MRI findings of chronic abruption-oligohydramnios sequence (CAOS): report of three cases

Chronic abruption-oligohydramnios sequence (CAOS), characterized by chronic vaginal hemorrhage and oligohydramnios, is a rare clinical condition of pregnancy. Because CAOS is associated with preterm delivery and lung injury to the infant, it is a major clinical concern. This report describes three CAOS cases which presented characteristic MRI findings reflecting CAOS pathological mechanisms and pathological findings. First, in all cases, the placenta detached from the uterus at the peripheral portion of the placenta because of placental marginal hematoma. Because the cause of CAOS is presumed to be chronic peripheral separation of the placenta developing from bleeding from the peripheral vein of the placenta, the MRI finding corresponds to the CAOS pathophysiology. Second, the placental marginal hematoma spread extensively along the decidua. This MRI finding can explain the vaginal hemorrhage of CAOS patients. Finally, the amniotic fluid of all patients showed high signal intensity on T1-weighted images, suggesting that amniotic fluid contains blood-derived products. In CAOS patients, chronic venous bleeding engenders the release of blood-derived products into the amniotic cavity. The aspiration of these products might be a cause of lung injury to the fetus. We presented these MRI findings with radiologic–pathologic correlation.