[Ultrasonic diagnosis of liver tumors--with special reference to its limitations in predicting histology]

Since 1980, ultrasound has become the main diagnostic modality in detecting small hepatocellular carcinomas. We laparotomized 72 patients with 93 hepatocellular carcinomas less than 5 cm in diameter and resected 86 tumors in 68 patients. Sensitivities for these small hepatocellular carcinomas were: ultrasound 90.1%, angiography 86.8%, and CT 91.3%. Ultrasound was the most excellent diagnostic modality in diagnosing the location of the tumor, because of its capability of demonstrating the portal and the hepatic venous branches simultaneously. The characteristics of small hepatocellular carcinomas were a mosaic pattern of internal echos, posterior echo enhancement, thin halo and lateral shadows. These findings were recognized in 68%, 61%, 37% and 18% of cases respectively. However, most of the tumors less than 2 cm appeared as simple low-echo areas. In tumors measuring from 2.1 to 5 cm, these findings were demonstrated in 77%, 74%, 48% and 23% of cases respectively. Liver tumors with a mosaic pattern and posterior echo enhancement were seen only in case of hepatoma. Predictability of hepatocellular carcinoma with these two findings was 60% in patients with hepatocellular carcinomas 2.1 to 5 cm in diameter. Predicting the histology of liver tumors less than 2 cm in diameter was difficult with any diagnostic modalities. However, since small hemangiomas less than 2 cm in diameter were delineated as characteristic echogenic areas, there were patients in whom only ultrasound could predict the tumor histology, even if other diagnostic methods could not. In order to diagnose the histology of small liver tumors, ultrasonically guided aspiration cytology has been generally accepted as a reliable procedure. However aspiration cytology made correct diagnoses in about half the tumors which could not be predicted with any other diagnostic modalities. Among hepatomas less than 2 cm in diameter, those due to low grade malignancy hepatocellular carcinomas are very common (33%). Needle biopsy of the tumor is therefore indispensable.