Clinical application of combination [¹¹C]C-methionine and [¹³N]N-ammonia PET/CT in recurrent functional pituitary adenomas with negative MRI or [¹⁸F]F-FDG PET/CT

We assessed the value of positron emission tomography/computed tomography (PET/CT) with [¹³N]N-ammonia ([¹³N]N-NH3) and [¹¹C]C-methionine ([¹¹C]C-MET) for the evaluation and management of recurrent secreting pituitary adenoma, which could not be detected by magnetic resonance imaging (MRI) or fluorine-18 fluorodeoxyglucose ([¹⁸F]F-FDG) PET.

Nine consecutive patients with biochemical and clinical evidence of active recurrent tumor not detected by MRI and [¹⁸F]F-FDG PET were enrolled in this study. All of the patients underwent [¹³N]N-NH3 and [¹¹C]C-MET PET/CT, after which the pattern of tracer uptake was studied, the tumor position was located, and a clinical decision was made.

In general, [¹¹C]C-MET had a higher uptake in pituitary adenomas (PAs) than that in pituitary tissues, while [¹³N]N-NH3 had a higher uptake in pituitary tissue than in pituitary adenomas. Increased [¹¹C]C-MET uptake was observed in all nine PAs and three pituitary tissues, while all pituitary tissues and only one pituitary adenoma showed increased [¹³N]N-NH3 uptake. Four patients had concordant imaging and surgical findings indicative of biochemical remission without hypopituitarism after treatment. Radiotherapy was adopted in two patients, medication in another two, and follow-up observation in one case.

Combined [¹¹C]C-MET and [¹³N]N-NH3 PET/CT is effective in the differentiation of PAs from pituitary tissue in recurrent functional PAs with negative MRI or [¹⁸F]F-FDG PET. These results provide a valuable reference for further disease management.