Introduction Positron Emission Tomography (PET) scans detect metabolically active tissue and are a useful tool for evaluation of malignancy and sometimes benign inflammatory conditions. Occasionally areas of increased uptake are detected incidentally in other regions within the field of the scan. In this study we assessed the frequency of lesions detected on endoscopic examination in patients with incidentally detected colorectal abnormalities during PET or PET/CT scans.
Method We retrospectively assessed all PET or PET/CT scans performed at our institution from 2009 to 2014. Patients with incidental colorectal abnormalities were identified from the Radiology database; those undergoing scanning for staging or detecting recurrence of colorectal cancer were excluded. Endoscopy and histology reports were retrieved from the hospital software systems. Data was collected for demographic details, indications for PET scan, colonoscopy findings and histology results.
Results A total of 1939 PET scans were performed during the study period. Incidental colorectal FDG uptake was detected in 105 (5.4%) patients; 44 of these patients underwent endoscopic evaluation. The mean age of the subjects was 67.9 (range 31–89) years and 38.6% were females. Thirty-nine patients had a PET scan for evaluation of confirmed or suspected malignant lesions and five patients had the scan for evaluation of benign disease. Overall, increased colorectal FDG uptake was noted at 46 sites in the 44 patients. Rectum and/or sigmoid colon was the commonest site of abnormal uptake (73.9%) followed by caecum/ascending colon (13%), transverse colon (10.9%) and descending colon (2.2%). Forty-four sites were examined endoscopically and pathology was identified in 28 (63.6%) cases: 20 polyps (17 adenomatous, 3 hyperplastic), 6 cancers, and 2 cases of colitis (both of these had diffuse FDG uptake). One of the 17 adenomatous polyps had features of high grade dysplasia on histology. Five of the 6 patients with tumour underwent surgical resection, whilst one had endoscopic resection. Of the 42 cases of focal incidental colorectal FDG uptake, neoplasia was detected in 23 (57.8%); advanced neoplasia (invasive cancer or high-grade dysplasia) was detected in 16.7%.
Median survival for the 44 patients undergoing endoscopic evaluation was 38.5 months (range 4–71), and 18 months (range 1–72) for the overall group of 105 patients with incidental colorectal FDG uptake.
Conclusion Endoscopic evaluation of incidental colorectal findings on PET or PET/CT scans yields a high percentage of clinically significant results. However, careful selection of patients for colonoscopy is important due to the poor survival in this patient group.
Disclosure of interest None Declared.