A newborn with a lumbar myelomeningocele develops progressive hydrocephalus in the first week of life. MRI shows downward displacement of the cerebellar vermis and medulla through the foramen magnum with crowding of the posterior fossa. Which malformation explains the hydrocephalus?

• A Aqueductal stenosis as an isolated lesion
• B Arnold-Chiari type II malformation ✓
• C Dandy-Walker malformation
• D Communicating hydrocephalus following intraventricular hemorrhage

Explanation

Nearly all children with open spinal dysraphism have the Arnold-Chiari type II malformation: caudal displacement of the cerebellar vermis, medulla, and fourth ventricle into the cervical canal, obstructing CSF flow at the foramen magnum. This produces hydrocephalus in the great majority of these infants and typically requires VP shunting at or soon after back closure. Dandy-Walker features an enlarged posterior fossa with vermian aplasia rather than descent, and isolated aqueductal stenosis is not linked to myelomeningocele.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.