Adrenal Molecular Imaging

Abstract

The major workload in the field of adrenal imaging comprises patients with adrenal tumors incidentally depicted by imaging performed for other reasons than adrenal disease. These so-called 'incidentalomas' are generally managed by CT and MRI, and molecular imaging techniques are required only for a few patients. PET/CT with 18F-fluorodeoxyglucose (18F-FDG) is useful for establishing whether an adrenal metastasis is the only lesion, and therefore is available for surgical resection, or if the disease is disseminated. 18F-FDG PET/CT may be applied to differ benign from malignant incidentalomas and can be helpful in the imaging of pheochromocytoma and adrenocortical cancer (ACC). 11C-metomidate PET/CT can differentiate adrenocortical from nonadrenocortical tumors and a suspected ACC may be characterized and staged before surgery. 11C-metomidate PET/CT is currently also used to help diagnose Conn's adenomas in primary aldosteronism, but further development is needed. Scintigraphy with 123I/131I-metaiodobenzylguanidine (MIBG) remains the mainstay for molecular imaging of pheochromocytoma and is mandatory in patients for whom 131I-MIBG therapy is considered. A PET tracer for the imaging of pheochromocytoma is the norepinephrine analogue (11)C-hydroxyephedrine that can be used to characterize equivocal lesions and for the follow-up and diagnosis of recurrent malignant disease. Other specialized PET tracers for the imaging of pheochromocytoma are 18F-fluorodihydroxyphenylalanine (18F-DOPA) and 18F-fluorodopamine.