Utility of the clivo-axial angle in assessing brainstem deformity: pilot study and literature review

Fraser C Henderson,William A Wilson,Alexander S Mark,Myles Koby

doi:10.1007/s10143-017-0830-3

Abstract

There is growing recognition of the kyphotic clivo-axial angle (CXA) as an index of risk of brainstem deformity and craniocervical instability. This review of literature and prospective pilot study is the first to address the potential correlation between correction of the pathological CXA and postoperative clinical outcome. The CXA is a useful sentinel to alert the radiologist and surgeon to the possibility of brainstem deformity or instability. Ten adult subjects with ventral brainstem compression, radiographically manifest as a kyphotic CXA, underwent correction of deformity (normalization of the CXA) prior to fusion and occipito-cervical stabilization. The subjects were assessed preoperatively and at one, three, six, and twelve months after surgery, using established clinical metrics: the visual analog pain scale (VAS), American Spinal InjuryAssociation Impairment Scale (ASIA), Oswestry Neck Disability Index, SF 36, and Karnofsky Index. Parametric and non-parametric statistical tests were performed to correlate clinical outcome with CXA. No major complications were observed. Two patients showed pedicle screws adjacent to but not deforming the vertebral artery on post-operative CT scan. All clinical metrics showed statistically significant improvement. Mean CXA was normalized from 135.8° to 163.7°. Correction of abnormal CXA correlated with statistically significant clinical improvement in this cohort of patients. The study supports the thesis that the CXA maybe an important metric for predicting the risk of brainstem and upper spinal cord deformation. Further study is feasible and warranted.

Highlights

Craniocervical junction malformations and instability are not uncommon in degenerative and heritable disorders of collagen and bone [15]
Van Gilder was the first to suggest that a clivo-axial angle (CXA) less than 150° may be associated with ventral cord compression [80, 158]
Measurements by surgeons and radiologists contend with variability, and multiple methodologies for assessing interrater reliability have been established [149]; while applying such a methodology to studies of the CXA may be warranted in future, the goal of this study was not to establish reliability among radiologists, but to have a single method consistently utilized by one reader whose opinion was utilized to direct and assess clinical outcomes

Summary

Introduction

Craniocervical junction malformations and instability are not uncommon in degenerative and heritable disorders of collagen and bone [15]. Others reported that the kyphotic CXA in traumatic, developmental, heritable hypermobility, or degenerative conditions may cause deformation of the brainstem and uppercervical spinal cord [18, 65, 83, 99, 147] and that there may be salutary consequences to the correction of the CXA [15, 65, 81, 89]. Concurrent to the recognition of the kyphotic CXA and brainstem deformation, has been the growing understanding of mechanically induced neural injury [5, 18, 30, 55, 61, 63,64,65,66,67,68, 82, 91, 97, 153, 156, 161, 162]

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