Sequential changes of sonographic and computed tomography findings in the normal rabbit liver after percutaneous ethanol injection. Correlation with pathologic findings.

RATIONALE AND OBJECTIVES

The authors assessed the sequential sonographic and computed tomographic (CT) findings and their correlations with pathologic findings of the normal rabbit liver after percutaneous ethanol injection (PEI).

METHODS

In 30 anesthetized rabbits, 1 mL of ethanol was injected percutaneously under sonographic guidance. The animals were divided into five groups of six rabbits each according to the times of sonography and CT examinations after PEI: day 1 (immediately after), day 3, week 1, week 2, and week 4. The radiologic findings were analyzed regarding echogenicity (sonography) and density patterns before and after contrast administration (CT). The relations between radiologic findings and pathologic findings were examined using statistical analysis. The lesion size was measured using sonography and CT and compared with the actual size of the pathologic specimen.

RESULTS

Sonography and CT showed various radiologic findings according to the time elapsed after PEI. The livers were hyperechoic in 100% (6/6) of the rabbits on day 1; this changed to isoechoic (67%, 12/18) or slightly hypoechoic (22%, 4/18) after week 1 through week 4 after PEI on sonography. CT scanning showed well-defined, hypodense lesions with no contrast enhancement in 100% (6/6) of the rabbits on day 1, and the lesions were slightly hypodense and relatively poorly defined in 88% (21/24) after day 3. Peripheral enhancement was noted in 83% (15/18) after week 1. Histopathologic examination revealed thrombosis and atrophic hepatic cell cords correlating well with hyperechogenicity on sonography and very low density on CT immediately after PEI. Coagulation necrosis was a main pathologic finding in the central portion of the lesions after day 3 and correlated with the CT findings of central low density without contrast enhancement. After week 1, peripheral granulation tissue and fibrosis were correlated with peripheral contrast enhancement on CT. Lesion size was largest in the week 1 group, and the size difference was statistically significant between the week 1 group and the day 1 group.

CONCLUSIONS

Sonographic and CT findings of the PEI-treated normal rabbit liver varied with time in a predictable manner and correlated with pathologic findings. After a week, the PEI-treated normal liver shows perilesional enhancement that is nodular and irregular (particularly until 2 weeks); this must be taken into account when evaluating the therapeutic effect after PEI using conventional CT studies. Although long-term data are missing, control CT scans for residual tumor should not be performed before the second week after PEI because of the difficulty discerning enhancing tumor from enhancing fibrosis.