OBSOLETE: Arnold-Chiari malformation type II

Arnold-Chiari malformation type II (also known as Chiari II malformation) is a congenital structural defect of the brain characterized by downward displacement (herniation) of the cerebellar vermis, brainstem, and fourth ventricle through the foramen magnum into the spinal canal. This condition is nearly always associated with myelomeningocele (open spina bifida), a neural tube defect in which the spinal cord and its surrounding membranes protrude through an opening in the spine. Note that this Orphanet entry (ORPHA:1136) is marked as obsolete, as the condition has been reclassified or merged under broader categorizations of Chiari malformations and neural tube defects. The condition primarily affects the central nervous system, including the brain, brainstem, and spinal cord. Key clinical features include hydrocephalus (accumulation of cerebrospinal fluid in the brain), which occurs in the majority of affected individuals and often requires surgical shunting. Brainstem dysfunction can lead to breathing difficulties (including apnea), swallowing problems, stridor, and cranial nerve palsies. Lower limb weakness, bladder and bowel dysfunction, and varying degrees of paralysis below the level of the spinal defect are common due to the associated myelomeningocele. Symptoms typically present at birth or in early infancy. Treatment is primarily surgical and multidisciplinary. Closure of the myelomeningocele is usually performed within the first days of life, and prenatal surgical repair has shown benefits in reducing the severity of the Chiari II malformation and hydrocephalus. Ventriculoperitoneal shunting is frequently required to manage hydrocephalus. Posterior fossa decompression surgery may be necessary in cases of symptomatic brainstem compression. Long-term management involves neurosurgery, neurology, urology, orthopedics, and rehabilitation services to address the complex needs of affected individuals.

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