Validation of a Lymphedema Index Score Based on Noncontrast Magnetic Resonance Lymphangiography: Correlation with Clinical Staging and Indocyanine Green Lymphangiography.

Background: A standardized lymphedema grading system is a prerequisite for accurately and objectively evaluating its severity, both preoperatively and postoperatively. The purpose of this study was to establish a clinically feasible noncontrast magnetic resonance lymphangiography (NMRL) protocol and a standardized scoring system for the evaluation of lymphedema. Methods and Results: From January 2020 to February 2021, 39 patients who had been clinically diagnosed with lymphedema and had undergone NMRL were included. The severity and circumferential extent of lymphedema were assessed using magnetic resonance imaging, and a combined index was devised as the sum of the product of the severity and extent scores determined at four different levels. A magnetic resonance imaging (MRI) stage was allocated based on the combined index score, its correlation with clinical indices was analyzed. The MR and clinical staging showed a percentage agreement of 85.9% and a kappa coefficient of 0.641, indicating moderate agreement (p < 0.001). Both the interlimb volume and interlimb impedance ratios differed significantly between groups (p < 0.001 for both). The correlation analysis revealed a significant correlation between the combined index score and the inter-limb volume ratio (r = 0.70, p < 0.001) and inter-limb impedance ratio at both 1 kHz (r = 0.71, p < 0.001) and 5 kHz (r = 0.71, p < 0.001). The interobserver agreement was moderate for the severity score, extent score, and combined score. Conclusion: The proposed standardized scoring system for evaluating lymphedema based on NMRL can reproducibly determine the severity and extent of lymphedema in both the upper and lower extremities, and correlates strongly with established clinical measures.