• Parisa Aminzadeh, Ekaterina Alibrahim, Andrew Dobrotwir, Eldho Paul, and Stacy Goergen.
• Royal Women's Hospital, Parkville, Victoria, Australia.
• Br J Radiol. 2021 Mar 1; 94 (1119): 20200483.

ObjectiveTo assess accuracy of and interobserver agreement on multiparametric MR findings to distinguish uterine leiomyoma (LM) from uterine leiomyosarcoma (LMS) and soft tissue tumour of unknown malignant potential.MethodsInclusion criteria: All females over 18 years with least one uterine mass measuring 5 cm or more in at least one of the three standard orthogonal dimensions on MR with histopathological confirmation of LM, LMS, or soft tissue tumour of unknown malignant potential (STUMP) in the 3 months following MR. Patients with LMS were drawn from a larger cohort being assessed for MR-guided focussed ultrasound (MRgFUS) suitability. Image evaluation: Assessed variables were: lesion margin, margin definition, T2 signal homogeneity, >50% of lesion with T2 signal brighter than myometrium, haemorrhage, restricted diffusion, contrast enhancement (CE), CE pattern, local lymphadenopathy and ascites.Results32 LM, 10 LMS and 1 STUMP were evaluated. Ill-defined (p-value = 0.0003-0.0004) or irregular (p = 0.003-0.004) lesion margin, T2 hyperintensity >50% (p = 0.001-0.004), and peripheral CE (p = 0.02-0.05) were significantly more common in LMS/STUMP than LM for both radiologists. 10/11 (Reader 2) and 11/11 (Reader 1) LMS/STUMP displayed restricted diffusion but so did 63-80% of LM. Agreement was greatest for margin characteristics (κ = 0.73-0.81).ConclusionIrregular/ill-defined lesion margin best distinguished LMS/STUMP from LM with good interrater reliability.Advances In KnowledgeAssessment of agreement regarding MR parameters distinguishing LM from LMS and STUMP has not previously been undertaken in a cohort including a large number of patients with LMS. This will help inform evaluation of females considering minimally invasive LM treatment.

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