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

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.

Succenturiate Placental Lobe Abruption

Placental development is a complex process which sets the stage for normal fetal development. Any variation/disruption occurring during the initial stages of placental formation leads to placental malfunction causing increased maternal-fetal morbidity and mortality. The succenturiate lobe is a structural variation of the placenta that usually appears as a distinct lobe from the main placental mass. Succenturiate lobe is a rare placental anomaly, with high risk of fetal distress, hemorrhage, abruptio placentae and even fetal death because the vessels of this succenturiate lobe are vulnerable to both compression and laceration. Prenatal imaging diagnosis of this pathology improves the fetal prognosis through more careful surveillance and, in case of complications such as abruptio placentae, by shortening the time-to-decision making in favor of cesarean delivery. We present the case of a 27-year-old patient, without risk factors for placental abnormalities, diagnosed antenatally with succenturiate placenta, who presented at 34 weeks of pregnancy for abruptio placentae.

Single-cell and spatial transcriptomics reveal alterations in trophoblasts at invasion sites and disturbed myometrial immune microenvironment in placenta accreta spectrum disorders

BACKGROUND

Placenta accreta spectrum disorders (PAS) are a severe complication characterized by abnormal trophoblast invasion into the myometrium. The underlying mechanisms of PAS involve a complex interplay of various cell types and molecular pathways. Despite its significance, both the characteristics and intricate mechanisms of this condition remain poorly understood.

METHODS

Spatial transcriptomics (ST) and single-cell RNA sequencing (scRNA-seq), were performed on the tissue samples from four PAS patients, including invasive tissues (ST, n = 3; scRNA-seq, n = 4), non-invasive normal placenta samples (ST, n = 1; scRNA-seq, n = 2). Three healthy term pregnant women provided normal myometrium samples (ST, n = 1; scRNA-seq, n = 2). ST analysis characterized the spatial expression landscape, and scRNA-seq was used to identify specific cellular components in PAS. Immunofluorescence staining was conducted to validate the findings.

RESULTS

ST slices distinctly showed the myometrium in PAS was invaded by three subpopulations of trophoblast cells, extravillous trophoblast cells, cytotrophoblasts, and syncytiotrophoblasts, especially extravillous trophoblast cells. The pathways enriched by genes in trophoblasts, smooth muscle cells (SMC), and immune cells of PAS were mainly associated with immune and inflammation. We identified elevated expression of the angiogenesis-stimulating gene PTK2, alongside the cell proliferation-enhancing gene EGFR, within the trophoblasts of PAS group. Trophoblasts mainly contributed the enhancement of HLA-G and EBI3 signaling, which is crucial in establishing immune escape. Meanwhile, SMC regions in PAS exhibited upregulation of immunomodulatory markers such as CD274, HAVCR2, and IDO1, with CD274 expression experimentally verified to be increased in the invasive SMC areas of the PAS group.

CONCLUSIONS

This study provided information of cellular composition and spatial organization in PAS at single-cell and spatial level. The dysregulated expression of genes in PAS revealed a complex interplay between enhanced immune escape in trophoblasts and immune tolerance in SMCs during invasion in PAS. These findings will enhance our understanding of PAS pathogenesis for developing potential therapeutic strategies.

Deep Learning Radiomic Analysis of MRI Combined with Clinical Characteristics Diagnoses Placenta Accreta Spectrum and its Subtypes

BACKGROUND

Different placenta accreta spectrum (PAS) subtypes pose varying surgical risks to the parturient. Machine learning model has the potential to diagnose PAS disorder.

PURPOSE

To develop a cascaded deep semantic-radiomic-clinical (DRC) model for diagnosing PAS and its subtypes based on T2-weighted MRI.

STUDY TYPE

Retrospective.

POPULATION

361 pregnant women (mean age: 33.10 ± 4.37 years), suspected of PAS, divided into segment training cohort (N = 40), internal training cohort (N = 139), internal testing cohort (N = 60), and external testing cohort (N = 122).

FIELD STRENGTH/SEQUENCE

Coronal T2-weighted sequence at 1.5 T and 3.0 T.

ASSESSMENT

Clinical characteristics such as history of uterine surgery and the presence of placenta previa, complete placenta previa and dangerous placenta previa were extracted from clinical records. The DRC model (incorporating radiomics, deep semantic features, and clinical characteristics), a cumulative radiological score method performed by radiologists, and other models (including a radiomics and clinical, the clinical, radiomics and deep learning models) were developed for PAS disorder diagnosing (existence of PAS and its subtypes).

STATISTICAL TESTS

AUC, ACC, Student's t-test, the Mann-Whitney U test, chi-squared test, dice coefficient, intraclass correlation coefficients, least absolute shrinkage and selection operator regression, receiver operating characteristic curve, calibration curve with the Hosmer-Lemeshow test, decision curve analysis, DeLong test, and McNemar test. P < 0.05 indicated a significant difference.

