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

We describe a case of dysplastic glioneuronal lesion in the right cerebellar hemisphere. A 13-year-old boy presented with headache since 1998. He had no neurological deficits. The computerized tomograph (CT) scan showed prominent calcification, and magnetic resonance imaging (MRI) revealed a non-enhancing 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. Histologically, the lesion was composed of poorly defined small to intermediate sized cells arranged in fibrillar background. Although few neuronal cells having large nuclei with small nucleoli were present, no ganglion cells could be seen. Immunohistochemically, these poorly defined cells were non-reactive to various glial and neuronal markers. However, GFAP, synaptophysin, neurofilament and vimentin-reactive intercellular matrix and few nonneoplastic GFAP-positive glial cells and neurofilament-positive neuronal cells were seen. A very low MIB-1-labelling index of less than 0.1% was noted. Ultrastructurally, two different populations of the cells were seen. A few neuronal cells were larger and had an oval nucleus with small nucleolus and cytoplasm containing various cytoplasmic organelles, Golgi apparatus, mitochondria, ribosomes, lipofuscin, rough endoplasmic reticulum, microtubules and neurofilaments. 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 lesion. Based on these radiological, histological and ultrastructural findings of the lesion of low proliferative potential, we considered it dysplastic in nature.