Abstract
BACKGROUND: Fixed focal fluorine 18 fluorodeoxyglucose ((18)F-FDG) uptake in colorectal areas is commonly seen in PET/CT scan and may indicates malignant tumor. This study aims to investigate the diagnostic efficacy of dual-time-point (18)F-FDG PET/CT in detecting colorectal carcinoma or advanced adenoma in patients with fixed focal colorectal (18)F-FDG uptake. METHODS: A retrospective analysis was conducted on patients who underwent dual-time-point (18)F-FDG PET/CT scans between January 2019 and December 2023. Patients showing fixed focal colorectal (18)F-FDG uptake in both early and delayed scans, and subsequently undergoing colonoscopy within one month, were included in the study. Advanced adenoma was defined as an adenoma larger than 10 mm in diameter and/or with villous histology and/or presenting with high-grade dysplasia. The maximum standardized uptake value (SUV) in the early and delayed scans, as well as the retention index (RI), were compared between colorectal carcinoma/advanced adenomas and non-advanced lesions. Predictive factors for colorectal carcinoma/advanced adenoma were identified by uni- and multivariable analysis. RESULTS: A total of 122 patients were enrolled in this study. A total of 141 lesions was studied, 80 (56.7%) of which were diagnosed as colorectal carcinoma or advanced adenoma. When compared with non-advanced lesions, colorectal carcinoma/advanced adenoma had higher SUVmax in delayed scan (25.1 ± 14.2 vs. 14.5 ± 7.5, P<0.001), and higher RI (32.9%±25.4% vs. 7.8%±28.4%, P<0.001) in dual-time-point PET/CT. SUVmax in delayed scan (odds ratio [OR],1.084; 95% confidence interval [CI]: 1.037, 1.134; P<0.001) and RI (OR, 20.120; 95% CI: 4.068, 99.516; P<0.001) were identified as independent predictors for colorectal carcinoma/advanced adenoma by multivariable logistic regression analysis. When combining the SUVmax in the delayed scan with the retention index, the area under the receiver operating characteristic (ROC) curve achieved 0.801, and the sensitivity and specificity for predicting colorectal carcinoma/advanced adenoma were found to be 65.0% and 80.3%, respectively. Based on the threshold values of SUVmax in the delayed scan and RI, we observed prediction rates of 13.9% (5 out of 36), 58.6% (34 out of 58), and 87.2% (41 out of 47) for colorectal carcinoma/advanced adenoma in the low-, moderate-, and high-risk subgroups, respectively. CONCLUSIONS: Dual-time-point PET/CT aids in distinguishing between colorectal cancer/advanced adenoma and non-advanced lesions in fixed focal FDG uptake. Higher SUVmax in delayed scan and higher RI are predictive factors for colorectal carcinoma/advanced adenoma.