Neuroimaging Features of Ectopic Cerebellar Tissue: A Case Series Study of a Rare Entity.

Ectopic cerebellar tissue is a rare entity likely secondary to multiple, interacting, developmental errors during embryogenesis. Multiple sites of ectopic cerebellar tissue have been reported, including extracranial locations; however, an intracranial location is most common. We report on the MR imaging findings of a multi-institutional series of 7 ectopic cerebellar tissue cases (2 males, 4 females, 1 fetal) ranging from 22 weeks 5 days' gestational age to 18 years of age. All cases of ectopic cerebellar tissue were diagnosed incidentally, while imaging was performed for other causes. Ectopic cerebellar tissue was infratentorial in 6/7 patients and supratentorial in 1/7 patients. All infratentorial ectopic cerebellar tissue was connected with the brain stem or cerebellum. MR imaging signal intensity was identical to the cerebellar gray and white matter signal intensity on all MR imaging sequences in all cases. Ectopic cerebellar tissue should be considered in the differential diagnoses of extra-axial masses with signal characteristics similar to those of the cerebellum. Surgical biopsy or resection is rarely necessary, and in most cases, MR imaging is diagnostic.