Multinuclide evaluation of hepatic mass lesions

Radionuclide imaging with labeled colloids is widely used to evaluate and localize primary and metastatic tumors of the liver. The method is fairly sensitive, but the nonspecificity of focal defects remains a significant limitation. Lesions such as cysts and abscesses appear as space occupying areas that are indistinguishable from neoplastic masses. Utilizing a variety of radiopharmaceuticals, one may obtain additional information concerning such lesions. Hepatic blood flow scintiphotography is performed with the Anger camera following the intravenous injection of a high activity, small volume bolus of 99m-Tc pertechnetate. Vascular lesions such as hepatomas or hemangiomas will show increased activity in the lesion which should easily differentiate them from avascular processes such as abscesses, cirrhotic pseudomasses and most metastatic lesions, all of which remain "cold" on these flow studies. If one does not posses a camera, useful blood pool rectilinear scans of these lesions may be obtained with 131-I or 99m-Tc human serum albumin or ionic 113m-In. Additional information concerning the metabolic activity of focal defects on the colloid study is obtained using 75-Se-selenomethionine or 67-Ga. The former is an indicator of active protein metabolism while the latter attaches to lysozymes of metabolically active cells. With either agent, hepatomas show avid uptake, metastatic lesions show variable uptake, and cysts or chronic pseudotumors of cirrhosis show poor uptake. The two agents differ in abscess detection where 75-Se-selenomethionine uptake is poor while 67-Ga concentration generally is intense. 131-I-Rose Bengal occasionally may prove useful in demonstrating impression by an atypically positioned gallbladder or focal dilatation of the biliary tract as a cause of a defect on the colloid scan. Ultrasound examination may complement the radionuclide studies. It is useful for corroborating the presence of lesions and for evaluating their consistency (cystic vs. solid). The information obtained from this multinuclide approach has made scintigraphy examination of the livermore specific. After the completion of this non-invasive series of studies, one generally may venture an intelligent opinion concerning the etiology of the space occupying disease.