FDG-PET: False Positive for Cancer

Fig. 1: Scout CT image shows a right hilar mass with right upper lobe opacity and volume loss. Findings are concerning for obstructive pneumonia due to carcinoma in the right hilum.
Fig. 2: Axial CT image shows right hilar lymphadenopathy (arrow) with consolidation, air bronchograms and cavities in the posterior segment of the right upper lobe (star)
Fig. 3: FDG-PET image shows markedly increased uptake of the right upper lobe consolidation, however the right hilar lymph node is not FDG avid.

False Positives FDG-PET in Lung Lesions

• Infection: Pneumonia, mycobacterium avium complex infection, TB, fungal infection
• Inflammation: Sarcoidosis, lipoid pneumonia, aspiration pneumonia, organizing pneumonia, amyloidosis, radiation pneumonitis

Why False Positive?

• 18F-FDG is not specific for tumor.
• Tissues with glucose uptake also takes FDG, especially tissues with metabolically active macrophages
• High expression of gene such as GLUT-1 may also be a reason for high FDG uptake in inflammatory lesions

Our case - surgical resection shows organizing pneumonia in the right upper lobe.

Reference:
Gilman MD, Aquino SL. State-of-the-art FDG-PET imaging of lung cancer. Semin Roentgenol 2005;40:144.