Colonic melanosis

Colon melanosis coli (MC) is a non-inflammatory bowel disease characterized by melanosis of the colonic mucosa. Its essence is that macrophages in the propria of the colonic mucosa contain a large amount of lipofuscin. There have been many foreign reports in the past and domestic reports. Less, colon melanosis has shown a clear upward trend in China in recent years. There are varying degrees of pigmentation on the normal mucosa of the colon, with brown or brown, black stripes or tiger skin-like localized or diffuse distributions. Those with polyps are pink or white. The submucosal vascular network is unclear. The colonic mucosal epithelial cells are generally normal, the submucosa is thickened and edema, there are a large number of dense or scattered macrophages in the lamina propria, the shape is irregular, the cytoplasm is full of pigment particles, the nucleus is covered (Figure 1), and sometimes giant Pigment particles can also be seen outside the phagocytic cells. In patients with severe colonic melanosis, macrophages and pigment particles containing pigment particles can also be seen in the submucosa or mesenteric lymph nodes. At this time, melanin staining (Fontana silver staining) is positive. Iron staining was negative, and the number and volume of macrophages were significantly increased in the lamina propria of the mucosa under electron microscope. A large amount of lipofuscin was deposited in the cytoplasm and surrounding connective tissue, near the myelinated nerve fibers of the intestinal plexus. Macrophages containing lipofuscin particles were also seen, and phagocytosis of fibroblasts was also seen.

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