Skull base growth in children with Chiari malformation Type I.

Object: The goal of this study was to establish whether children with Chiari malformation Type I (CM-I) have abnormal skull base geometry.
Methods: Distances and angles between skull base landmarks were measured on preoperative magnetic resonance images obtained in 30 children (age range 36-204 months) with symptomatic isolated CM-I; 16 of them (53%) had syringomyelia. Comparisons were made with 42 children of similar age who comprised the control group by using one-way analysis of variance.
Results: The angle formed by the crista galli (CG), dorsum sellae (DS), and foramen magnum (FM) was larger than normal in individuals with CM-I than in those without (145 degrees in patients with CM-I but no syringomyelia and 151 degrees in those with CM-I and syringomyelia compared with 135 degrees in controls; p = 0.000). The angle formed by the left internal auditory meatus (IAM), FM, and right IAM was also larger than normal in the patients (122 degrees in patients with CM-I but no syringomyelia and 123 degrees in those with CM-I and syringomyelia compared with 110 degrees in controls; p = 0.001). The angle formed by the anterior clinoid process (ACP), CG, and right ACP was smaller than normal (29 degrees in all patients with CM-I compared with 34 degrees in controls; p = 0.000). The distance between the two IAMs was longer than normal (75 mm in patients with CM-I but no syringomyelia and 63 mm in those with CM-I and syringomyelia compared with 58 mm in controls; p = 0.000). The distance between the two ACPs was shorter than normal in the syringomyelia group (31 mm in patients with CM-I but no syringomyelia and 27 mm in those with CM-I and syrinx compared with 32 mm in controls; p = 0.001). Within the group of patients with CM-I, the DS-FM and left ACP-right ACP distances were smaller in the syringomyelia group (p = 0.009 and p = 0.037, respectively).
Conclusions: Children with CM-I have abnormal geometrical measurements of their entire skull base, not only the posterior fossa, irrespective of presence of syringomyelia. This may indicate a mesodermal defect as a possible cause of the malformation.