Radiocolloid imaging in primary liver cancer and amoebic liver abscess. Accuracy of differential diagnosis and extent of inter-observer variability.

Radiocolloid liver scans from 58 patients with primary liver cancer and 56 patients with amoebic liver abscess were examined 'blind' and independently by three nuclear physicians and one registrar in training in order to evaluate the accuracy of the differential diagnosis between the two conditions and to assess the extent of inter-observer variability in the interpretation of these scans. Each of the observers incorrectly interpreted about 12% of scintiphotographs and at least one observer was wrong in 25% of the scans. The difference in diagnostic accuracy between individual observers was not statistically significant. Observers disagreed in 21,6% of the scans. The main reasons for misdiagnosis were failure to realize that excessive extrahepatic uptake of radiocolloid can occur with liver abscesses, and the indistinguishable appearance of the defect or defects in some cases of primary liver cancer and amoebic liver abscess. This margin of error and of inter-observer variability must be borne in mind when interpreting liver scans of patients thought to have either primary liver cancer of amoebic liver abscess.