Observations on the function of normal adrenomedullary tissue in patients with phaeochromocytomas and other paragangliomas.

123I-MIBG is a norepinephrine analogue used for imaging phaeochromocytomas and other paragangliomas. In this study 7 normal volunteers and 31 subjects with high or borderline high plasma catecholamine and urinary metanephrine and VMA levels were investigated. In the normals the uptake by the adrenal medulla was in the range of 0.01%-0.21% of the injected dose at 22 h. In 22 subjects there was no evidence for any paraganglioma, with the uptake by the adrenal medulla in the range of 0.01%-0.22% of the injected dose at 22 h. In nine patients there was evidence of a paraganglioma on imaging which was confirmed on surgery. The uptake by the tumours was in the order of 0.001%-0.14% of the injected dose per gram of tumour tissue. In all nine cases the non-tumorous adrenal medulla could be visualized; the uptake in the adrenals was in the range of 0.01%-0.21% of the injected dose. This study shows that in the presence of elevated plasma catecholamines of tumour origin the unaffected adrenal medullary tissue retains the capacity for 123I-MIBG uptake. In the two cases also studied by adrenal venous sampling, catecholamine release was also within the normal range.