What are the causes of pseudo-lesions on hepatic imaging? One cause is illustrated by the following case. The patient was a 51-year-old man who was investigated because of fatigue. He had a moderate intake of alcohol and had previously had a cholecystectomy. Laboratory investigations revealed a mild elevation of bilirubin and alkaline phosphatase as well as hyperlipidemia. Serological tests for hepatitis B and C were negative. An ultrasound study showed that most of the liver was of increased echogenicity consistent with a fatty liver. However, a relatively hypoechoic area was noted in the medial segment of the liver (segment IV). Color and pulsed-wave Doppler studies suggested the presence of a venous vessel in segment IV that was different from normal portal vein branches. A computed tomography scan during arterial portography (CTAP) showed an irregular perfusion defect in segment IV (Fig. 1) that was identical to the area demonstrated by ultrasonography. Subselective left gastric arterial angiography was then used to demonstrate that the right gastric vein drains directly to segment IV and (→) branches out to the anterior portion of segment IV during the venous phase (Fig. 2). A CT scan during left gastric arteriography also showed that the right gastric vein anastomoses with a branch of the portal vein in segment IV and that contrast enhancement in segment IV corresponded to the perfusion defect on CTAP and the hypoechoic area on ultrasound.
Focally spared areas in fatty liver are usually located on the posterior edge of segment IV. The typical appearance is that of wedge-shaped or round lesions but the current case is unusual in that the area is large and irregular. However, in contrast to tumors, the lesion does not have a mass effect on hepatic vessels. The investigations indicate that the spared area has a reduced blood supply from the portal vein and an aberrant blood supply from the right gastric vein. How this results in spared areas in a fatty liver remains unclear but concentrations of lipids, hormones or other nutritional elements may play a role.