Giant area of transient hepatic attenuation difference, mimicking incidentaloma at liver ultrasound

Abstract

Concurrent with recent advances in diagnostic imaging techniques, the incidental finding of liver tumors, or incidentalomas, is increasing in asymptomatic and healthy individuals [1]. A 56-year-old healthy man underwent an abdomen ultrasound for a clinical check-up. A diffuse bright liver echo-pattern (indicating a low-moderate grade steatosis) and an unusual image (diameter approximately 10 cm) in the VI–VII hepatic segment, characterized by a massive giant hypoechoic lesion with poorly defined margins and a near rounded hyperechoic area (diameter about 4 cm) in the context were found (Fig. 1). The ultrasonographer suspected an angioma as first diagnostic hypothesis; however the large hypoechoic area around it, was not unique interpretation. In order to clarify the nature of the lesion, a contrast-enhancement examination was indicated to exclude an incidentaloma. Contrast-enhanced ultrasound revealed an irregularly circular lesion, characterized by early arterial nodular enhancement with delayed centripetal fill-in during the arterial phase. At 36 seconds, the lesion had almost completely filled in. At 45 seconds, the lesion was completely enhanced and sustained enhancement was observed in the late phase scan. The picture was suggestive for hepatic angioma (Fig. 2). Contrast-enhanced MultiSlice computed tomography (CT scan) (Fig. 3) was performed to confirm the diagnosis that proved to be an angioma in the VI hepatic segment (diameter about 4.6 cm), revealing in contour a segmental area of transiently increased enhancement during the arterial phase, with isodense aspect to hepatic parenchyma on venous phase thus suggesting transient hepatic attenuation differences (THAD). THAD is a hepatic perfusion anomaly, caused by an aberrant dual blood supply associated with numerous liver disorders, and it is visible on a contrast-enhanced biphasic spiral CT scan as parenchymal areas of high attenuation in the arterial phase, becoming an isodense image with the normal parenchyma in the portal venous phase [2]. Occasionally, attenuation differences may persist up to the portal venous phases due to a concurrent obstruction of a hepatic vein branch. THADs can be confused with tumor lesions, and are a compensatory relationship between two liver sources of blood supply so that the arterial flow increases as the portal flow decreases. In other words, this particular condition, also called steal syndrome, is seen when there are extensive anastomoses between two vascular beds, and the arterial supply to one is stenosed or occluded, resulting in diversion of blood to the other vascular bed. This is a result of communication between the main vessels, sinusoids, and peribiliary venules, which open in response to the autonomic nervous system, and humoral factors activated by the liver’s demand for oxygen and metabolites. These lesions do not cause a mass effect on the vascular structures, and normal hepatic vascular structures can be seen passing through them. The lesions can be encountered in an entire lobe (lobar), segment (segmental), subsegment (subsegmental) or in a sub-capsular area of the liver. THADs may be noted to accompany hypervascular tumors, generally malignant but also benign (hepatocellular carcinoma, hypervascular metastases, cholangiocarcinoma, hemangioma, focal nodular hyperplasia, pyogenic abscess and focal eosinophilic necrosis) due to a steal syndrome [3]. However, they may also occur in patients without hepatic focal G. Parrinello D. Torres (&) G. Licata Biomedical Department of Internal and Specialty Medicine, Di.Bi.Mi.S., Internistic and Cardiovascular Diagnostic Ultrasound Laboratory, A.O.U Policlinico Paolo Giaccone, University of Palermo, Piazza delle Cliniche 2, 90127 Palermo, Italy e-mail: daniele_torres@libero.it