Ectopic cerebellum in anterior cranial fossa: Report of a unique case associated with skull congenital malformations and epilepsy.

An isolated, well-differentiated ectopic cerebellum arising outside the posterior fossa is extremely rare. We present a unique case of ectopic cerebellum in 25-year-old woman with hypertelorism, skull deformation, and a longstanding history of epileptic seizures. Magnetic resonance imaging revealed a mass lesion at the base of the frontal lobes with no apparent connections to the adjacent brain structures. Total resection of the lesion was performed. On gross inspection, its surface resembled cerebellar cortex with densely packed folia. Histologically, the cerebellar cortex was composed of well-differentiated external molecular, Purkinje cell, and internal granular cell layers. The deeper part of white matter displayed the features of neuroglial, hamartomatouslike abnormalities. There were numerous neuronal and/or glial heterotopias ranging from single dysplastic neurons to well-circumscribed clusters of neuronal and/or glial cells surrounded by neuropil. Some large neurons looked like mature ganglion cells, Purkinje cells, or dentate neurons. Large irregular islands of heterotopic tissue displaying well-differentiated cerebellar cortex could also be seen. Other parts of the ectopic cerebellum revealed loosening of tissue with dispersed glioneuronal elements. The ectopic brain tissue may arise from disturbed migration of primitive pluripotent stem cells during embryogenesis. The presented case of cerebellar ectopia associated with skull congenital malformations exhibited multiple dysontogenetic abnormalities. To our knowledge, this is the first report of totally isolated, well-differentiated ectopic cerebellum in the anterior cranial fossa accompanied by skull deformation and epilepsy.