NQ-102 Answer: (E) Typically not associated with other malformation of the CNS

Diagnosis: Chiari II malformation

Pathology of the case: The salient gross abnormal findings here included the malformed tectal plate into a triangular shape reminiscent of the beak of a bird the so-called tectal-beaking, abnormal inferior extension of cerebellar vermis, and overall elongation of the pons and medulla. These are classic features of Chiari II malformation.

Chiari malformations are malformations of the cerebellum and range from mild (without clinical significance) to severe (incompatible with life). Four types are recognized (I-IV):

• Chiari I malformation – herniation of cerebellar tonsils through foramen magnum. May be clinically asymptomatic.

• Chiari II malformation (aka “classic” Chiari malformation, Arnold-Chiari malformation) – characterized by beaking of the midbrain tectum, elongation of the brainstem often with displacement of the medulla/4^th ventricle through the foramen magnum, and cerebellar tonsillar/vermis herniation (through foramen magnum). This malformation is often associated with a myelomeningocele. Symptoms may range from mild to severe.

• Chiari III malformation – Chiari malformation + occipital encephalocele. This malformation often is associated with severe neurologic deficits, but may be incompatible with life, depending on the extent of the encephalocele.

• Chiari IV malformation (very rare) – cerebellar hypoplasia (incomplete cerebellar development). This version is incompatible with life.

Hydrocephalus is a nonspecific finding and may be seen in association with many CNS malformations, including Chiari malformations.