The value of specific MRI features in the evaluation of suspected placental invasion

Perspective in diagnostic accuracy of prenatal ultrasound and MRI for placenta accreta

PURPOSE

Placenta accreta (PA) significantly increases the risk of life-threatening maternal outcomes, and its rising prevalence, driven by the increase in cesarean deliveries, underscores the need for precise diagnostic tools to improve clinical management and outcomes. This study aims to evaluate the advanced diagnostic capabilities of prenatal ultrasound and magnetic resonance imaging (MRI) in the detection of PA, a severe obstetric complication characterized by abnormal adherence of the placenta to the myometrium.

MATERIALS AND METHODS

The study utilized a review of current literature and clinical studies to assess the diagnostic accuracy and clinical utility of ultrasound and MRI in identifying PA. Both imaging modalities were evaluated for their ability to assess the depth and extent of placental invasion, as well as their complementary roles in prenatal diagnosis. The experimental system included detailed imaging protocols for ultrasound and MRI, focusing on placental and uterine structures, and their application in real-world clinical settings.

RESULTS

The findings demonstrate that ultrasound and MRI are highly effective in diagnosing PA, with each modality offering unique advantages. Ultrasound is widely accessible and serves as the first-line diagnostic tool, providing detailed visualization of placental adherence and vascular patterns. MRI, on the other hand, offers superior soft tissue contrast and is particularly valuable in complex cases or when ultrasound findings are inconclusive. Together, these imaging techniques enable accurate evaluation of placental invasion, facilitating timely and targeted prenatal interventions. The study also highlights the potential for improved maternal and fetal outcomes through early diagnosis and optimized pregnancy management.

CONCLUSIONS

Prenatal ultrasound and MRI are indispensable tools in the diagnosis and management of placenta accreta, offering complementary insights that enhance diagnostic precision. Their combined use allows for detailed assessment of placental and uterine structures, guiding clinical decision-making and improving outcomes for both mothers and infants. Future advancements in imaging technology and research hold promise for further enhancing diagnostic accuracy and expanding clinical applications, ultimately contributing to safer and more effective care for patients with PA.

Grading magnetic resonance imaging signs for diagnosing invasive placenta accreta spectrum disorders

INTRODUCTION

Placenta accreta spectrum (PAS) disorders result from abnormal placental attachment, leading to varying degrees of myometrial invasion. Magnetic resonance imaging (MRI) plays a crucial role in assessing the depth and extent of placental invasion. This study aims to evaluate the correlation between quantified MRI findings and the diagnosis of PAS, as classified according to the FIGO system.

MATERIALS AND METHODS

A retrospective analysis was conducted on 556 high-risk PAS patients, defined as those with placenta previa or a history of previous cesarean sections. Ten predefined MRI signs were assessed board certified radiologists. Multivariate logistic regression was used to identify independent predictors of invasive PAS. The positive predictive value (PPV) and negative predictive value (NPV) were calculated to assess the diagnostic performance of signs.

RESULTS

Among the 556 cases, 150 (26.98 %) were classified as non-PAS, 180 (32.37 %) as placenta accreta, 158 (28.42 %) as placenta increta, and 68 (12.23 %) as placenta percreta. Four MRI signs were identified as significant predictors of invasive PAS: bladder wall interruption (odd ratio [OR] = 160.17), placental ischemic infarction (OR = 19.91), placental protrusion (OR = 14.66), and myometrial thinning (OR = 14.07). The PPV of these signs ranged from 70 % to 85 %, while the NPV ranged from 65 % to 72 %. Multivariate analysis confirmed these MRI findings as independent predictors of invasive PAS.

CONCLUSIONS

This study identified four key MRI signs as reliable predictors of invasive PAS, which can effectively inform clinical decision-making regarding surgical interventions, such as cesarean hysterectomy.

Comparison of MRI findings for predicting massive hemorrhage during cesarean section in patients with placental malposition: partial placental volume of lower uterine segment is an accurate and objective indicator

PURPOSE

To comprehensively compare the diagnostic ability and inter-reader agreement of magnetic resonance imaging (MRI) findings for predicting massive hemorrhage after cesarean section in patients with placental malposition, aiming to identify the most reliable and objective indicators.

METHODS

Totally, 148 consecutive patients with placental malposition underwent MRI and cesarean section at our hospital between January 2014 and July 2021. The patients were divided into massive and non-massive hemorrhage groups. MRI findings of placenta accreta, placental position, and placental volume were evaluated by two radiologists, and inter-reader agreement was calculated. Diagnostic ability for predicting massive hemorrhage was evaluated using receiver operating characteristic analysis.

RESULTS

Intraplacental T2 dark bands (100% vs. 58.2%, p = 0.001), placental bulge (50% vs. 3.7%, p < 0.001), loss of retroplacental T2 hypointense line (100% vs. 67.2%, p = 0.01), myometrial thinning (92.9% vs. 57.5%, p = 0.009), total placenta previa (64.3% vs. 23.9%, p = 0.033), and anterior placenta (35.7% vs. 10.5%, p = 0.02) were significantly observed in massive hemorrhage group. Partial placental volume of lower uterine segment (PVpartial) was larger in massive hemorrhage group (166 [108-214] cm3 vs. 70 [43-112] cm3 p < 0.001), had the second highest intraclass correlation coefficient (0.84), and had the highest area under the curve (0.81) for diagnosing massive hemorrhage.

CONCLUSION

This study revealed PVpartial is an accurate and objective indicator for massive hemorrhage, independent of radiologists' experience. This indicator potentially enables prediction of massive hemorrhage, improving pre-operative planning in high-risk pregnancies.

Diffusion lacunae: a novel MR imaging finding on diffusion-weighted imaging for diagnosing placenta accreta spectrum

OBJECTIVE

To evaluate the usefulness of novel diffusion-weighted imaging (DWI) findings for diagnosing placenta accreta spectrum (PAS).

MATERIALS AND METHODS

This retrospective study included 49 pregnant women with suspected PAS who underwent 1.5 T placental MRI. Diffusion lacunae were defined as intraplacental areas showing hypointensity on DWI and hyperintensity on the apparent diffusion coefficient map. Two radiologists evaluated the number and size of placental lacunae on DWI, and flow void in the diffusion lacunae on T2-weighted imaging. The radiologists also evaluated established MRI features of PAS described in the SAR-ESUR consensus statement. Pearson's chi-square test or Mann-Whitney U test was used to compare findings between patients with and without PAS. Interobserver reliability for DWI and established MRI features was also assessed. Optimal thresholds for the number and maximum size of diffusion lacunae for differentiating PAS from the no-PAS group were determined using receiver operating characteristic curve analyses.

