Temporal evolution of diffusion lacunae into thrombus: A case report with serial MRI and MR–pathologic correlation

We report a case demonstrating the evolution of diffusion lacunae (DL) into thrombus, supported by serial MRI and MR–pathologic correlation. A 36-year-old woman with a pregnancy achieved via frozen–thawed embryo transfer presented with complete placenta previa and vaginal bleeding. MRI at 27 weeks of gestation revealed an irregular intraplacental hypointense area on diffusion-weighted imaging corresponding to DL. Follow-up MRI at 32 weeks showed that the DL had become less discernible and appeared hyperintense, similar to the surrounding placenta. On the following day, the patient developed hemorrhagic shock and underwent emergency cesarean delivery, without evidence of placental adherence and decidual deficiency, indicating that the DL represented a placental lake rather than placental lacunae. Histopathologic examination demonstrated a paucity of chorionic villi and thrombus formation with lines of Zahn in the DL area. These findings provide direct evidence that DL may undergo thrombus formation over time, reflecting dynamic changes related to blood flow stasis within the placenta.