Ravindra Vijay M, Iyer Rajiv R, Yahanda Alexander T, Bollo Robert J, Zhu Huirong, Joyce Evan, Bethel-Anderson Tammy, Meehan Thanda, Smyth Matthew D, Strahle Jennifer M, Park Tae Sung, Limbrick David D, Brockmeyer Douglas L
1Division of Pediatric Neurosurgery, Primary Children's Hospital, University of Utah, Salt Lake City, Utah.
2Division of Neurosurgery, University of California, San Diego, California.
J Neurosurg Pediatr. 2021 Jun 4;28(2):176-182. doi: 10.3171/2020.12.PEDS20809. Print 2021 Aug 1.
The condylar-C2 sagittal vertical alignment (C-C2SVA) describes the relationship between the occipitoatlantal joint and C2 in patients with Chiari malformation type I (CM-I). It has been suggested that a C-C2SVA ≥ 5 mm is predictive of the need for occipitocervical fusion (OCF) or ventral brainstem decompression (VBD). The authors' objective was to validate the predictive utility of the C-C2SVA by using a large, multicenter cohort of patients.
This validation study used a cohort of patients derived from the Park-Reeves Syringomyelia Research Consortium; patients < 21 years old with CM-I and syringomyelia treated from June 2011 to May 2016 were identified. The primary outcome was the need for OCF and/or VBD. After patients who required OCF and/or VBD were identified, 10 age- and sex-matched controls served as comparisons for each OCF/VBD patient. The C-C2SVA (defined as the position of a plumb line from the midpoint of the O-C1 joint relative to the posterior aspect of the C2-3 disc space), pBC2 (a line perpendicular to a line from the basion to the posteroinferior aspect of the C2 body), and clival-axial angle (CXA) were measured on sagittal MRI. The secondary outcome was the need for ≥ 2 CM-related operations.
Of the 206 patients identified, 20 underwent OCF/VBD and 14 underwent repeat posterior fossa decompression. A C-C2SVA ≥ 5 mm was 100% sensitive and 86% specific for requiring OCF/VBD, with a 12.6% misclassification rate, whereas CXA < 125° was 55% sensitive and 99% specific, and pBC2 ≥ 9 was 20% sensitive and 88% specific. Kaplan-Meier analysis demonstrated that there was a significantly shorter time to second decompression in children with C-C2SVA ≥ 5 mm (p = 0.0039). The mean C-C2SVA was greater (6.13 ± 1.28 vs 3.13 ± 1.95 mm, p < 0.0001), CXA was lower (126° ± 15.4° vs 145° ± 10.7°, p < 0.05), and pBC2 was similar (7.65 ± 1.79 vs 7.02 ± 1.26 mm, p = 0.31) among those who underwent OCF/VBD versus decompression only. The intraclass correlation coefficient for the continuous measurement of C-C2SVA was 0.52; the kappa value was 0.47 for the binary categorization of C-C2SVA ≥ 5 mm.
These results validated the C-C2SVA using a large, multicenter, external cohort with 100% sensitivity, 86% specificity, and a 12.6% misclassification rate. A C-C2SVA ≥ 5 mm is highly predictive of the need for OCF/VBD in patients with CM-I. The authors recommend that this measurement be considered among the tools to identify the "high-risk" CM-I phenotype.
髁突-C2矢状面垂直排列（C-C2SVA）描述了I型Chiari畸形（CM-I）患者枕寰关节与C2之间的关系。有人提出，C-C2SVA≥5mm可预测枕颈融合术（OCF）或腹侧脑干减压术（VBD）的必要性。作者的目的是通过使用一个大型多中心患者队列来验证C-C2SVA的预测效用。
这项验证性研究使用了来自帕克-里夫斯脊髓空洞症研究联盟的患者队列；确定了2011年6月至2016年5月期间接受治疗的年龄<21岁的CM-I和脊髓空洞症患者。主要结局是是否需要OCF和/或VBD。在确定需要OCF和/或VBD的患者后，为每名OCF/VBD患者匹配10名年龄和性别相匹配的对照作为比较。在矢状面MRI上测量C-C2SVA（定义为从枕-寰椎关节中点引出的铅垂线相对于C2-3椎间盘间隙后缘的位置）、pBC2（一条垂直于从颅底到C2椎体后下方面连线的直线）和斜坡-枢椎角（CXA）。次要结局是是否需要≥2次与CM相关的手术。
在确定的206例患者中，20例接受了OCF/VBD，14例接受了重复后颅窝减压术。C-C2SVA≥5mm对需要OCF/VBD的敏感性为100%，特异性为86%，错误分类率为12.6%，而CXA<125°的敏感性为55%，特异性为99%，pBC2≥9的敏感性为20%，特异性为88%。Kaplan-Meier分析表明，C-C2SVA≥5mm的儿童二次减压时间明显更短（p = 0.0039）。接受OCF/VBD与仅接受减压的患者相比，平均C-C2SVA更大（6.13±1.28 vs 3.13±1.95mm，p<0.0001），CXA更低（126°±15.4°vs 来对C-C2SVA≥5mm进行二元分类时，kappa值为0.47。
这些结果使用一个大型多中心外部队列验证了C-C2SVA，其敏感性为100%，特异性为86%，错误分类率为12.6%。C-C2SVA≥5mm高度预测CM-I患者需要OCF/VBD。作者建议在识别“高危”CM-I表型的工具中应考虑这种测量方法。
