• Shengxi Wang, Zhijian Huang, Rui Xu, Zhengbu Liao, Yi Yan, Wenyuan Tang, and Yongzhi Xia.
• Department of Neurosurgery, the First Affiliated Hospital of Chongqing Medical University, Chongqing, China.
• World Neurosurg. 2020 Nov 1; 143: e640-e647.

BackgroundChiari malformation type I (CMI) cases are frequently associated with basilar invagination (BI), which complicates the understanding of the pathology of CMI. We specifically evaluated the morphometric and volumetric alterations in the bony structures of CMI patients without BI.MethodsFifty adult CMI patients without BI treated at our institution from January 2015 to December 2019 were retrospectively studied. The morphometric and volumetric characteristics of the posterior cranial fossa (PCF) were analyzed using thin-slice computed tomography images.ResultsCompared with the controls, the clivus length (P < 0.001), supraoccipital length (P < 0.001), Klaus height index (P < 0.001), axial length (P < 0.001), clivo-axial angle (P < 0.001), tentorial angle (P < 0.05), and bony PCF volume (P < 0.001) of the CMI-only group were significantly smaller, and the distance between the Chamberlain line and the dens axis (P < 0.001), clivus angle (P < 0.001), and basal angle (P < 0.001) of the CMI-only group were significantly larger, while the distance between the McRae line and the dens axis, McRae line, anteroposterior diameter of the PCF, occipital angle, occipital canal angle, and tentorial Twining line angle showed no significant difference between the 2 groups.ConclusionsHypoplasia of the clivus and occipital bone were confirmed in CMI patients without BI, thus providing further evidence for the notion that CMI is secondary to the underdevelopment of the PCF.Copyright © 2020 Elsevier Inc. All rights reserved.

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