Endocrine Abstracts (2018) 59 OC4.6 | DOI: 10.1530/endoabs.59.OC4.6

11C-Methionine PET/MRI is superior to MRI for localisation of functioning prolactinomas and may facilitate targeted intervention

Waiel Bashari1,2, Andrew Powlson2, Russell Senanayake1,2, Arvindh Sekaran1, Laura Serban3, Olympia Koulouri2, Daniel Gillet4, Heok Cheow4, Iosif Mendichovszky4 & Mark Gurnell1,2


1University of Cambridge, School of Clinical Medicine, Cambridge, UK; 2Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, UK; 3Wolfson Diabetes & Endocrinology Centre, Cambridge, UK; 4Radiology Department, Addenbrooke’s Hospital, Cambridge, UK.


Background: Prolactinomas are the commonest hormone-secreting pituitary adenomas. First-line treatment is dopamine agonist (DA) therapy. However, side-effects are increasingly recognised, leading to an increasing consideration of transsphenoidal surgery (TSS) and/or radiotherapy. Co-registration of 11C-methionine Positron Emission Tomography (Met-PET) imaging with Spoiled Gradient Recalled Acquisition MRI (SPGR MRI), referred to in combination as Met-PET/MRI, can aid accurate localisation of de novo or residual/recurrent adenomas, directing targeted intervention. We compare this modality with MRI alone for localisation of prolactinomas.

Methods/patients: 23 patients (10 male, 13 female; 10 microadenoma, 13 macroadenoma) with a confirmed prolactinoma (single centre, 2010–2018) were identified. 16 with de novo tumours underwent initial DA titration but failed this primary medical therapy. Seven failed medical therapy for residual/recurrent disease after transsphenoidal resection. Each then had Met-PET/MRI and standard MRI to localize functional tumour.

Results: Medical therapy failed predominantly due to development of DA side effects, of which dizziness and behavioural changes were commonest (38% of the cohort each). Met-PET/MRI demonstrated focal tumour uptake in 20 patients with hypersecretion at time of scanning. Three patients on medical therapy had a serum prolactin within reference limits at the time of PET scanning, which did not demonstrate active tumour in these cases. In comparison, MRI alone only located tumour confidently in 8/23 patients. For the subgroup with a prior surgical procedure, residual active tumour was detected by PET in all (7/7) cases, whereas MRI alone identified tumour in just 4/7. Six patients (4 macroadenomas, 2 microadenomas) have to date undergone TSS guided by Met-PET/MRI. All demonstrated significant biochemical improvement postoperatively, with three attaining remission.

Conclusion: Met-PET/MRI can be used as an adjunct to conventional MRI in prolactinoma with failed medical therapy, with greater sensitivity than conventional MRI alone, thereby potentially facilitating targeted surgery/radiotherapy.