RESULTS

In PAS diagnosis, the DRC-1 outperformed than other models (AUC = 0.850 and 0.841 in internal and external testing cohorts, respectively). In PAS subtype classification (abnormal adherent placenta and abnormal invasive placenta), DRC-2 model performed similarly with radiologists (P = 0.773 and 0.579 in the internal testing cohort and P = 0.429 and 0.874 in the external testing cohort, respectively).

DATA CONCLUSION

The DRC model offers efficiency and high diagnostic sensitivity in diagnosis, aiding in surgical planning.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 2.

Development and validation of MRI-based scoring models for predicting placental invasiveness in high-risk women for placenta accreta spectrum

OBJECTIVES

To develop and validate MRI-based scoring models for predicting placenta accreta spectrum (PAS) invasiveness.

MATERIALS AND METHODS

This retrospective study comprised a derivation cohort and a validation cohort. The derivation cohort came from a systematic review of published studies evaluating the diagnostic performance of MRI signs for PAS and/or placenta percreta in high-risk women. The significant signs were identified and used to develop prediction models for PAS and placenta percreta. Between 2016 and 2021, consecutive high-risk pregnant women for PAS who underwent placental MRI constituted the validation cohort. Two radiologists independently evaluated the MRI signs. The reference standard was intraoperative and pathologic findings. The predictive ability of MRI-based models was evaluated using the area under the curve (AUC).

RESULTS

The derivation cohort included 26 studies involving 2568 women and the validation cohort consisted of 294 women with PAS diagnosed in 258 women (88%). Quantitative meta-analysis revealed that T2-dark bands, placental/uterine bulge, loss of T2 hypointense interface, bladder wall interruption, placental heterogeneity, and abnormal intraplacental vascularity were associated with both PAS and placenta percreta, and myometrial thinning and focal exophytic mass were exclusively associated with PAS. The PAS model was validated with an AUC of 0.90 (95% CI: 0.86, 0.93) for predicting PAS and 0.85 (95% CI: 0.79, 0.90) for adverse peripartum outcome; the placenta percreta model showed an AUC of 0.92 (95% CI: 0.86, 0.98) for predicting placenta percreta.

CONCLUSION

MRI-based scoring models established based on quantitative meta-analysis can accurately predict PAS, placenta percreta, and adverse peripartum outcome.

CLINICAL RELEVANCE STATEMENT

These proposed MRI-based scoring models could help accurately predict PAS invasiveness and provide evidence-based risk stratification in the management of high-risk pregnant women for PAS.

KEY POINTS

• Accurately identifying placenta accreta spectrum (PAS) and assessing its invasiveness depending solely on individual MRI signs remained challenging. • MRI-based scoring models, established through quantitative meta-analysis of multiple MRI signs, offered the potential to predict PAS invasiveness in high-risk pregnant women. • These MRI-based models allowed for evidence-based risk stratification in the management of pregnancies suspected of having PAS.

Placenta previa percreta with surrounding organ involvement: a proposal for management

Placenta accreta spectrum encompasses cases where the placenta is morbidly adherent to the myometrium. Placenta percreta, the most severe form of placenta accreta spectrum (grade 3E), occurs when the placenta invades through the myometrium and possibly into surrounding structures next to the uterine corpus. Maternal morbidity of placenta percreta is high, including severe maternal morbidity in 82.1% and mortality in 1.4% in the recent nationwide U.S. statistics. Although cesarean hysterectomy is commonly performed for patients with placenta accreta spectrum, conservative management is becoming more popular because of reduced morbidity in select cases. Treatment of grade 3E disease involving the urinary bladder, uterine cervix, or parametria is surgically complicated due to the location of the invasive placenta deep in the maternal pelvis. Cesarean hysterectomy in this setting has the potential for catastrophic hemorrhage and significant damage to surrounding organs. We propose a step-by-step schema to evaluate cases of grade 3E disease and determine whether immediate hysterectomy or conservative management, including planned delayed hysterectomy, is the most appropriate treatment option. The approach includes evaluation in the antenatal period with ultrasound and magnetic resonance imaging to determine suspicion for placenta previa percreta with surrounding organ involvement, planned cesarean delivery with a multidisciplinary team including experienced pelvic surgeons such as a gynecologic oncologist, intra-operative assessment including gross surgical field exposure and examination, cystoscopy, and consideration of careful intra-operative transvaginal ultrasound to determine the extent of placental invasion into surrounding organs. This evaluation helps decide the safety of primary cesarean hysterectomy. If safely resectable, additional considerations include intra-operative use of uterine artery embolization combined with tranexamic acid injection in cases at high risk for pelvic hemorrhage and ureteral stent placement. Availability of resuscitative endovascular balloon occlusion of the aorta is ideal. If safe resection is concerned, conservative management including planned delayed hysterectomy at around 4 weeks from cesarean delivery in stable patients is recommended.

