Value of fluorine-18-fluorodeoxyglucose PET/CT in localizing the primary lesion in adrenocorticotropic hormone-dependent Cushing syndrome.

OBJECTIVE

This study aimed to present a proper understanding of the fluorine-18-fluorodeoxyglucose (F-FDG) PET/computed tomography (CT) value in localizing the primary lesion in adrenocorticotropic hormone (ACTH)-dependent Cushing syndrome in a relatively large case cohort.

PATIENTS AND METHODS

This retrospective study included 47 patients with ACTH-dependent Cushing syndrome, who underwent an F-FDG PET/CT examination in our hospital from November 2010 to January 2018. The serum cortisol, 24 h urine cortisol, serum ACTH, and high-dose dexamethasone suppression test were measured in all the patients. Bilateral inferior petrosal sinus sampling was performed in 28/47 patients. Pituitary magnetic resonance imaging and whole-body F-FDG PET/CT were performed in all patients.

RESULTS

Serum ACTH at 8 a.m. higher than 161.8 pg/ml as the cut-off value showed the best diagnostic accuracy (73.9%) for the successful localization of the primary lesions. In Cushing disease patients, the pituitary maximum standardized uptake value F-FDG PET/CT (n=11) did not show significant differences compared with that in ectopic ACTH syndrome (EAS) patients (n=20). In terms of EAS, the descending order of maximum standardized uptake value was 13.2±8.3 (4.8-26.4) in pancreatic neuroendocrine tumors (n=4), 7.1±2.4 (3.5-10.1) in mediastinal carcinoid (n=11), and 2.0±0.1 (1.9-2.2) in bronchial carcinoid (n=4). This study first reported the F-FDG PET/CT images of ACTH-secreting olfactory neuroblastoma.

CONCLUSION

Serum ACTH level determines the success rate of localization of the primary ACTH-secreting tumor in ACTH-dependent syndrome. F-FDG PET/CT plays a role in localizing the site for EAS, although it plays a limited role in Cushing disease.