Nomogram model for predicting invasive placenta in patients with placenta previa: integrating MRI findings and clinical characteristics

This study aims to validate a nomogram model that predicts invasive placenta in patients with placenta previa, utilizing MRI findings and clinical characteristics. A retrospective analysis was conducted on a training cohort of 269 patients from the Second Affiliated Hospital of Fujian Medical University and a validation cohort of 41 patients from Quanzhou Children's Hospital. Patients were classified into noninvasive and invasive placenta groups based on pathological reports and intraoperative findings. Three clinical characteristics and eight MRI signs were collected and analyzed to identify risk factors and develop the nomogram model. The mode's performance was evaluated in terms of its discrimination, calibration, and clinical utility. Independent risk factors incorporated into the nomogram included the number of previous cesarean sections ≥ 2 (odds ratio [OR] 3.32; 95% confidence interval [CI] 1.28-8.59), type-II placental bulge (OR 17.54; 95% CI 3.53-87.17), placenta covering the scar (OR 2.92; CI 1.23-6.96), and placental protrusion sign (OR 4.01; CI 1.06-15.18). The area under the curve (AUC) was 0.908 for the training cohort and 0.803 for external validation. The study successfully developed a highly accurate nomogram model for predicting invasive placenta in placenta previa cases, based on MRI signs and clinical characteristics.

Placenta accreta spectrum in early and late pregnancy from an imaging perspective. A scoping review

Placenta accreta spectrum (PAS) disorders (with increasing order of the depth of invasion: accreta, increta, percreta) are quite challenging for the purpose of diagnosis and treatment. Pathological examination or imaging evaluation are not very dependable when considered as stand-alone diagnostic tools. On the other hand, timely diagnosis is of great importance, as maternal and fetal mortality drastically increases if patient goes through the third phase of delivery in a not well-suited facility. A multidisciplinary approach for diagnosis (incorporating clinical, imaging, and pathological evaluation) is mandatory, particularly in complicated cases. For imaging evaluation, the diagnostic modality of choice in most scenarios is ultrasound (US) exam; patients are referred for MRI when US is equivocal, inconclusive, or not visualizing placenta properly. Herewith, we review the reported US and MRI features of PAS disorders (mainly focusing on MRI), going over the normal placental imaging and imaging pitfalls in each section, and lastly, covering the imaging findings of PAS disorders in the first trimester and cesarean section pregnancy (CSP).

Prediction of placenta accreta spectrum in patients with placenta previa using a clinical, US and MRI combined model: A retrospective study with external validation

PURPOSE

To build and validate a predictive model of placental accreta spectrum (PAS) in patients with placenta previa (PP) combining clinical risk factors (CRF) with US and MRI signs.

METHOD

Our retrospective study included patients with PP from two institutions. All patients underwent US and MRI examinations for suspicion of PAS. CRF consisting of maternal age, cesarean section number, smoking and hypertension were retrieved. US and MRI signs suggestive of PAS were evaluated. Logistic regression analysis was performed to identify CRF and/or US and MRI signs associated with PAS considering histology as the reference standard. A nomogram was created using significant CRF and imaging signs at multivariate analysis, and its diagnostic accuracy was measured using the area under the binomial ROC curve (AUC), and the cut-off point was determined by Youden's J statistic.

RESULTS

A total of 171 patients were enrolled from two institutions. Independent predictors of PAS included in the nomogram were: 1) smoking and number of previous CS among CRF; 2) loss of the retroplacental clear space at US; 3) intraplacental dark bands, focal interruption of the myometrial border and placental bulging at MRI. A PAS-prediction nomogram was built including these parameters and an optimal cut-off of 14.5 points was identified, showing the highest sensitivity (91%) and specificity (88%) with an AUC value of 0.95 (AUC of 0.80 in the external validation cohort).

CONCLUSION

A nomogram-based model combining CRF with US and MRI signs might help to predict PAS in PP patients, with MRI contributing more than US as imaging evaluation.

Topography-based feature extraction of the human placenta from prenatal MR images

Magnetic resonance imaging (MRI) has gained popularity in the field of prenatal imaging due to the ability to provide high quality images of soft tissue. In this paper, we presented a novel method for extracting different textural and morphological features of the placenta from MRI volumes using topographical mapping. We proposed polar and planar topographical mapping methods to produce common placental features from a unique point of observation. The features extracted from the images included the entire placenta surface, as well as the thickness, intensity, and entropy maps displayed in a convenient two-dimensional format. The topography-based images may be useful for clinical placental assessments as well as computer-assisted diagnosis, and prediction of potential pregnancy complications.

Accuracy of Magnetic Resonance Imaging in Diagnosing Placenta Accreta: A Systematic Review and Meta-Analysis

Background

The disease burden and incidence of placenta accreta are increasing worldwide. The morbidity and mortality associated with undiagnosed placenta accreta are both high, highlighting the important of early diagnosis and intervention. In recent years, increasing studies are exploring the diagnostic value of magnetic resonance imaging (MRI) for placenta accreta. Compared with traditional ultrasound, MRI has the advantages of high-resolution, multiangle imaging, and less influence by amniotic fluid and intestinal gas. However, the reported diagnostic accuracy among studies was inconsistent. Therefore, this study is aimed at exploring the diagnostic value of MRI for placenta accreta by systematic review and meta-analysis.

Methods

Relevant literature were systematically searched in PubMed, Ovid, Embase, ScienceDirect database, CNKI, and Wanfang database by using medical subject headings and relevant diagnostic terminologies such as sensitivity, specificity, likelihood ratio, receiver-operating characteristic curve, and area under the curve. The sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and area under the curve of the included literature were analyzed using stata 17.0 software. Publication bias of the included studies was assessed by Deek's funnel plot. Cochrane Q statistics and I² statistics were used to test the heterogeneity.

Results

A total of 10 primary publications, comprising 4 retrospective studies and 6 prospective studies, were included in this meta-analysis. The gestational weeks of pregnant women ranged from 32 to 35 weeks, and the sample size ranged from 37 cases to 575 cases. Only 4 studies used the blind method in the process of clinical diagnosis by MRI. The combined sensitivity, specificity, and area of curve under summary receiver-operating characteristic for the diagnosis of placenta accreta by MRI were 0.88 (95% CI, 0.79-0.93), 0.79 (95% CI, 0.68-0.87), and 0.91 (95% CI, 0.88.-0.93), respectively. The combined positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio, and diagnostic score were 4.17 (95% CI, 2.62-6.66), 0.16 (95% CI, 0.09-0.29), 26.61 (95% CI, 10.22-69.28), and 3.28 (95% CI, 2.32-4.24), respectively. No publication bias was noted.

