Dysembryoplastic neuroepithelial tumour (DNET)

Case contributed by Royal Melbourne Hospital

Presentation

Five likely partial seizures with one witnessed secondary generalized tonic clonic seizure.

Patient Data

Age: 45 years
Gender: Female

Non contrast CT demonstrates an ill-defined region of low attenuation in the right temporal lobe. 

MRI

MRI brain

There are two high T2 signal subependymal lesions within the right temporal pole. They appear high in T2 signal. The larger is 10 x 23 x 8 mm  and appears to arises from the lateral aspect of the right hippocampus abutting the lateral margin of the right lateral temporal horn. The smaller lesion is medial to the right lateral temporal horn measuring 7mm. Both have a well defined margin with a high signal rim on FLAIR, and the centre of the lesions do not attenuate. No associated vasogenic oedema, haemorrhage or restricted diffusion. No increased cerebral blood flow is seen on the RBC arterial spin labelling study (not shown). A small focus of enhancement is demonstrated in the larger of the two lesions. 

The ventricles and CSF spaces are unremarkable. Mucosal thickening of the right maxillary, right frontal and right ethmoidal sinuses. 

Conclusion

Appearances suggest of a low grade temporal lobe tumour and are most in keeping with a dysembryoblastic neuroepithelial tumour (DNET), with a differential including ganglioglioma or pleomorphic xanthastrocytoma (PXA)

The patient went on to have a resection of both lesions. 

Pathology

Histology

MACROSCOPIC DESCRIPTION: Two fragments of soft gelatinous tissue up to 3mm.

MICROSCOPIC DESCRIPTION: Paraffin section shows small feragments of moderately hypercellular tissue. These are composed of cells with uniform small round nuclei with an open chromatin arrangement and delicate processes. These are arranged in columns consistent with glioneuronal elements. Spaces filled with mucinous material are noted throughout the tissue fragments. An occasional mature neuron is identified (NeurN stain). No mitotic figures are identified and there is no vascular endothelial cell hyperplasia and no necrosis. Immunohistochemistry shows strong staining for synaptobrevin in the small cells. The features are of dysembryoplastic neuroepithelial tumour (DNET). The topoisomerase labelling index is <1%.

DIAGNOSIS: Dysembryoplastic neuroepithelial tumour (DNET) WHO Grade I 

Case Discussion

This case illustrates a relatively typical appearance of DNET, namely a high T2 signal lesion with a 'bubbly' appearance located in the temporal lobe and resulting in temporal lobe epilepsy. Typically these lesions do not have any enhancement, although a degree of enhancement is certainly recognised in a minority of cases. Usually patients are younger when they first present. 

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Case information

rID: 14465
Case created: 28th Jul 2011
Last edited: 13th Sep 2017
Inclusion in quiz mode: Included

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