• Alessandro De Benedictis, Maria Camilla Rossi-Espagnet, Francesca Diomedi-Camassei, Sabrina Rossi, Elena Fontana, Franco Randi, Viviana Ponzo, Carlotta Nucci, Giacomo Esposito, Giovanni Paternò, Carolina Brunetti, Alessandra Savioli, Andrea Carai, and Carlo Efisio Marras.
• Neurosurgery Unit, Department of Neuroscience and Neurorehabilitation, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy. Electronic address: alessandro.debenedictis@opbg.net.
• World Neurosurg. 2020 May 1; 137: 158-163.

BackgroundCerebellar ectopy is a rare finding, with few cases previously reported. Intraventricular localized cerebellar ectopy was described in only 1 case within the fourth ventricle.Case DescriptionA 9-year-old girl suffered for 2 years from bilateral frontoparietal headaches, sometimes accompanied by vomiting and photophobia. Magnetic resonance imaging demonstrated an oval-shaped lesion within the left lateral ventricle, characterized by well-defined margins without a clear cleavage plane from the adjacent choroid plexus. The mass presented an intermediate signal on T1- and T2-weighted sequences, similar to gray matter, and reduced ADC values on ADC maps compared with white matter, with no enhancement after gadolinium-based contrast injection. After resection, macroscopic examination revealed an organoid structure with leptomeningeal lining and a clear-cut cortex and white matter components. Histology demonstrated normal cerebellum with a double-layered cortex and normal underlying white matter. The cerebellar ectopy was focally covered by bundles of capillary vascular structures covered by a monostratified ependymal cell lining, consistent with choroid plexus.ConclusionsWe describe, for the first time to our knowledge, the case of a child with ectopic cerebellar tissue harboring the supratentorial ventricular system. Plausible etiologic mechanism consists in the herniation of the cerebellar germinal tissue into the ventricular system through the ependyma, allowing cell migration to the supratentorial compartment, followed by maturation into the normal cerebellum.Copyright © 2020 Elsevier Inc. All rights reserved.

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