Pituitary adenoma: Incidentaloma identified by F18-FDG PET/CT

Objectives The purpose of this study was to determine the incidence of F18-FDG avid pituitary incidentalomas detected on PET/CT and correlate the FDG PET/CT findings to all available data.

Methods We retrospectively reviewed 8431 consecutive total whole-body (TWB) F18-FDG PET/CT reports of cancer patients. Studies reporting focal FDG uptake in the pituitary gland were evaluated for further analysis. Quantification of pituitary metabolic activity was obtained by using the maximum standardized uptake value (SUVmax). Findings were correlated with hormone assays, brain MRI, and/or CT.

Results 13 (0.2%) of the 8431 patients had an incidental focal FDG uptake in the region of pituitary gland. Further workup with brain MRI and/or CT was available in 10 (77%) of 13 patients. In 6 (46%) of 13 patients, brain MRI and/or CT revealed pathologic pituitary adenoma. 1 of 13 patients (8%) had normal CT and elevated prolactin level. 3 of 13 patients (23%) were false positives and had normal MRI and/or CT. Follow-up data were not available in 3 of 13 patients (23%). The maximum SUV for focal pituitary uptake was significantly higher in the true positive patients than in false positives (11.5, SD 6.6 vs. 3.3, SD 0.3, p < 0.04).

Conclusions Although incidental focal pituitary lesion on whole-body FDG PET/CT scans is an unusual finding (0.2%), the incidence of pituitary adenoma among those with focal FDG uptake is at least 54%. The degree of FDG uptake determined by maximum SUV can be helpful to determine abnormal pituitary uptake which warrant further diagnostic evaluation. Using a maximum SUV of 4 as a cutoff can significantly increase the accuracy of F18-FDG PET/CT in detecting pituitary adenoma. However, such cutoff needs to be further evaluated prospectively