Conclusion

Diagnosis of placenta accreta by MRI has good accuracy and predictive value that warrants clinical promotion.

Effectiveness of a fetal magnetic resonance imaging scoring system for predicting the prognosis of pernicious placenta previa: A retrospective study

Background: The value of multiple magnetic resonance imaging (MRI) signs in predicting pernicious placenta previa (PPP) with placenta accreta spectrum disorders (PAS) is still controversial. This study aimed to investigate the value of a self-made fetal magnetic resonance imaging scoring system in predicting the different types of PAS in pernicious placenta previa and its associated risk of bleeding.

Methods: This retrospective study included 193 patients diagnosed with PPP based on MRI findings before delivery. Based on pathological and intraoperative findings, we divided patients into four groups: non-PAS, placental adhesion, placental implantation, and placenta percreta. Receiver operator characteristic curves of the MRI total score and placental implantation type were drawn using pROC packages in the R Studio environment, and cutoff values of each type were calculated, as well as diagnostic evaluation indexes, such as sensitivity, specificity, and the Youden index. Hemorrhage during surgery was compared between the groups.

Results: The boundary value between the non-PAS and placental adhesion was 5.5, that between placental adhesion and placental implantation was 11.5, and that between placental implantation and placenta percreta was 15.5 points. The respective specificities were 0.700, 0.869, and 0.958, and the respective sensitivities were 0.994, 0.802, and 0.577. The Youden indices were 0.694, 0.671, and 0.535, respectively. The median (minimum, maximum) quantities of hemorrhage during the operation in the non-PAS, placental adhesion, placental implantation, and placenta percreta groups were 225 (100, 3700), 600 (200, 6000), 1500 (300, 7000), and 3000 (400, 6300) ml, respectively. Hemorrhage was significantly different between the four groups (p < 0.001).

Conclusion: These results suggest that the proposed MRI scoring system could be an effective diagnostic tool for assessing PPP types and predicting the associated bleeding risk.

Texture analysis of myometrium-derived T2WI in the evaluation of placenta increta: An observational retrospective study

INTRODUCTION

MRI has demonstrated its potential in the diagnosis of placenta percreta. Texture analysis is a novel technique to quantify tissue heterogeneity. The study aimed to evaluate the feasibility of using texture analysis based on myometrium-derived T2WI to differentiate placenta accreta from increta.

METHODS

Participants with MRI and clinical or histopathological diagnosis of placenta increta were retrospectively enrolled. Texture analysis of T2WI was implemented on normal myometrium and placenta increta by MaZda software. With the Fisher discriminant method, parameter selection and reduction were done automatically. Multivariate analysis was used for the comparison of response variables between two groups. The contours of multivariable average vectors were compared using profile analysis. Two-step clustering was performed to assess the importance of parameters.

RESULTS

There were a total of 23 participants (median age 29 years, range 22-43 years). The pixel intensity distribution was narrow and wide in two first-order histograms taken from normal myometrium and placenta increta, respectively. Multivariate analysis showed nine second-order parameters derived from the histogram were statistically significant (P < 0.05). The results of two-step clustering indicated that three second-order parameters (Mean, Percentile 90%, and Percentile 99%) were important (predictor importance > 0.8). Multivariate analysis of three second-order parameters further showed they were different between normal myometrium and placenta increta.

DISCUSSION

Texture analysis based on myometrium-derived T2WI may be a useful add-on to MRI in diagnosing placenta increta.

TRIAL REGISTRATION

Registration number: ChiCTR2000038604 and name of registry: Evaluation of diagnostic accuracy of MRI multi-parameter imaging combined with texture analysis for placenta accreta spectrum disorders (PAD).

Achados na ressonância magnética do espectro do acretismo placentário: ensaio iconográfico

Resumo Acretismo placentário é uma condição caracterizada pela implantação anormal da placenta, que pode ser subdividida em três espectros de acordo com o seu grau de invasão: placenta acreta (ultrapassa a decídua basal e adere ao miométrio), placenta increta (penetra o miométrio) e placenta percreta (invasão da serosa uterina ou de tecidos/órgãos adjacentes). A incidência de acretismo placentário aumentou significativamente nas últimas décadas, principalmente em função da elevação das taxas de cesarianas, sendo este o seu principal fator de risco. A sua identificação pré-natal precisa permite um tratamento ideal com equipe multidisciplinar, minimizando significativamente a morbimortalidade materna. Os exames de escolha são a ultrassonografia e a ressonância magnética (RM), sendo a RM um método complementar indicado quando a avaliação ultrassonográfica é duvidosa, para pacientes com fatores de risco para acretismo placentário ou quando a placenta tem localização posterior. A RM é preferível também para avaliar invasão de órgãos adjacentes, oferecendo um campo de visão mais amplo, o que melhora o planejamento cirúrgico. Diversas características na RM são descritas no acretismo placentário, incluindo bandas hipointensas em T2 intraplacentárias, protuberância uterina anormal e heterogeneidade placentária. O conhecimento desses achados e a combinação de mais de um critério aumentam a confiabilidade do diagnóstico.

Artificial intelligence applied to fetal MRI: A scoping review of current research

Artificial intelligence (AI) is defined as the development of computer systems to perform tasks normally requiring human intelligence. A subset of AI, known as machine learning (ML), takes this further by drawing inferences from patterns in data to 'learn' and 'adapt' without explicit instructions meaning that computer systems can 'evolve' and hopefully improve without necessarily requiring external human influences. The potential for this novel technology has resulted in great interest from the medical community regarding how it can be applied in healthcare. Within radiology, the focus has mostly been for applications in oncological imaging, although new roles in other subspecialty fields are slowly emerging.In this scoping review, we performed a literature search of the current state-of-the-art and emerging trends for the use of artificial intelligence as applied to fetal magnetic resonance imaging (MRI). Our search yielded several publications covering AI tools for anatomical organ segmentation, improved imaging sequences and aiding in diagnostic applications such as automated biometric fetal measurements and the detection of congenital and acquired abnormalities. We highlight our own perceived gaps in this literature and suggest future avenues for further research. It is our hope that the information presented highlights the varied ways and potential that novel digital technology could make an impact to future clinical practice with regards to fetal MRI.