RESULTS

Eighteen patients were diagnosed with PAS, and 31 patients with placental previa without PAS. The number and maximum size of diffusion lacunae were significantly larger in patients with than in patients without PAS (p < 0.0001). Combining assessment of the number of diffusion lacunae with assessment of their maximum size yielded a diagnostic performance with sensitivity, specificity and accuracy of 83%, 94% and 90%, respectively. Flow voids within the diffusion lacunae had sensitivity, specificity and accuracy of 88%, 84% and 86%, respectively.

CONCLUSION

The number and size of diffusion lacunae, and T2 flow void in diffusion lacunae may be useful findings for diagnosing PAS.

Magnetic Resonance Imaging Findings of Placenta Accreta Spectrum Disorder: A Pictorial Review

ABSTRACT

Magnetic resonance imaging (MRI) is used for diagnosing placenta accreta spectrum disorders (PASDs) because of its advanced soft-tissue contrast and spatial resolution capabilities, offering better contrast, improved spatial resolution, and a wider field of view compared with ultrasound. Using a 1.5-Tesla MRI protocol with multiple sequences, MRI can detect indicative signs of PASD such as placental signal heterogeneity, interruption of the myometrium-placenta interface, and abnormal vascularization. Specific sequences such as T2 SSFSE, FIESTA, and T1-weighted and diffusion-weighted imaging are used to assess placental attachment, myometrial invasion, and intraplacental hemorrhages. Significant MRI findings include thick low-signal T2 intraplacental bands, invasions into the cervix or bladder, and abnormal periplacental vascularity. MRI complements ultrasound and is crucial for the prenatal diagnosis of PASD, aiding in treatment planning and patient management, thereby reducing the associated fetal and maternal morbidity and mortality. The objective of this pictorial review was to outline the placental MRI technique and review the main imaging findings in placental MRI for PASD. This review encompasses anonymized patient images obtained following written consent.

Placental T2-weighted MRI-based radiomics-clinical nomogram to predict postpartum hemorrhage of placenta previa

BACKGROUND

Placenta previa is an obstetric complication related to severe maternal morbidity and mortality. Magnetic resonance imaging (MRI) can be used for the preoperative evaluation of postpartum hemorrhage.

PURPOSE

To investigate the value of MRI-based radiomics analysis in predicting postpartum hemorrhage among pregnant women with placenta previa.

MATERIAL AND METHODS

Preoperative T2-weighted MRI and related clinical data of 371 patients were retrospectively collected, and these patients were randomly allocated into two subsets: the training dataset (n = 260) and the validation dataset (n = 111). The logistic regression (LR) classifier was used for the development of the radiomics model and the calculation of the radiomics score (Radscore).

RESULTS

A total of eight radiomics features and five clinical features were selected for model development. The area under the receiver operating characteristic curve (AUC) of the radiomics model in the training and validation datasets were 0.929 (95% confidence interval [CI] = 0.891-0.957) and 0.914 (95% CI = 0.846-0.959), respectively. Combined with clinical factors, nomograms demonstrated improved diagnostic efficacy, with an AUC of 0.968 (95% CI = 0.939-0.986) in the training dataset and 0.947 (95% CI = 0.888-0.981) in the validation dataset.

CONCLUSION

The MRI-based model has certain value in predicting postpartum hemorrhage in pregnant women with placenta previa.

The MRI estimations of placental volume, T2 dark band volume, and cervical length correlate with massive hemorrhage in patients with placenta accreta spectrum disorders

PURPOSE

To identify whether placental volume, T2 dark band volume, and cervical length measured by MRI correlate with massive hemorrhage (MH) in patients with placenta accreta spectrum (PAS) disorders.

METHODS

A total of 163 pregnant women with PAS underwent preoperative MRI examination were divided into MH group and non-MH group. The placental volume, T2 dark band volume, and cervical length of PAS patients were measured and evaluated their ability to identify MH in patients with PAS.

RESULTS

Patients with MH had a significantly larger placental volume, larger T2 dark band volume, and shorter cervical length than patients without MH (all P < 0.001). Multivariable logistic regression showed that placental volume (> 890 cm3), T2 dark band volume (> 35 cm3), and cervical length (< 30 mm) were significant independent risk factor in identification of MH. In all PAS patients, a positive linear correlation was found between placental volume and amount of blood loss (r = 0.527), and between T2 dark band volume and amount of blood loss (r = 0.642), and a negative linear correlation was found between cervical length and amount of blood loss (r = - 0.597). When combined with the three MRI indicators, the sensitivity and specificity in identifying cases at high risk for MH were 91.638% and 94.051%, respectively, with area under the curve (AUC) of 0.923.

CONCLUSION

The placental volume, T2 dark band volume, and cervical length might be used to predict MH in patients with PAS.

MR imaging findings of massive perivillous fibrin deposition of the placenta: A case report

Massive perivillous fibrin deposition (MPFD) of the placenta is characterized by the obliteration of the villous trophoblast with extensive deposition of fibrinoid material in the intervillous space. Here, we describe the MRI findings of a case of MPFD. The placenta demonstrates linear and geographical hypointensity on T2-weighted imaging, which is suggested to mainly reflect fibrin deposition. This finding should be noted, particularly in patients with miscarriage in their past history.

Multimodality Imaging for Rare Presentation of Placenta Increta in the First Trimester in a Patient with Previous Cesarean Section and Asherman Syndrome

We report multi-modality imaging (Ultrasound and Magnetic Resonance Imaging) findings of a rare complication in a multi-gravida patient with history of Asherman syndrome presenting with placenta increta in a cesarean scar ectopic pregnancy. The appropriate diagnosis was established with imaging and patient was managed surgically with total abdominal hysterectomy and bilateral salpingectomy. Asherman syndrome and its management of hysteroscopic adhesiolysis are associated with increased odds of placenta accreta spectrum and postpartum hemorrhage. Patients with Asherman syndrome are considered high risk in pregnancy and should be closely monitored for placental site abnormalities during current and subsequent pregnancies.

Placental T2WI MRI-based radiomics-clinical nomogram predicts suspicious placenta accreta spectrum in patients with placenta previa

BACKGROUND

The incidence of placenta accreta spectrum (PAS) increases in women with placenta previa (PP). Many radiologists sometimes cannot completely and accurately diagnose PAS through the simple visual feature analysis of images, which can affect later treatment decisions. The study is to develop a T2WI MRI-based radiomics-clinical nomogram and evaluate its performance for non-invasive prediction of suspicious PAS in patients with PP.

METHODS

The preoperative MR images and related clinical data of 371 patients with PP were retrospectively collected from our hospital, and the intraoperative examination results were used as the reference standard of the PAS. Radiomics features were extracted from sagittal T2WI MR images and further selected by LASSO regression analysis. The radiomics score (Radscore) was calculated with logistic regression (LR) classifier. A nomogram integrating Radscore and selected clinical factors was also developed. The model performance was assessed with respect to discrimination, calibration and clinical usefulness.

