Endocrine Abstracts

After establishing a biochemical diagnosis, pheochromocytomas and paragangliomas can be localized using different imaging modalities. Appropriate imaging is critical for primary tumor localization, the detection of multiple primary tumors and the detection of metastases. This will guide the optimal choice between curative surgery and palliative treatment options.

First line anatomical imaging modalities for pheochromocytoma and paraganglioma imaging include computed tomography (CT) or magnetic resonance imaging (MRI). The specificity of these techniques is limited, however. Functional imaging is complimentary to anatomical imaging and provides specific information about the tumor’s functional characteristics. Nuclear medicine scanning techniques include planar scintigrapy, single-photon emission computed tomography (SPECT) and positron emission tomography (PET). The most widely used radiotracers for pheochromocytoma and paraganglioma scintigraphy are (123I)-labeled metaiodobenzylguanidine (123I-MIBG) and 111In-DTPA-pentetreotide scintigraphy. They have long been considered as the ‘gold standard’ modalities. However, several studies have demonstrated the limitations of using 123I-MIBG scintigraphy alone in the staging of hereditary and metastatic pheochromocytoma/paraganglioma. The use of 123I-MIBG may lead to significant underestimation of metastatic disease. Novel PET tracers been proven to be very useful for the functional imaging of pheochromocytomas and paragangliomas. These include 6-(18F)-fluorodopamine (18F-FDA), 6-(18F)-fluoro-L-3,4-dihydroxyphenylalanine (18F-DOPA) and 2-(18F)-Fluoro-2-deoxy-D-glucose (18F-FDG). The performance of the different functional imaging modalities is largely determined by tumor location (adrenal pheochromocytoma and extra-adrenal paraganglioma versus head and neck paraganglioma), benign versus metastatic disease and the underlying hereditary syndrome. The main purpose of 123I-MIBG or somatostatin receptor based scintigraphy in a patient with metastases is to determine if internal targeted radiotherapy is an appropriate treatment choice. Current recommendations regarding the optimal functional imaging strategy for these tumors are made available as part of the Endocrine Society clinical practice guideline on pheochromocytoma and Paranglioma. Precise identification of the clinical context and genetic status of patients enables personalized use of functional imaging modalities.