Chiari ''malformation'' in Crouzon syndrome.

Background.- Use of MRI makes the association Chiari malformation-cranio-facial synostosis more frequent than expected. The aim of this work was to ascertain the true incidence of Chiari malformation and to understand the reasons of the association between a bone pathology and a CNS malformation. Patients and methods.- The anatomy of the posterior cranial fossa in Crouzon syndrome was retrospectively studied on MRI scan in 49 patients. Results.- A chronic tonsillar hemiation, similar to a Chiari malformation was observed in 71.4% of the cases. All the patients with Crouzon syndrome and progressive hydrocephalus had a Chiari malformation, but only 19 out of the 33 patients without associated hydrocephalus had a Chiari malformation (57.6%). Significant differences between the pattern of lambdoid suture closure were founded between both groups, with and without Chiari malformation, the lambdoid closure appearing earlier in patients with Chiari malformation. Conclusion.- The high incidence of chronic tonsillar herniation in Crouzon syndrome seems related to the premature synostosis of the lambdoid suture.