Evaluation and interpretation of iron in the liver.
Faced with hepatic siderosis, the pathologist must (1) determine the parenchymal, mesenchymal, or mixed type of iron overload; (2) quantify liver iron by either histology or biochemistry; (3) seek for associated iron-related lesions, especially sideronecrosis, fibrosis, and iron-free-foci; and (4) assess any other liver damage. The discovery of the HFE gene has modified the management of hemochromatosis. Because homozygosity for the C282Y mutation is diagnostic of the condition regardless of the liver iron concentration-to-age ratio, indication for liver biopsy in C282Y homozygotes is restricted to the assessment of prognostic lesions, such as fibrosis and iron-free-foci. In patients with a phenotype compatible with hemochromatosis but nonhomozygous for the C282Y mutation, liver biopsy remains mandatory to assess nonhemochromatosis causes of iron overload (rare hereditary defects of iron metabolism and transport and iron overload secondary to polymetabolic syndrome, to porphyria cutanea tarda, or to cirrhosis). The evaluation of iron distribution within liver cells and throughout lobules and the assessment of associated lesions are the most important features that allow for correct classification of nonhemochromatosis iron-overload syndromes.