Automatic Segmentation of Uterine Cavity and Placenta on MR Images Using Deep Learning

Magnetic resonance imaging (MRI) is useful for the detection of abnormalities affecting maternal and fetal health. In this study, we used a fully convolutional neural network for simultaneous segmentation of the uterine cavity and placenta on MR images. We trained the network with MR images of 181 patients, with 157 for training and 24 for validation. The segmentation performance of the algorithm was evaluated using MR images of 60 additional patients that were not involved in training. The average Dice similarity coefficients achieved for the uterine cavity and placenta were 92% and 80%, respectively. The algorithm could estimate the volume of the uterine cavity and placenta with average errors of less than 1.1% compared to manual estimations. Automated segmentation, when incorporated into clinical use, has the potential to quantify, standardize, and improve placental assessment, resulting in improved outcomes for mothers and fetuses.

Diagnostic performance of radiologists with different levels of experience in the interpretation of MRI of the placenta accreta spectrum disorder

OBJECTIVES

There have been no investigations on the association between previous abdominopelvic MRI experience without placental MRI experience and diagnostic accuracy of placenta accreta spectrum (PAS). To evaluate the diagnostic performance of radiologists with different experience levels in interpreting PAS-related MRI findings.

METHODS

This retrospective study included 60 women who underwent MRI for placental assessment between 2016 and 2020. MR images were reviewed by four radiologists who were blinded to the clinical outcomes and had different experience levels in interpreting PAS-related MRI findings. The radiologists' diagnostic performance was evaluated according to the pathologic and surgical outcomes. Simple κ statistics were calculated to determine agreement among the radiologists.

RESULTS

Of 60 women, 46 were diagnosed with PAS. The maternal age mean ± SD was 33.0 years ± 5.0 for the PAS absent group and 36.0 ± 4.3 for the PAS present group (p = 0.013). Overall, the most experienced radiologist had the highest sensitivity (100%, 95% confidence interval (CI): 92.3-100%) and NPV (100%, 95% CI: 63.1-100%) in PAS diagnoses. However, the PPV and specificity were independent of experience. The most experienced radiologist had the highest diagnostic accuracy in PAS (90%, 95% CI: 79.5-96.2%) and placenta percreta (95%, 95% CI: 86.1-99.0%). There was a strong association between definitive PAS diagnoses and the highest experience level. The κ values for the interobserver agreement regarding PAS diagnoses were 0.67 for the most experienced radiologist (p < 0.001) and 0.38, 0.40, and 0.43 for the other radiologists (p = 0.001) and regarding placenta percreta diagnoses were 0.87 for the senior radiologist (p < 0.001) and 0.63, 0.57, and 0.62 for the other radiologists (p < 0.001).

CONCLUSION

Previous experience in interpreting PAS-related MRI findings plays a significant role in accurately interpreting such imaging findings. Previous abdominopelvic MRI experience without specific placental MRI experience did not improve diagnostic performance.

ADVANCES IN KNOWLEDGE

We believe that our study makes a significant contribution to the literature and that this paper will be of interest to the readership of your journal because to the best of our knowledge, this study is the first in which the correlation between previous experience in abdominopelvic MRI with no specific experience in PAS-related MRI and diagnostic accuracy of radiologists has been explored. Our results could aid in setting up specialized multidisciplinary teams to assist women with PAS disorders.

Deep learning-based segmentation of the placenta and uterus on MR images

Purpose: Magnetic resonance imaging has been recently used to examine the abnormalities of the placenta during pregnancy. Segmentation of the placenta and uterine cavity allows quantitative measures and further analyses of the organs. The objective of this study is to develop a segmentation method with minimal user interaction. Approach: We developed a fully convolutional neural network (CNN) for simultaneous segmentation of the uterine cavity and placenta in three dimensions (3D) while a minimal operator interaction was incorporated for training and testing of the network. The user interaction guided the network to localize the placenta more accurately. In the experiments, we trained two CNNs, one using 70 normal training cases and the other using 129 training cases including normal cases as well as cases with suspected placenta accreta spectrum (PAS). We evaluated the performance of the segmentation algorithms on two test sets: one with 20 normal cases and the other with 50 images from both normal women and women with suspected PAS. Results: For the normal test data, the average Dice similarity coefficient (DSC) was 92% and 82% for the uterine cavity and placenta, respectively. For the combination of normal and abnormal cases, the DSC was 88% and 83% for the uterine cavity and placenta, respectively. The 3D segmentation algorithm estimated the volume of the normal and abnormal uterine cavity and placenta with average volume estimation errors of 4% and 9%, respectively. Conclusions: The deep learning-based segmentation method provides a useful tool for volume estimation and analysis of the placenta and uterus cavity in human placental imaging.

Development and validation of a magnetic resonance imaging-based nomogram for predicting invasive forms of placental accreta spectrum disorders

AIM

The aim of the study was to develop and validate a magnetic resonance imaging (MRI)-based nomogram for predicting invasive forms of placental accreta spectrum (PAS) disorders (placenta increta and percreta) with "uncertain ultrasound diagnosis."

METHODS

This was a retrospective cohort study of a primary cohort of 118 patients and a validation cohort of 65 patients with "uncertain ultrasound diagnosis," who were further evaluated by MRI. MRI signs associated with PAS disorders were analyzed between invasive and noninvasive groups by both univariate and logistic regression to construct the nomogram. The accuracy and discriminative ability of the nomogram were measured by concordance index (C-index) and calibration curve internally and externally.

RESULTS

The history of previous cesarean deliveries (odds ratio [OR], 3.27; 95% confidence interval [CI], 1.16-9.27), loss of double-line sign (OR, 9.49; 95% CI, 3.06-29.48), abnormal uterine bulging (OR, 4.05; 95% CI, 1.53-10.69), and disorganized abnormal placenta vascularity (OR, 3.38; 95% CI, 1.09-10.50) were imputed for the nomogram. The C-index of the nomogram was 0.85 for internal validation and 0.84 for external validation. Calibration curve showed good agreement with predicted risk and actual observation for both primary and validation cohort.

CONCLUSIONS

MRI can be a useful adjunct for clinical staging of patients with "uncertain ultrasound diagnosis."

Prediction of placenta accreta spectrum in patients with placenta previa using clinical risk factors, ultrasound and magnetic resonance imaging findings

OBJECTIVES

To predict placental accreta spectrum (PAS) in patients with placenta previa (PP) evaluating clinical risk factors (CRF), ultrasound (US) and magnetic resonance imaging (MRI) findings.

METHODS

Seventy patients with PP were retrospectively selected. CRF were retrieved from medical records. US and MRI images were evaluated to detect imaging signs suggestive of PAS. Univariable analysis was performed to identify CRF, US and MRI signs associated with PAS considering histology as standard of reference. Receiver operating characteristic curve (ROC) analysis was performed, and the area under the curve (AUC) was calculated. Multivariable analysis was also performed.

