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, 20102018) 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.