Topographic anatomy and pneumatization of the posterior clinoid process in Chiari type I malformation.

OBJECTIVE: This study aimed to examine pneumatization and topographic location of the posterior clinoid process (PCP) in Chiari type I malformation (CIM) for skull base approaches.

METHODS: Computed tomography images of 52 (23 males / 29 females) CIM subjects aged 23.87±16.09 years, and 71 (26 males / 45 females) healthy subjects aged 42.48±21.48 years constituted the study universe.

RESULTS: The distances of PCP to the foramen magnum (p=0.037), superior orbital fissure (p<0.001), foramen rotundum (p<0.001), and foramen ovale (p<0.001) were smaller, but the distance of PCP to the crista galli (p=0.038) was greater in CIM patients, compared to normal subjects. In CIM, the fusion between PCP and the anterior clinoid process was observed in nine sides (8.70%), while in controls, in 12 sides (8.50%). PCP pneumatization was observed in 40 sides (38.50%) in CIM patients, while in 28 sides (19.70%) in normal subjects. This data displayed that PCP pneumatization was affected by CIM (p<0.001).

CONCLUSION: The distances of PCP to the crista galli and foramen magnum indicate the anterior fossa length and the posterior fossa depth, respectively; thus, CIM patients have longer anterior fossa and shallow posterior fossa. In addition, the distances of PCP to superior orbital fissure, foramen rotundum and foramen ovale indicate the middle fossa width; thence, CIM patients have less middle fossa width than normal individuals. CIM patients have approximately 50% higher PCP pneumatization rate, and this may increase the risk of complications such as cerebrospinal fluid fistula during the application of posterior clinoidectomy.