RESULTS

At univariable analysis, the number of previous cesarean section, smoking, loss of the retroplacental clear space, myometrial thinning < 1 mm, placental lacunae, intraplacental dark bands (IDB), focal interruption of myometrial border (FIMB) and abnormal vascularity were statistically significant. The AUC in predicting PAS progressively increased using CRF, US and MRI signs (0.69, 0.79 and 0.94, respectively; p < 0.05); the accuracy of MRI alone was similar to that obtained combining CRF, US and MRI variables (AUC = 0.97) and was significantly higher (p < 0.05) than that combining CRF and US (AUC = 0.83). Multivariable analysis showed that only IDB (p = 0.012) and FIMB (p = 0.029) were independently associated with PAS.

CONCLUSIONS

MRI is the best modality to predict PAS in patients with PP independently from CRF and/or US finding. It is reasonable to propose the combined assessment of CRF and US as the first diagnostic level to predict PAS, sparing MRI for selected cases in which US findings are uncertain for PAS.

Prenatal prediction and typing of placental invasion using MRI deep and radiomic features

BACKGROUND

To predict placental invasion (PI) and determine the subtype according to the degree of implantation, and to help physicians develop appropriate therapeutic measures, a prenatal prediction and typing of placental invasion method using MRI deep and radiomic features were proposed.

METHODS

The placental tissue of abdominal magnetic resonance (MR) image was segmented to form the regions of interest (ROI) using U-net. The radiomic features were subsequently extracted from ROI. Simultaneously, a deep dynamic convolution neural network (DDCNN) with codec structure was established, which was trained by an autoencoder model to extract the deep features from ROI. Finally, combining the radiomic features and deep features, a classifier based on the multi-layer perceptron model was designed. The classifier was trained to predict prenatal placental invasion as well as determine the invasion subtype.

RESULTS

The experimental results show that the average accuracy, sensitivity, and specificity of the proposed method are 0.877, 0.857, and 0.954 respectively, and the area under the ROC curve (AUC) is 0.904, which outperforms the traditional radiomic based auxiliary diagnostic methods.

CONCLUSIONS

This work not only labeled the placental tissue of MR image in pregnant women automatically but also realized the objective evaluation of placental invasion, thus providing a new approach for the prenatal diagnosis of placental invasion.

Role of Ultrasound and MRI in Diagnosis of Severe Placenta Accreta Spectrum Disorder: An Intraindividual Assessment With Emphasis on Placental Bulge

Background: The placental bulge sign (focal area of myometrial-placental bulging beyond the normal uterine contour) on ultrasound (US) or MRI is postulated to represent deeper venous invasion in placental accreta spectrum (PAS) disorder and may represent severe PAS. Objective: To evaluate the diagnostic performance and interobserver agreement of US and MRI features for diagnosis of severe PAS, with an emphasis on the placental bulge sign. Method: This retrospective study included 62 pregnant women (mean age 33.2±5.5 years) with clinically suspected PAS who underwent both US and MRI. Five independent reviewers (two maternal-fetal medicine specialists for US; three abdominal radiologists for MRI) independently reviewed images for the given modality, blinded to the final diagnosis, and recorded presence of a range of findings (nine on US, eight on MRI) including placental bulge. Intraoperative and pathologic findings were used to separate patients into those with and without severe PAS, based on International Federation of Gynaecology and Obstetrics classification. Diagnostic performance of US and MRI findings for severe PAS were evaluated; multivariable logistic regression was performed; and interobserver agreement was assessed. Results: A total of 58.1% (36/62) of patients had severe PAS. On US, the finding with highest accuracy for severe PAS was placental bulge (85.5%), which was associated with sensitivity of 91.7% and specificity of 76.9%. On MRI, the finding with highest accuracy was also placental bulge (90.3%), which was associated with sensitivity of 94.4% and specificity of 84.6%. At multivariable regression, placental bulge was an independent predictor of severe PAS for US [odds ratio (OR)=8.94; p=.02] and MRI (OR=45.67; p=.003). Interobserver agreement analysis demonstrated kappa for placental bulge of 0.48 for MRI and 0.40 for US. Given wide 95% CIs, differences among features for a given modality as well as differences between modalities were not statistically significant. Conclusion: The findings suggest strong performance of placental bulge in diagnosing severe PAS on both US and MRI, with potentially relatively stronger performance on MRI. Nonetheless, interobserver agreement remains suboptimal on both modalities. Clinical impact: Accurate prenatal diagnosis of severe PAS by imaging could help guide maternal counseling and selection between hysterectomy and uterine-preserving surgery.

Quantifying magnetic resonance imaging features to classify placenta accreta spectrum (PAS) in high-risk gravid patients

OBJECTIVE

This study aimed to quantify the magnetic resonance imaging (MRI) features of placenta accreta spectrum (PAS) and to use MRI-based scores to classify them in high-risk gravid patients.

MATERIALS AND METHODS

The clinical data and MRI features of 65 high-risk gravid patients diagnosed with PAS were retrospectively reviewed. The MRI features of PAS were analysed and compared using the chi-squared test, and the odds ratios (ORs) for significant risk factors for classification of PAS were identified via a multivariate logistic regression model. A receiver-operating characteristic (ROC) curve was used to calculate cut-off values and their corresponding sensitivity, specificity, and accuracy in classifying PAS.

RESULTS

We identified 3 significant risk features for classification of PAS, including placental heterogeneity (OR = 13.604), abnormal vascularization at the placental-maternal interface (OR = 9.528), and focal myometrial interruption (OR = 118.779). The significant risk features for classification of PAS were scored according to their OR values, as 3 points (OR ≥ 20), 2 points (10 ≤ OR < 20), or 1 point (OR < 10). Based on the scores of the 3 risk features, a cut-off score of 4.5 points achieved optimal sensitivity (94.3%), specificity (90%), and accuracy (92.3%) for classifying PAS in high-risk gravid patients.

CONCLUSION

Quantifying these MRI features including placental heterogeneity, abnormal vascularization at the placental-maternal interface, and focal myometrial interruption can make a classification of PAS in high-risk gravid patients.

