Colloidal iron staining used for amniotic fluid in lung sections of stillborn infants in histopathology

In forensic pathology, intrauterine amniotic fluid aspiration must be examined in lung sections of a stillborn fetus in late pregnancy. Alcian blue staining and immunohistochemistry are routinely performed using anti-cytokeratin antibody to detect the components. Colloidal iron staining is another method for acidic mucus polysaccharides. Retrospectively, we examined 15 forensic cases of stillborn and neonatal deaths with autopsies conducted at our department. Colloidal iron staining caused positive features of amniotic mucin in 14 cases, but Alcian blue staining could not be confirmed clearly in 8 cases because of weak color development. For detection of amniotic mucin, colloidal iron staining showed a richer color with contrast than other methods. Moreover, mucin masses were observed in two live-born infants, and in all stillborn infants, one of which was clinically diagnosed as having meconium aspiration syndrome. Non-specific reaction to iron ions such as hemosiderin-phagocytic macrophages might occur in the lung sections. However, colloidal iron staining should be the alternative routine for lung tissue from stillborn infants.