Chiari Type II malformation: past, present, and future.

OBJECT: The Chiari Type II malformation (CM II) is a unique hindbrain herniation found only in patients with myelomeningocele and is the leading cause of death in these individuals younger than 2 years of age. Several theories exist as to its embryological evolution and recently new theories are emerging as to its treatment and possible prevention. A thorough understanding of the embryology, anatomy, symptomatology, and surgical treatment is necessary to care optimally for children with myelomeningocele and prevent significant morbidity and mortality.
METHODS: A review of the literature was used to summarize the clinically pertinent features of the CM II, with particular attention to pitfalls in diagnosis and surgical treatment.
CONCLUSIONS: Any child with CM II can present as a neurosurgical emergency. Expeditious and knowledgeable evaluation and prompt surgical decompression of the hindbrain can prevent serious morbidity and mortality in the patient with myelomeningocele, especially those younger than 2 years old. Symptomatic CM II in the older child often presents with more subtle findings but rarely in acute crisis. Understanding of CM II continues to change as innovative techniques are applied to this challenging patient population.