Chiari malformations

Abstract

Chiari malformations designate a group of developmental disorders characterized by anatomical deformities of the posterior fossa. They are either evident at birth or even prenatally or become symptomatic during adolescence or adulthood. Diagnosis relies mainly on MRI. Chiari type I is the most common form and is characterized by herniation of the cerebellar tonsils through the foramen magnum and consecutive forward compression of the lower brainstem. Chiari type II mainly combines a caudal herniation of the cerebellar vermis and brainstem, lumbar myelomeningocele, and supratentorial abnormalities typically of the corpus callosum. Chiari type III associates some intracranial defects of Chiari type II with a high cervical meningomyelocele. Chiari type IV is characterized by cerebellar hypoplasia with aplasia of the tentorium cerebelli. Syringomyelia is the most common spinal cord defect found in association with Chiari malformations. About 40-80% of patients with Chiari type I malformations have a syrinx. The central cavitation is usually located at the cervical level, but may extend cranially to the brainstem or caudally to the lower segments of the spinal cord. Asymptomatic patients diagnosed with Chiari type I in the absence of concomitant syringomyelia are not considered as candidates for surgical therapy in most cases. Surgery of symptomatic malformations consists usually in decompression of the foramen magnum. Nonsurgical therapies include management of neuropathic pain, physical therapy, and rehabilitation.