Magnetic resonance imaging improves diagnosis of placenta accreta spectrum requiring hysterectomy compared to ultrasound

Abstract

Background: Magnetic resonance imaging has been used increasingly as an adjunct for ultrasound imaging for placenta accreta spectrum assessment and preoperative surgical planning, but its value has not been established yet. The ultrasound-based placenta accreta index is a well-validated standardized approach for placenta accreta spectrum evaluation. Placenta accreta spectrum-magnetic resonance imaging markers have been outlined in a joint guideline from the Society of Abdominal Radiology and the European Society of Urogenital Radiology.

Objective: This study aimed to compare placenta accreta spectrum-magnetic resonance imaging parameters with the ultrasound-based placenta accreta index in pregnancies at high risk for placenta accreta spectrum and to assess the additional diagnostic value of magnetic resonance imaging for placenta accreta spectrum that requires a cesarean hysterectomy.

Study design: This was a single-center, retrospective study of pregnant patients who underwent magnetic resonance imaging, in addition to ultrasonography, because of suspected placenta accreta spectrum. The ultrasound-based placenta accreta index and placenta accreta spectrum-magnetic resonance imaging parameters were obtained. Student's t test and Fisher's exact test were used to compare the groups in terms of the primary outcome (hysterectomy vs no hysterectomy). The diagnostic performance of magnetic resonance imaging and the ultrasound-based placenta accreta index was assessed using multivariable logistic regressions, receiver operating characteristics curves, the DeLong test, McNemar test, and the relative predictive value test.

Results: A total of 82 patients were included in the study, 41 of whom required a hysterectomy. All patients who underwent a hysterectomy met the International Federation of Gynecology and Obstetrics clinical evidence of placenta accreta spectrum at the time of delivery. Multiple parameters of the ultrasound-based placenta accreta index and placenta accreta spectrum-magnetic resonance imaging were able to predict hysterectomy, and the parameter of greatest dimension of invasion by magnetic resonance imaging was the best quantitative predictor. At 96% sensitivity for hysterectomy, the cutoff values were 3.5 for the ultrasound-based placenta accreta index and 2.5 cm for the greatest dimension of invasion by magnetic resonance imaging. Using this sensitivity, the parameter of greatest dimension of invasion measured by magnetic resonance imaging had higher specificity (P=.0016) and a higher positive predictive value (P=.0018) than the ultrasound-based placenta accreta index, indicating an improved diagnostic threshold.

Conclusion: In a suspected high-risk group for placenta accreta spectrum, magnetic resonance imaging identified more patients who will not need a hysterectomy than when using the ultrasound-based placenta accrete index only. Magnetic resonance imaging has the potential to aid patient counseling, surgical planning, and delivery timing, including preterm delivery decisions for patients with placenta accreta spectrum requiring hysterectomy.

Keywords: MRI; hysterectomy; placenta accreta index; placenta accreta spectrum; ultrasound.

FIGURE 1. Flowchart of selection of pregnant patients included in this study

MRI, magnetic resonance imaging; PAS, placenta accreta spectrum; US-PAI, ultrasound-based placenta accreta index.

FIGURE 2. Ultrasound and MRI images of a PAS case requiring hysterectomy

A−F, 30 year-old patient, gravida 2, para 1, with a history of 1 cesarean delivery and vasa previa (arrows, A: transvaginal ultrasound image; D: sagittal bSSFP=Balanced Steady State Free Precession MR image). The placenta accreta index was 5 with an anterior low-lying placenta (<2 cm from the internal os), grade 3 lacunae, multiple bridging vessels (arrowheads, B: transabdominal US image), and smallest anterior myometrial thickness of <1 mm. MRI reports noted partial placenta previa, an anterior bulge (arrows, F: axial T2W MR image), and multiple dark linear intraplacental bands and along the bladder serosal interface (arrows, C and E: sagittal and axial T2W MR image). The greatest dimension of invasion measured by MRI was 13.7 cm. MRI, magnetic resonance imaging.

FIGURE 3. ROC curves of US-PAI and major PAS-MRI parameters predicting hysterectomy outcome

Receiver operating characteristic (ROC) curves for the greatest dimension of invasion by MRI (AUC, 0.93; 0.88−0.98), radiologist impression of invasion degree (AUC, 0.94; 0.89−0.98), and US-PAI (AUC, 0.86; 0.79−0.94) with differentiation between hysterectomy no hysterectomy outcomes. A line demonstrating a 96% sensitivity threshold is included. AUC, area under the curve; MRI, magnetic resonance imaging; US-PAI, ultrasound-based placenta accreta index.

FIGURE 4. Scatter plot of US-PAI and greatest dimension of invasion by MRI values comparing hysterectomy and no hysterectomy groups

The cutoff points to achieve a sensitivity of 96% for the 2 parameters are indicated. MRI, magnetic resonance imaging; US-PAI, ultrasound-based placenta accreta index.