Conventional and nuclear medicine imaging in Ectopic Cushing's syndrome. a systematic review

CONTEXT: Ectopic Cushing's Syndrome (ECS) can be a diagnostic challenge with the hormonal source difficult to find. This study analyzes the accuracy of imaging studies in ECS localization. EVIDENCE ACQUISITION: Systematic review of medical literature for ECS case series providing individual patient data on at least one conventional imaging technique (CT/MRI) and one of (111)In-pentetreotide (OCT), (131)/(123)I-Metaiodobenzylguanidine (MIBG), (18)F-fluoro-2-deoxyglucose (FDG-PET), (18)F-fluorodopa (F-DOPA-PET), 68Ga-DOTATATE-PET/CT or 68Ga-DOTATOC-PET/CT scan (68Ga-SSTR-PET/CT). Evidence Summary: The analysis comprised 231 patients (female 50.2%; 42.6±17 years). Overall, 52.4% had 'overt' (121/231), 18.6% 'occult' and 29% 'covert' ECS. Tumors were located in the lung (55.3%), mediastinum-thymus (7.9%), pancreas (8.5%), adrenal glands (6.4%), gastrointestinal tract (5.4%), thyroid (3.7%) and other sites (12.8%), and primary tumors were mostly bronchial neuroendocrine tumors [NETs] (54.8%), pancreatic-NETs (8%), mediastinum-thymus-NETs (6.9%) gastrointestinal NETs (5.3%), pheochromocytoma (6.4%), neuroblastoma (3.2%), and medullary thyroid carcinoma (3.2%). Tumors were localized by CT in 66.2% (137/207), MRI in 51.5% (53/103), OCT in 48.9% (84/172), FDG-PET in 51.7% (46/89), F-DOPA-PET in 57.1% (12/21), MIBG in 30.8% (4/13), 68Ga-SSTR-PET/CT in 81.8% (18/22) of cases. Molecular imaging discovered 79.1% (53/67) of tumors unidentified by conventional radiology, with OCT the most commonly used, revealing the tumor in 64%, followed by FDG-PET in 59.4%. F-DOPA-PET was used only in 7 coverts (sensitivity 85.7%). Notably, 68Ga-SSTR-PET/CT had 100% sensitivity among covert cases. CONCLUSIONS: Nuclear medicine improves the sensitivity of conventional radiology when tumor site identification is problematic. OCT offers a good availability/reliability ratio and FDG-PET was proven useful; 68Ga-SSTR-PET/CT use was infrequent, despite offering the highest sensitivity.