large neurons in lamina I and malorientation of neurons in deeper laminae are also noted.

FISH shows no loss of either chromosome 1p or chrommosome 19q.

FINAL DIAGNOSIS:

Low grade glioneuronal lesion with features most consistent with dysembryoplastic neuroepithelial tumor (DNET)

Comment

This is an unusual lesion and it would be difficult to make a pre-operative diagnosis on imaging alone. The presence of intense enhancement would make DNET less likely, favoring gangliglioma or pleomorphic xanthastrocytoma. Small foci of signal loss, if calcificaiton would further argue against DNET, favoring ganglioglioma over the other diagnoses. 

Pathology is also not absolutely conclusive.