Segmentation methods applied to MRI-derived radiomic analysis for the prediction of placenta accreta spectrum in patients with placenta previa

PURPOSE

To retrospectively evaluate the performance of different manual segmentation methods of placenta MR images for predicting Placenta Accreta Spectrum (PAS) disorders in patients with placenta previa (PP) using a Machine Learning (ML) Radiomics analysis.

METHODS

64 patients (n=41 with PAS and n= 23 without PAS) with PP who underwent MRI examination for suspicion of PAS were retrospectively selected. All MRI examinations were acquired on a 1.5 T using T2-weighted (T2w) sequences on axial, sagittal and coronal planes. Ten different manual segmentation methods were performed on sagittal placental T2-weighted images obtaining five sets of 2D regions of interest (ROIs) and five sets of 3D volumes of interest (VOIs) from each patient. In detail, ROIs and VOIs were positioned on the following areas: placental tissue, retroplacental myometrium, cervix, placenta with underneath myometrium, placenta with underneath myometrium and cervix. For feature stability testing, the same process was repeated on 30 randomly selected placental MRI examinations by two additional radiologists, working independently and blinded to the original segmentation. Radiomic features were extracted from all available ROIs and VOIs. 100 iterations of 5-fold cross-validation with nested feature selection, based on recursive feature elimination, were subsequently run on each ROI/VOI to identify the best-performing method to classify instances correctly.

RESULTS

Among the segmentation methods, the best performance in predicting PAS was obtained by the VOIs covering the retroplacental myometrium (Mean validation score: 0.761, standard deviation: 0.116).

CONCLUSION

Our preliminary results show that the VOI including the retroplacental myometrium using T2w images seems to be the best method when segmenting images for the development of ML radiomics predictive models to identify PAS in patients with PP.

Use of super resolution reconstruction MRI for surgical planning in Placenta accreta spectrum disorder: Case series

INTRODUCTION

Comprehensive imaging using ultrasound and MRI of placenta accreta spectrum (PAS) aims to prevent catastrophic haemorrhage and maternal death. Standard MRI of the placenta is limited by between-slice motion which can be mitigated by super-resolution reconstruction (SRR) MRI. We applied SRR in suspected PAS cases to determine its ability to enhance anatomical placental assessment and predict adverse maternal outcome.

METHODS

Suspected PAS patients (n = 22) underwent MRI at a gestational age (weeks + days) of (32+3±3+2, range (27+1-38+6)). SRR of the placental-myometrial-bladder interface involving rigid motion correction of acquired MRI slices combined with robust outlier detection to reconstruct an isotropic high-resolution volume, was achieved in twelve. 2D MRI or SRR images alone, and paired data were assessed by four radiologists in three review rounds. All radiologists were blinded to results of the ultrasound, original MR image reports, case outcomes, and PAS diagnosis. A Random Forest Classification model was used to highlight the most predictive pathological MRI markers for major obstetric haemorrhage (MOH), bladder adherence (BA), and placental attachment depth (PAD).

RESULTS

At delivery, four patients had placenta praevia with no abnormal attachment, two were clinically diagnosed with PAS, and six had histopathological PAS confirmation. Pathological MRI markers (T2-dark intraplacental bands, and loss of retroplacental T2-hypointense line) predicting MOH were more visible using SRR imaging (accuracy 0.73), in comparison to 2D MRI or paired imaging. Bladder wall interruption, predicting BA, was only easily detected by paired imaging (accuracy 0.72). Better detection of certain pathological markers predicting PAD was found using 2D MRI (placental bulge and myometrial thinning (accuracy 0.81)), and SRR (loss of retroplacental T2-hypointense line (accuracy 0.82)).

DISCUSSION

The addition of SRR to 2D MRI potentially improved anatomical assessment of certain pathological MRI markers of abnormal placentation that predict maternal morbidity which may benefit surgical planning.

Factors Limiting Magnetic Resonance Imaging Diagnosis of Placenta Accreta Spectrum

OBJECTIVE

Placenta accreta spectrum (PAS) disorders are characterized by an abnormal adherence of the placenta to the uterine myometrium. Magnetic resonance imaging (MRI) is an important adjunct in antenatal diagnosis. We sought to determine if there are patient and MRI characteristics that limit the accuracy of PAS diagnosis and degree of invasion.

STUDY DESIGN

We conducted a retrospective cohort analysis of patients who were evaluated for PAS by MRI from January 2007 to December 2020. Patient characteristics evaluated included number of prior cesarean deliveries, history of dilation and curettage (D&C) or dilation and evacuation (D&E), short interval pregnancy less than 18 months, and delivery body mass index (BMI). All patients were followed until delivery and MRI diagnosis was compared with final histopathology.

