Whole-Body MRI Versus 18F-FDG-PET/CT for the Detection of Nodal and Distant Metastases in Pediatric Patients with Solid Tumors

Background/Objectives: Pediatric patients with solid tumors (non-lymphoma) require adequate staging prior to and during therapy. 18F-FDG-PET/CT is commonly used for the detection of tumorous lesions, with the drawback of exposure to ionizing radiation. Whole-body MRI (WB-MRI) can be considered as a complementary method according to clinical guidelines. The main objective of this study was to assess the diagnostic performance of the aforementioned methods for the detection of metastases, both separately and in combination. Methods: We retrospectively assessed sensitivity and specificity of 18F-FDG-PET/CT, WB-MRI, and the combination of both methods for the detection of lymph node and distant metastases in pediatric patients with solid tumors. Results: A total of 21 patients who underwent both 18F-FDG-PET/CT and WB-MRI were included in this study. We found 109 confirmed metastatic lesions in 1322 body regions. Sensitivity and specificity for the whole collective were 63.4%/99.3% for 18F-FDG-PET/CT, 91.3%/98.6% for WB-MRI, and 100%/98.2% for the combination of both methods. In 11 therapy-naïve patients, both 18F-FDG-PET/CT and WB-MRI exhibited a sensitivity of 84.7%, while specificity was 98.8% for 18F-FDG-PET/CT and 98.5% for WB-MRI. The combination of both methods led to a significant increase in sensitivity to 100% in both therapy-naïve patients and patients under chemotherapy (both p < 0.001), while specificity remained high (97.7%/98.7%). Conclusions: 18F-FDG-PET/CT in combination with WB-MRI showed a higher sensitivity for the detection of metastases in solid malignant pediatric tumors than either of the methods alone. Thus, the combination allows for the most accurate staging.