Kinematic Analysis of the Hindbrain via Dynamic Neck Motion in Adult Patients with Chiari Malformation Type I: A Radiological Study with Clinical Implications.

BACKGROUND

The influence of cervical motion on the hindbrain in patients with Chiari malformation type I (CMI) remains under investigation. In this study, the kinematic effects of cervical extension and flexion on cerebellar tonsillar herniation were evaluated.

METHODS

The clinical data of 27 adult CMI patients were retrospectively studied, and sex- and age-matched patients with cervical spondylopathy were included as controls. Several linear, angular variables related to the hindbrain and mobility of the neck were assessed on midsagittal views of neutral and dynamic cervical magnetic resonance images.

RESULTS

The distance of cerebellar tonsillar herniation (D-Ton) in the CMI group was 10.15 ± 0.74 mm in the cervical neutral position, 11.24 ± 0.81 mm (P <0.001) in flexion, and 9.12 ± 0.65 mm (P <0.001) in extension. D-Ton in the control group remained unchanged in three different cervical positions. No significant differences were found in the tissue strain of the tonsils (Ton-Strain), the distance from the obex (D-Obex), the anterior margin of the pontomedullary (D-Pon), or the cervicomedullary (D-Medu) junction to the McRae line between different cervical positions in either group.

CONCLUSIONS

The mobility of the ectopic tonsils and the degree of cervical motion were verified in adult CMI patients. The herniated tonsils largely ascended with extension and descended with flexion, without obvious tonsillar tissue strain, whereas the brain stem remained stable. Tonsillar motion may be a potential marker of CMI and may therefore help surgeons confirm CMI as well as tailor surgical procedures for such patients.