RESULTS

Of the 353 patients with suspected PAS, 152 (43%) underwent MRI evaluation and were included in the final analysis. In patients who underwent MRI evaluation, 105 (69%) had confirmed PAS on pathology. Patient characteristics were similar between groups and not associated with accuracy of MRI diagnosis. MRI was accurate in diagnosing PAS and the associated degree of invasion in 83 (55%) patients. Accuracy was associated with lacunae (8 vs. 0%, p = 0.02), abnormal bladder interface (25 vs. 6%, p = 0.002), and T1 hyperintensity (13 vs. 1%, p = 0.002). Of the 69 (45%) patients in whom MRI was inaccurate, overdiagnosis was seen in 44 (64%) patients and underdiagnosis in 25 (36%) patients. Overdiagnosis was significantly associated with dark T2 bands (45 vs. 22%, p = 0.005). Underdiagnosis was associated with earlier gestational age at MRI (28 vs. 30 weeks, p = 0.049) and lateral placentation (16 vs. 2.4%, p = 0.025).

CONCLUSION

Patient factors did not change MRI accuracy of PAS diagnosis. MRI is associated with a significant overdiagnosis of PAS when dark T2 bands are present, and underdiagnose PAS when performed earlier in gestation or when lateral placentation is present.

KEY POINTS

· Patient factors are not associated with MRI accuracy of PAS diagnosis.. · MRI overdiagnoses PAS invasion when there are dark T2 bands.. · MRI underdiagnoses PAS invasion when performed earlier in gestation.. · Underdiagnosis of PAS is associated with lateral placentation..

Imaging of Acute Abdominopelvic Pain in Pregnancy and Puerperium-Part I: Obstetric (Non-Fetal) Complications

Acute abdominopelvic pain in pregnant and postpartum patients presents clinical and therapeutic challenges, often requiring quick and accurate imaging diagnosis. Ultrasound remains the primary imaging investigation. Magnetic resonance imaging (MRI) has been shown to be a powerful diagnostic tool in the setting of acute abdominal pain during pregnancy and puerperium. MRI overcomes some drawbacks of US, avoiding the ionizing radiation exposure of a computed tomography (CT) scan. Although CT is not usually appropriate in pregnant patients, it is crucial in the emergency evaluation of postpartum complications. The aim of this article is to provide radiologists with a thorough familiarity with the common and uncommon pregnancy and puerperium abdominal emergencies by illustrating their imaging appearances. The present first section will review and discuss the imaging findings for acute abdominopelvic pain of obstetric (non-fetal) etiology.

Prediction of placenta accreta spectrum with nomogram combining radiomic and clinical factors: A novel developed and validated integrative model

OBJECTIVE

To develop and validate a clinicoradiomic nomogram based on sagittal T2WI images to predict placenta accreta spectrum (PAS).

METHODS

Between October 2016 and April 2022, women suspected of PAS by ultrasound were enrolled. After taking into account exclusion criteria, 132 women were retrospectively included in the study. The variance threshold SelectKBest and the least absolute shrinkage and selection operator were applied to select radiomic features, which was further used to calculate the Rad-score. Multivariable logistic regression was used to screen clinical factor.

RESULTS

Based on 13 radiomic features, five radiomic models were constructed. A clinical factor of intraplacental T2-hypointense bands was obtained by multivariate logistic regression. The area under the curve (AUC) value of the stochastic gradient descent (SGD) radiomic model was 0.82 in the training cohort and 0.78 in the test cohort. After adding clinical factors to the SGD radiomic model, the AUC value of the clinicoradiomic model was significantly increased from 0.82 and 0.78 to 0.84 in both the training and test cohorts. The nomogram of the clinicoradiomic model was constructed, which had good performance verified by calibration and a decision curve.

CONCLUSION

The presented nomogram could be useful for predicting PAS.

Developments in functional imaging of the placenta

The placenta is both the literal and metaphorical black box of pregnancy. Measurement of the function of the placenta has the potential to enhance our understanding of this enigmatic organ and serve to support obstetric decision making. Advanced imaging techniques are key to support these measurements. This review summarises emerging imaging technology being used to measure the function of the placenta and new developments in the computational analysis of these data. We address three important examples where functional imaging is supporting our understanding of these conditions: fetal growth restriction, placenta accreta, and twin-twin transfusion syndrome.

Placenta accreta spectrum in major placenta previa diagnosed only by MRI: incidence, risk factors, and maternal morbidity

BACKGROUND

Antenatal assessment of maternal risk factors and imaging evaluation can help in diagnosis and treatment of placenta accreta spectrum (PAS) in major placenta previa (PP). Recent evidence suggests that magnetic resonance imaging (MRI) could complement ultrasonography (US) in the PAS diagnosis.

OBJECTIVES

Evaluate the incidence, risk factors, and maternal morbidity related to the MRI diagnosis of PAS in major PP.

DESIGN

A 10-year retrospective cohort study.

SETTING

Tertiary care hospital.

PATIENTS AND METHODS

We report on patients with major PP who had cesarean delivery in Abha Maternity and Children's Hospital (AMCH) over a 10-year period (2012-2021). They were evaluated with ultrasonography (US) and color Doppler for evidence of PAS. Antenatal MRI was ordered either to confirm the diagnosis (if equivocal US) or to assess the depth of invasion/extra-uterine extension (if definitive US).

MAIN OUTCOME MEASURES

Risk factors for PAS in major PP and maternal complications.

