Pitfalls of FDG PET/CT imaging

1046 Objectives: FDG-PET/CT is widely used in the management of a variety of malignancies. Unfortunately, numerous non-malignant lesions can also result in increased FDG accumulation, thus leading to false-positive interpretations for the presence of tumor. Awareness of benign conditions associated with PET/CT will increase diagnostic accuracy. Methods: Sixteen false-positive FDG-PET studies were documented over a four-month period out of approximately 1000 scans. Lesions were defined as false-positive when pathological biopsy was interpreted as negative for tumor. The false positive cases found are presented as educational examples of alternative causes of increased uptake on PET FDG imaging, rather than as a systematic evaluation of the specificity of PET scanning. Results: Two cases of FDG-avid pulmonary nodules in patients undergoing evaluation of lung cancer were due to infectious or inflammatory process. Two cases of FDG-avid masses in the abdomen and mediastinum in patients without known malignancy were due to benign lymphoid hyperplasia and benign neurofibroma. Two patients with cervical cancer, one with anal cancer and two with lung cancer demonstrated post-treatment FDG-avid residual masses, with biopsies showing tumor necrosis, post-radiation fibrosis and inflammatory changes. One patient presented with FDG-avid masses in the liver and colon on initial staging examination; biopsy of the liver mass demonstrated cholangiocarcinoma while the colonic mass was found to be a benign adenoma. One patient presented with FDG-avid masses in the lung and in the uterus on initial staging examination; biopsy of the lung mass revealed adenocarcinoma while the uterine mass was found to be a uterine leiomyoma. Four patients with known primary cancer presented with FDG-avid masses on re-staging examinations. The biopsies were negative for malignancy. Conclusions: FDG-PET/CT plays an important role in both staging and restaging of malignant diseases. Studies have shown that in many cases lack of reduction of tumoral masses after chemoradiation therapy does not necessarily mean persistence of the disease. FDG-PET/CT has a high negative predictive value, but it has a lower positive predictive value for tumor because FDG-PET/CT is associated with a significant number of false-positive findings, which necessarily have major therapeutic implications. In addition to neoplasm, any active infectious or inflammatory process, benign hyperplasia and treated tumor can show increased FDG activity. Awareness of benign conditions associated with PET/CT images increases the diagnostic accuracy and may avoid unnecessary surgery.