Sections of the cerebellum show a proliferation of large neurons in the cortex, merging focally with the much smaller neurons of the internal granular layer. The large neurons have vesicular nuclei and prominent nucleoli. Bi or multinucleated cells are absent. They are somewhat unevenly distributed. The neuropil of the white matter is prominently vacuolated with elongated appearance. No mitoses, endothelial cell hyperplasia or necrosis are seen. No atypical astrocytes are identified. There is no evidence of malignancy. The features are those of dysplastic cerebellar gangliocytoma (Lhermitte-Duclos disease). There is a strong association between this entity and Cowden syndrome with PTEN mutations.
DIAGNOSIS: Dysplastic cerebellar gangliocytoma (WHO Grade I).