SAMPLE SIZE

299 patients RESULTS: Among 299 patients, MRI confirmed the PAS diagnosis in 91/299 (30.5%) patients. The independent risk factors for MRI diagnosis of PAS in major PP included only repeated cesarean sections and advanced maternal age. The commonest maternal morbidity in major PP with PAS was significantly excessive intraoperative bleeding.

CONCLUSION

MRI may be a valuable adjunct in the evaluation of PAS in major PP; as a complement, but not substitute US. MRI may be suitable in major PP/PAS patients who are older and have repeated cesarean deliveries with equivocal results or deep/extra-uterine extension on US.

LIMITATION

Single center, small sample size, lack of complete histopathological diagnosis.

CONFLICT OF INTEREST

None.

Ultrasonography of the Explanted Uterus in Placenta Accreta Spectrum: Correlation With Intraoperative Findings and Gross Pathology

OBJECTIVE

To better understand placenta accreta spectrum (PAS) by correlating postoperative ultrasonographic findings of the explanted uteroplacental interface with intraoperative findings and gross pathology.

METHODS

We enrolled consecutive pregnant patients aged 18 years and older with a prior cesarean delivery and antenatal diagnosis of lower uterine segment PAS who planned to undergo hysterectomy into this prospective, descriptive study. All underwent cesarean hysterectomy with standardized intraoperative photography. Ultrasonography of explanted postsurgical uteruses was performed by expert radiologists to obtain standard detailed images of the myometrial-placental interface and other areas of interest. Sagittal views of the gross pathologic specimen were photographed. We correlated the intraoperative, ultrasonographic, and gross pathologic findings as a study team and report four consistent patterns that emerged from this systematic evaluation.

RESULTS

Thirty-four consecutive eligible patients were enrolled. The following consistent observations emerged: 1) The uteroplacental interface in the explanted specimen was smooth and distinct. At the point of maximal placental protrusion, the myometrium was imperceptible, but the placenta was confined by a smooth thin echogenic line of uterine serosa (the scar shell) unless surgically disrupted. 2) Every specimen of PAS grade 2-3 showed placenta bulging through the lower uterine segment in the region of prior hysterotomy. 3) Placentas extended to, but not through, the uterovesical interface or scar shell. Dense adhesive disease was found between the placenta and bladder. There were no cases of true bladder invasion. 4) Placental extension beyond the serosa (invasion) has a distinct appearance on postoperative ultrasonography with irregular frond-like protrusion of placental tissue. This appearance was always the result of surgical manipulation and was not present before delivery of the neonate.

CONCLUSION

These findings suggest that PAS severity is likely mediated by progressive scar dehiscence and uterine remodeling, not placental invasion. This challenges the existence of in situ invasive percreta as it is currently described.

A prospective cohort study: can advanced ultrasonography replace magnetic resonance imaging in the diagnosis of placental adhesion disorders?

OBJECTIVES

To define and compare the diagnostic accuracy of ultrasonography (USG) and magnetic resonance imaging (MRI) for the placental adhesive disorder (PAD).

METHODS

A prospective study was conducted between January 2019 and February 2020 in a tertiary referral university hospital. A total of 115 placenta previa cases were included in the study during the third trimester of gestation. USG examination was performed, and the placenta was scanned in a systematic manner using gray-scale ultrasound, color Doppler flow mapping, and 3-D imaging for each participant. Thereafter, all participants underwent an MRI examination. USG and MRI findings were compared with histopathological findings.

RESULTS

Loss of the retroplacental sonolucent zone (71% [95% CI 47-88]) and an irregular retroplacental sonolucent zone (71% [95% CI 47-88]) were the most sensitive USG parameters. For MRI, the uterine bulging parameter was the most sensitive (60% [95% CI 36-80]) and specific (91% [95% CI 83-96]) findings, and it had the highest accuracy rate (85% [95% CI 77-91]). Overall, the USG sensitivity, specificity, and accuracy rates were 77% (95% CI 54-92), 87% (95% CI 79-93), and 85% (95% CI 77-91), respectively. The MRI sensitivity, specificity, and accuracy rates for all participants were 81% (95% CI 59-94), 85% (95% CI 76-92), and 84% (95% CI 76-90), respectively.

CONCLUSIONS

In the diagnosis of PAD, the specificity and accuracy of USG are higher than that of MRI, whereas the sensitivity of MRI is better than that of USG.

Prediction of placenta accreta spectrum by combining deep learning and radiomics using T2WI: a multicenter study

PURPOSE

To achieve prenatal prediction of placenta accreta spectrum (PAS) by combining clinical model, radiomics model, and deep learning model using T2-weighted images (T2WI), and to objectively evaluate the performance of the prediction through multicenter validation.

