Intracranial extracerebral neuroglial heterotopia: A case report and review of the literature.

Heterotopic masses of neuroglial tissue are uncommon and most frequently involve extracranial midline structures. We report an unusual case of an intracranial, extracerebral neuroglial heterotopia involving the middle and anterior cranial fossae of a 5-year-old girl who presented with facial asymmetry. The lesion was composed of mature but disorganized gray and white matter admixed with surrounding soft tissues and exhibited histologic features reminiscent of cortical dysplasia. These rare lesions have been postulated to arise from a protrusion of tissue from the neuraxis through a pial defect, from abnormalities in the migration of embryonic neuroepithelial tissue, or from an accessory evagination of the neural tube inferior to the telencephalic vesicles. Regardless of the underlying pathogenic mechanism, these lesions must be histologically distinguished from both teratomas and primary central nervous system neoplasms.