Bone marrow disease in rhabdomyosarcoma visualized by 2-[${}^{18}$F]fluorodeoxyglucose positron emission tomography/computed tomography

Bone marrow metastases---noted in 6% of patients with rhabdomyosarcoma---have been linked to very poor outcomes. Bilateral bone marrow sampling from iliac crests has been the gold standard for bone marrow examination in rhabdomyosarcoma, but sampling errors due to patchy bone marrow involvement may limit its sensitivity. Here, we report the case of a 6-year-old boy with embryonal rhabdomyosarcoma of the skull base and multiple 2-[${}^{18}$F]fluoro-2-deoxy-D-glucose (2-[${}^{18}$F]FDG)-avid bone marrow metastases visualized by positron emission tomography and computed tomography (2-[${}^{18}$F]FDG PET/CT). His bone marrow aspirates were tumor-free. This case illustrates the diagnostic value of 2-[${}^{18}$F]FDG PET/CT in the detection of bone marrow metastases in rhabdomyosarcoma patients, which may re-shape the definition of bone marrow disease and, ultimately, alter disease staging and risk stratification.