How MRI helps in diagnosing abnormal placental implantation

The management of a pregnant woman with PAS requires planned delivery, with a surgical team consisting of specialists from various fields, including obstetrician-gynecologists, vascular surgeons, interventional surgeons, anesthesiologists, transfusionists, neonatologists, and others, depending on the location of placental invasion into adjacent organs.

Timely prenatal diagnosis is crucial to ensure the proper management of such cases to reduce maternal and fetal complications. Diagnosing placenta accreta is challenging because of its vague clinical presentation and the absence of specific ultrasound signs in cases in which the placenta remains normally located and minimally invades the myometrium.

Ultrasound imaging is the "gold standard" for PAS diagnosis, but this method does not always allow visualization of the required area and reliable assessment of signs of invasion.

Many specialists suggest detecting PAS using magnetic resonance imaging (MRI), which is essential for accurate visualization and assessment of topography and tissue relationships, especially when the abnormal placentation is located along the posterior uterine wall and is inaccessible to ultrasound imaging.

This approach is the subject of an article (Journal of Obstetrics and Gynecology, No. 12) by specialists at Pavlov First St. Petersburg State Medical University.

In their study, the researchers investigated the potential of magnetic resonance imaging in optimizing the surgical treatment strategy in patients with placenta accreta spectrum. They analyzed the medical records of 87 patients who gave birth at an obstetrics and gynecology clinic. Pregnant women with placenta accreta (n=45, 52%) were divided into two groups based on the outcome of surgical delivery. Group 1 included 30 (66.7%) patients who underwent cesarean section and metroplasty, whereas Group 2 comprised 15 patients (33.3%) who had to undergo hysterectomy.  The diagnosis was confirmed postoperatively in all the patients through histopathological examination. The control group included 42 pregnant women (48 %) with no placental pathologies.

Based on the study findings, the researchers concluded that the most common MRI marker of placenta accreta, present in 82.2% of the cases, was an abnormal structure of the uteroplacental interface. The second most common marker was the presence of hypointense stripes in placental tissues, observed in 73.3% of the cases. When analyzing the sensitivity (Se) and specificity (Sp) indicators, the following results were obtained: disruption of the structure of the uteroplacental interface: Se 82.2%, Sp 76.2%; deformation of the bladder wall: Se 85.7%, Sp 81.6%; presence of wide hypointense bands in the placenta: Se 73.3%, Sp 100%; changes in the structure of placental tissue and thinning of the myometrium in the area of the lower segment: Se 64.4%, Sp 66.7%; intramural and parametric hypervascularization: Se 62.2%, Sp 83.3%.

Significantly, in forms of placenta accreta characterized by the deepest invasion into the cervix and underlying structures, such as the parametrium, the MRI marker "naked vessel" was encountered more frequently. In all cases with this sign found during the MRI studies, surgical delivery had to be completed with hysterectomy.

The researchers concluded by emphasizing that MRI is an adjunct to the diagnosis of placenta accreta. However, when it is necessary to assess pathological changes in uterine blood supply and topography of placental invasion, MRI is of greater interest than ultrasound imaging.