RESULTS

A total of 6 radiomics features and 1 clinical factor were selected for model construction. The Radscore was significantly associated with suspicious PAS in both the training (p < 0.001) and validation (p < 0.001) datasets. The AUC of the nomogram was also higher than that of the Radscore in the training dataset (0.891 vs. 0.803, p < 0.001) and validation dataset (0.897 vs. 0.780, p < 0.001), respectively. The calibration was good, and the decision curve analysis demonstrated the nomogram had higher net benefit than the Radscore.

CONCLUSIONS

The T2WI MRI-based radiomics-clinical nomogram showed favorable diagnostic performance for predicting PAS in patients with PP, which could potentially facilitate the obstetricians for making clinical decisions.

Magnetic Resonance Imaging-Based Radiomics Nomogram to Predict Intraoperative Hemorrhage of Placenta Previa

OBJECTIVE

Placenta previa (PP) is associated with intraoperative and postpartum hemorrhage, increased maternal morbidity and mortality. We aimed to develop a magnetic resonance imaging (MRI)-based nomogram to preoperative prediction of intraoperative hemorrhage (IPH) for PP.

STUDY DESIGN

A total of 125 PP pregnant women were divided into a training set (n = 80) and a validation set (n = 45). An MRI-based model was built for the classification of patients into IPH and non-IPH groups in a training set and a validation set. Multivariate nomograms were built according to radiomics features. Receiver operating characteristic (ROC) curve was used to assess the model. Predictive accuracy of nomogram were assessed by calibration plots and decision curve analysis.

RESULTS

In multivariate analysis, placenta position, placenta thickness, cervical blood sinus, and placental signals in the cervix were significantly independent predictors for IPH (all ps < 0.05). The MRI-based nomogram showed favorable discrimination between IPH and non-IPH groups. The calibration curve showed good agreement between the estimated and the actual probability of IPH. Decision curve analysis also showed a high clinical benefit across a wide range of probability thresholds. Area under the ROC curve was 0.918 (95% confidence interval [CI]: 0.857-0.979) in the training set and 0.866 (95% CI: 0.748-0.985) in the validation set by the combination of four MRI features.

CONCLUSION

The MRI-based nomograms might be a useful tool for the preoperative prediction of IPH outcomes for PP. Our study enables obstetricians to perform adequate preoperative evaluation to reduce blood loss and cesarean hysterectomy.

KEY POINTS

· MRI is an important method for preoperative assessment of the risk of placenta previa.. · MRI-based nomogram can assess the risk of intraoperative bleeding of placenta previa.. · MRI is helpful for more comprehensive evaluation of placenta previa and adequate preoperative preparation..

A Deep Learning Pipeline Using Prior Knowledge for Automatic Evaluation of Placenta Accreta Spectrum Disorders With MRI

BACKGROUND

The diagnosis of prenatal placenta accreta spectrum (PAS) with magnetic resonance imaging (MRI) is highly dependent on radiologists' experience. A deep learning (DL) method using the prior knowledge that PAS-related signs are generally found along the utero-placental borderline (UPB) may help radiologists, especially those with less experience, to mitigate this issue.

PURPOSE

To develop a DL tool for antenatal diagnosis of PAS using T2-weighted MR images.

STUDY TYPE

Retrospective.

SUBJECTS

Five hundred and forty pregnant women with clinically suspected PAS disorders from two institutions, divided into training (409), internal test (103), and external test (28) datasets.

FIELD STRENGTH/SEQUENCE

Sagittal T2-weighted fast spin echo sequence at 1.5 T and 3 T.

ASSESSMENT

An nnU-Net was trained for placenta segmentation. The UPB straightening approach was used to extract the utero-placental boundary region. The UPB image was then fed into DenseNet-PAS for PAS diagnosis. DenseNet-PP learnt placental position information to improve the PAS diagnosis performance. Three radiologists with 8, 10, and 12 years of experience independently evaluated the images. Two radiologists marked the placenta tissue. Histopathological findings were the reference standard.

STATISTICAL TESTS

Area under the curve (AUC) was used to evaluate the classification. Dice coefficient evaluated the segmentation between radiologists and the model performance. The Mann-Whitney U-test or the chi-squared test assessed the significance of differences. Decision curve analysis was used to determine clinical effectiveness. DeLong's test was used to compare AUCs.

RESULTS

Of the 540 patients, 170 had PAS disorders confirmed by histopathology. The DL model using UPB images and placental position yielded the highest AUC of 0.860 and 0.897 in internal test and external test cohorts, respectively, significantly exceeding the performance of three radiologists (internal test AUC, 0.737-0.770).

DATA CONCLUSION

By extracting the UPB image, this fully automatic DL pipeline achieved high accuracy and may assist radiologists in PAS diagnosis using MRI.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 2.

Deep Learning Model Based on Multisequence MRI Images for Assessing Adverse Pregnancy Outcome in Placenta Accreta

BACKGROUND

Preoperative assessment of adverse outcomes risk in placenta accreta spectrum (PAS) disorders is of high clinical relevance for perioperative management and prognosis.

PURPOSE

To investigate the association of preoperative MRI multisequence images and adverse pregnancy outcomes by establishing a deep learning model in patients with PAS.

STUDY TYPE

Retrospective.

POPULATION

323 pregnant women (age from 20 to 46, the median age is 33), suspected of PAS, underwent MRI to assess the PAS, divided into the training (N = 227) and validation datasets (N = 96).

FIELD STRENGTH/SEQUENCE

1.5T scanner/fast imaging employing steady-state acquisition sequence and single shot fast spin echo sequence.

ASSESSMENT

Different deep learning models (i.e., with single MRI input sequence/two sequences/multisequence) were compared to assess the risk of adverse pregnancy outcomes, which defined as intraoperative bleeding ≥1500 mL and/or hysterectomy. Net reclassification improvement (NRI) was used for quantitative comparison of assessing adverse pregnancy outcome between different models.

STATISTICAL TESTS

The AUC, sensitivity, specificity, and accuracy were used for evaluation. The Shapiro-Wilk test and t-test were used. A P value of <0.05 was considered statistically significant.

RESULTS

215 cases were invasive placenta accreta (67.44% of them with adverse outcomes) and 108 cases were non-invasive placenta accreta (9.25% of them with adverse outcomes). The model with four sequences assessed adverse pregnancy outcomes with AUC of 0.8792 (95% CI, 0.8645-0.8939), with ACC of 85.93% (95%, 84.43%-87.43%), with SEN of 86.24% (95% CI, 82.46%-90.02%), and with SPC of 85.62% (95%, 82.00%-89.23%) on the test cohort. The performance of model with four sequences improved above 0.10 comparing with that of model with two sequences and above 0.20 comparing with that of model with single sequence in terms of NRI.

DATA CONCLUSION

The proposed model showed good diagnostic performance for assessing adverse pregnancy outcomes.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 2.

