Endocrine Abstracts

Background: Patients with acromegaly without detectable pituitary adenoma on conventional MRI are often excluded from adenomectomy due to inherent challenges of precise surgical planning, significantly limiting both their therapeutic options and chances of curation. Previous research showed that O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) PET-MRI is an accurate diagnostic tool to detect small functional pituitary adenomas (1). The present study aims to investigate the diagnostic yield of [18F]FET-PET-MRI in a cohort of acromegaly patients with suspected small adenomas.

Methods : Patients with acromegaly and a suspected primary or recurrent small functional pituitary adenoma underwent [18F]FET PET-MRI with administration of gadolinium, at 20 minutes post-injection. A PET-scan was defined as positive in case focal uptake of [18F]FET was detected as assessed by a nuclear radiologist. The accompanying MRI was evaluated separately by a single neuroradiologist. Outcomes were compared with clinical follow-up and sensitivity and positive predictive value (PPV) were calculated using post-operative pathology reports as reference.

Results : Fourteen acromegaly patients, 71.4% female, mean age 55 years (range 35-73 years) were included. Six patients (42.9%) had undergone transsphenoidal surgery prior to PET imaging. Positive [18F]FET uptake was seen in ten patients (71.4%), identifying five additional lesions missed by previous MRIs. During PET imaging, 8/14 patients used somastotatin analogues, and 2/14 cabergoline. The accompanying MRI showed a lesion in eight patients (57.1%), including one cystic lesion. Following positive PET, 1/10 patients received adjuvant radiotherapy and 4/10 underwent surgery. The other 5/10 are awaiting or have declined surgery. Histopathological examination confirmed that 4/4 resected tumours were adenomas staining positive for growth hormone, yielding an estimated sensitivity of 71.4% (95% CI 41.9 – 91.6%) and a PPV of 100% (95% CI 69.2-100%) for the detection of small GH-producing adenomas. Following transsphenoidal surgery, 2/4 patients achieved biochemical remission, the third patient was able to reduce the dose of medication and the last patient switched from pegvisomant to lanreotide. The patient who received adjuvant radiotherapy had no change in medication use.

Conclusion : [18F]FET PET-MRI increases the yield for detection of small GH-producing pituitary adenomas. [18F]FET PET-MRI emerges as a superior diagnostic tool to detect small functional pituitary adenomas and may enhance surgical planning and outcomes for acromegaly patients.1. Pruis IJ, Verburg FA, Balvers RK, Harteveld AA, Feelders RA, Vernooij MW, Marion Smits M, Neggers SJCMM and Veldhuijzen van Zanten SEM. [18F]FET PET-MRI; a novel and accurate technique for detection of small functional pituitary tumours. J Nucl Med. 2024 (accepted)