Dysembryoplastic neuroepithelial tumour (DNET)
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Mass effect involves the hippocampal head, amygdala, adjacent portion of the anterior temporal lobe, with the thin section axial T2 scans and the previous coronal T2 scans demonstrating a micro cystic appearance. The lesion is centred on grey matter with some extension into the white matter. There is no abnormal contrast enhancement. No vasogenic oedema extends beyond the lesion. The left cerebral hemisphere is normal.
The patient went on to have a resection.
Paraffin sections show fragments consisting predominantly of cerebral cortex with white matter included. These show loss of normal laminar architecture with a haphazard arrangement of enlarged, mildly dysmorphic neurones. Many of these lack discernible apical dendrites. Many smaller neurones are maloriented. No binucleate or balloon neurones are identified. There is moderate astrocytic gliosis. The features are of malformation of cortical development (focal cortical dysplasia - Taylor Type IB). No evidence of tumour is seen.
Additional sections shows a fagment of cerebral cortex in which there is a small focus of dysembryoplastic neuroepithelial tumour (DNET). This measures 3mm in greatest dimension and consists of a circumscribed collection of small immature neuronal cells which are dispersed in a myxomatous stroma. Scattered large mature neurones are admixed with the small immature neuronal cells. Poorly formed glioneuronal elements are noted. The small immature neuronal cells show strong granular immunostaining for synaptophysin. The Toposiomerase IIb labeling index is <1%. The adjacent cerebral cortex shows dyslamination and malorientation of neurones.
- Malformation of cortical development (focal cortical dysplasia - Taylor Type Ib);
- Dysembryoplastic neuroepithelial tumour (DNET) in deep temporal specimen