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DOI: 10.1055/s-2007-972256
The expression of the Vesicular Monoamine Transporter type 1 (VMAT-1) is necessary for functional imaging of pheochromocytomas with [123J]-Metaiodobenzylguanidine (MIBG) scintigraphy – Superiority of 6-[18F]- Fluorodopamin Positron Emission Tomography (DOPA-PET) for the localization of VMAT-1 negative tumors
Objective: The functional imaging of choice for a pheochromocytoma is MIBG-scintigraphy. However, in some cases, it fails to detect pheochromocytomas (PHEO). Recent data show that alternatively DOPA-PET can be used to localize PHEO. The aim of the study was, to compare the diagnostic utility of DOPA-PET vs. MIBG-scintigraphy in patients with PHEO or paraganglioma (PGL) and to correlate imaging results with histological examination of catecholamine-transporter expression.
Methods: We studied 25 patients with biochemically confirmed PHEO. 13 patients had hereditary PHEO-syndromes (2 MEN II, 9 SDHD, 1 VHL, 1 NF-1), the remaining 12 were classified as sporadic. Imaging modalities included CT-scan and/or MRI as well as both, MIBG-Scintigraphy and DOPA-PET. Tumors found by morphological and functional imaging were operated and examined for expression of VMAT-1 and -2, Tyrosinhydroxylase, Chromogranin A and Synaptophysin expression. Imaging results were correlated with histological findings.
Results: All 25 patients had positive adrenal or extraadrenal findings on CT/MRI, consistent with the presence of a PHEO/PGL. DOPA-PET was positive in all patients but one with an extraadrenal abdominal PGL, whereas in contrast 9 patients had negative MIBG-Scintigraphy. All adrenal and extraadrenal abdominal lesions except one could be visualized by both DOPA-PET and MIBG-Scintigraphy. In contrast, only 1 of 19 extraadrenal thoracic and head and neck PGL was positive on MIBG-Scintigraphy, whereas all of them could be detected with DOPA-PET. Patients with extraadrenal PHEO/PGL detected only with DOPA-PET showed a predominant secretion of norepinephrine and occurred as part of hereditary syndromes. Histological examination revealed that all PHEO/PGLs negative on MIBG-Scintigraphy did not express VMAT-1, whereas VMAT-2 expression was detectable in all tumors, indicating that VMAT-1 expression is a prerequisite for positive functional imaging with MIBG-scintigraphy.
Conclusion: DOPA-PET was found to be a superior imaging method in patients with VMAT-1 negative, mainly extraadrenal PHEO.