Noninvasive evaluation of craniovertebral junction instability in 2 patients following Chiari decompression with rigid C-collar immobilization: illustrative cases

BACKGROUND: The complex Chiari malformation has been identified in a subset of Chiari patients at higher risk for worsening symptoms following Chiari decompression. Although parameters such as the clivoaxial angle and the perpendicular distance of the dens to the line from the basion to the inferoposterior part of the C2 body (pBC2) have been evaluated to help with the prediction of risk, the decision to pursue an occipitocervical fusion in lower-risk patients does not come without inherent risk. OBSERVATIONS: The authors present 2 patients who had symptoms of worsening ventral brainstem compression following Chiari decompression, neither of whom was categorized in the highest risk category for occipitocervical instability. In addition, neither patient had gross instability on radiographic imaging. A trial with rigid C-collar immobilization provided relief of symptoms in both patients and allowed reassurance of the likelihood of success of occipitocervical fusion. LESSONS: In patients without clear radiographic instability following Chiari decompression, a C-collar trial may provide a noninvasive option for assessing the potential success of occipitocervical fusion.