Placental volume as a novel sign for identifying placenta accreta spectrum in pregnancies with complete placenta previa

BACKGROUND

Placenta accreta spectrum (PAS) carries an increased risk of maternal-fetal mortality and morbidity, and magnetic resonance imaging (MRI) features for PAS have been used for preoperative identification. This study aims to investigate the role of placental volume evaluated by MRI in identifying PAS in pregnant women with complete placenta previa.

METHODS

Totally 163 cases of complete placenta previa pregnant women with a history of cesarean section underwent MRI for suspected PAS were included. We categorized the patients into two groups according to the presence or absence of PAS, and the maternal-fetal perinatal outcomes and placental volume analyzed by 3D Slice software were compared.

RESULTS

There were significantly more gravidity, parity, and number of previous cesarean delivery in the PAS group (P < 0.05). Significant differences were also found between the two groups with respect to the following baseline characteristics: gestational age at delivery, intraoperative blood loss, blood transfusion, and neonatal birth weight (P < 0.05). Of 163 women in the study, 7 (4.294%) required cesarean hysterectomy for high-grade PAS or pernicious bleeding during cesarean section, and PAS was confirmed with histologic confirmation in 6 (85.714%) cases. The placental volume in PAS group was greater than that in the non-PAS group (P < 0.05). With a threshold of more than 887 cm3, the sensitivity and specificity in identifying PAS were 85.531% and 83.907% respectively, with AUC 0.908 (95% CI: 0.853-0.948).

CONCLUSIONS

Placental volume may be a promising indicator of PAS in complete placenta previa patients with a history of cesarean section.

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.

Focal Placenta Accreta in a Congenitally Malformed Uterus: A Case Report

Placenta accreta is defined as an abnormal trophoblast invasion of part or all of the placenta into the myometrium of the uterine wall. It is a well-known cause of maternal morbidity and mortality. Here, we present a unique case of focal placenta accreta due to a bicornuate uterus and a history of septum resection. We also discuss its management and outcome. The patient underwent a classical cesarean section and reinforcement of the anterior and posterior uterine wall. The patient had a history of surgery for correction of uterine malformation, which may have resulted in an abnormal adherence of the placenta.

Risk factors of MRI findings for predicting patient outcomes of placenta accreta spectrum and placenta previa after prophylactic balloon occlusion of the internal iliac artery

PURPOSE

Our study aimed to identify the risk factors of magnetic resonance imaging (MRI) findings for predicting patient outcomes of placenta accreta spectrum (PAS) and placenta previa after prophylactic balloon occlusion of the internal iliac artery (PBOIIA).

MATERIALS AND METHODS

This retrospective analysis was performed using the clinical records of 46 patients diagnosed with PAS and placenta previa who underwent PBOIIA during caesarean section (CS). The possible clinical risk factors for adverse maternal outcomes were evaluated by consulting patients' clinical records. The inclusion criteria for the massive bleeding group were as follows: estimated blood loss (EBL) > 2500 mL, packed red blood cell (pRBC) transfusion (>4 units), and need for hysterectomy or transcatheter arterial embolization after delivery. The MRI features were compared between the massive and non-massive bleeding groups.

RESULTS

Patients in the massive bleeding group (n = 22) had a significantly longer operation time (p < 0.001), more EBL (p < 0.001), more pRBC transfusions (p < 0.001), and a prolonged postoperative hospital stay (p < 0.05). MRI features showed a T2 dark bands, placenta bulge, and abnormal blood vessels in the placental bed more frequently in the massive bleeding group (p < 0.05). In the multiple logistic regression analysis, T2 dark bands (odds ratio 9.1, p = 0.048) and placental bulge (odds ratio 5.1, p = 0.014) remained statistically significant.

CONCLUSION

T2 dark bands and placental bulges observed on an MRI can predict adverse maternal outcomes in patients with PAS and placenta previa undergoing PBOIIA. If these findings are observed on a preoperative MRI, effective management strategies should be prepared for the possibility of massive hemorrhage during CS.

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.

Evaluation of the Tramline Sign in the Prediction of Placenta Accreta Spectrum and Perioperative Outcomes in Anterior Placenta Previa

PURPOSE

 To evaluate perioperative outcomes and the prognostic role of the tramline sign in a cohort of women with anterior placenta previa.

MATERIALS AND METHODS

 Retrospective analysis of 3D ultrasound volumes from women with anterior placenta previa who underwent ultrasound examination beyond 32 weeks. 3D and 3D color volumes were obtained from a sagittal section of the uterus bisecting a partially full bladder and processed using Crystal Vue and Crystal Vue Flow rendering to look for the "tramline sign". "Partial obliteration" was defined as a loss of some or part of the uterine-serosal interface and "full obliteration" as when both interfaces were interrupted. Postnatal ascertainment of placenta accreta spectrum (PAS) was confirmed by findings recorded intraoperatively or on a pathology report.

RESULTS

 65 cases were included. The tramline sign was "partially" (17) or "fully" (19) obliterated in 36 cases (55.4 %), and present in 29 (44.6 %). Obliteration was associated with earlier gestational age at delivery (35 + 1 (26 + 3-38 + 3) vs. 36 + 4 (25 + 3-38 + 0) weeks, p = 0.005), greater estimated blood loss (800 (400-11 000) vs. 600 (300-2100) mls, p = 0.003), longer operative time (155 (60-240) vs. 54 (25-80) minutes, p < 0.001), higher rate of hysterectomy (97.2 % vs. 0.0 %, p < 0.001), longer postoperative admission (7 (3-19) vs. 3 (1-5) days, p < 0.001) and a 100 % rate of postnatal diagnosis of PAS. The finding of an "obliterated" tramline sign identified all women that required hysterectomy and all cases of PAS.

CONCLUSION

 A "partially or fully obliterated" tramline sign is strongly associated with indicators of operative complexity, the postnatal confirmation of PAS, and the need for peripartum hysterectomy.

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.

The maximum length of T2-dark intraplacental bands may help predict intraoperative haemorrhage in pregnant women with placenta accreta spectrum (PAS)

PURPOSE

To investigate the relationship between the maximum length of T2-dark intraplacental bands (MLTIB) and intraoperative haemorrhage in pregnant women with placenta accreta spectrum (PAS).

METHODS

Between February 2018 and February 2021, 86 pregnant women with PAS who delivered in Taizhou Hospital of Zhejiang Province and underwent preoperative magnetic resonance imaging (MRI) examination were retrospectively recruited. The presence of T2-dark intraplacental bands, placental/uterine bulge, loss of retroplacental T2-hypointense line, myometrial thinning, bladder wall interruption, focal exophytic mass, and abnormal vascularization of placental bed were recorded, and the MLTIB was measured. The relative risk ratios of the MRI findings and intraoperative bleeding were measured. Receiver operating characteristic (ROC) analysis was used to evaluate the ability of the MLTIB to help predict intraoperative haemorrhage in pregnant women with PAS.

