Department of Orthopaedic Surgery, Kyushu University Hospital

In intradural extramedullary tumors (IDEMTs), the tumor occupancy rate within the spinal canal is known to correlate with symptom onset and postoperative prognosis. However, clinical outcomes in the cervical spine often vary significantly even among cases with similar occupancy rates. We previously reported that the Shape factor (SF)—a quantitative MRI-based indicator that quantifies spinal cord cross-sectional shape, ranging from 1 (circular) to 0 (flat)—is a valuable postoperative prognostic factor for thoracic IDEMTs. This study aimed to determine whether SF serves as a useful postoperative prognostic indicator for cervical IDEMTs, which are anatomically and functionally distinct. We retrospectively analyzed 35 patients with benign cervical IDEMTs followed for at least one year. Clinical outcomes were evaluated using the cervical Japanese Orthopaedic Association (JOA) score. Radiological evaluations included MRI-based SF and occupancy rate, as well as X-ray parameters such as alignment, range of motion, and dynamic instability, defined as a total slippage of 3 mm or more. Patients were divided into the Full Recovery group (postoperative JOA score of 17, n=19) and the Non-full Recovery group (JOA score <17, n=16). While there were no significant differences in patient backgrounds, preoperative JOA scores, or X-ray dynamic factors, the preoperative SF was significantly higher in the Full Recovery group (0.49 vs. 0.41, p=0.048). Notably, the Full Recovery group showed a significantly greater improvement specifically in the upper limb sensory function score compared to the Non-full Recovery group (p=0.01). Multivariate analysis identified SF as a significant independent predictor of achieving a full JOA score (OR: 2.24 per 0.1 increase, p=0.048), whereas age and occupancy rate were not. The ROC curve for SF showed a cutoff value of 0.57 (AUC: 0.697). In conclusion, Shape factor is a valuable morphological indicator for predicting functional recovery after the resection of cervical IDEMTs.