![]() ![]() ![]() It also seems unlikely that this material could be effectively suctioned out of the airway postpartum. It is reasonable to speculate that had such an infant lived, this viscous material would have interfered with ventilation (see short case 1). Some autopsies of stillborn infants demonstrate large quantities of viscous meconium distending and plugging the proximal airways. This does not prove that meconium could not cause lung disease, but at least it is not inflammatory. In the absence of chorioamnionitis, they are not associated with inflammation. Scattered particles of meconium (squames and pigmented protein) or of vernix in the lung are visible markers of either shallow or deep inspiration. If there is deep gasping with asphyxia the content of the amniotic fluid will flood the lungs including invisible substances such as mediators of inflammation. The fetus in utero has shallow respiration that results in some aspiration of amniotic fluid content, including meconium if it is present. With chorioamnionitis there will be neutrophils and sometimes bacteria seen in the airways. In almost all stillborn lungs there are some squames, the shed surface epithelial cells of the skin, in the lung. Second is the observation of the effects of meconium on tissue. First is observation of what is anatomically found in the lungs The pathologist’s contribution to understanding meconium aspiration falls into two categories. Asphyxia and shock lung complicate attributing the syndrome of respiratory distress and pulmonary hypertension to the meconium per se. This potentially leads to the meconium aspiration syndrome, a topic reviewed in an article aptly entitled “Meconium aspiration syndrome: reflections on a murky subject” 7,8. ![]() If there is meconium in the amniotic fluid, whether from asphyxia or otherwise, the predictable result is that amniotic fluid with meconium will also be forcibly aspirated into the lung. Intrauterine asphyxia causes fetal gasping. The second exception is meconium aspiration syndrome. Conversely, infants with acute asphyxia often demonstrate meconium passage. Despite the relatively much more common benign passage of meconium, some studies show an association of meconium passage with fetal asphyxia or hypoxic/ischemic brain injury. Such acute severe asphyxia is relatively uncommon in human labor, but occurs for example in cord prolapse or uterine rupture. Severe acute asphyxia in the experimental model results in passage of meconium 6. The first exception is that meconium can be a marker of fetal asphyxia. Meconium passage does occur in many (up to 20%) of mature fetuses for no discernable reason and usually without serious consequence. One study relied on meconium corpuscles to identify aspirated meconium in early gestation, but this is suspect since such corpuscles are apoptotic bodies, and apoptotic cells are commonly found in the lungs of previable gestation infants without evidence of other material suggestive of meconium 2,5. Green amniotic fluid is frequently obtained with mid gestation amniocentesis, however this is most likely due to bile pigments formed directly from the breakdown of hemoglobin that has diffused into the fluid 2-4. There is some evidence that the fetus passes meconium in utero very early in gestation. Most infants, approximately 75%, do not pass visible meconium until after birth, and this may be due to an active suppression of the anal sphincter by signals such as corticotrophin releasing factor 1. The meconium is usually sterile, although in previable gestation infants with chorioamnionitis, neutrophils and even bacteria may be seen in the colon at autopsy. The former contributes the green yellow pigments biliverdin and bilirubin from hemoglobin digestion. The components include bile secreted from the liver, swallowed fetal amniotic fluid with its shed skin cells and lanugo hair, and proteins and cells contributed by the gastrointestinal tract. ![]() The material is green and readily seen in the colon during the autopsy of a stillborn infant. Meconium is the material collected in the fetal colon prior to birth. ![]()
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