In using radionuclide imaging of the inferior vena cava (RIVC) to investigate the prevalence of membranous obstruction of the inferior vena cava (IVC) in patients with hepatocellular carcinoma, it was necessary first to determine if this technique would distinguish membranous obstruction of the IVC both from other causes of IVC obstruction likely to be encountered in these patients and from the picture obtained with severe ascites. RIVC readily distinguished an obstructed from a normally patent IVC. However, membranous obstruction of the IVC could not in most instances be differentiated from extrinsic compression of the IVC by an enlarged tumourous liver, occlusion of the lumen of the IVC by tumour, or the effect of severe ascites. In a proportion of the patients with membranous obstruction of the IVC, flow of the radionuclide through large superficial collateral vessels was seen, enabling this diagnosis to be made with confidence. Thus, if RIVC shows the IVC to be obstructed or if severe ascites is present, contrast venography will usually be necessary to determine the nature of the obstructing lesion.
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