A fetal MRI study obtained at 21 weeks' gestation revealed a suboccipital meningocele without hydrocephalus. One day after term birth, MRI demonstrated an acquired cerebellar encephalocele, and MRI obtained 5 months later showed progressive enlargement of the encephalocele, still without obvious hydrocephalus. The patient underwent an operation in which an external ventricular drain was placed, the grossly normal cerebellum was reduced into the posterior fossa without resection, and the dural defect was closed. The drain was weaned out over 5 days, and no ventriculoperitoneal shunt was placed. Postoperative MR images revealed normal cerebellum and no hydrocephalus. The patient is developmentally normal. Meningocele and encephalocele are embryologically distinct. An acquired encephalocele could develop from hydrocephalus (which was not present in this case), or secondary to the lower resistance to expansion into the dural defect of the meningocele relative to the resistance to expansion of the fetal skull. The cerebellar tissue was normal in this case, and was thus preserved. The developmental prognosis is excellent. To the authors' knowledge, this is the first reported case of this occurrence. It is important to differentiate between congenital and acquired encephalocele etiologies, because resection of the cerebellar tissue in an acquired encephalocele (as is routinely done in cases of congenital encephalocele) would be expected to result in neurological deficits.
Keywords: congenital; encephalocele; meningocele; paraxial mesoderm.