Magnetic Resonance Imaging of Placenta Accreta Spectrum: A Step-by-Step Approach

Placenta accreta spectrum (PAS) is an abnormal placental adherence or invasion of the myometrium or extrauterine structures. As PAS is primarily staged and managed surgically, imaging can only guide and facilitate diagnosis. But, imaging can aid in preparations for surgical complexity in some cases of PAS. Ultrasound remains the imaging modality of choice; however, magnetic resonance imaging (MRI) is required for evaluation of areas difficult to visualize on ultrasound, and the assessment of the extent of placenta accreta. Numerous MRI features of PAS have been described, including dark intraplacental bands, placental bulge, and placental heterogeneity. Failure to diagnose PAS carries a risk of massive hemorrhage and surgical complications. This article describes a comprehensive, step-by-step approach to diagnostic imaging and its potential pitfalls.

Application of Indirect Signs of Magnetic Resonance Imaging (MRI) in Prenatal Diagnosis of Abnormally Invasive Placenta

BACKGROUND The aim of this study was to assess the value of indirect MRI signs in the prenatal diagnosis of abnormally invasive placenta (AIP). MATERIAL AND METHODS This study involved the retrospective analysis of indirect signs of 109 patients with AIP and 59 patients without AIP. The numbers of cases of placenta increta, accreta, and percreta confirmed by surgical and pathological results were 54, 19, and 36, respectively. The indirect signs included the following: dark intraplacental bands in T2WI sequence, focal outward bulging of the placenta, abnormal placental vascularity, and heterogeneous placental signal intensity. RESULTS There were significant differences in dark intraplacental bands in T2WI sequence, focal outward bulging of the placenta, and abnormal placental vascularity between the AIP and the non-AIP groups. There was no significant difference in dark intraplacental bands in T2WI sequence between the placenta percreta and increta groups, but there was a significant difference between the other 2 AIP groups and the placenta accreta group. Focal outward bulging of the placenta was significantly different between the percreta group and the placenta accreta group, but there was no significant difference between the other 2 AIP groups and the placenta increta group. There were no significant differences in abnormal placental vascularity among the3 subtypes of AIP. CONCLUSIONS The indirect signs of dark intraplacental bands in T2WI sequence, focal outward bulging of the placenta, and abnormal placental vascularity are reliable signs of AIP. The indirect sign of dark intraplacental bands in T2WI sequence may be used to distinguish placental accreta from the other 2 subtypes of AIP.

ACR Appropriateness Criteria® Placenta Accreta Spectrum Disorder

Placenta accreta spectrum disorder (PASD) is the current terminology recommended by the International Federation of Obstetrics and Gynecology (FIGO) and should replace terms such as abnormally adherent/invasive placenta or morbidly adherent placenta. PASD refers to a variety of potential clinical complications, which may result from abnormal placental implantation. More specifically, placenta accreta refers to a defect in the decidua basalis where the chorionic villi adhere directly to the myometrium with trophoblastic invasion. Accurate antenatal diagnosis is needed to plan for an appropriate delivery strategy at an experienced center in order to reduce maternal and potential fetal morbidity and mortality. Obtaining radiologic and clinical data when PASD is first suspected can play a significant role in formulating an appropriate delivery strategy. Depending on the clinical risk factors and initial imaging findings, transabdominal ultrasound of the pregnant uterus with duplex Doppler and transvaginal ultrasound as needed are the most appropriate imaging procedures. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Segmentation of uterus and placenta in MR images using a fully convolutional neural network

Segmentation of the uterine cavity and placenta in fetal magnetic resonance (MR) imaging is useful for the detection of abnormalities that affect maternal and fetal health. In this study, we used a fully convolutional neural network for 3D segmentation of the uterine cavity and placenta while a minimal operator interaction was incorporated for training and testing the network. The user interaction guided the network to localize the placenta more accurately. We trained the network with 70 training and 10 validation MRI cases and evaluated the algorithm segmentation performance using 20 cases. The average Dice similarity coefficient was 92% and 82% for the uterine cavity and placenta, respectively. The algorithm could estimate the volume of the uterine cavity and placenta with average errors of 2% and 9%, respectively. The results demonstrate that the deep learning-based segmentation and volume estimation is possible and can potentially be useful for clinical applications of human placental imaging.

Nonfetal Imaging During Pregnancy: Placental Disease

Placenta is a vital organ that connects the maternal and fetal circulations, allowing exchange of nutrients and gases between the two. In addition to the fetus, placenta is a key component to evaluate during any imaging performed during pregnancy. The most common disease processes involving the placenta include placenta accreta spectrum disorders and placental masses. Several systemic processes such as infection and fetal hydrops can too affect the placenta; however, their imaging features are nonspecific such as placental thickening, heterogeneity, and calcifications. Ultrasound is the first line of imaging during pregnancy, and MR imaging is reserved for problem solving, when there is need for higher anatomic resolution.

Society of Abdominal Radiology (SAR) and European Society of Urogenital Radiology (ESUR) joint consensus statement for MR imaging of placenta accreta spectrum disorders

OBJECTIVES

This study was conducted in order to establish the joint Society of Abdominal Radiology (SAR) and European Society of Urogenital Radiology (ESUR) guidelines on placenta accreta spectrum (PAS) disorders and propose strategies to standardize image acquisition, interpretation, and reporting for this condition with MRI.

METHODS

The published evidence-based data and the opinion of experts were combined using the RAND-UCLA Appropriateness Method and formed the basis for these consensus guidelines. The responses of the experts to questions regarding the details of patient preparation, MRI protocol, image interpretation, and reporting were collected, analyzed, and classified as "recommended" versus "not recommended" (if at least 80% consensus among experts) or uncertain (if less than 80% consensus among experts).

RESULTS

Consensus regarding image acquisition, interpretation, and reporting was determined using the RAND-UCLA Appropriateness Method. The use of a tailored MRI protocol and standardized report was recommended.

CONCLUSIONS

A standardized imaging protocol and reporting system ensures recognition of the salient features of PAS disorders. These consensus recommendations should be used as a guide for the evaluation of PAS disorders with MRI.

KEY POINTS

• MRI is a powerful adjunct to ultrasound and provides valuable information on the topography and depth of placental invasion. • Consensus statement proposed a common lexicon to allow for uniformity in MRI acquisition, interpretation, and reporting of PAS disorders. • Seven MRI features, namely intraplacental dark T2 bands, uterine/placental bulge, loss of low T2 retroplacental line, myometrial thinning/disruption, bladder wall interruption, focal exophytic placental mass, and abnormal vasculature of the placental bed, reached consensus and are categorized as "recommended" for diagnosing PAS disorders.

