Clinically significant findings in patients with focal incidental colorectal abnormalities on positron emission tomography-CT scans

Introduction: The aim of this study was to determine the clinical significance of focal incidentally detected colorectal abnormalities on ¹⁸F- Fluoro-2-Deoxy-D-Glucose (FDG) PET-CT scans. Methods: Retrospective audit of PET-CT scans performed at our institution between 2009 and 2014. Demographic and clinical details were retrieved from electronic patient records. An advanced adenoma was defined as: ≥1 cm in size, tubullo-villous histology, or displaying high grade dysplasia. A high-risk lesion (HRL) was defined as an advanced adenoma or colorectal cancer (CRC). Results: Of the 1911 PET-CT eligible scans, focal incidental colorectal FDG uptake was detected in 99 (5.2%) patients. Colonoscopy was undertaken in 43 (43.4%) patients and 45 FDG-avid sites were evaluated. The commonest site of abnormal FDG uptake was the rectosigmoid region, with 34 (75.6%) of the 45 foci being located in this area. Overall, 23 (53.5%) of these patients had clinically significant pathology. Of the 45 focal PET-CT abnormalities evaluated, 17 (37.8%) were adenomas, of which 11 (24.4%) were advanced adenomas, and six (13.3%) were cancers, with a total of 17 (37.8%) HRLs. Five of the six patients with CRC underwent surgical resection, whilst one had endoscopic resection. The overall survival for the entire cohort was 18 months (range 1–72 months) with those that underwent colonoscopy having higher overall survival compared to those that did not (38 vs. 13.5 months). Conclusion: Incidental colorectal abnormalities on PET-CT scans are often clinically significant. However, careful selection for colonoscopy is important due to the poor survival in these patients related to the underlying primary malignancy.