RESULTS

Of the 86 pregnant women, 32 had intraoperative blood loss ≥ 1000 ml; of these, 18 had intraoperative blood loss ≥ 2000 ml. Abnormal vascularization of placental bed was associated with the highest relative risk ratio for the detection of intraoperative haemorrhage (RR = 10.66), followed by the presence of T2-dark intraplacental bands (RR = 8.02). The optimal cut-off of the MLTIB for predicting intraoperative haemorrhage (≥ 1000 ml) in pregnant women with PAS was 28.95 mm, and the AUC was 0.91 (sensitivity: 84%; specificity: 91%). The optimal cut-off of the MLTIB for predicting massive intraoperative haemorrhage (≥ 2000 ml) was 35.65 mm, and the AUC was 0.94 (sensitivity: 89%; specificity: 85%).

CONCLUSION

MLTIB was related to intraoperative haemorrhage in pregnant women with PAS. An MLTIB greater than 28.95 mm is an effective predictor of intraoperative haemorrhage. An MLTIB of 35.65 mm or greater strongly suggests the possibility of massive intraoperative haemorrhage.

Intraplacental T2-hypointense bands may help predict placental invasion depth and postpartum hemorrhage in placenta accrete spectrum disorders in high-risk gravid patients

INTRODUCTION

Accurate noninvasive prenatal diagnosis of placenta accreta spectrum (PAS) disorder is critical for delivery management.

PURPOSE

To evaluate the diagnostic ability of MRI features in predicting the PAS, invasive depth and postpartum hemorrhage (PPH) in high-risk gravid patients.

MATERIALS AND METHODS

Between February 2019 and November 2020, women with ultrasound (US)-suspected PAS were enrolled. With the exclusion criteria, 80 women were included in the study. Two experienced genitourinary radiologists reviewed and recorded the MRI features. The chi square test was used to compare the effectiveness of MRI features. Relative risk ratios were computed to test the association of intraplacental T2-hypointense bands with poor outcomes of cesarean section. Receiver operating characteristic (ROC) analyses based on the number and area of intraplacental T2-hypointense bands were used to predict PAS, invasion depth, and PPH.

RESULTS

PAS was diagnosed in 56 of 80 women (70%). At delivery, 24 of 80 women (30%) experienced PPH (≥1000 mL). Intraplacental T2-hypointense bands were detected at MRI in 28 of 56 women with PAS (50%). The relative risk ratio of intraplacental T2-hypointense bands was 1.51 for PAS, 3.17 for depth of PAS invasiveness and 4.74 for PPH. The largest areas of intraplacental T2-hypointense bands for predicting PAS, invasion depth and PPH were 0.66 cm², 1.68 cm² and 1.99 cm², respectively.

DISCUSSION

The appearance of intraplacental T2-hypointense bands has important diagnostic value for PAS, its invasion depth and PPH. The area of the largest T2-hypointense band in the placenta can predict poor outcomes of cesarean section.

Morbidly Adherent Placenta in the First Trimester with Consecutive Hysterectomy

Background Morbidly adherent placenta (MAP) represents a risk factor for a maternal adverse outcome and its incidence continues to rise following the increasing rate of caesarean deliveries. The detection of a pathology of placental adherence in the first trimester is challenging. Transvaginal ultrasound represents (TVUS) a reliable tool for accurate and timely diagnosis. Case We report on a case of MAP in a pregnant woman at 10 weeks of gestation with two prior caesarean deliveries. She presented with abdominal pain and hematometra. The first trimester diagnosis was made with TVUS and confirmed with magnetic resonance imaging. The patient required an urgent hysterectomy. Conclusion Antenatal care in the first trimester in women with a previous cesarean delivery should include a detailed examination of the placenta with TVUS.

The Volume of T2 Low-Signal Band and the Width of the Widest Blood Vessel in Placenta Measured by MRI in Pregnant Women with Different Types of Placental Implantation and Its Differential Value

Objective

To explore the value of magnetic resonance imaging (MRI) in measuring the volume of T2 low-signal band and the width change of the widest blood vessel in placenta in pregnant women with different types of placenta implantation (PI).

Methods

From November 2020 to August 2021, 116 patients in our hospital who underwent placental MRI because of ultrasound or clinical suspicion of PI were selected as the research object. According to the "gold standard" (clinical or surgical pathological results), 79 cases with PI were diagnosed as PI group, and 37 cases without PI were no PI group. The clinical features, MRI signs, T2 hyposignal zone volume, and the width of the widest blood vessel in placenta were compared between the two groups and different types of PI patients. Logistic regression was used to analyze the influencing factors of PI and PI classification, and the receiver-operating characteristic (ROC) was used to analyze the value of T2 low-signal zone volume and the widest blood vessel width in the placenta for different types of PI.

Results

The history of cesarean section, uneven placental signal, the proportion of T2 low-signal band shadow, the volume of T2 low-signal band, and the width of the widest blood vessel in placenta in PI group were higher than those in non-PI group (p < 0.05); the history of cesarean section, uneven placental signal, T2 hypointense band shadow, the volume of T2 hypointense band, and the increase of the width of the widest blood vessel in placenta are independent risk factors for PI (p < 0.05); with the increase of implantation depth, the proportion of T2 hypointense band shadow, the volume of T2 hypointense band, and the width of the widest blood vessel in placenta gradually increased (p < 0.05); T2 hypointense band shadow, T2 hypointense band volume, and the widest blood vessel width in placenta are all influencing factors of PI classification (p < 0.05); ROC showed that the volume of T2 low-signal band and the width of the widest blood vessel in placenta, the AUC of combined identification of adhesive PI, implanted PI, implanted PI, and penetrating PI were 0.846 and 0.899, respectively, which was higher than that of single identification (p < 0.05).

Conclusion

MRI measurement of T2 hyposignal zone volume and the widest blood vessel width in placenta can be used for PI diagnosis and classification differentiation and provide reliable basis for clinical prenatal preparation and treatment planning.

Evaluation of classic and novel ultrasound signs of placenta accreta spectrum

OBJECTIVES

Improvement in the antenatal diagnosis of placenta accreta spectrum (PAS) would allow preparation for delivery in a referral center, leading to decreased maternal morbidity and mortality. Our objectives were to assess the performance of classic ultrasound signs and to determine the value of novel ultrasound signs in the detection of PAS.

