Absence of the falx cerebelli in a Chiari II malformation.

After a review of the literature, we found no descriptions of the falx cerebelli in the Chiari II population. Other dural partitions in this group have been well-described. The aim of our study was to radiologically and at autopsy search for the falx cerebelli in this population. We retrospectively analyzed 50 CTs and 50 MRIs in children with a known Chiari II malformation, searching for either the falx cerebelli or internal occipital crest, the bony attachment for the falx cerebelli; these structures were also investigated in two patients at autopsy. We were unable to observe the falx cerebelli or internal occipital crest on any of the radiologic images or at autopsy. We theorize that a "crowded" posterior cranial fossa in these patients inhibits the development of the falx cerebelli and internal occipital crest. Copyright 2002 Wiley-Liss, Inc.