Incidental findings on integrated PET/CT that do not accumulate 18F-FDG

The purpose of this study was to report the prevalence of abnormalities that do not show increased 18F-FDG uptake on the CT component of integrated PET/CT in patients with non-small cell lung cancer.

Images from all PET/CT studies performed consecutively between April and October 2003 on patients with non-small cell lung cancer were retrospectively reviewed. All abnormalities present on the CT component of the PET/CT scans that did not show abnormally increased 18F-FDG uptake were documented.

Three hundred twenty-one patients with non-small cell lung cancer (179 men, 142 women; mean age, 67 years; age range, 38-91 years) underwent initial staging (198/321 [62%]) or restaging (123/321 [38%]) PET/CT imaging during the study period. In 263 (82%) of the patients, CT showed 1,231 abnormalities that were not 18F-FDG avid. The abnormalities were located in the thorax (n = 650), abdomen and pelvis (n = 444), head and neck (n = 69), and bony skeleton (n = 68). In total, 298 (24%) of the abnormalities that were not 18F-FDG avid were located outside the range of a standard thoracic CT scan. The clinical importance of these abnormalities was classified as major (n = 48 [4%]), moderate (n = 465 [38%]), or minor (n = 718 [58%]). Four (1%) of the patients had findings of major clinical importance that did not show increased 18F-FDG uptake and were previously unsuspected.

Among patients with non-small cell lung cancer undergoing PET/CT, there is a high prevalence of CT abnormalities that do not show correlative 18F-FDG avidity but that may be clinically important.