False-positive 2-[F-18]-fluoro-2-deoxy-D-glucose positron emission tomography studies for evaluation of focal pulmonary abnormalities

Positron emission tomography (PET) with 2-[F-18]-fluoro-2-deoxy-D-glucose (FDG) can demonstrate the glucose metabolism characteristics of a lesion, which may be helpful in differentiating between benign and malignant focal pulmonary lesions. Malignant cells demonstrate higher glucose metabolic activity than benign lesions. However, some inflammatory processes also show significant FDG uptake. We present two cases where high FDG uptake was found in inflammatory lesions in the lungs. The first case was that of a 38-year-old woman with chronic cough for more than 20 years. FDG PET revealed a hypermetabolic lesion with a lesion-to-background ratio of 8.0 at the posterior aspect of the right middle lung. She underwent thoracotomy and tumor resection, and was diagnosed with cryptococcosis. The second case was that of a 72-year-old woman who had pulmonary tuberculosis previously with cavitation in the left lower lobe. She suffered from fever, chills and severe hemoptysis for several days before this admission. FDG PET revealed a hypermetabolic ring at the periphery of the cavity. The lesion-to-background ratio was 7.8. Echo-guided biopsy showed no evidence of malignancy. She was treated with antibiotics and the symptoms subsided gradually. Lung abscess complicating a pre-existing cavity was diagnosed. These two cases substantiate that positive FDG PET results should be interpreted with caution in differentiating benign from malignant pulmonary abnormalities, especially in regions with a high prevalence of granulomatous lesions.