Dysplastic glioneuronal lesion arising in the cerebellum: a clinicopathological, immunohistochemical and ultrastructural study

We describe a case of dysplastic glioneuronal lesion in the right cerebella r hemisphere. A 13-year-old boy presented with headache since 1998. He had no neurological deficits. The computerized tomograph (CT) scan showed promi nent calcification, and magnetic resonance imaging (MRI) revealed a non-enh ancing mass of 15 x 15 x 5 cm in the right cerebellar hemisphere. The mass had low intensity in T1- and high intensity in T-1-weighted images. Histolo gically, the lesion was composed of poorly defined small to intermediate si zed cells arranged in fibrillar background. Although few neuronal cells hav ing large nuclei with small nucleoli were present, no ganglion cells could be seen. Immunohistochemically, these poorly defined cells were non-reactiv e to various glial and neuronal markers. However, GFAP, synaptophysin, neur ofilament and vimentin-reactive intercellular matrix and few nonneoplastic GFAP-positive glial cells and neurofilament-positive neuronal cells were se en. A very low MIB-1-labelling index of less than 0.1% was noted. Ultrastru cturally, two different populations of the cells were seen. A few neuronal cells were larger and had an oval nucleus with small nucleolus and cytoplas m containing various cytoplasmic organelles, Golgi apparatus, mitochondria, ribosomes, lipofuscin, rough endoplasmic reticulum, microtubules and neuro filaments. Many other cells had a scant cytoplasm and thus poorly defined. Cytoplasmic processes with axono-dendritic synapses and foci of bundles of intermediate filaments were present in the intercellular areas of the lesio n. Based on these radiological, histological and ultrastructural findings o f the lesion of low proliferative potential, we considered it dysplastic in nature.