The anatomic abnormality of cervical spinal canal in adult patients with Chiari I malformation and syringomyelia, and its relationship with syrinxs

Abstract

Objective To compare the anatomic features of the cervical spinal canal in adults with Chiari I malformation and syringomyelia (CMS) versus age- and gender-matched controls, and to explore the relationship between syrinx size and the cervical spinal canal dimensions. Methods A total of 48 adult CMS patients (21 males and 27 females; mean age, 24.6 years, range 18-47 years) treated at our center between January 2008 and June 2015 were retrospectively reviewed. A cohort of 48 age-and gender-matched healthy adults were selected as the control group. Transverse images parallel to each cervical vertebral body were constructed using multiplanar reconstruction with 64-slice spiral CT. Cross-sectional area (CSA) of the spinal canal was measured at the middle level of each cervical segment, and a linear trend line was fit by least-square regression to calculate the taper ratio of the cervical spinal canal. Taper ratios as well as CSA of the spinal canal were compared between the two groups at each cervical level. In the CMS group, CSA of the syrinx was also measured at each cervical level on MR images, and the correlation between the CSAs of spine canal and the syrinx was analyzed. Results Syringomyelia was most frequently located at the levels of C4 to C7 in patients with CMS. At each cervical level from C3 to C7, CAS of the spinal canal in the CMS group was significantly larger than in the control group, and a significant positive correlation was found between the area of syrinx and CSA of the spinal canal at each segment level (r=0.676-0.765, P<0.001). Taper ratios for C1-C4, C4-C7, and C1-C7 averaged (-58.5±29.9) mm2/level, (-0.1±7.3) mm2/level, (-25.6±6.8) mm2/level, respectively, in the control group, compared to (-54.7±33.2) mm2/level, (8.8±13.5) mm2/level, (-15±16.4) mm2/level in the CMS group. The C1-C4 taper ratio did not differ significantly between the two groups, whereas C1-C7 and C4-C7 taper ratios were, respectively, smaller and greater in CMS patients as compared to their normal counterparts. Conclusion Adults with Chiari I malformation have regional enlargement of the cervical spinal canal at the level of syrinx, along with steeper C4-C7 tapering as compared to healthy controls. The cross-sectional area of the spinal canal is significantly correlated with the size of syrinx at the same level, suggesting that syringomyelia may affect the development of the cervical spinal canal in patients with Chiari I malformation. Key words: Cervical vertebrae; Arnold-Chiari malformation; Syringomyelia; Spinal canal; Tomography, spiral computed