Diagnostic value of integrated 18F-fluorodeoxyglucose PET/MRI in initial staging and recurrence detection of Ewing sarcoma

OBJECTIVES: Ewing sarcoma (EwS) is the second most common malignant bone tumour in children and adolescents. Due to its highly aggressive nature, rapid and accurate initial diagnosis as well as reliable recurrence detection are essential for treatment planning. Standard diagnostic work-up includes MRI for local tumour assessment and whole-body MRI or 18F-fluorodeoxyglucose-PET-computed tomography (18F-FDG-PET/CT) for metastatic evaluation. 18F-FDG-PET/MRI combines the soft-tissue contrast of MRI with the metabolic information of PET while reducing radiation exposure. As data on PET/MRI in EwS are limited, we assessed its accuracy in primary staging and recurrence detection in a high-volume sarcoma center. METHODS: In this monocentric retrospective study, whole-body 18F-FDG-PET/MRI scans of 38 therapy-naïve EwS patients were analyzed for local and distant tumor spread. Additional scans of 43 EwS patients were evaluated for recurrence. PET/MRI findings were compared with whole-body MRI alone and a composite reference standard by two independent readers. Sensitivity and specificity were calculated. RESULTS: PET/MRI showed higher sensitivity than MRI alone for lymph node metastases in both initial (91.7% vs. 25%) and follow-up staging (100% vs. 33.3%), with equally high specificity (96.8%). PET/MRI also showed slightly higher sensitivity for soft-tissue recurrence (100% vs. 90%). No difference between PET/MRI and MRI was found for bone or lung lesions, although both were less sensitive than chest CT (60% vs. 100%). CONCLUSION: 18F-FDG-PET/MRI is a feasible tool for both primary and follow-up imaging of EwS, providing excellent local tumor evaluation and high sensitivity for metastases and recurrence. However, chest CT remains necessary for small lung lesion detection.