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.