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Placenta

Placental gross/microscopic abnormalities, non-neoplastic

Meconium staining

Reviewers: Mandolin Ziadie, M.D. (see Reviewers page)
Revised: 15 November 2011, last major update October 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.

Etiology
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● Passage of meconium in utero is due to bowel peristalsis and relaxation of anal sphincter and may be indicative of fetal distress
● Meconium components diffuse into placenta and cord, leading to vasoconstriction and hypoperfusion; damage to fetus increases with length of exposure
● Neonates are at risk for meconium aspiration
● Meconium is unlikely in fetuses prior to 30 weeks gestation

Gross description
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● Green-brown discoloration of the cord, fetal surface and membranes: differentiate between deposition of slimy green meconium across placental surface that is washed off with a gentle rinse (normal fetus that passes meconium shortly after delivery) and true mecomium staining (exposure to meconium for several hours)
● Membranes may be edematous or slimy

Gross images
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Green-black meconium

Micro description
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● Vacuolation of the amnionic epithelium, edema of the soft tissue plane between the amnion and chorion and pigment-laden macrophages within the amnion and chorion
● Prior to 34 weeks, pigment in the membranes is usually hemosiderin
● When prolonged, exposure to meconium can lead to necrosis of individual myocytes in the umbilical and chorionic plate vessels (meconium-induced vascular necrosis); this finding increases the risk of neurologic sequelae
● Mild - superficial necrotic or sloughed amniotic epithelium with meconium containing macrophages confined to the surface
● Moderate - ballooning of vacuolated amniotic epithelium with obvious meconium containing macrophages adjacent to chorionic tissue; indicates meconium discharge at least 2-3 hours before delivery
● Severe - moderate histologic findings but with more macrophages; may have meconium induced necrosis of umbilical vessels with myocyte necrosis; indicates fetal meconium discharge 6-12 hours before delivery
● Associated chorioamnionitis may be present but is not caused by meconium

Micro images
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Macrophages

End of Placenta > Placental gross/microscopic abnormalities, non-neoplastic > Meconium staining

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