METHODS

This was a retrospective cohort study of women with second-trimester placenta previa who underwent third-trimester transvaginal ultrasound and all women with PAS in seven medical centers. A retrospective image review for signs of PAS was conducted by three maternal-fetal medicine physicians. Classic signs of PAS were defined as placental lacunae, bladder-wall interruption, myometrial thinning and subplacental hypervascularity. Novel signs were defined as small placental lacunae, irregular placenta-myometrium interface (PMI), vascular PMI, non-tapered placental edge and placental bulge towards the bladder. PAS was diagnosed based on difficulty in removing the placenta or pathological examination of the placenta. Multivariate regression analysis was performed and receiver-operating-characteristics (ROC) curves were generated to assess the performance of combined novel signs, combined classic signs and a model combining classic and novel signs.

RESULTS

A total of 385 cases with placenta previa were included, of which 55 had PAS (28 had placenta accreta, 11 had placenta increta and 16 had placenta percreta). The areas under the ROC curves for classic markers, novel markers and a model combining classic and novel markers for the detection of PAS were 0.81 (95% CI, 0.75-0.88), 0.84 (95% CI, 0.77-0.90) and 0.88 (95% CI, 0.82-0.94), respectively. A model combining classic and novel signs performed better than did the classic or novel markers individually (P = 0.03). An increasing number of signs was associated with a greater likelihood of PAS. With the presence of 0, 1, 2 and ≥ 3 classic ultrasound signs, PAS was present in 5%, 24%, 57% and 94% of cases, respectively.

CONCLUSIONS

We have confirmed the value of classic ultrasound signs of PAS. The use of novel ultrasound signs in combination with classic signs improved the detection of PAS. These findings have clinical implications for the detection of PAS and may help guide the obstetric management of patients diagnosed with these placental disorders. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Magnetic resonance imaging and previous cesarean section in placenta accrete spectrum disorder: Predictor model

OBJECTIVE

To evaluate objective criteria of Magnetic Resonance Imaging (MRI) of Placenta Accreta Spectrum disorder (PAS) analyzing interobserver agreement and to derive a model including imaging and clinical variables to predict PAS.

METHODS

A retrospective review including patients submitted to MRI with suspicious findings of PAS on ultrasound. Exclusion criteria were lack of pathology or surgical information and missing or poor-quality MRI. Two radiologists analyzed six MRI features, and significant clinical data were also recorded. PAS confirmed on pathology or during intraoperative findings were considered positive for the primary outcome. Variables were tested through logistic regression models.

RESULTS

Final study included 96 patients with a mean age of 33 years and 73.0% of previous C-sections. All MRI features were significantly associated with PAS for both readers. After logistic regression fit, including MRI signs with a moderate or higher interobserver agreement, intraplacental T2 dark band was the most significant radiologic criteria, and ROC analysis resulted in an AUC = 0.782. After including the most relevant clinical data (previous C-section) to the model, the ROC analysis improved to an AUC = 0.893.

CONCLUSION

Simplified objective criteria on MRI, including intraplacental T2 dark band associated with clinical information of previous C-sections, had the highest accuracy and was used for a predictive model of PAS.

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.

Prediction of placenta accreta spectrum using texture analysis on coronal and sagittal T2-weighted imaging

PURPOSE

To separately perform visual and texture analyses of the axial, coronal, and sagittal planes of T2-weighted images and identify the optimal method for differentiating between the normal placenta and placenta accreta spectrum (PAS).

METHODS

Eighty consecutive patients (normal group, n = 50; PAS group, n = 30) underwent preoperative MRI. A scoring system (0-2) was used to evaluate the degree of abnormality observed in visual analysis (bulging, abnormal vascularity, T2 dark band, placental heterogeneity). The axial, coronal, and sagittal planes were manually segmented separately to obtain texture features, and seven combinations were obtained: axial; coronal; sagittal; axial and coronal; axial and sagittal; coronal and sagittal; and axial, coronal, and sagittal. Feature selection using the least absolute shrinkage and selection operator method and model construction using a support vector machine algorithm with k-fold cross-validation were performed. AUC was used to evaluate diagnostic performance.

RESULTS

The AUC of visual analysis was 0.75. The model 'coronal and sagittal' had the highest AUC (0.98) amongst the seven combinations. The fivefold cross-validation for the model 'coronal and sagittal' showed AUCs of 0.85 and 0.97 in training and validation sets, respectively. The AUC of the model 'coronal and sagittal' for all subjects was significantly higher than that of visual analysis (0.98 vs. 0.75; p < 0.0001).

CONCLUSION

The model 'coronal and sagittal' can accurately differentiate between the normal placenta and PAS, with a significantly better diagnostic performance than visual analysis. Texture analysis is an optimal method for differentiating between the normal placenta and PAS.

Comparison of Magnetic Resonance Imaging of the Lower Uterine Segment in Pregnant Women with Central Placenta Previa with and without Placenta Accreta Spectrum from a Single Center

BACKGROUND Placenta accreta spectrum (PAS) includes placenta increta, placenta percreta, and placenta accreta. PAS is due to abnormal decidualization and can lead to severe maternal hemorrhage and occurs in up to 3% of women with central placental previa (CPP). This study from a single center aimed to compare the magnetic resonance imaging (MRI) changes in the lower uterine segment in pregnant women with CPP, with and without PAS. MATERIAL AND METHODS This retrospective study includes 90 pregnant women with PAS and 66 pregnant women without PAS. All participants were confirmed to have CPP by MRI. Eight MRI parameters were assessed and compared with perinatal outcomes for mothers and newborns. RESULTS The pregnancies in the non-PAS group had less operative time (P=0.001), less intrapartum hemorrhage (P<0.001), and less blood transfusion than the PAS group (P<0.001). The 8 MRI variables with different odds ratios were placenta thickness (4.20), cervical lengths (3.27), placental dark T2 bands area (5.10), cervical marginal sinus (3.04), bladder bulge (3.55), myometrial thinning (6.41), lower uterine segment bulge (4.61), and placental signals in the cervix (9.14). The sensitivity and specificity of MRI in the diagnosis of PAS were 82.22% and 91.09%, respectively, by the combined 8 MRI features, and the area under the curve (AUC) was 0.816. CONCLUSIONS The findings from this study showed that MRI of the lower uterine segment had high sensitivity and specificity for the diagnosis of PAS in pregnant women with CPP.

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."

Dynamic contrast enhanced magnetic resonance imaging: A review of its application in the assessment of placental function

It is important to develop a better understanding of placental insufficiency given its role in common maternofetal complications such as preeclampsia and fetal growth restriction. Functional magnetic resonance imaging offers unprecedented techniques for exploring the placenta under both normal and pathological physiological conditions. Dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) is an established and very robust method to investigate the microcirculatory parameters of an organ and more specifically its perfusion. It is currently a gold standard in the physiological and circulatory evaluation of an organ. Its application to the human placenta could enable to access many microcirculatory parameters relevant to the placental function such as organ blood flow, fractional blood volume, and permeability surface area, by the acquisition of serial images, before, during, and after administration of an intravenous contrast agent. Widely used in animal models with gadolinium-based contrast agents, its application to the human placenta could be possible if the safety of contrast agents in pregnancy is established or they are confirmed to not cross the placenta.

