Incidental detection of colorectal malignancies using FDG PET-CT

The aim of this study was to evaluate the detection rate of incidental colorectal malignancies using whole-body 18FDG-PET/CT at an Irish teaching hospital. We performed a retrospective review of the records of 800 consecutive patients undergoing PET-CT scans at our institution from January 2009 - August 2009. The radiologic reports were analysed and all scans with focal colonic FDG uptake were audited. The colonoscopic and histologic records of the patients who underwent further investigation were reviewed for cancerous and pre-cancerous histology. A total of 643 patients were included in the study. Forty-eight patients (7.5%) had scans which demonstrated focal colonic FDG uptake. Of the 21 patients who underwent further investigation with endoscopy, 14 (66.7%) had biopsies which were positive for dysplasia, this represented 2.2% of the total patients undergoing PET-CT. Eight of these fourteen patients (1.2% of the total) had biopsies demonstrating adenocarcinoma. Four of these patients (50%) had TNM stage 1 or 2 colorectal carcinoma and underwent subsequent curative surgical resection. We found a 2.2% rate of incidentally-diagnosed colorectal malignant and premalignant lesions in patients undergoing PET-CT at our institution. A 1.2% rate of adenocarcinoma was identified. This rate is higher than previously described in the literature.