Extracerebellar ectopic brain tissue in the posterior fossa.

This article presents the case study of a 27-year old woman at 28 weeks' gestation with the diagnosis of a round mass in the fetal posterior fossa. Tests found were highly suggestive of heterotropic or ectopic brain tissue. Surgical resection was not performed due to the atypicality of the case. The pathogenesis of this rare developmental disease is offered.