Arnold–Chiari Malformation

Arnold–Chiari malformations are structural defects of the cerebellum, brainstem, and spinal cord, most commonly involving downward displacement of cerebellar tonsils through the foramen magnum. Types range from asymptomatic (Type I) to severe hindbrain anomalies with hydrocephalus and myelomeningocele (Type II). Clinical features include headaches, ataxia, cranial nerve dysfunction, and syringomyelia. Diagnosis relies on MRI demonstrating herniation and associated anomalies. Management is individualized, with surgical decompression indicated for symptomatic patients, and prognosis varies by malformation type and severity.