Clinical use of [¹⁸F]fluoro-ethyl-L-tyrosine PET co-registered with MRI for localizing prolactinoma remnants

To assess the utility of [¹⁸F]fluoroethyl-L-tyrosine PET co-registered with magnetic resonance imaging ([¹⁸F]FET-PET/MRI^CR) in patients with difficult-to-localize prolactinoma to inform clinical decision-making and (surgical) treatment planning.

Retrospective cohort study of 17 consecutive patients with prolactinoma undergoing [¹⁸F]FET-PET/MRI^CR between October 2020 and September 2022 for either (1) additional information in case of difficult-to-visualize remnants after prior transsphenoidal surgery (TSS), or pharmacological treatment, or (2) radiological diagnosis in absence of a (clear) adenoma on diagnostic/post-treatment conventional MRI.

[¹⁸F]FET-PET/MRI^CR identified a lesion in 14/17 patients, yet failed to identify active lesions in 2 patients with negative conventional MRI despite prolactin > 7.5 times upper limit of normal. [¹⁸F]FET-PET/MRI^CR results were inconclusive in 1 patient due to diffuse tracer uptake 10 weeks post-surgery. [¹⁸F]FET-PET/MRI^CR was completely concordant with a suspected lesion on conventional MRI in 10/17 patients, and partially concordant in 3/17 patients. New foci were identified in 4/17 patients. The [¹⁸F]FET-PET/MRI^CR conclusions influenced clinical shared decision-making in 15/17 patients, of whom 7 patients underwent TSS and 8 refrained from TSS. One patient underwent TSS despite negative [¹⁸F]FET-PET/MRI^CR, and one patient underwent additional imaging. Intraoperative findings corresponded with [¹⁸F]FET-PET/MRI^CR in 5/8 patients, and immunohistochemistry was positive in 5/8 patients. The treatment goal was achieved in 7/8 patients, and remission was achieved in 5/7 patients in whom total resection was considered feasible.

[¹⁸F]FET-PET/MRI^CR can be of added value in the preoperative decision-making process for selected patients with difficult-to-localize prolactinoma (remnants), or patients lacking a substrate on conventional MRI.