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

A 6.5-year-old previously healthy boy presented with ptosis, double vision, and dysesthesias of the left side of the face. Magnetic resonance imaging (MRI, Magnetom Avanto Fit, Siemens, Erlangen, Germany) and computed tomography (CT, Somatom Definition Flash, Siemens, Erlangen, Germany) revealed a large parameningeal mass adjacent to the internal carotid artery, extending from the sella turcica into the fossa temporalis and infratemporalis (Fig. 1). The mass was biopsied, and rhabdomyosarcoma of the embryonal subtype without evidence for a FOXO1 breakpoint was diagnosed. Staging examinations included MRI of the chest, abdomen, and extremities, chest CT, 2-[¹⁸F]FDG PET/CT (Gemini TF TOF 64, Philips, Hamburg, Germany), and bilateral bone marrow aspirates obtained from the iliac crests. Microscopic evaluation of bilateral bone marrow aspirates did not reveal infiltration by tumor cells. Bone marrow biopsies were not performed. Multiple 2-[¹⁸F]FDG-avid foci were detected involving thoracic (T) and lumbar (L) vertebrae (T4, T8, T12, L1, L2, L3) (Fig. 1), the sacrum (Fig. 1), and the left femur (Fig. 1). At these sites, the bone marrow space exhibited foci of increased signal in the fat-saturated T2 MRI sequences (Fig. 1). CT did not reveal any cortical destruction or osteolytic/ osteoblastic alteration of the trabecular bone structure (Fig. 1). No associated soft tissue masses and no additional sites of bone marrow metastases were visualized by MRI (Fig. 1). The lesions were considered bone marrow metastases. Chemotherapy was administered according to standard-of-care recommendations for treatment of metastatic rhabdomyosarcomas and well-tolerated. Restaging after three cycles of chemotherapy revealed an excellent response: the previously detected hypermetabolic metastatic sites in the vertebrae, sacral bone, and left femur were metabolically inactive, and the primary tumor was smaller in size and FDG-negative (images not shown). The patient went on to complete proton beam irradiation of the primary tumor site, nine cycles of intensive chemotherapy, and six cycles of oral maintenance therapy. He continues to be in first complete remission 7.5 years after diagnosis.