Detection of incidental colorectal pathology on positron emission tomography/computed tomography

Positron emission tomography/computed tomography (PET/CT) is an important modality in cancer imaging. With its increasing availability and use, it is not uncommon to detect incidental focal colorectal ¹⁸ F-FDG uptake which poses a diagnostic challenge, as they may be associated with malignant or pre-malignant colorectal lesions. The aim of our study is to determine the proportion of these findings which represents true pathology.

Patients with incidental focal colorectal ¹⁸ F-FDG uptake on PET/CT who subsequently underwent colonoscopy between January 2002 to September 2013 were identified from a prospective database in a tertiary referral centre. PET/CT results were correlated with colonoscopy and pathology results in these patients. Positive predictive values (PPVs) and 95% confidence intervals (CIs) of PET/CT in the detection of incidental colorectal pathology were calculated.

A total of 148 patients (92 men and 56 women), with a mean age 73 years (range of 36 to 93 years) were included in the study. A total of 170 foci of colorectal ¹⁸ F-FDG uptake were detected on PET/CT. Of these, 101 foci corresponded to a malignant or pre-malignant lesion (PPV 59%; 95% CI: 52-67%). On a per-patient analysis, 93 patients had at least one focus of colorectal ¹⁸ F-FDG uptake which corresponded to a pre-malignant or malignant lesion (PPV 63%; 95% CI: 54-71%).

Focal colorectal ¹⁸ F-FDG uptake on PET/CT is associated with a significant proportion of malignant or pre-malignant lesions. Further evaluation with colonoscopy is recommended.