Figure 1. There is a markedly hypermetabolic mass in the left adductor magnus muscle (SUV_max 7.4) with central photopenia suggestive of necrosis. There is associated subcutaneous inflammatory stranding.

Figure 2. The spleen has increased FDG uptake (SUV_max 2.5), without focal abnormalities. There is generalized increase in bone marrow FDG uptake (up to SUV_max 2.2). Mild FDG tracer uptake is also present in bilateral external iliac and superior femoral arteries and veins.

FDG-PET/CT has been proven useful in early identification of active human infections. Infectious and inflammatory processes have increased FDG uptake as activated white cells have increased glycolysis. The CT component of this fused modality also helps clarify non-tumoural focal FDG uptake, though infection remains an important cause for false positive interpretation in the assessment for malignancy. Intramuscular abscess may appear as ring-like FDG avidity, reflecting uptake in the abscess wall.

The differential diagnosis for diffuse, less intense skeletal muscle uptake (unlike this case) includes: insulin administration, recent exercise, anxiety and Graves’ disease.