RATIONALE AND OBJECTIVES. To elucidate the characteristic clinicopathologic features of hepatocellular carcinomas (HCCs) undetected on two-phased incremental computed tomography (CT). methods. Computed tomographic scans of 115 surgically resected small (≤3 cm) HCCs from 83 patients were performed 45 seconds and 6 minutes after the administration of contrast material. These scans were compared with corresponding angiographic and histopathologic findings. RESULTS. Eighty HCCs (70%) were depicted on the early images; 73 (63%) on the delayed images; and 89 (77%) using two-phased incremental CT. The small HCCs undetected on the early images but seen histologically had the following characteristics: (1) absence of a fibrous capsule, (2) well-differentiated tumor, (3) replacing growth patterns of the tumors, (4) lack of fatty metamorphosis and/or clear cell changes, (5) liy-povascular on angiography. Those not seen on delayed images had the following characteristics: (1) absence of a fibrous capsule, (2) replacing growth patterns, and (3) presence of portal tracts in the tumors. conclusions. The replacing growth pattern and the presence of portal tracts correlate with the undetectability on CT. For HCCs undetected on CT, treatment methods must be considered carefully, because the HCCs may be receiving transsi-nusoidal and portal blood supplies.
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