Radiographic characteristics of benign liver tumors: Focal nodular hyperplasia and hepatic adenoma

Abstract

The imaging characteristics of focal nodular hyperplasia are varied. Unenhanced computed tomography reveals the attenuation of these lesions, in general, to be slightly less than that of normal liver; after contrast enhancement, their attenuation is equal to (isodense) or greater than (hyperdense) that of normal liver. This, of course, depends on the rate at which the contrast material is injected and the timing of scans after its injection. Central scar, a helpful finding when present, was not noted as a common finding at the time of computed tomography or ultrasound examination. Ultrasound examinations, in general, showed these lesions to be homogeneous, isoechoic or hypoechoic tumors. The angiographic findings revealed them, in general to be more vascular than the normal liver with an intense, homogeneous capillary stain. Hypovascular focal nodular hyperplasia does occur, but rarely. The blood supply to these tumors was most commonly from peripheral vessels, in contrast to previous reports of a central blood supply being more common. The technetium-99m sulfur colloid liver-spleen scan is often the key to the diagnosis of focal nodular hyperplasia. The majority of these tumors at the time of liver-spleen scanning will be seen as areas of normal or increased uptake; this is a reliable clue to the diagnosis of focal nodular hyperplasia. lf the radionuclide scan is not diagnostic, however, the combined findings of CT, ultrasound and angiography often are. Hepatic adenomas also clearly have a varied imaging presentation. The angiographic findings show these tumors to be hypervascular with small areas of hypovascularity within them. Blood is supplied to the adenomas by peripheral vessels in most cases, and there is no intense capillary stain. Computed tomography shows hepatic adenomas, in general, to be hypodense in the absence of contrast enhancement. Yet on contrast enhanced scans, they are complex lesions with multiple ranges of attenuation located within them. Acute hemorrhage can be seen in approximately half the unenhanced CT scans. By sonography, hepatic adenomas, in general, display intrinsic areas that are isoechoic, hyperechoic, and hypoechoic; and they are invariably nonhomogeneous lesions. These tumors appear as focal defects in all cases on technetium-99m sulfur colloid liver-spleen scans.