Gluteal injection site granulomas : false positive finding on FDG-PET in patients with non-small cell lung cancer

Positron-emission-tomography (PET) with fludeoxyglucose F-18 ([18F] fluoro-2-deoxy-D-glucose, FDG) has become an established imaging modality in patients with lung cancer for mediastinal lymph node staging and the detection of extrathoracic metastases. However, tracer accumulations are not limited to malignant tissue but are also found in muscles and benign inflammatory processes. We report on two patients with lung cancer in whom FDG-PET revealed suspicious tracer accumulations in the buttock. Ultrasound (US) revealed a hyperechogenic nodule with poorly defined margins in both patients. On specific inquiry both patients reported on repeated “intramuscular” gluteal injections. Histology after US guided biopsy showed an accumulation of macrophages within fibrous tissue, compatible with injection site granulomas. The reported cases underline that 18F-FDG may accumulate in benign, ancillary processes that have to be distinguished from distant metastases. Tracer accumulation in the buttocks may be highly sugg...