METHODS

A total of 407 pregnant women from two centers undergoing preoperative magnetic resonance imaging (MRI) were retrospectively recruited. The patients from institution I were divided into a training cohort (n = 298) and a validation cohort (n = 75), while patients from institution II served as the external test cohort (n = 34). In this study, we built a clinical prediction model using patient clinical data, a radiomics model based on selected key features, and a deep learning model by mining deep semantic features. Based on this, we developed a combined model by ensembling the prediction results of the three models mentioned above to achieve prenatal prediction of PAS. The performance of these predictive models was evaluated with respect to discrimination, calibration, and clinical usefulness.

RESULTS

The combined model achieved AUCs of 0.872 (95% confidence interval, 0.843 to 0.908) in the validation cohort and 0.857 (0.808 to 0.894) in the external test cohort, both of which outperformed the other models. The calibration curves demonstrated excellent consistency in the validation cohort and the external test cohort, and the decision curves indicated high clinical usefulness.

CONCLUSION

By using preoperative clinical information and MRI images, the combined model can accurately predict PAS by ensembling clinical model, radiomics model, and deep learning model.

Placental and Umbilical Cord Anomalies Diagnosed by Two- and Three-Dimensional Ultrasound

The aim of this review is to present a wide spectrum of placental and umbilical cord pathologies affecting the pregnancy. Placental and umbilical cord anomalies are highly associated with high-risk pregnancies and may jeopardize fetal well-being in utero as well as causing a predisposition towards poor perinatal outcome with increased fetal and neonatal mortality and morbidity. The permanent, computerized perinatology databases of different international centers have been searched and investigated to fulfil the aim of this manuscript. An extended gallery of prenatal imaging with autopsy correlation in specific cases will help to provide readers with a useful iconographic tool and will assist with the understanding and definition of this critical obstetrical and perinatological issue.

Placenta Accreta Spectrum (PAS) Disorder: Ultrasound versus Magnetic Resonance Imaging

OBJECTIVE

PAS is one of the most dangerous conditions associated with pregnancy and remains undiagnosed before delivery in from half to two-thirds of cases. Correct prenatal diagnosis is essential to reduce the burden of maternal and fetal morbidity. The purpose of our study is to evaluate the accuracy of US and MRI in the diagnosis of PAS.

STUDY DESIGN

In this retrospective study, 104 patients with suspected placenta accreta were enrolled and had been investigated with US and MRI. They were divided into four groups: no PAS, accreta, increta, and percreta.

RESULTS

Compared to MRI, US results were higher in the diagnosis and in the identification of PAS severity (85% US vs. 80% MRI). For both methods, in the case of posterior placenta, there is greater difficulty in identifying the presence/absence of the disease (67% in both methods) and the severity level (61% US vs. 55% MRI).

CONCLUSION

US, properly implemented with the application of defined and standardized scores, can be superior to MRI and absolutely sufficient for the diagnosis of PAS, limiting the use of MRI to a few doubtful cases and to cases in which surgical planning is necessary.

MRI-radiomics-clinical-based nomogram for prenatal prediction of the placenta accreta spectrum disorders

OBJECTIVES

To investigate whether an MRI-radiomics-clinical-based nomogram can be used to prenatal predict the placenta accreta spectrum (PAS) disorders.

METHODS

The pelvic MR images and clinical data of 156 pregnant women with pathologic-proved PAS (PAS group) and 115 pregnant women with no PAS (non-PAS group) identified by clinical and prenatal ultrasonic examination were retrospectively collected from two centers. These pregnancies were divided into a training (n = 133), an independent validation (n = 57), and an external validation (n = 81) cohort. Radiomic features were extracted from images of transverse oblique T2-weighted imaging. A radiomics signature was constructed. A nomogram, composed of MRI morphological findings, radiomic features, and prenatal clinical characteristics, was developed. The discrimination and calibration of the nomogram were conducted to assess its performance.

RESULTS

A radiomics signature, including three PAS-related features, was associated with the presence of PAS in the three cohorts (p < 0.001 to p = 0.001). An MRI-radiomics-clinical nomogram incorporating radiomics signature, two prenatal clinical features, and two MRI morphological findings was developed, yielding a higher area under the curve (AUC) than that of the MRI morphological-determined PAS in the training cohort (0.89 vs. 0.78; p < 0.001) and external validation cohort (0.87 vs. 0.75; p = 0.003), while a comparable AUC value in the validation cohort (0.91 vs. 0.81; p = 0.09). The calibration was good.

CONCLUSIONS

An MRI-radiomics-clinical nomogram had a robust performance in antenatal predicting the PAS in pregnancies.

KEY POINTS

• An MRI-radiomics-clinical-based nomogram might serve as an adjunctive approach for the treatment decision-making in pregnancies suspicious of PAS. • The radiomic score provides a mathematical formula that predicts the possibility of PAS by using the MRI data, and pregnant women with PAS had higher radiomic scores than those without PAS.

Assessment of postpartum haemorrhage for placenta accreta: Is measurement of myometrium thickness and dark intraplacental bands using MRI helpful?

Background

This study aimed to investigate the predictive values of magnetic resonance imaging (MRI) myometrial thickness grading and dark intraplacental band (DIB) volumetry for blood loss in patients with placenta accreta spectrum (PAS).