Placental magnetic resonance imaging Part II: placenta accreta spectrum

The human placenta remains an enigma to many. Its position as the point of communication between distinct maternal and fetal circulations means that it must act as both source of nourishment and gatekeeper for the developing pregnancy. In vivo assessment of the placenta is perhaps the greatest challenge, yet it is most essential for diagnostic and prognostic purposes. In particular, there is a need for improved diagnostic accuracy in recognizing the invasive forms of the placenta accreta spectrum that require surgical intervention at delivery and often cesarean hysterectomy. The costs of insufficient sensitivity and specificity are high, with well-documented cases of adverse outcomes ranging from unnecessary surgery to maternal hemorrhage and even death. In Part I of this pictorial essay series, we reviewed the appearance of the normal developing placenta across gestation by MRI. With this as a background, we here consider the varied appearances of the placenta accreta spectrum (placenta accreta, increta, percreta), which is a growing challenge given the rapidly expanding number of women worldwide with history of cesarean section delivery. Accurate prenatal imaging is crucial for recognizing cases of the placenta accreta spectrum and for planning the necessary surgery.

A retrospective analysis of the treatment on abdominal aortic balloon occlusion-related thrombosis by continuous low-flow diluted heparin

Thrombosis is one of the serious complications related to prophylactic balloon occlusion of the abdominal aorta (PBOAA). This study aims to retrospectively analyze the efficacy and safety of continuous low-flow infusion of diluted heparin saline to prevent this complication related to PBOAA and further to provide the theory and evidences for using PBOAA.A study was carried out at our hospital from March 2016 to December 2018. Women with pernicious placenta previa (PPP) were treated PBOAA to prevent massive bleeding during CS. According to whether continuous low-flow infusion of diluted heparin saline was used to prevent catheter-related thrombosis or not, they were divided into 2 groups, the test group and the control group. The incidence of thrombosis between the 2 groups was compared and the effective treatment of thrombosis was also discussed. The comparison of nonparametric values was accomplished by using Fisher exact test. Statistical significance was set at P < .05.There were 31 women with PPP who received PBOAA during CS who were included in our study. Six of 19 women in control group (31.6%) developed thrombotic complications, while none of 12 women in test group. There were statistically significant differences in the incidence of thrombosis between the 2 groups (P = .037). There was no statistically significant difference in the amount of estimated blood loss and blood transfusion during CS between the 2 groups, nor was there statistically significant difference in the hospital days after CS (P > .05). All 6 women with thrombotic complications had no positive symptoms and thrombotic sequelae. The managements of thrombus included systemic anticoagulation, catheter-directed thrombolysis, and catheter-directed anticoagulation. One of the 6 women was lost to follow-up, and the thrombus of the other 5 women were completely dissolved. No other adverse outcomes or complications related to PBOAA were observed in all women in this study.Continuous low-flow infusion of diluted heparin saline is a safe procedure when PBOAA is performed for patients with PPP. It can effectively reduce or even avoid thrombosis without increasing intraoperative blood loss during CS for PPP patients.

Radiomics analysis of placenta on T2WI facilitates prediction of postpartum haemorrhage: A multicentre study

BACKGROUND

Identification of pregnancies with postpartum haemorrhage (PPH) antenatally rather than intrapartum would aid delivery planning, facilitate transfusion requirements and decrease maternal complications. MRI has been increasingly used for placenta evaluation. Here, we aim to build a nomogram incorporating both clinical and radiomic features of placenta to predict the risk for PPH in pregnancies during caesarian delivery (CD).

METHODS

A total of 298 pregnant women were retrospectively enrolled from Henan Provincial People's Hospital (training cohort: n = 207) and from The Third Affiliated Hospital of Zhengzhou University (external validation cohort: n = 91). These women were suspected with placenta accreta spectrum (PAS) disorders and underwent MRI for placenta evaluation. All of them underwent CD and were singleton. PPH was defined as more than 1000 mL estimated blood loss (EBL) during CD. Radiomic features were selected based on their correlations with EBL. Radiomic, clinical, radiological, clinicoradiological and clinicoradiomic models were built to predict the risk of PPH for each patient. The model with the best prediction performance was validated with its discrimination ability, calibration curve and clinical application.

FINDINGS

Thirty-five radiomic features showed strong correlation with EBL. The clinicoradiomic model resulted in the best discrimination ability for risk prediction of PPH, with AUC of 0.888 (95% CI, 0.844-0.933) and 0.832 (95% CI, 0.746-0.913), sensitivity of 91.2% (95% CI, 85.8%-96.7%) and 97.6% (95% CI, 92.7%-100%) in the training and validation cohort respectively. For patients with severe PPH (EBL more than 2000 mL), 53 out of 55 pregnancies (96.4%) in the training cohort and 18 out of 18 (100%) pregnancies in the validation cohort were identified by the clinicoradiomic model. The model performed better in patients without placenta previa (PP) than in patients with PP, with AUC of 0.983 compared with 0.867, sensitivity of 100% compared with 90.8% in the training cohort, AUC of 0.832 compared with 0.815, sensitivity of 97.6% compared with 97.2% in the validation cohort.

INTERPRETATION

The clinicoradiomic model incorporating both prenatal clinical factors and radiomic signature of placenta on T2WI showed good performance for risk prediction of PPH. The predictive model can identify severe PPH with high sensitivity and can be applied in patients with and without PP.

Combining Clinical Characteristics and Specific Magnetic Resonance Imaging Features to Predict Placenta Accreta

The aim of this study was to explore the independent clinical and magnetic resonance imaging (MRI) performance risk factors for predicting placenta accreta.

Application of abdominal aortic balloon occlusion followed by uterine artery embolization for the treatment of pernicious placenta previa complicated with placenta accreta during cesarean section

OBJECTIVE

This study aimed to investigate the clinical effects of abdominal aortic balloon occlusion followed by uterine artery embolization for the treatment of pernicious placenta previa complicated with placenta accreta during cesarean section.

METHODS

We performed a retrospective analysis of the clinical data for 623 patients who experienced pernicious placenta previa complicated with placenta accreta and received treatment in our hospital from January 2013 to January 2019. All patients underwent abdominal aortic balloon occlusion before their cesarean section. Seventy-eight patients received bilateral uterine artery embolization, and among them, placenta accreta was found at the opening of the cervix in 13 patients. Due to suturing difficulty after the removal of the placenta, gauze packing was used to temporarily compress the hemorrhage. As soon as the uterus was sutured, emergent bilateral uterine artery embolization was performed. Active bleeding was noted in the remaining 65 patients when the lower part of the uterus was pressed after the placenta was removed and the uterus was sutured, therefor, bilateral uterine artery embolization was performed urgently.

