Amnion nodosum (placenta)
A 32 year old woman presented with PV bleeding 17 weeks into her second pregnancy. Ultrasound confirmed foetal death in utero. A misoprostol-induced labour took place and the placenta was sent for examination. Macroscopic examination revealed a 40g relatively intact placenta showing no significant macroscopically-evident abnormalities. The foetus was morphologically unremarkable and fresh tissue was sent for genetic karyotyping.
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The membranes showed no significant acute inflammatory cell infiltrate that would indicate an acute chorioamnionitis, however, as you can see from the images above, scattered clusters of intensely eosionphilic cellular material were present on the amniotic surface of the membranes. These clusters displayed varying degrees of degenerative change and appeared mostly amorphous and granular, but where more preserved, appeared to be partly composed of degenerate foetal squames. Careful inspection also revealed hemosiderin deposition (may not be seen in these images).
Clinical Association: Severe oligohydramnios (associated with foetal renal agenesis, prolonged premature rupture of membranes - also higher % in mothers with gestational diabetes and pre-eccplampsia)
Pathogenesis: There are a couple of ways that oligohydramnios is thought to result in amnion nodosum: firstly, that the concentrated amniotic fluid starts to adhere to the amniontic surface, causing degeneration of amniotic epithelium, and/or secondly, that in the context of reduced amniotic fluid volume, there is an increase in contact between the foetal and amniotic epithelium, causing erosion and resulting in foetal squames shedding and being incorporated into the eroded surface.
Other findings in this case: The placental disk also showed a mild diffuse chronic villitis without evidence of viral inclusions and chronic deciduitis along with changes consistent with uteroplacental malperfusion and foetal death in utero (prominent syncytial knots, decreased terminal villi showing sclerosis and loss of vessels and resultant increased intervillous space, intra-capillary karyorrhectic debris and obliteration of larger foetal vessels).
- Adeniran AJ, Stanek J. Amnion nodosum revisited: clinicopathologic and placental correlations. Arch Pathol Lab Med, 2007 Dec;131(12):1829-33. Full article link (free access)