Methods

Images and clinical data were acquired from patients who underwent placenta MRI examinations and were diagnosed with PAS from March 2015 to January 2021. Two radiologists jointly diagnosed, processed, and analysed the MR images of each patient. The analysis included MRI-based determination of placental attachment, as well as myometrial thickness grading and DIB volumetry. The patients included in the study were divided into three groups according to the estimated blood loss volume: in the general blood loss (GBL) group, the estimated blood loss volume was < 1000 ml; in the massive blood loss (MBL) group, the estimated blood loss volume was ≥ 1000 ml and < 2000 ml; and in the extremely massive blood loss (ex-MBL) group, the estimated blood loss volume was ≥ 2000 ml. The categorical, normally distributed, and non-normally distributed data were respectively analysed by the Chi-square, single-factor analysis of variance, and Kruskal–Wallis tests, respectively. The verification of correlation was completed by Spearman correlation analysis. The evaluation capabilities of indicators were assessed using receiver operating characteristic curves.

Results

Among 75 patients, 25 were included in the GBL group, 26 in the MBL group, and 24 in the ex-MBL group. A significant negative correlation was observed between the grade of myometrial thickness and the estimated blood loss (P < 0.001, ρ = − 0.604). There was a significant positive correlation between the volume of the DIB and the estimated blood loss (P < 0.001, ρ = 0.653). The areas under the receiver operating characteristic curve of the two MRI features for predicting blood loss ≥ 2000 ml were 0.776 and 0.897, respectively.

Conclusions

The grading and volumetric MRI features, myometrial thickness, and volume of DIB, can be used as good prediction indicators of the risk of postpartum haemorrhage in patients with PAS.

An update of diagnostic efficacy of ultrasound and magnetic resonance imaging in the diagnosis of clinically significant placenta accreta spectrum disorders

PURPOSE OF REVIEW

Systematic screening and diagnosis of placenta accreta spectrum disorder (PAS) either by ultrasound or magnetic resonance imaging (MRI) would allow referral of high-risk women to specialized multidisciplinary teams. We aimed to report recent findings regarding the diagnostic accuracy of ultrasound and magnetic resonance imaging in the diagnosis of PAS.

RECENT FINDINGS

Recent evidence from the literature shows that both ultrasound and MRI are good tests to identify PAS in high-risk populations. Ultrasound can also be used safely to guide management decisions, concentrating greater resources in patients with the higher risk of clinically significant PAS requiring complex peripartum management. Moreover, there are increasing data showing that routine contingent screening for PAS disorders based on the finding of a placenta implanted low in the uterine cavity and previous uterine surgery is effective in a public healthcare setting. A contingent screening strategy for PAS is feasible if placental location is routinely assessed during routine scans, and may even start from the first trimester of pregnancy.

SUMMARY

Ultrasound is an effective tool to screen pregnancies at high risk of PAS. In such pregnancies, ultrasound and MRI are effective imaging modalities for guiding management.

Unexpected uterine body placenta accreta spectrum with placenta previa in a subsequent pregnancy after uterine artery embolization: a case report

BACKGROUND

A subsequent pregnancy after uterine artery embolization (UAE) raises several concerns, one of which is placenta accreta spectrum (PAS). Placenta previa is the strongest risk factor for PAS, which is most likely to occur in the lower uterine segment. PAS without placenta previa (i.e., uterine body PAS) is considered relatively rare.

CASE PRESENTATION

A 35-year-old woman, gravida 2 para 1, had undergone UAE for postpartum hemorrhage due to uterine atony after vaginal delivery in her previous pregnancy. She developed placenta previa during her subsequent pregnancy and was therefore evaluated for PAS in the lower uterine segment. On the basis of examination findings, we considered PAS to be unlikely. During cesarean section, we found that the placenta was not detached from the uterine body, and the patient was determined to have uterine body PAS. Ultimately, a hysterectomy was performed.

CONCLUSIONS

PAS can occur in a subsequent pregnancy after UAE. When a subsequent pregnancy after UAE is accompanied by placenta previa, it is important to maintain a high index of suspicion of uterine body PAS without being misled by the presence of placenta previa.

Placenta Accreta Spectrum Disorders and Radiomics: Systematic review and quality appraisal

PURPOSE

Ultrasound and magnetic resonance imaging are the imaging modalities of choice for placenta accrete spectrum (PAS) disorders assessment. Radiomics could further increase the value of medical images and allow to overcome the limitations linked to their visual assessment. Aim of this systematic review was to identify and appraise the methodological quality of radiomics studies focused PAS disorders applications.

METHOD

Three online databases (PubMed, Scopus and Web of Science) were searched to identify original research articles on human subjects published in English. For the qualitative synthesis of results, data regarding study design (e.g., retrospective or prospective), purpose, patient population (e.g., sample size), imaging modalities and radiomics pipelines (e.g., segmentation and feature extraction strategy) were collected. The appraisal of methodological quality was performed using the Radiomics Quality Score (RQS).

