Basilar Invagination: A Craniocervical Kyphosis

BACKGROUND: For more than a century, odontoid process prolapse, which compresses cranial base structures, has been the hallmark of basilar invagination (BI). The angulation of the whole skull toward the cervical spine may be considered to contribute to BI and odontoid prolapse. The objective of this study was to evaluate the craniocervical angular craniometry of patients with BI compared with patients with Chiari malformation (CM) and normal subjects. METHODS: Angular craniocervical relationships among midline magnetic resonance imaging scans from patients with BI, patients with CM, and normal subjects were evaluated and compared. Angles were measured by Meazure 2.0 software from digitalized images. RESULTS: Using data from 121 images, 42 patients with BI (14 type I BI, 28 type II BI), 47 patientswith CM, and 32 control subjects were evaluated. The BI group had a more acute kyphotic angle than the CM group (P < 0.01) and control group. The kyphosis difference was 17.57 +/- 2.3 degrees (P < 0.01) between the BI and CM groups and 21.19 +/- 2.3 degrees (P < 0.01) between the BI and control groups. Basal angles were significantly larger in the BI group compared with the other 2 groups. A strong correlation was found with kyphosis and CLV and the clivuscanal angle and cervical lordosis angle (P < 0.01). CONCLUSIONS: Craniocervical kyphosis in patients with BI was approximately 20 degrees greater than in normal subjects and patients with CM. Craniocervical kyphosis should be considered a pathophysiologic condition in BI.