RESULTS

Of the 623 patients, 545 patients underwent only abdominal aortic balloon occlusion and 78 patients underwent additional emergent bilateral uterine artery embolization due to hemorrhaging during or after their cesarean section. No hysterectomies were performed. In the 78 patients, the amount of bleeding was 800-3,200 ml with an average of 1,650 ml during the operation; the volume of blood transfused was 360-1,750 ml (average: 960 ml). The fetal fluoroscopy time was 3-8 s (average: 5 s). The dose of radiation exposure was (4.2 ± 2.9) mGy. Fetal appearance, pulse, grimace, activity, and respiration (Apgar) score were normal. No serious complications were observed during or after the operation in the follow-up visits. Conclusion: For patients with pernicious placenta previa complicated with placenta accreta who experience active bleeding after cesarean section and abdominal aortic balloon occlusion, bilateral uterine artery embolization can effectively reduce blood loss and requirement of blood transfusion during the operation, and lowers the risk of hysterectomy.

MRI evaluation of the placenta from normal variants to abnormalities of implantation and malignancies

Even though the placenta has been known for millennia, it is still considered one of the most complex and least understood human organs. Imaging of the placenta is gaining attention due to its impact on fetal and maternal outcomes. MRI plays a vital role in evaluation of inconclusive cases by ultrasonography. It enables precise mapping of placental abnormalities for proper multidisciplinary planning and management. In this article we provide a comprehensive in-depth review of the role of antenatal MR in evaluating "The Placenta." We will describe the protocols and techniques used for MRI of the placenta, review anatomy of the placenta, describe MRI features of major placental abnormalities including those related to position, depth of implantation, hemorrhage, gestational trophoblastic neoplasia, and retained products of conception and discuss the added value of MRI in the management and preoperative planning of such abnormalities. Level of Evidence: 3 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2019;50:1702-1717.

Magnetic resonance imaging of the placenta and gravid uterus: a pictorial essay

The placenta is commonly overlooked on magnetic resonance imaging of the pregnant patient, which is frequently performed for alternative reasons such as to characterize fetal or uterine anomalies or to investigate the etiology of acute pelvic pain in pregnancy. Placental disorders have potential for significant maternal and fetal morbidity and peripartum complications if not recognized and treated in a timely manner. The radiologist must be familiar with normal placental variants and the spectrum of benign to life-threatening conditions affecting the placenta so that the Obstetrician can be promptly notified and patient management altered, if necessary. In this pictorial essay, we will describe our MR protocol for placental imaging, provide an image-rich review of the normal placenta, placental variants, and a variety of pathological conditions affecting the placenta and gravid uterus.

Morphological evaluation of cervix using MRI at 32 to 36 weeks of gestation: Findings for predicting invasive placenta previa

This study is to investigate the role of cervical morphology evaluated by magnetic resonance imaging (MRI) in predicting invasive placenta previa (IPP).Totally 105 cases of pregnant women underwent prenatal placental MRI at 32 to 36 weeks of gestation for suspected IPP were included in this study. Cervical morphology (cervical length and placental protrusion) was evaluated independently by 2 radiologists. The association between the cervical morphology and surgery findings was analyzed.Totally, 57 pregnant women were confirmed as IPP. For invasion degree, there were 17 cases with placenta percreta and 40 with accreta. For invasion topography, there were 27 cases with S1 invasion and 30 with S2 invasion. The sensitivity and specificity for the MRI sign of placental protrusion in evaluating cervical invasion of IPP were 100% and 100%, respectively. All the 7 IPP patents with cervical invasion received total hysterectomy and had severe blood loss (3500-6000 mL). The IPP patients with S2 invasion had shorter cervical length than those with S1 invasion (2.66 ± 0.66 cm vs 3.24 ± 0.64 cm, P <.001). However, cervical lengths did not correlate with the degree of invasion (placenta percreta vs placenta accreta: 2.82 ± 0.86 vs 2.99 ± 0.60, P = .21).Placental protrusion is a reliable MRI sign for cervical invasion of IPP, and cervical lengths correlate with the invasion topography.

Interobserver agreement and diagnostic performance of individual MRI criteria for diagnosis of placental adhesion disorders

AIM

To assess the diagnostic accuracy of several criteria for the diagnosis of placental adhesion disorder (PAD) on magnetic resonance imaging (MRI) and to assess interobserver agreement and reader accuracy based on years of interpretive experience.

MATERIALS AND METHODS

Blinded evaluation of the placental MRI studies of 28 randomly selected women, 18 with PADs and 10 without PADs, was undertaken by three radiologists with 10, 5, and 2 years' experience in placental MRI interpretation. The presence of placenta praevia, dark intraplacental bands, heterogeneity, uterine bulging, "shaggy dog" appearance of the uterine serosa, subjective impression of extraplacental invasion, and dark intraplacental bands on diffusion-weighted imaging were assessed. Placental histology was reviewed blinded to the original reports and to MRI interpretation and this, along with clinical information at the time of delivery, formed the reference standard.

RESULTS

Dark intraplacental bands on T2-weighted imaging were the most sensitive and specific as well as the most agreed upon (kappa=0.7) criterion for PAD for the three readers. Assessment of uterine bulging (kappa=0.42) and placental heterogeneity (kappa=0.48) did not improve diagnostic accuracy. DWI improved sensitivity but decreased specificity for the least experienced reader and did not change sensitivity or specificity for the more experienced readers.

CONCLUSION

Assessment of the placenta for dark bands is the most sensitive, specific, and reproducible criterion for diagnosis of PADs using MRI.

Endovascular Interventions for the Morbidly Adherent Placenta

Morbidly adherent placentas are a spectrum of abnormalities ranging from placental invasion of the myometrium to invasion past the myometrium and muscular layers into adjacent structures. This entity is becoming more prevalent recently with increased number of cesarean deliveries. Given the high risk of morbidity and mortality, this was traditionally treated with pre-term planned cesarean hysterectomy. However, recently, uterine preservation techniques have been implemented for those women wishing to preserve future fertility or their uterus. Early identification is crucial as studies have shown better outcomes for women treated at tertiary care facilities by a dedicated multidisciplinary team. Interventional radiologists are frequently included in the care of these patients as there are several different endovascular techniques which can be implemented to decrease morbidity in these patients both in conjunction with cesarean hysterectomy and in the setting of uterine preservation. This article will review the spectrum of morbidly adherent placentas, imaging, as well as the surgical and endovascular interventions implemented in the care of these complex patients.