Deep learning and radiomics analysis for prediction of placenta invasion based on T2WI

The purpose of this study was to explore whether the Nomogram, which was constructed by combining the Deep learning and Radiomic features of T2-weighted MR images with Clinical factors (NDRC), could accurately predict placenta invasion. This retrospective study included 72 pregnant women with pathologically confirmed placenta invasion and 40 pregnant women with normal placenta. After 24 gestational weeks, all participants underwent magnetic resonance imaging. The uterus and placenta regions were segmented in magnetic resonance images on sagittal T2WI. Ninety-three radiomics features were extracted from the placenta region, and 128 deep features were extracted from the uterus region using a deep neural network. The least absolute shrinkage and selection operator (LASSO) algorithm was used to filter these 221 features and to form the combined signature. Then the combined signature (CS) and clinical factors were combined to construct a nomogram. The accuracy, sensitivity, specificity and AUC of the nomogram were compared with four machine learning methods. The model NDRC was trained on the dataset of 78 pregnant women in the training cohort. Finally, the model NDRC was compared with four machine learning methods on the independent validation cohort of 34 pregnant women. The results showed that the prediction accuracy, sensitivity, specificity and AUC of the NDRC model were 0.941, 0.952, 0.923 and 0.985 respectively, which outperforms the traditional machine learning methods which rely on radiomics features and deep learning features alone.

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.

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.

Postpartum Hemorrhages: Prevention

The strict correlation between abnormal invasive placentation and postpartum hemorrhage suggests that a widespread antenatal diagnosis of placental anomalies would improve the management of these challenging patients; acting preventive solutions at the moment of delivery reduces blood loss and avoid hysterectomies. The role of endovascular procedures in this field has been encouraged by multiple studies reporting prophylactic uterine arteries embolization and iliac/aortic balloon catheters positioning. This paper aims to review the main imaging diagnostic findings of placental implant anomalies and summarize the principal preventive endovascular strategies proposed in literature.

What we know about placenta accreta spectrum (PAS)

Placenta accreta spectrum (PAS) is an umbrella term for a variety of pregnancy complications due to abnormal placental implantation, including placenta accreta, placenta increta and placenta percreta. During the past several decades, the prevalence of PAS has been increasing, and the clinical importance of this disease is significant because of the severe complications. In this review, we summarized the available evidence-based data for PAS in various aspects: prevalence, risk factors, pathogenesis, clinical presentation and prenatal screening, and clinical management. Meanwhile, we provided a series of prospects in each section for further studies on PAS. Moreover, we first present a visualized workflow for the management of PAS from three steps: predelivery, during delivery and postdelivery.

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.

Intraplacental Fetal Vessel Diameter May Help Predict for Placental Invasiveness in Pregnant Women at High Risk for Placenta Accreta Spectrum Disorders

Background Prenatal identification of placenta accreta spectrum (PAS) disorder is essential for treatment planning. More objective means for predicting PAS and clinical outcome may be provided by MRI descriptors. Purpose To investigate the association of intraplacental fetal vessel (IFV) diameter at MRI with PAS and peripartum complications. Materials and Methods Between March 2016 and October 2019, 160 gravid women suspected of having PAS underwent placental MRI as part of a prospective trial. Secondary analysis was performed by two experienced genitourinary radiologists for presence and maximum diameter of IFVs. Relative risk ratios were computed to test the association of IFVs with presence and depth of PAS invasiveness. Receiver operating characteristic analysis was used to evaluate the ability of IFV diameter to help predict PAS, placenta percreta, and peripartum complications and for comparison of the area under the curve (AUC) versus that from other combined MRI predictors of PAS (eg, myometrial thinning, intraplacental T2-hypointense bands, uterine bulge, serosal hypervascularity, and signs of extrauterine placental spread). Intraoperative and histopathologic findings were the reference standard. Results A total of 155 women were evaluated (mean age, 35 years ± 5 [standard deviation]; mean gestational age, 32 weeks ± 3). PAS was diagnosed in 126 of 155 women (81%) (placental percreta in 68 of 126 [54%]). At delivery, 30 of 126 women (24%) experienced massive blood loss (>2000 mL). IFVs were detected at MRI in 109 of 126 women with PAS (86%) and in 67 of 68 women with placental percreta (98%). The relative risk ratio was 2.4 (95% CI: 1.6, 3.4; P < .001) for PAS and 10 (95% CI: 1.5, 70.4; P < .001) for placental percreta when IFVs were visible. IFVs of 2 mm or greater were associated with PAS (AUC, 0.81; 95% CI: 0.67, 0.95; P = .04). IVFs of 3 mm or greater were associated with placenta percreta (AUC, 0.81; 95% CI: 0.73, 0.89; P < .001) and with peripartum complications, including massive bleeding (AUC, 0.80; 95% CI: 0.71, 0.89; P < .001). Combining assessment of IFVs with other MRI descriptors improved the ability of MRI to predict PAS (AUC, 0.94 vs 0.89; P = .009). Conclusion Assessment of intraplacental fetal vessels with other MRI descriptors improved the ability of MRI to help predict PAS. Vessel diameter of 3 mm or greater was predictive of placenta percreta and peripartum complications. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Dighe in this issue.

Review of MRI imaging for placenta accreta spectrum: Pathophysiologic insights, imaging signs, and recent developments

Placenta Accreta Spectrum (PAS) refers to the range of abnormally adhesive and penetrative placental tissue at a uterine scar. PAS is divided into accreta, increta, and percreta based on degree of myometrial invasion. Its incidence has increased, and PAS is now the leading indication for emergency peripartum hysterectomy in the setting of catastrophic hemorrhage from a non-separating placenta. The recent release of the International Federation of Gynecology and Obstetrics (FIGO) guidelines in 2018 coupled with the joint consensus statement from the Society of Abdominal Radiology (SAR) and European Society of Urogenital Radiology (ESUR) in 2020 reflect decades worth of diagnostic and therapeutic advances in this field. Although the increasing role of MRI in PAS diagnosis is evident, the literature on PAS reveals several disparate but conceptually overlapping MRI signs. Identifying and differentiating between placenta increta and percreta on imaging may be quite challenging even with MRI and sometimes even on final pathology. In this review, we aim to (i) provide a clarified understanding of PAS pathophysiology, (ii) comprehensively review and classify MRI signs based on pathophysiologic underpinnings, (iii) highlight shortcomings in the current PAS literature; and (iv) highlight best practice guidelines for imaging diagnosis of PAS.

