Abstract
Purpose: Ectopic adrenocorticotropic hormone (ACTH)-secreting lung tumours represent the most common cause of ectopic Cushing syndrome (ECS). Pulmonary opportunistic infections are associated with ECS and occasionally difficult to differentiate from tumours by using computed tomography (CT) alone. The aim of the present study was to evaluate the usefulness of 18F-fluorodeoxyglucose (FDG) positron emission tomography/CT (18F-FDG PET/CT) for differentiating ectopic ACTH-secreting lung tumours from tumour-like pulmonary infections in patients with ECS.Methods: We retrospectively reviewed the imaging data for 24 patients with ECS who were suspected to have ACTH-secreting lung tumours and underwent 18F-FDG PET/CT between 2008 and 2019.Results: In total, 18 patients had lung tumours (17 carcinoids and 1 small cell lung cancer) and six had pulmonary infections (cryptococcosis, n = 3; aspergillosis, n = 4; pulmonary abscess, n = 1). The primary source of ECS remained occult in the six patients with pulmonary infections. The maximum standardized uptake value (SUVmax) for pulmonary infections was significantly higher than that for tumours (P = 0.008). Receiver operating characteristic analysis was performed, and it was found that a cut-off SUVmax of 4.95 helped in differentiating lung tumours from infections with 75% sensitivity and 94.4% specificity. In subgroup analysis of 12 typical and five atypical carcinoids, there was no significant between-group difference with respect to SUVmax, the lesion size, the ACTH level, and the prevalence of regional lymph node metastasis.Conclusions: Our findings suggest that pulmonary infections exhibit significantly higher FDG uptake than do ACTH-secreting lung tumours in 18F-FDG PET/CT. Therefore, SUVmax (cut-off 4.95) may be useful for differentiating the two conditions. Typical and atypical ACTH-secreting lung carcinoids may show a similar clinical behaviour and appearance on 18F-FDG PET/CT.
Use of 18F-FDG PET/CT to differentiate ectopic adrenocorticotropic hormone-secreting lung tumours from tumour-like pulmonary infections in patients with ectopic Cushing syndrome