Utility of 11C-Methionine and 18F-FDG PET/CT in Patients With Functioning Pituitary Adenomas

Purpose MRI is commonly used in the evaluation of pituitary adenomas (PAs). However, it has difficulty to locate the lesions sometimes, especially microadenomas and/or postoperative recurrent tumors. We aimed to evaluate the role of combined C-11-methionine (MET) and F-18-FDG PET/CT in patients with functioning PAs. Patients and Methods This study included 43 patients: 15 had Cushing disease, 16 had acromegaly, and 12 had a prolactinoma. F-18-FDG PET/CT was performed on all of the patients; C-11-MET PET/CT was performed on 39 of the patients. The PET images and surgical findings were analyzed. Results On F-18-FDG PET/CT, 29 (67%) of 43 cases had positive results, all of which were true positives, including 2 cases with equivocal MRI results. On C-11-MET PET/CT, 37 (95%) of 39 cases had positive results, of which 2 were false positives. All patients underwent surgery, and the results of PET/CT scans were confirmed by surgery and pathological examination. All F-18-FDG PET/CT results were negative when C-11-MET PET/CT results were negative. However, 12 patients with positive C-11-MET PET/CT results had negative F-18-FDG PET/CT results. The positive rate of F-18-FDG PET/CT in patients with somatostatin analog treatment, radiosurgery, transsphenoidal surgery, and microadenoma was 63% (5/8), 50% (1/2), 33% (4/12), and 48%(10/21), respectively, while that of C-11-MET PET/CT was 86% (6/7), 50% (1/2), 100% (12/12), and 100% (21/21), respectively. In the 9 patients with a recurrent microadenoma, the positive rate of F-18-FDG PET/CT was as low as 22% while that of C-11-MET PET/CT was 100%. There was no significant difference in the positive rate of C-11-MET and F-18-FDG PET/CT between the 3 types of PA. Conclusions PET/CT may be useful to detect tumors in patients with equivocal MRI results. C-11-MET PET/CT can provide valuable diagnostic information when F-18-FDG PET/CT yields negative results, especially in patients with recurrent microadenomas.