|ECR 2018 / C-1129|
|18F-FDG PET/MRI with DWI: one-stop shop for paediatric sarcomas|
Sixteen patients met the inclusion criteria (nine males, seven females; mean age 8.8 ± 4.9 years). Histology revealed nine rhabdomyosarcoma, two Ewing-sarcoma, diffuse myofibromatosis, chondroblastic osteosarcoma, angiosarcoma, extrarenal-rhabdoid tumor and undifferentiated sarcoma one each. The overall inter-observer agreement between the two teams turned out to be very high (κ=0.994). Discordant results emerged only for the detection of a local lymph node in a patient affected by a rhabdoid-tumor and for two peritoneal metastases in a patient with angiosarcoma. When compared to the reference standard, PET/MRI showed 100% specificity for the diagnosis of the primary tumor (Fig. 1), recurrence, and also for the detection of nodal and distant metastases. One primary lesion (i.e., mediastinal rhabdomyosarcoma) was missed at restaging (Sensitivityprimary=93.3%) since it met only the morphological MRI criteria without showing any pathologic uptake at PET or restricted diffusion at DWI. On the contrary, two recurrences (i.e., respectively one rhabdomyosarcoma and one extra-renal rhabdoid tumor) were correctly diagnosed, despite the absence of pathologic glycolytic activity, because of the pathologic morphologic features at MRI and the restricted diffusion at DWI (Fig. 2). No local or distant nodal lesions were missed at PET/MR (Sensitivitylocal_nodal=100%; Sensitivitydistant_nodal=100%). Regarding the detection of distant metastases, two pulmonary (i.e, two patients respectively affected by rhabdomyosarcoma and undifferentiated sarcoma) and six bone metastases (i.e., all in one patient with rhabdomyosarcoma examined after treatment) were not detected at PET/MRI (Sensitivitylung50%; Sensitivityskeletal=75%). All other metastatic lesions affecting different sites than the above-mentioned ones (e.g., intramuscular, intraperitoneal, and mediastinal metastases) were correctly diagnosed (Sensitivitymeta_others=100%) (Fig. 3). Overall, PET/MRI showed 90.9% sensitivity and 100% specificity for pediatric sarcomas.
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