Snapshot An infant boy presents with trouble swallowing, bilateral arm and leg weakness, and stridor. The infant was born to a 28-year-old woman who did not seek prenatal care. On physical exam, the infant barely moves his arms and legs and has stridor. A meningomyelocele is appreciated in the lumbosacral area. Magnetic resonance imaging of the head shows downward displacement of the cerebellar vermis and tonsils through the foramen magnum. (Chiari II malformation) Introduction Clinical definition Chiari malformations describes a heterogenous group of neurological anatomic anomalies involving the cerebellum, brainstem, and craniocervical junction along with the cerebellum being downwardly displaced Epidemiology incidence Chiari malformation type I is the most common type Pathogenesis unclear Associated conditions meningomyelocele spinal cavitations Robin sequence neurofibromatosis type I Noonan syndrome Chiari Malformations Chiari Malformation Type Comments Chiari I Findings typically asymptomatic in children abnormally shaped cerebellar tonsils are downwardly displaced through theforamen magnum Associated conditionsyringomyelia Chiari II (Arnold-Chiari malformation) Findings typically symptomatic cerebellar vermis and tonsil are downwardly displaced through the foramen magnum Associated condition spinal meningomyelocele