2023 Volume 50 Issue 1 Pages 81-84
Superb Microvascular Imaging (SMI; Canon Medical Systems) can be used to detect minute vessels, which allows us to demonstrate pathological findings of the placenta antenatally. We report a case in which the placenta was not completely expelled for 6 days after delivery, and which was diagnosed as simple retained placenta not on the placenta accreta spectrum using SMI. On gray-scale ultrasonography, the entire uterine myometrium was thick and contracted without defect or thinning. A slightly hyperechoic mass image (placenta 4 cm in size) was found in the uterus. Scatter image indicated the maternal blood flow in the intervillous space could be depicted on all the maternal placental surface without any defects. Ultrasound diagnosis of simple retained placenta not on the placenta accreta spectrum was made, and we attempted placental manual removal under spinal anesthesia. Using placental forceps, placental tissue was detached easily and was completely removed. In the case of placenta accreta spectrum, invasion of placental tissue into the uterine myometrium is so great that a narrow intervillous space and reduced blood flow in the intervillous space may be observed. During investigation with SMI at such sites, a blood flow defect from the uterine myometrium to the intervillous space would be observed. In this case, since such flows were preserved, we could make the diagnosis of retained placenta without placental invasion. When making the diagnosis and determining the treatment strategy in patients with retained placenta, it would be helpful to evaluate the blood flow from the uterine myometrium into the intervillous space using SMI.
