Parsing the Utility of CT and MRI in the Subaxial Cervical Spine Injury Classification (SLIC) System: Is CT SLIC Enough?

Objective: The aim of our blinded retrospective study was to evaluate the diagnostic performance of the Subaxial Cervical Spine Injury Classification (SLIC) System in predicting the need for surgical intervention after subaxial cervical spine injury; SLIC scores were determined using CT alone or both CT and MRI.

Materials And Methods: Patients were included if they had injuries that were subaxial (C3-C7), if they had undergone CT and MRI within 48 hours of admission, if they were either treated surgically or had sufficient clinical documentation describing nonsurgical management (halo device or hard collar), and if the SLIC neurologic score could be determined from a documented neurologic examination. Two hundred two consecutive patients (139 surgical patients and 63 nonsurgical control subjects) from January 2010 through December 2013 met all criteria and were included in the study. Additionally, 40 patients were randomly selected from this group for the purpose of determining interrater agreement. Initially, readers gave a SLIC score (< 4 for nonsurgical, 4 = indeterminate, > 4 for surgical) based on neurologic status and CT only. After waiting 4 weeks to minimize recall bias, the readers repeated scoring with the addition of MRI. Diagnostic performance values-that is, sensitivity, specificity, AUC under the ROC curve, and interrater agreement (Cohen kappa)-for both trials were determined.

Results: Using a SLIC score of 4 as the cutoff value for surgical intervention, we found that SLIC scoring based on CT and MRI had a sensitivity of 94.6%, specificity of 71.0%, and AUC of 0.87 with a kappa value of 0.28. SLIC scoring based on CT alone had a sensitivity of 86.2%, specificity of 77.3%, and AUC of 0.88 with a kappa value of 0.52.

Conclusion: SLIC scoring based on CT alone performs similarly to SLIC scoring based on CT and MRI but with improved interobserver agreement. Although MRI is useful for surgical planning, these results indicate that MRI may have limited added value in the initial triage of patients with subaxial cervical spine injury for conservative versus surgical management.