Speakers

Chiari type I malformation and associated syringomyelia in children: evolution of disease concept and treatment
1109 08:52-09:07
Interim Meeting of AASPN/303A
Originally, Chiari I and II malformations were classified according to the severity of the hindbrain herniation from autopsy findings. In the late 1990s, Chiari malformation without myelomeningocele were referred to as Chiari I malformation. In 1997, overcrowding of the posterior fossa possibly due to abnormal development of the occipital somite was demonstrated in adult cases with idiopathic Chiari I malformation. In 2000s, small posterior fossa was shown also in pediatric cases. Recently, craniovertebral instability could be the cause. In the treatment of symptomatic Chiari I malformation without syringomyelia bony decompression with or without duraplasty is effective to decompress the hindbrain and improve the pressure difference between the posterior fossa and the cervical subarachnoid space. Given its natural history, asymptomatic children are not rare and tend to remain asymptomatic for years. As the initiation of associated syrinx formation, in the 1960s Gardner proposed an influx of CSF into the central canal of the spinal cord via the obex; in 1970, Williams proposed that the expansion of syringomyelia was caused by pressure differences due to herniated tonsils and syrinx cavity, but later no connection between the obex and the syrinx was observed on MRI in most cases. In the 1980s, based on these two theories, syringomyelia was treated by bony decompression with duraplasty and obex plugging. Later, bony decompression with duraplasty was found to be effective by restoring CSF movement at the major cistern. Simple bony decompression without duraplasty also improves syringomyelia, with fewer complications but a higher reoperation rate. The main cause of recurrent syringomyelia is inadequate restoration of CSF movement at the major cistern. Hindbrain herniation in Chiari I malformation should be considered a deformity rather than a malformation of the hindbrain, but whether the most likely cause, the small posterior fossa, is a malformation should be investigated further.