THU090 18F-FET PET-MRI; A Novel And Improved Technique For Detection Of Small Functional Pituitaryadenomas

Disclosure: I. Pruis: None. E. verbrug: None. M. smits: None. M. vernooij: None. R.A. Feelders: None. R. Blavers: None. S. velthuijzen: None. S.J. Neggers: None. Background Small functional pituitary adenomas can cause severely disabling symptoms and early death, however, surgical planning is often complicated due to inconclusive diagnostic MRI in up to 40% of patients and therefore hamper cure rates. We here introduce a novel method for the detection of small functional pituitary adenoma by O-(2-[18F]-fluoroethyl)-L-tyrosine ([18F]FET) PET-MRI. Methods Patients with Cushing’s disease (CD) or acromegaly with a suspected primary or recurrent small functional pituitary adenoma underwent [18F]FET PET-MRI. Focal uptake of [18F]FET was evaluated by a single nuclear radiologist and MRI was separately evaluated by a single neuroradiologist. Outcomes were compared with clinical follow-up and sensitivity and positive predictive values (PPV) were calculated. Findings Consecutive 28 patients, 68% female, mean age 50 years (range: 24–71), with CD (n=22; 79% or acromegaly (n=6; 21%) were scanned. 17 CD patients with a primary diagnosis had also undergone IPSS and 3 (50%) had a primary acromegaly diagnosis. 14/22 CD patients (64%) and 1/6 acromegaly underwent transsphenoidal surgery after [18F]FET PET, others are waiting or refused. Twenty-two CD patients (100%) had a positive [18F]FET PET, allowing to identify pituitary adenomas as small as 3 mm in size on accompanying MRI. 11/14 CD patients who underwent subsequent transsphenoidal surgery are biochemically in remission; rendering an estimated sensitivity of 100% and a PPV between 78–100% to detect CD. Four acromegaly patients (67%) had a positive [18F]FET PET. One acromegaly patient was biochemically in remission after transsphenoidal surgery. Conclusion [18F]FET PET-MRI shows high accuracy for localizing small functional pituitary adenoma in patients with CD and acromegaly. The diagnostic yield of this hybrid imaging technique exceeds that of MRI alone and IPSS and provides a welcome improvement for diagnosis, planning of surgery and follow-up. Presentation: Thursday, June 15, 2023