Long Term Effects of Thorium Dioxide (Thorotrast) Administration on Human Liver Ultrastructual Localization of Thorium Dioxide in Human Liver by Analytical Electron Microscopy

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Abstract
The ultrastructural localization of thorium dioxide was examined in liver biopsy specimens from 2 patients injected > 30 yr before with thorotrast [a carcinogenic hepatotoxic contrast medium]. An energy dispersive X-ray microanalysis spectrometer (Kevex 5100) was used to identify Th in the liver tissue. By EM, most of the Th particles were found in the cells of the RES, such as macrophages of the portal triad and Kupffer cells in the hepatic sinusoid. Thorium dioxide particles were mainly located within the phagosomes, but larger aggregates existed in the cytoplasm with no visible limiting membrane. The deposition of Th granules in a few hepatocytes was also confirmed by EM. Two main pathways of elimination were evidently still functioning in the late period, but the hepatocytic pathway appears to be less effective than the RES.