A Pictorial Review of Postpartum Complications

The postpartum period, also known as the puerperium, begins immediately after delivery of the neonate and placenta and ends 6-8 weeks after delivery. The appearance of physiologic uterine changes during puerperium can overlap with that of postpartum complications, which makes imaging interpretation and diagnosis difficult. Obstetric and nonobstetric postpartum complications are a considerable source of morbidity and mortality in women of reproductive age, and the radiologist plays an important role in the assessment of these entities, which often require a multimodality imaging approach. US and contrast material-enhanced CT are the techniques of choice in the emergency department, and they can show characteristic radiologic findings that enable differentiation between normal and abnormal features to help radiologists and emergency department practitioners to reach a correct diagnosis and provide timely treatment. The spectrum of postpartum complications ranges from relatively self-limiting to life-threatening conditions that can be divided into six categories: infectious conditions (endometritis), thrombotic complications (eg, deep vein thrombosis, ovarian vein thrombophlebitis, HELLP [hemolysis, elevated liver enzymes, and low platelet count] syndrome, or cerebral sinus thrombosis), hemorrhagic conditions (eg, uterine atony, trauma of the lower portion of the genital tract, retained products of conception, uterine artery arteriovenous malformations, or uterine artery pseudoaneurysm), cesarean delivery-related complications (eg, bladder flap hematoma, subfascial hematoma, rectus sheath hematoma, abscess formation, uterine dehiscence, uterine rupture, vesicovaginal fistula, or abdominal wall endometriosis), iatrogenic conditions (eg, uterine perforation), and nonobstetric complications (eg, acute cholecystitis, acute appendicitis, uterine fibroid degeneration, renal cortical necrosis, pyelonephritis, posterior reversible encephalopathy syndrome, or pituitary gland apoplexy). The online slide presentation from the RSNA Annual Meeting is available for this article. ^©RSNA, 2020.

Placental adhesion disorder: magnetic resonance imaging features and a proposal for a structured report

Placental adhesion disorder encompasses the various types of abnormal placentation that occur when the chorionic villi penetrate the uterine wall. Placenta accreta has become more common, mainly because of the increasing rates of cesarean section. Although ultrasound is the first-line imaging modality for evaluation of the placenta, it plays a limited role in cases of posterior placenta accreta and inconclusive findings. In such cases, magnetic resonance imaging (MRI) is indicated, mainly because it is a more accurate means of identifying placental invasion of extrauterine structures in high-risk pregnant women. In this review article, we present the ten major and minor MRI features of placental adhesion disorder, as described in the international literature. In addition, we propose a template for structured reports of MRI examinations of the placenta. We have also devised a guided questionnaire in order to identify risk factors in patients scheduled to undergo such examinations, with the objective of facilitating the multidisciplinary treatment planning needed in order to minimize maternal morbidity and mortality.

Role of placenta accreta index in prediction of morbidly adherent placenta: A reliability study

Objective

To estimate the level of interobserver agreement in the calculation of placenta accreta index (PAI) as well as to evaluate the accuracy of PAI in prediction of morbidly adherent placenta.

Materials and methods

This was a prospective study where 45 pregnant women (from 28 to 37 weeks of gestational age) with at least one previous Caesarean section and ultrasound-proven placenta previa were included. A known and previously published scoring system, the PAI, was evaluated independently by two radiologists and the cases were followed for the delivery and histopathology outcome. The accuracy of the PAI and the level of interrater agreement was analysed using cross-table analysis, intraclass correlation efficient and Cohen's kappa as statistical variables.

Results

Adherent placenta was found in 15 patients accounting for 33% of cases. The PAI showed nearly 90% sensitivity, specificity and the predictive values. Interrater agreement in calculation of PAI by the two radiologists was perfect with an intraclass correlation efficient of 0.959. An easy-to-use morbid adherent placenta score was also predicted to simplify the results of PAI, which showed moderate agreement (κ = 0.746).

Conclusions

The PAI can be helpful in stratifying the individual risk of placental invasion above the baseline risk. The PAI-derived, simplified scoring system called morbid adherent placenta score can be used as a simple tool to interpret and convey the results of PAI.

Prenatal Diagnosis of Placental Invasion: A Systematic Review and Meta-analysis on Accuracy of Ultrasonography and MRI in Diagnosis of Placental Invasion

Objective:

The aim of this systematic review and meta-analysis was to evaluate and compare the diagnostic accuracy of ultrasonography (US) and magnetic resonance imaging (MRI) in the diagnosis of placental invasion.

Method:

Two independent scientists carried out a series of searches to obtain relevant research, released from January 1, 2009, to December 31, 2018. National databases (Magiran and SID), KoreaMed, and LILACS were reviewed for literature, released in other languages. A series of MeSH keywords was employed as part of the searching strategy (e.g., pregnancy, pregnant, placental invasion, accreta). A forest plot was built with Meta-DiSc, version 1.4.

Results:

For placental invasion, the sensitivity and specificity of MRI were 89% (95% confidence interval [CI], 83%–93% with a 95% confidence interval) and 97% (95% CI, 93%–99%), respectively. The sensitivity and specificity of US were 73% (95% CI, 66%–79%) and 89% (95% CI, 84%–93%), respectively. In the detection of placenta accreta solely (as the first grade of placental invasion), the sensitivity and specificity of MRI were 89.3% (95% CI, 86%–92%) and 84% (95% CI, 77%–89.6%). The sensitivity and specificity of US detection were 95.4% (95% CI, 93.8%–96.6%) and 87.3% (95% CI, 81.4%–91.9%), respectively.

Conclusion:

Due to the increased cesarean sections, placental invasion may be increasing. The diagnosis of prenatal placental invasion is important to reduce maternal morbidity and mortality. Recent trends indicate an increased use of MRI to evaluate placental invasion as a complement to US. The most accurate imaging findings are using US for placental lacunae and MRI to detect the dark intraplacental band.

New Frontiers in Placenta Tissue Imaging

The placenta is a highly vascularized organ with unique structural and metabolic complexities. As the primary conduit of fetal support, the placenta mediates transport of oxygen, nutrients, and waste between maternal and fetal blood. Thus, normal placenta anatomy and physiology is absolutely required for maintenance of maternal and fetal health during pregnancy. Moreover, impaired placental health can negatively impact offspring growth trajectories as well as increase the risk of maternal cardiovascular disease later in life. Despite these crucial roles for the placenta, placental disorders, such as preeclampsia, intrauterine growth restriction (IUGR), and preterm birth, remain incompletely understood. Effective noninvasive imaging and image analysis are needed to advance the obstetrician's clinical reasoning toolkit and improve the utility of the placenta in interpreting maternal and fetal health trajectories. Current paradigms in placental imaging and image analysis aim to improve the traditional imaging techniques that may be time-consuming, costly, or invasive. In concert with conventional clinical approaches such as ultrasound (US), advanced imaging modalities can provide insightful information on the structure of placental tissues. Herein we discuss such imaging modalities, their specific applications in structural, vascular, and metabolic analysis of placental health, and emerging frontiers in image analysis research in both preclinical and clinical contexts.