A Mass With High Uptake of Fluorodeoxyglucose on Positron Emission Tomography

Abstract

An adolescent girl presented with a 3-month history of a growing, painless mass in the right thigh. A magnetic resonance imaging (MRI) scan showed an inhomogeneous nodule in the subcutaneous layer with a largest diameter of approximately 5 cm. No enlarged lymph nodes were detectable in the groin. Results of a complete blood cell count and levels of alkaline phosphatase, lactic dehydrogenase, and C-reactive protein were unremarkable. An ultrasonography-guided core needle biopsy was performed, and histopathologic evaluation showed the aspects of a small round-cell tumor, which was confirmed to be a Ewing sarcoma by immunohistochemical and molecular analysis (with positivity for the EWS-FLI1 fusion gene [OMIM 133450]). The patient then underwent disease staging with computed tomography (CT) of the chest and whole-body fluorodeoxyglucose positron emission tomography (FDG-PET). The CT findings were negative for secondary lesions; the FDG-PET scan demonstrated, as expected, high uptake in the right thigh (maximum standard uptake variable [SUVmax], 8.4) at the site of the subcutaneous tumor and at a second lesion in the left ankle joint (SUVmax, 12.0). The patient reported vague pain around the left ankle but no functional limitations and no history of trauma at that site. A radiograph of the ankle did not show calcifications within the soft-tissue lesion. An MRI scan of the ankle showed a 1.5-cm soft tissue mass in the posterior recess of the ankle joint with a low to intermediate signal in T1-and T2-weighted sequences and moderate contrast enhancement throughout the lesion (Figure 1). Diagnosis B. Tenosynovial giant cell tumor