Clinical significance of incidental FDG PET uptake in the gastrointestinal tract: a retrospective cohort study.

Background: Incidental gastrointestinal tract (GIT) uptake is found in up to 6.3% of patients undergoing positron emission tomography (PET). This may be physiologic or pathologic and requires endoscopic assessment.

Aim: To determine the diagnostic yield of endoscopy in this setting and characterise PET avidity as a predictor of clinically significant findings.

Methods: We retrospectively reviewed all consecutive patients undergoing upper endoscopy or colonoscopy for incidental FDG PET positivity in the GIT.

Results: A total of 255 patients (62% male, median age 67 years) underwent colonoscopy or sigmoidoscopy for 276 separate areas of PET avidity in the colon. Malignancy was found in 44 cases (16%), and a significant polyp was found in an additional 103 cases (37%). Neoplastic change was found more often in the case of intense compared with non-intense PET avidity (odds ratio (OR) 3.40, 95% confidence interval (CI) 1.95-5.93, P < 0.001), and in focal compared with diffuse uptake (OR 5.97, 95% CI 2.9-12.2, P < 0.001). Upper GIT endoscopy was performed in 75 patients (46 male, median age 63 years) for 77 isolated areas with PET avidity. Malignancy was found in 16 cases (21%), and all were new primary lesions. Numerically, malignant findings were more common in intense (29.7%) than non-intense (12.5%) PET avidity (OR 2.96, 95%, CI 0.92-9.57, P = 0.069).

Conclusions: Both focal and intense colonic FDG uptake correlate strongly with a high-risk polyp or malignant lesion. Up to 21% of all gastroscopies performed for evaluation of incidental PET uptake diagnosed a new primary malignancy. These referrals need appropriate triaging and timely endoscopic assessment.