Endocrine Abstracts

Background: Detection of MRI-negative ACTH-producing pituitary adenomas is a challenge in

the management of patients with Cushing’s disease. There are some data on the

ability of pituitary adenomas to accumulate 18F-fluorodeoxyglucose during the 18F-FDG positron emission tomography and computer tomography (18F-FDG PET/CT).

Aim: To study the potential of using a standardized uptake value (SUV) and a tumor –background ratio (TBR) when evaluating the results of PET/CT 18F-FDG of the brain for localization ofMRI-negative ACTH-producing pituitary adenomas.

Materials and methods: 40 patients were enrolled. 32 patients had Cushing’s disease, pituitary MRI scans were negative in all these patients. In all patients the pituitary source of ACTH hyperproduction was confirmed by bilateral cavernous and inferiorpetrosal sinuses sampling. Eight patients had neuroendocrine tumors with ACTH-ectopic production (NETs). Control group consisted of 19 persons without hypercortisolism. Brain 18F-fluorodeoxyglucose PET/CT was performed in all patients. Tumor –background ratio (TBR) was calculated as the ratio of the SUVmax in the pituitary gland to SUVmax in the reference zone of interest, drown above the fat tissue of the cheek. SUVmax in the pituitary gland and TBR were compared between patients with Cushing’s disease and control group; patients with NETs and control group; patients with Cushing’s disease and control group plus patients with NETs. The optimal threshold value of TBR for detection of MRI-negative ACTH-producing pituitary adenoma was calculated with ROC-analysis.

Results: All 32 patients with Cushing’s disease patients had focal increased 18F-FDG uptake on pituitary 18F-FDG PET/CT scans. In control group and in patients with NETs there was no focus of increased accumulation of 18F-FDG. SUVmax in the pituitary gland did not differ in patients with Cushing’s disease and control group (P=0.208); patients with Cushing’s disease and patients with NETs (P=0.63); patients with Cushing’s disease and control group plus patients with NETs (P=0.23). On the contrary TBR in the pituitary gland differ in patients with Cushing’s disease and control group (P=0.000); patients with Cushing’s disease and patients with NETs (P=0.000095); patients with Cushing’s disease and control group plus patients with NETs (P=0.000). The optimal threshold value of TBR for detection of MRI-negative ACTH-producing pituitary adenoma calculated with ROC-analysis was 6.55. The sensitivity and specificity of the method were 90.6% and 89.5%, respectively (р <0.001, AUC=0.961, 95% CI=0.914-1.000).

Conclusion: Brain 18F-fluorodeoxyglucose PET/CT may be useful for localization of MRI-negative ACTH-producing pituitary adenomas. Application of the TBR, but not of the SUVmax is optimal for evaluating it’s results.