Massive platelet‐rich thrombus formation in small pulmonary vessels in amniotic fluid embolism: An autopsy study.

Objective: To identify pulmonary/uterine thrombus formation in amniotic fluid embolism (AFE). Design: Retrospective, observational. Setting: Nationwide. Population: Eleven autopsy cases of AFE and control cases. Methods: We assessed pulmonary and uterine thrombus formation and thrombus area in AFE and pulmonary thromboembolism (PTE) as a control. The area of platelet glycoprotein IIb/IIIa, fibrin, neutrophil elastase, citrullinated histone H3 (a neutrophil extracellular trap marker) and mast cell chymase immunopositivity was measured in 90 pulmonary emboli, 15 uterine thrombi and 14 PTE. Main outcome measures: Pathological evidence of thrombus formation and its components in AFE. Results: Amniotic fluid embolism lung showed massive thrombus formation, with or without amniotic emboli in small pulmonary arteries and capillaries. The median pulmonary thrombus size in AFE (median, 0.012 mm2; P < 0.0001) was significantly smaller than that of uterine thrombus in AFE (0.61 mm2) or PTE (29 mm2). The median area of glycoprotein IIb/IIIa immunopositivity in pulmonary thrombi in AFE (39%; P < 0.01) was significantly larger than that of uterine thrombi in AFE (23%) and PTE (15%). The median area of fibrin (0%; P < 0.001) and citrullinated histone H3 (0%; P < 0.01) immunopositivity in pulmonary thrombi in AFE was significantly smaller than in uterine thrombi (fibrin: 26%; citrullinated histone H3: 1.1%) and PTE (fibrin: 42%; citrullinated histone H3: 0.4%). No mast cells were identified in pulmonary thrombi. Conclusions: Amniotic fluid may induce distinct thrombus formation in the uterus and lung. Pulmonary and uterine thrombi formation may contribute to cardiorespiratory collapse and/or consumptive coagulopathy in AFE. [ABSTRACT FROM AUTHOR]