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Endocrine Abstracts (2021) 77 OP3.3 | DOI: 10.1530/endoabs.77.OP3.3

1Cambridge Endocrine Molecular Imaging Group, Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, NIHR Cambridge Biomedical Research Centre, University of Cambridge and Cambridge University Hospitals, Cambridge, United Kingdom; 2Department of Neurosurgery, Cambridge University Hospitals NHS Foundation Trust, Cambridge Biomedical Campus, Hills Road,, Cambridge, United Kingdom; 3Department of Ear, Nose and Throat Surgery, Cambridge University Hospitals NHS Foundation Trust, Cambridge Biomedical Campus, Hills Road,, Cambridge, United Kingdom; 4Department of Nuclear Medicine, Cambridge University Hospitals NHS Foundation Trust, Cambridge Biomedical Campus, Hills Road,, Cambridge, United Kingdom


Background: In a sub-group of patients with newly diagnosed pituitary adenomas, conventional MRI will fail to confidently localise the tumour. The role of molecular imaging for these patients is increasingly being recognised, both in terms of confirming diagnosis and in guiding targeted therapy; 11C-Methionine PET co-registered with volumetric MRI (Met-PET/MRCR) can enhance decision making in this group of patients. However, in some cases distinguishing tumoral tracer uptake from that of the normal gland can still be challenging (especially for small microadenomas). Additionally, co-existent incidental non-functioning adenomas can demonstrate a confounding focus of tracer avidity. We hypothesised that performing PET on two occasions, with targeted suppression of tumour activity in the interim, can permit greater confidence in determining tumour localisation.

Methods: In 14 patients with secretory microadenomas (including prolactinomas, somatotropinomas, thyrotropinomas & corticotropinomas) we performed Met-PET/MRCR pre-and-post appropriate endocrine suppression. We developed a novel algorithm which permitted calculation of the normalised difference in signal between pre-and-post scan datasets – this allowed the creation of a ‘subtraction image’.

Results: In 13 patients we observed a significant reduction in focal tracer uptake at the site of the suspected adenoma following endocrine suppression. In each of these cases the ‘subtraction image’ clearly demonstrated a focus of suppressible tracer uptake (Figure 1). Six patients elected to continue with medical management. In six patients, the location of the tumour was confirmed at subsequent transsphenoidal surgery with histopathological correlation. One patient is awaiting surgery.

Conclusion: For the first time we report a novel approach to molecular imaging in which imaging pre-and-post suppression of tumour activity allowed precise localisation of the site of a functioning microadenoma.

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Volume 77

Society for Endocrinology BES 2021

Edinburgh, United Kingdom
08 Nov 2021 - 10 Nov 2021

Society for Endocrinology 

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