Discordant localization of 2-[f]-fluoro-2-deoxy-d-glucose in 6-[f]-fluorodopamine- and [i]-metaiodobenzylguanidine-negative metastatic pheochromocytoma sites

BACKGROUND: Although the majority of pheochromocytomas (PHEO) are benign, a subset is malignant. Computed tomography (CT) and magnetic resonance imaging (MRI) localize PHEO with high sensitivity but, because of limited specificity, [I]- or [I]-metaiodobenzylguanidine ([I]- or [I]-MIBG) is often used as a complementary agent. 6-[F]-fluorodopamine ([F]-DA) has been developed as a radiopharmaceutical for the targeting of noradrenergic pathways, and has been shown to result in a better detection rate of PHEO sites than MIBG; however, [F]-DA has shown a lack of accumulation in some patients with metastatic PHEO. METHODS: Five patients with widespread metastatic PHEO who had CT and MRI evidence of metastatic disease (one man and four women; age range, 25-64 years), and who underwent imaging with [I]-MIBG, [F]-DA and 2-[F]-fluoro-2-deoxy-D- glucose ([F]-FDG), were evaluated retrospectively. Tomographic imaging was performed and positron emission tomography (PET) images were inspected visually and quantitatively. RESULTS: All five patients had [I]-MIBG scans that grossly underestimated the extent of disease when compared with conventional CT and MRI. All lesions seen on [I]-MIBG scans were detected on [F]-DA scans, which also detected additional lesions. Nonetheless, [F]-DA also failed to detect numerous lesions seen on CT and MRI. In all of these cases, [F]-FDG PET showed lesions that were not detected on either [I]-MIBG or [F]-DA scans. CONCLUSIONS: When [I]-MIBG or [F]-DA fails to localize lesions seen on conventional imaging studies, [F]-FDG may be recommended as an ancillary test for the diagnosis and localization of metastatic PHEO. This is particularly important in patients with aggressive PHEO.