Endocrine Abstracts

JOINT2725

Background: Transsphenoidal surgery is the first treatment option for Cushing’s Disease (CD). Unfortunately, conventional dedicated pituitary MRI – the current golden standard – fails to detect the culprit lesion in approximately 30-50% of patients. Novel imaging techniques using positron emission tomography (PET) with specific radioactive tracers and co-registration with MR images have been used in patients with pituitary adenomas and might improve the surgical outcomes of corticotroph adenomas.

Aim/Objective: To assess functional imaging-guided diagnostic and surgical accuracy of ¹¹C-methionine PET-CT co-registered with MRI (¹¹C-MET-PET/MRI), and ¹⁸F-fluoroethyl-l-tyrosine PET/CT co-registered with MRI (¹⁸F-FET-PET/MRI) for patients with CD with an inconclusive MRI and high treatment need.

Methods: This cohort study included 31 patients with CD undergoing ¹¹C-MET-PET/MRI or ¹⁸F-FET-PET/MRI in the diagnostic trajectory followed by surgery (2017-2024). Indication for functional imaging was determined by an experienced multidisciplinary team. Some patients underwent two functional imaging scans followed by surgery, resulting in a total of 36 evaluable functional imaging-treatment episodes. Outcomes were evaluated using histopathological confirmation and biochemical remission 6 months postoperatively.

Results: 26 patients were female (71.0%), and mean age was 48 (11-73) years. Functional imaging was performed (¹⁸F-FET-PET/MRI n = 15 and ¹¹C-MET-PET/MRI n = 21) mainly because of an unclear remnant lesion following prior surgery (24/36, 66.7%), or uncertain invasion/extension following surgery in 10/36 cases (27.8%). At the time of functional imaging, clinical severity of symptomatology was mild in 50% of patients, whereas the other 50% of patients had moderate or severe symptomatology. 32/36 cases (88.9%) had undergone previous surgery, only 4 patients were treatment-naïve. Functional imaging resulted in a positive “PET-signal” in 30/36 cases (83.3%), of which solely 10 (33.3%) could be related a lesion on the simultaneous MRI nor retrospectively on previous MRIs. Of the PET-positive lesions, confirmation was obtained by histopathology in 11/30 (36.7%), biochemical remission in 17/30 (56.7%), or either in 21/30 cases (70.0%). Regarding the entire cohort without clear surgical target, biochemical remission was obtained in 21/36 cases (58.3%). For repeat surgery, remission rates were 72.7% (16/22 cases) for patients with unclear remnants, and 40.0% (4/10 cases) for patients with unclear invasion/extension. In treatment-naïve patients, 1/4 cases (25.0%) achieved remission.

Conclusion: Functional imaging with ¹⁸F-FET-PET/MRI and ¹¹C-MET-PET/MRI in complex patients lacking surgical target on conventional MRI showed a PET-positive lesion in 89%, which could be surgically confirmed in 70%, and yielded a remission rate of 60%, particularly in patients undergoing repeat surgery. Therefore, functional imaging should be considered in complex patients with CD.