Chiari I malformation after cranial radiation therapy in childhood: a dynamic process associated with changes in clival growth.

OBJECT: The small posterior fossa is believed to be relevant to the development of Chiari I malformation (CMI). In this study, we evaluated children with supratentorial tumors developing CMI after radiation therapy (RT) that involved the skull base. Changes in clivus and supraocciput growth rate were correlated with tonsillar herniation.

METHODS: Ten children who underwent RT for supratentorial tumors at St. Jude Children's Research Hospital (1994-2008) developed CMI on follow-up magnetic resonance imaging (MRI). Four other patients with supratentorial tumor and CMI who did not receive RT were identified. Length of the supraocciput, basisphenoid, and basichondrium and extent of tonsillar herniation were measured on serial midsagittal MRI.

RESULTS: Over the median follow-up of 85.5 months, basisphenoid annual growth rate was significantly lower in children receiving RT for suprasellar tumor (n=8) than those who did not (p=0.04). Growth of clivus and basisphenoid was significantly lower in the first 12 months after RT in children who received RT for suprasellar tumor (p=0.03 and p=0.04, respectively). In these patients, tonsillar herniation increased over 24 months after RT, reaching maximal descent at a mean of 20.2 months; this resolved as clival growth returned to normal. No patient was symptomatic.

CONCLUSIONS: In these children, restriction of clival growth occurred after RT for suprasellar tumors. Changes in clival growth were associated with changes in the extent of tonsillar herniation. This supports the importance of the small posterior fossa and reduced clival length in the etiology of CMI.