Resource optimization in soft-tissue oncology: Comparable diagnostic performance of CT and MRI in the initial work-up of peripheral adipocytic soft-tissue tumors.

PURPOSE: Adipocytic tumors are often detected incidentally on CT. This study compared the diagnostic accuracy of computed tomography (CT) and magnetic resonance imaging (MRI) for differentiating atypical/malignant from benign adipocytic soft-tissue tumors, using histopathology as reference standard. MATERIALS AND METHODS: In this retrospective single-center study, 67 adult patients evaluated for soft-tissue adipocytic tumors of the extremities and trunk wall between January 2015 and July 2022 were included if they underwent both CT and MRI within 3 months, followed by core needle biopsy or surgical resection. Retroperitoneal, abdominopelvic, and mediastinal tumors were excluded. Two radiologists assessed qualitative imaging features according to European consensus criteria. Quantitative analysis measured tumor-to-fat density ratios on CT and signal ratios on MRI. Diagnostic accuracies were compared using McNemar test. RESULTS: CT and MRI achieved identical accuracy (55 %, 95 % CI: 43-67), sensitivity (95 %, 95 % CI: 77-100) but limited specificity (36 %, 95 % CI: 22-51) for identifying atypical/malignant lesions. Inter-observer and modality agreement was perfect for qualitative imaging features. At their respective optimal thresholds (0.83 for CT, 0.80 for MRI), the density ratio on CT achieved a higher diagnostic accuracy (85 %, 95 % CI: 75-92) than the MRI signal ratio (73 %, 95 % CI: 62-82) with a significantly higher AUC than the MRI signal ratio (p = 0.008). CONCLUSION: In this single-center study, CT showed diagnostic performance comparable to that of MRI for the initial characterization of selected, adequately imaged peripheral and trunk-wall adipocytic soft-tissue tumors, with superior quantitative discrimination at optimal density-ratio thresholds.