Chronic abruption-oligohydramnios sequence (CAOS) revisited: possible implication of premature rupture of membranes

Aim The pathogenic mechanism of chronic abruption-oligohydramnios sequence (CAOS) remains unknown, and there are no objective standards for diagnosis on imaging or using pathological evidence. We aimed to reconsider and clarify the true pathology of CAOS by integrating clinical, magnetic resonance imaging (MRI) and histopathological findings of the placenta. Material and Methods This is a case series of patients with CAOS managed at our hospital between 2010 and 2020. The clinical data of the patients, including MRI findings and placental pathology, were reviewed retrospectively. Results A total of 18 patients were eligible. Preterm birth occurred in 17 (94%) cases; the median gestational age at delivery was 25. Three neonates (17%) died within two years, and 10 neonates (56%) developed chronic lung disease. MRI was performed in 13 cases and clearly showed intrauterine hematoma and hemorrhagic amniotic fluid. Pathologically, in all cases, retroplacental hematoma was not detected, and fetal membranes were extremely fragile and ragged. Shedding and necrosis of the amniotic epithelium was a characteristic finding, which was confirmed in 17 cases (94%). Diffuse chorionic hemosiderosis (DCH) was detected in all cases. Conclusions The fundamental cause of CAOS is repeated intrauterine hemorrhage and subsequent subchorionic hematoma, which induces hemorrhagic amniotic fluid and DCH. Consequently, these factors result in the necrosis and weakening of the amnion. Therefore, the true pathology of CAOS is believed to be premature rupture of membranes rather than chronic abruption.

Automated summary

The pathogenic mechanism of chronic abruption-oligohydramnios sequence (CAOS) remains unknown, with no objective standards for diagnosis on imaging or using pathological evidence. This study aimed to clarify the true pathology of CAOS through integration of clinical, magnetic resonance imaging (MRI) and histopathological findings. A retrospective review of clinical data, MRI findings and placental pathology of 18 patients with CAOS between 2010 and 2020 showed preterm birth in 94% of cases, with median gestational age at delivery of 25 weeks. Three neonates (17%) died within two years, and 10 neonates (56%) developed chronic lung disease. MRI revealed intrauterine hematoma and hemorrhagic amniotic fluid, while histopathological findings showed shedding and necrosis of the amniotic epithelium as a characteristic feature in 94% of cases. Diagnosis of diffuse chorionic hemosiderosis (DCH) was confirmed in all cases. The true pathology of CAOS is believed to be premature rupture of membranes rather than chronic abruption, caused by repeated intrauterine hemorrhage and subchorionic hematoma leading to necrosis and weakening of the amnion.