Multicenter Study of MRI Features in Uterine Myxoid Leiomyosarcoma: Revealing and Overcoming a Critical Pitfall in Current Consensus Criteria

Abstract

Objective To clarify the qualitative and quantitative MRI features of myxoid leiomyosarcoma (MLMS) in comparison with conventional leiomyosarcoma (cLMS) and to identify the specific diagnostic pitfalls of the current consensus criteria when applied to the MLMS subtype. Materials and Methods This retrospective multicenter study (12 institutions) included patients with histopathologically confirmed leiomyosarcoma (MLMS or cLMS) who underwent preoperative MRI. A total of 38 women (15 with MLMS and 23 with cLMS; median age, 55 years) were evaluated. Three radiologists independently evaluated features, including T2 signal patterns (purely hyperintense, mixed, iso-to-moderately hyperintense) and a characteristic “marbled appearance” (heterogeneous signal intermingling). The tumors were classified as benign or malignant on the basis of the apparent diffusion coefficient (ADC) values in accordance with the current consensus criteria. A histogram analysis was performed using multiparametric sequences. Results MLMS frequently exhibited purely T2-hyperintense or mixed patterns (12 of 15 [80%]), whereas cLMS predominantly showed T2-isointensity to moderate hyperintensity (21 of 23 [91%]) (P < 0.001). The “marbled appearance” was identified in 11 of 15 (73%) MLMS cases and 2 of 23 (9%) cLMS cases (P < 0.001). Median ADC values of the most restricted component were significantly higher in MLMS (1.14 × 10-3 mm2/s) than in cLMS (0.80 × 10-3 mm2/s) (P < 0.001). Consequently, the consensus ADC criteria misclassified 10 of 12 (83%) MLMS cases as benign, in comparison with 3 of 21 (14%) cLMS cases (P < 0.001). Notably, among these 10 misclassified MLMS cases, 8 (80%) demonstrated the “marbled appearance.” Histogram analysis confirmed that patients with MLMS had higher median normalized T2-weighted imaging signal intensity ratios (1.97 vs. 1.36; P = 0.019) and ADC ratios (1.39 vs. 0.82; P = 0.007). Conclusion Strict reliance on ADC-based consensus criteria may lead to systematic under-recognition of MLMS. Recognizing the “marbled appearance” on MRI is crucial to prevent misclassifying these tumors as benign.