T2-weighted balanced steady-state free procession MRI evaluated for diagnosing placental adhesion disorder in late pregnancy

OBJECTIVE

This study evaluated the imaging characteristics and accuracy of T2-weighted (T2W) balanced steady-state free procession (b-SSFP) magnetic resonance imaging, relative to b-SSFP or single-shot fast spin echo (SSFSE), for the diagnosis of placental adhesion disorder (PAD).

METHODS

Fifty-one pregnant patients suspected of PAD were examined with T2W b-SSFP, b-SSFP and SSFSE. The image types were independently analysed for signs of PAD: abnormal placental bulge (APB), dark intraplacental bands (DIB), placental heterogeneity (PH) and placental protrusion into adjacent structures (PPAS). The sequences were compared for muscle-to-placenta signal ratio, signs of PAD and area under the receiver operating characteristic curve (AUC) for diagnostic accuracy of PAD.

RESULTS

PAD was confirmed in 34 women. The muscle-to-placenta signal ratio was highest in the T2W b-SSFP. The diagnostic rates of APB in T2W b-SSFP were comparable to that of b-SSFP, but were significantly higher than that of SSFSE. The rates of PH in SSFE were comparable to that of b-SSFP, but both were significantly lower than that of T2W b-SSFP. The rates of DIB were significantly higher in T2W b-SSFP images compared with SSFSE. Rates of PPAS were comparable among three sequences. The AUCs of the T2W b-SSFP, b-SSFP and SSFSE were 0.966, 0.890 and 0.823, respectively.

CONCLUSION

T2W b-SSFP has high diagnostic accuracy for PAD relative to SSFSE or b-SSFP, which may be due to its high SNR, T2-weighting and lack of blur.

KEY POINTS

• Signal myometrium-to-placenta ratio was highest in the T2W b-SSFP images. • Diagnostic rate of APB in T2W b-SSFP was highest. • Diagnostic rate of DIB was higher in T2W b-SSFP than in SSFSE. • Diagnostic rate of PH in T2W b-SSFP was highest. • Maximum AUC for diagnostic accuracy of PAD was in T2W b-SSFP.

MRI findings of complications related to previous uterine scars

Although the World Health Organization suggests 10–15% as the adequate cesarean delivery rate to assure optimal prognosis for mother and children, cesarean rates have continuously increased worldwide over the last three decades, even in primiparous women. Moreover, uterine scars after myomectomies, complications of obstetrical interventions and more recently, after fetal surgery, are often observed. This review article describes the most commonly seen complications related to prior uterine scars and discusses their imaging findings, with emphasis on the increasing role of Magnetic Resonance Imaging for diagnosis.

The morbidly adherent placenta: when and what association of signs can improve MRI diagnosis? Our experience

PURPOSE

We aimed to verify whether combination of specific signs improves magnetic resonance imaging (MRI) accuracy in morbidly adherent placenta (MAP).

METHODS

MRI findings for MAP were retrospectively evaluated in 27 women. Histopathology was the reference standard, showing MAP in eight of 27 cases. Specificity, sensitivity, positive predictive value, and negative predictive value were calculated for all MRI signs. Two skilled radiologists analyzed MRI findings, resolving discrepancies by consensus, using three alternative diagnostic criteria during three consecutive sections. First criterion: at least one of reported MRI signs indicates MAP and the absence of any sign is normal; second criterion: at least one statistically significant sign indicates MAP and no sign or nonsignificant sign is normal; third criterion: at least two statistically significant signs indicate MAP and no sign, nonsignificant sign, or only one significant sign is normal.

RESULTS

Using the first criterion yielded an unacceptable rate of false positive results (78.9%). Using the second criterion there were less false positive results (31.5%), and diagnostic accuracy of the second criterion was significantly higher than the first; the third criterion correctly classified 100% of cases.

CONCLUSION

Only specific MRI signs can correctly predict MAP at histopathology, particularly when multiple (at least two) specific signs are observed together.

Placental recess accompanied by a T2 dark band: a new finding for diagnosing placental invasion

PURPOSE

Our aim was to assess the usefulness of a new magnetic resonance imaging (MRI) finding, the placental recess, for diagnosing placental invasion.

METHODS

This retrospective study included 51 patients (mean age 34.1 years, range 26-43 years) with suspected placental invasion who underwent cesarean section. Preoperative MRI was performed using a 1.5-T unit and included axial, sagittal, and coronal T2-weighted imaging (T2WI) with half-Fourier fast spin-echo sequences. Overall, 9 patients showed placental invasion, and 42 did not. Placental recess was defined as a placental deformity with contraction of the placental surface and outer rim of the uterus accompanied by a T2 dark band. Two radiologists independently assessed the presence of the placental recess and conventional findings including uterine bulging, abnormal placental vascularity, placental heterogeneous intensity on T2-weighted imaging (T2WI), and the T2 dark band. Fisher's two-sided exact test was used to compare findings between patients with and without placental invasion. Interobserver reliability was assessed using the kappa statistic.

RESULTS

MRI features had interobserver reliability of >0.40. Placental recess yielded the highest kappa value (0.898). Significant differences were identified between patients with and without placental invasion regarding abnormal placental vascularity, placental heterogeneous intensity, a T2 dark band, and the placental recess on T2WI (p = 0.0282, 0.0003, 0.0003, <0.0001, respectively). The placental recess had sensitivity, specificity, positive and negative predictive values, and accuracy of 56, 100, 100, 91, and 92%, respectively.

CONCLUSION

The placental recess was useful for diagnosing placental invasion, with high interobserver variability and accuracy.

The gravid uterus: MR imaging and reporting of abnormal placentation

Appropriate placentation is critical to maternal and fetal outcomes. Abnormal placentation, including placenta previa and morbidly adherent placenta, is increasing in incidence and is associated with multiple risk factors including advanced maternal age and history of prior cesarean delivery. Magnetic resonance imaging (MRI) is increasingly used in assessing the type and extent of abnormal placentation, often leading to modifications in surgical approach. Here, we review the MRI features and appropriate reporting of placenta previa and the placenta accreta spectrum.

MRI of Placenta Accreta, Placenta Increta, and Placenta Percreta: Pearls and Pitfalls

OBJECTIVE

The purpose of this article is to provide a primer for radiologists performing MRI for suspected placenta accreta, illustrating normal and abnormal findings and diagnostic pitfalls. Appropriate examination indications and recommendations for optimizing image acquisition and interpretation are summarized.

CONCLUSION

MRI increases the accuracy of the workup of high-risk patients and aids in multidisciplinary delivery planning to improve maternal outcome. Reader accuracy and confidence require adherence to examination performance, image interpretation criteria, and awareness of common pitfalls.