Chiari 1.5: A lesser known entity

Type II which is also known as the Arnold-Chiari malformation involves displacement of brainstem and lower cerebellum into the cervical spinal canal. The fourth ventricle is caudally displaced and extends below the foramen magnum. It is nearly always associated with lumbar myelomenigocele. Supratentorial anomalies are commonly seen. These include falx hypoplasia, hydrocephalus, callosal hypogenesis, fused enlarged massa intermedia, colpocephaly, abnormal gyral pattern, and Luckenschadel skull.