Meconium containing intestinal structures: a histological study using human fetuses

Meconium is changed from defoliated intestinal villi with apoptosis. A meconium corpuscle is a limited architecture in the meconium at the light microscopic level. In histological and immunohistochemical sections of the abdomen from 40 fetuses at 20-31 weeks of gestation, we found 12 fetuses with meconium and examined the architecture. A solid or loose meconium was seen depending on sites. The solid meconium in the colon and rectum contained numerous spherical or rugby ball-like corpuscles comprising of a core with tightly-packed atrophied cells and a laminar fibrous sheath. The solid meconium surrounded and incorporated villi that maintained the original architecture. The loose meconium was seen not only in the stomach and duodenum but also, depending on specimens, in the colon and rectum. It was composed of a large mucosal fold, a single small villus and/or fragmented epithelia. Notably, these mucosal tissues still contained chromogranin-positive gastrointestinal cells and cytokeratin-positive epithelia. A large ring-like meconium was composed of the entirely circular mucosa or epithelia that seemed to be detached along the muscularis mucosae or the basal lamina. A sheath-like fibrous structure in meconium seemed to originate from the lamina propria and basal lamina of villi. A defoliation of villi with apoptosis seemed difficult to explain a detachment of the entirely circular mucosa or epithelia in large fetuses examined. The latter event might require a specific mechanism such as an <i>in utero</i> intussusception in which a proximal side of the colon was invaginated into the distal lumen.