OBJECTIVETo investigate the value of incidental focal (18)F-FDG uptake in the colon and rectum and characteristics of functional anatomic form for differential diagnosis of colorectal benign or malignant diseases.

METHODSClinical data and images of incidental focal hypermetabolism focus in colon and rectum of 37 individuals undergoing (18)F-FDG PET-CT were analyzed retrospectively. According to the eventual outcomes of pathological examination and clinical follow-up, these cases were divided into four subgroups: malignant disease, benign tumor (including precancerous change), inflammation and physiological uptake. Radioactive uptake level (SUVmax) and change of delayed imaging (RI) of focal hypermetabolism focus were compared between groups. The data analysis was performed using variance analysis.

RESULTSThe average SUVmax was 6.3±3.7, 8.8±6.5, 5.2±1.4, and 3.8±0.9 in malignant disease (n=11), benign (precancerous) tumor (n=9), inflammation (n=9) and physiological uptaking (n=8) respectively. The average SUVmax was 7.6±5.6 in benign and malignant tumor, and 4.7±1.5 in inflammation and physiological uptake. The distinction of average SUVmax was not statistically significant between benign and malignant tumor or inflammation and physiological uptake. But it was higher in tumors as compared to inflammation or physiological uptake with a statistically difference (P<0.05). The RI was 0.3±0.2, 0.4±0.1, 0.3±0.2, 0.4±0.2 in above 4 groups respectively, and the differences were not statistically significant.

CONCLUSIONSThe incidental focal hypermetabolism focus in the colon the rectum during (18)F-FDG PET-CT may indicate potential colorectal malignant diseases and precancerous lesions. SUVmax value in focal hypermetabolism focus in the colon and rectum can help to distinguish tumor from inflammation or physiological uptake. But there is no diagnostic value for distinguishing malignant disease from benign tumor.