PET/CT detection of unexpected gastrointestinal foci of 18F-FDG uptake: incidence, localization patterns, and clinical significance.

Precise PET/CT localization of focal (18)F-FDG uptake in the gastrointestinal tract (GIT) may exclude malignancy in sites of physiologic activity but may also induce false-negative reports for malignant or premalignant lesions. The purpose of the present study was to retrospectively evaluate the nature and significance of unexpected focal (18)F-FDG uptake localized by PET/CT within the GIT. The files of 4,390 patients referred for (18)F-FDG PET/CT were retrospectively reviewed. The incidence of studies showing unexpected focal uptake of (18)F-FDG localized by PET/CT to the GIT was determined. The position of these foci along the GIT and their intensity were recorded. The etiology of the findings was confirmed histologically or by long-term follow-up. Unexpected focal (18)F-FDG uptake in the GIT was found in 58 patients (1.3%). Follow-up data were available for 34 of these patients, including 4 with sites in the stomach, 2 in the small bowel, and 28 in the colon. GIT-related disease was confirmed in 24 patients (71%). There were 11 malignant tumors, 9 premalignant lesions, and 4 benign processes including 2 benign polyps, 1 case of active gastritis, and 1 abscess of the sigmoid. Ten patients (29%) had no further evidence of GIT abnormality, and the suggestive sites were considered to be physiologic uptake. Maximal standardized uptake value was 17.3 +/- 10.2 in malignant lesions, 14.0 +/- 10.5 in premalignant lesions, 18.0 +/- 12.1 in benign lesions, and 11.1 +/- 7.4 in foci of physiologic (18)F-FDG uptake in the GIT, with no statistically significant difference among the 4 subgroups. Incidental focal (18)F-FDG uptake localized by PET/CT within the GIT is of clinical significance in most patients. These findings should be followed up with appropriate invasive procedures guided by hybrid imaging results.