Chemical Shift Artifact on Steady-State MRI Sequences for Detection of Vesical Wall Invasion in Placenta Percreta

Bladder involvement in placenta accreta spectrum disorder with placenta previa: MRI findings and outcomes correlation

BACKGROUND

Placental accreta spectrum (PAS) disorder with bladder involvement can be associated with maternal and neonatal morbidity. Magnetic resonance imaging (MRI) may provide accurate preoperative diagnoses.

OBJECTIVE

This study had 2 aims: to retrospectively review the MRI findings for bladder involvement in PAS with placental previa and to correlate bladder involvement with maternal and neonatal outcomes.

MATERIALS AND METHODS

MRI images of 48 patients with severe PAS (increta and percreta) with placenta previa/low-lying placenta were evaluated by 2 experienced radiologists blinded to the final diagnoses. Nine MRI findings and stepwise logistic regression analysis were assessed to identify predictive MRI findings for bladder involvement. The correlations between PAS patients with bladder involvement and clinical outcomes were analyzed using Fisher's exact test.

RESULTS

Of the 48 patients, 27 did not have bladder involvement, while 21 did. Logistic regression analysis identified 2 predictive MRI features for bladder involvement. They were abnormal vascularization (OR,6.94; 95 %CI,1.05-45.75) and loss of the chemical shift line at the uterovesical interface (OR, 4.41; 95 %CI, 0.63-30.98). The sensitivity and specificity of the combined MRI features were 38.1 % and 100 %, respectively (p = 0.001). A significant correlation was found between bladder involvement and massive blood loss during surgery (p = 0.022).

CONCLUSIONS

PAS with bladder involvement was significantly correlated with massive surgical blood loss. Prenatally, the disorder was predicted with high specificity by the combination of loss of chemical shift artifacts in the steady-state free precession sequence and abnormal vascularization at the uterovesical interface on MRI.

Comparison of T2-weighted and diffusion-weighted imaging for the diagnosis of placenta accreta spectrum abnormality

Background

Diffusion-weighted imaging (DWI) is feasible in prenatal imaging, and it exhibits better contrast between the placenta and the myometrium compared to T2-weighted (T2W) images.

Purpose

To compare magnetic resonance imaging (MRI) features of placenta accreta on T2W and DW imaging.

Material and Methods

In this retrospective study, 42 pregnant patients who underwent prenatal MRI were included. MRI was performed on a Siemens 1.5-T scanner. T2W and DWI sequences in the axial, sagittal, and/or coronal planes were compiled for review. Two radiologists independently interpreted T2W and DW images for placenta accreta. T2W and DWI scores were calculated based on the presence of features and graded as low, intermediate, and high risk. The association between imaging features and placental invasion on pathology was calculated using chi-square tests. Sensitivity, specificity, and positive and negative predictive values (NPV) were compared between T2W and DWI interpretations. Inter-reader agreement between the two radiologists for T2W and DWI scores was calculated using Cohen's kappa coefficient.

Results

Out of 42 pregnant patients, 10 were pathologically/surgically proven to have placenta accreta. There were no significant differences between T2W and DWI interpretations. Considering a cutoff >6 as positive, the T2W score had higher sensitivity (90% vs. 80%) and NPV (96.9% vs. 94.1%) than the DWI score. The specificity and positive predictive value were 100% for both scores. The inter-reader agreement of T2W score was higher (k = 0.943 vs. 0.882).

Conclusion

T2W and DWI are comparable in diagnosing placenta accreta spectrum. T2W sequences have higher sensitivity, NPV, and inter-reader agreement than DWI.

Utility of multiparametric MRI in Caesarean section scar characterization and preoperative prediction of scar dehiscence: a prospective study

Background Post-Caesarean uterine scar rupture during vaginal birth after Caesarean section (VBAC) is a potentially life-threatening complication. Prediction of scar dehiscence and scar rupture is vital in treatment planning and selecting candidates of trial of labor after a Caesarean section (CS). Purpose To assess the accuracy of magnetic resonance imaging (MRI) for evaluation of post-Caesarean uterine scar and to predict scar dehiscence during repeat CS. Material and Methods Thirty patients with a history of at least one previous CS underwent pelvic MRI for assessment of uterine scar during a subsequent gestation, all of whom underwent lower segment Caesarean section (LSCS) subsequently due to one of the established indications of CSs. Thickness, T1, T2 signal intensity ratio (SER), and apparent diffusion coefficient (ADC) value of scar site were charted. The lower uterine segment was assessed and graded intraoperatively and findings were correlated with MRI findings. Results A total of 30 participants were included in this study, of which nine were classified as having an abnormal scar (of various grades) based on surgical observations. T2 SER with a cutoff value of 0.935 showed the highest sensitivity of 100% and scar thickness value of 3.45 mm showed highest specificity of 91% in prediction of abnormal scar. On drawing a receiver operating characteristic (ROC) curve, T2 signal intensity ratio showed the highest area under the curve (AUC) closely followed by scar thickness values. Conclusion MRI derived parameters may be utilized for differentiation of an abnormal post-Caesarean uterine scar from a normal one. Both scar thickness and T2 SER measured on MRI can be used to predict scar dehiscence. However, T2 SER can serve as a more standardized and objective criterion.