Background: Although MRI remains the investigation of choice for pituitary imaging, it does not provide information about the functionality of lesions (e.g. residual adenoma vs post-surgical scar tissue), and cannot reliably identify all microadenomas. These limitations are of particular relevance in acromegaly where clinical and biochemical evidence of disease activity mandates (further) treatment.
Methods: We hypothesised that i) imaging with the PET ligand 11C-methionine, which is taken up at sites of peptide/protein synthesis, would permit more reliable identification of functioning pituitary adenoma in patients with acromegaly and ii) co-registration of PETCT with SPGR/volume MRI would yield more accurate anatomical localisation of the site(s) of 11C-methionine uptake.
Results: Thirty patients with acromegaly were scanned in our centre using this technique between 2011 and 2015. All patients had indeterminate MRI appearances with respect to primary or residual/recurrent adenomas. 11C-methionine PET co-registered with SPGR/volume MRI provided additional information to inform management in all but one patient. More specifically, we found that 11C-methionine PET: i) reliably identifies the primary culprit lesion (e.g. when two separate candidate lesions are present on MRI); ii) defines surgical targets in patients who have been deemed not to be surgical candidates based on MRI appearance (e.g. partially empty sella); iii) delineates targets amenable to repeat surgery or targeted radiotherapy in post-op patients with persistent disease but inconclusive MRI findings (e.g. residual adenoma vs post-operative change/scar tissue); and iv) identifies areas of residual adenoma after failed radiotherapy or gamma knife therapy.
Conclusions: To our knowledge, this is the largest series of patients with acromegaly evaluated with 11C-methionine PET/CTMRI. We have found that this technique offers significant advantages in different clinical scenarios when MRI is inconclusive, thus confirming its potential to contribute to better care and outcomes in patients with acromegaly.