Hepatic Arterioportal Shunts: Dynamic CT and MR Features

With the increased temporal resolution available in dynamic computed tomography (CT) and magnetic resonance imaging (MRI), hepatic arterioportal shunts are now more frequently encountered than in the past. The condition occurs in various hepatic diseases in which portal or hepatic venous flow is compromised. The underlying mechanism and the degree of shunt affect its appearance at dynamic imaging. The dynamic CT and MRI findings have been summarized as early enhancement of peripheral portal veins, and wedge-shaped transient parenchymal enhancement during the hepatic arterial phase. Recognition of arterioportal shunt can suggest the presence of a previously unsuspected disorder and avoids false-positive diagnosis or overestimation of a hepatic disease. Familiarity with the pathophysiology of arterioportal shunt also allows investigation of the hepatic hemodynamic changes occurring in various hepatic diseases.

Wedge-shaped Parenc hymal Enhancement Peripheral to the Hepatic Hemangioma: Two-phase Spiral CT Findings

PURPOSE: To determine the incidence of hepatic hemangiomas associated with wedge-shaped parenchymal enhancements adjacent to the tumors as seen on two-phase spiral CT images obtained during the hepatic arterial phase and to characterize the two-phase spiral CT findings of those hemangiomas. MATERIALS AND METHODS: One hundred and eight consecutive hepatic hemangiomas in 63 patients who underwent two-phase spiral CT scanning during an 11-month period were included in this study. Two-phase spiral CT scans were obtained during the hepatic arterial phase(30-second delay) and portal venous phase(65-second delay) after injection of 120mL of contrast material at a rate of 3mL/sec. We evaluated the frequency with which wedge-shaped parenchymal enhancement was adjacent to the hemangiomas during the hepatic arterial phase and divided hemangiomas into two groups according to whether or not wedge-shaped parenchymal enhancement was noted (Group A and Group B). The presence of such enhancement in hemangiomas was cor-related with tumor size and the grade of intratumoral enhancement. RESULTS: In 24 of 108 hemangiomas, wedge-shaped parenchymal enhancement adjacent to hepatic tumors was seen on two-phase CT images obtained during the hepatic arterial phase. Mean hemangioma size was 22mm in Group A and 24mm in Group B. There was no statistically significant relationship between lesion size and the presence of wedge-shaped parenchymal enhancement adjacent to a hemangioma. In 91.7% and 1 00% of tumors in Group A, and in 9.6% and 17.8% in Group B, hemangiomas showed more than 50% intra-tumoral enhancement during the arterial and portal venous phase, respectively. Wedge-shaped parenchymal enhancements peripheral to hepatic hemangiomas was more frequently found in tumors showing more than 50% intratumoral enhancement during these two phases(p<0.01). CONCLUSION: Wedge-shaped parenchymal enhancements is not uncommonly seen adjacent to hepatic heman-giomas on two-phase spiral CT images obtained during the hepatic arterial phase. A hemangioma showing-wedge-shaped parenchymal enhancement tends to show more than 50% intratumoral enhancements during the arterial and portal venous phase.

Nontumorous Perfusion Defects in the Liver during CT Arterial Portography: Correlation with Hepatic Arteriography

PURPOSE: To determine the relation between characteristic findings of hepatic arteriography and nontumorous perfusion defects which on CT arterioportography (CTAP) had been inadequately described. MATERIALS AND METHODS: To identify pseudolesions, the CTAP results of 46 patients with perfusion defects which were not recognized on conventional CT or ultrasonography were reviewed and compared with MRI, iodized-oil CT, surgical findings, and histopathologic reports. Typical and atypical pseudolesions were divided according to location, shape and cause, as revealed in previous reports. The number, shape and the location of pseudolesion seen on CTAP were determined and hepatic arteriography correlatively reviewed to determine vascular change in the corresponding area. RESULTS: Seventy-two additional lesions of 46 patients were detected. Among these, 12 cases were true lesions. Sixty pseudolesions were divided into typical (n = 18) and atypical (n = 42) ; the typical pseudolesions were found in familiar locations adjacent to the porta hepatis, falciform ligament or gall bladder and except for increased vascular staining around the gall bladder in two lesions, specific vascular changes were not seen. The shapes of the atypical pseudolesion were wedged (n = 22), nodular (n = 15) and flat (n = 5). They were located subcapsularly (n= 30) or nonspecifically within liver parenchyma (n = 12). The early appearance of a small portal vein branch with subsequent focal hepatic parenchymal staining, which suggests a small AP shunt, was identified on the hepatic arteriography, and on CTAP matched the areas of 96% atypical pseudolesions (26/34) which were more than 1cm in size. CONCLUSION: A small AP shunt should be regarded as a cause of nontumorous, nonsegmental perfusion defectson CTAP.

Small Arterioportal Shunt: A Pseudolesion Mimicking Hepatocellular Carcinoma in Angiography

PURPOSE: To document the findings of a small arterioportal(AP) shunt on hepatic angiography through the various diagnostic modalities, and to determine whether this shunt is related to hepatocelluar carcinoma. MATERIALS AND METHODS: During the hepatic angiography in 223 patients, a small AP shunt and subsequent focalparenchymal staining more than 1cm in diameter were found in 28 patients. We compared this angiographic abnormality using MR imaging(n=10), CTAP(n=12), iodized-oil CT(n=23), intraoperative ultrasonography(n=5) and follow-up hepatic angiography(n=11), as well as with conventional ultrasonography and CT scan. RESULTS: Arterioportal shunts noted on angiographic study matched with perfusion defects noted in CTAP(10/12) and also with the area of arterial enhancement seen on dynamic CT scan(3/4). In no case was a lesion found on MR and no Lipiodol uptake was seen on CT. There was no evidence of tumor growth around the AP shunts on follow-up angiographies, andno tumor was found during surgery. CONCLUSION: A small AP shunt was not related to the presence of a tumor. Ifthe hemodynamic changes resulfing from a small AP shunt are understood, confusion can be avoided in the interpretation of vascular imaging including CTAP and dynamic CT.