Endocrine Abstracts

JOINT1789

Introduction: The preoperative localisation of ACTH-producing pituitary adenomas remains challenging. Magnetic resonance imaging correctly visualize up to 75% of ACTH-producing adenomas. In many patients, pituitary exploration has to be performed, with a risk of unnecessarily extensive resection, increasing the risk of postoperative pituitary insufficiency, or incomplete tumor removal, resulting in persistent disease. We therefore aimed to evaluate the potential of [¹⁸F]Fluorethyltyrosine positron emission tomography ([¹⁸F]FET PET/CT) in localising ACTH-producing pituitary adenomas in patients with first diagnosis of Cushing’s disease.

Methods: [¹⁸F]FET PET/CT was conducted in all consecutive patients with a primary diagnosis of Cushing’s disease at LMU Hospital between June and December 2024 in addition to a preoperative MRI and inferior petrosal sinus sampling. Dynamic PET images were acquired 0-40 min after injection with a mean injected dose of 173 MBq. Maximal tumor-to-background ratios (TBR_max) were determined comparing maximum standardized uptake values of pituitary adenomas to mean standardized uptake values of the right frontal and temporal lobe. Numeric values were reported with median (interquartile range).

Results: A total of 10 patients were included, 5 with microadenoma, 2 with macroadenoma, 3 with no visible lesion on MRI. All patients had inferior petrosal sinus sampling confirming a pituitary origin of ACTH excess. The median preoperative ACTH level was 55.5 pg/mL (50.3-89.0), the median preoperative basal cortisol was 23.6 µg/dl (13.7-29.7). In all patients, dynamic [¹⁸F]FET PET/CT revealed a focal intrasellar hotspot indicating a pituitary adenoma (median TBR_max 3.2; 2.4-3.6). 6/10 patients underwent transsphenoidal surgery until January 2025. In all operated patients, the focal intrasellar hotspot was consistent with the histopathologically proven corticotroph adenoma. 2 patients are still awaiting surgery, 1 patient refused surgery, 1 patient postponed surgery due to hospitalisation for severe depression. All operated patients showed a postoperative remission with a median basal ACTH of 6.0 pg/mL (4.5-20) and basal cortisol of 1.1 µg/dl (0.4-3.1). No patient experienced a postoperative anterior pituitary insufficiency.

Conclusion: Functional imaging with [¹⁸F]FET PET/CT can be effective in localising ACTH-producing pituitary adenomas and can add valuable information to MRI and inferior petrosal sinus sampling.