RESULTS

10 articles were finally included and analyzed. All were retrospective and MRI-powered. The majority included more than 100 patients (6/10). Four were prognostic (focused on either the prediction of bleeding volume or the prediction of needed management) while six diagnostic (PAS vs not PAS classification) studies. The median RQS was 8, with maximum and minimum respectively equal to 17/36 and - 6/36. Major methodological concerns were the lack of feature stability to multiple segmentation testing and poor data openness.

CONCLUSIONS

Radiomics studies focused on PAS disorders showed a heterogeneous methodological quality, overall lower than desirable. Furthermore, many relevant research questions remain unexplored. More robust investigations are needed to foster advancements in the field and possibly clinical translation.

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.

A computerized diagnostic model for automatically evaluating placenta accrete spectrum disorders based on the combined MR radiomics-clinical signatures

We aimed to establish a computerized diagnostic model to predict placenta accrete spectrum (PAS) disorders based on T2-weighted MR imaging. We recruited pregnant women with clinically suspected PAS disorders between January 2015 and December 2018 in our institution. All preoperative T2-weighted imaging (T2WI) MR images were manually outlined on the picture archive communication system terminal server. A nnU-Net network for automatic segmentation and the corresponding radiomics features extracted from the segmented region were applied to build a radiomics-clinical model for PAS disorders identification. Taking the surgical or pathological findings as the reference standard, we compared this computerized model’s diagnostic performance in detecting PAS disorders. In the training cohort, our model combining both radiomics and clinical characteristics yielded an accuracy of 0.771, a sensitivity of 0.854, and a specificity of 0.750 in identifying PAS disorders. In the testing cohort, this model achieved a segmentation mean Dice coefficient of 0.890 and yielded an accuracy of 0.825, a sensitivity of 0.830 and a specificity of 0.822. In the external validation cohort, this computer-aided diagnostic model yielded an accuracy of 0.690, a sensitivity of 0.929 and a specificity of 0.467 in identifying placenta increta. In the present study, a machine learning model based on preoperative T2WI-based imaging had high accuracy in identifying PAS disorders in respect of surgical and histological findings.

Magnetic resonance imaging (MRI) of normal human placentae

INTRODUCTION

The MRI appearances of the human placenta in the absence of maternal or fetal pathology have not been extensively studied, with only a few studies reporting findings in the uncomplicated pregnancy. The purpose of this study is to review the placental MRI appearances in low-risk pregnancies in a prospective study.

METHODS

A prospective observational study of placental MRI in low-risk pregnancies was initially planned, however recruitment was terminated early due to the COVID19 pandemic. The protocol was subsequently modified to compare the placental appearances in the enrolled cohort with pregnancies having had MRI for non-placental pathologies. The data from the two groups were then pooled to assess the range of normal placental appearances.

RESULTS

Eighty-three pregnancies were prospectively assessed with MRI at a median gestation of 29 weeks (range 14-39) from a mixed group of prospective cases (n = 28) and retrospectively recruited obstetric MRI (n = 55). Placental thickness in the third trimester ranged from 18 to 35 mm. T2 heterogeneity was seen in 75% (25/33) at second trimester and by the third trimester 50% (25/50) were moderately or markedly heterogenous. T2 dark bands (>6 mm) were seen in 9% (3/33) and 20% (10/50) of second and third trimester pregnancies, respectively. Undetectable myometrium or loss of the subplacental myometrial plane was present in 15% (5/33) of second and 38% (19/50) of third trimester placentae.

CONCLUSION

This qualitative study of normal placental MRI appearances expands the current knowledge base by confirming they vary, evolve with gestation, and can overlap with signs of placenta accreta spectrum.

Comparison between 1.5-T and 3.0-T MRI for the diagnosis of placenta accreta spectrum disorders

PURPOSE

Accurate antenatal diagnosis of placenta accreta spectrum (PAS) is important for optimal management. The purpose of this study was to compare the respective capabilities of 1.5-T and 3.0-T MRI in the diagnosis of PAS.

MATERIALS AND METHODS

Between March 2016-March 2021, 190 pregnant women at high risk for PAS underwent dedicated prenatal MRI with either 1.5-T or 3.0-T units at a tertiary imaging center. Cesarian section and MRI were performed less than 6 weeks from each other. Prospectively collected data were evaluated by two experienced genitourinary radiologists for presence and extent of PAS. A comparative study was designed to investigate differences in predictive ability between 1.5-T and 3.0-T MRI groups. Sensitivity, specificity, accuracy, negative and positive prognostic values relative to intraoperative/histological findings, were computed for both groups and were compared with chi-square (χ 2) test. Interobserver agreement was estimated using Kappa test.

RESULTS

One hundred-eighty-two gravid women were included in the study; of these, 91/182 (50%) women were evaluated with 1.5-T (mean age, 35 ± 5.1 [SD] years; mean gestational age: 32.5 weeks) and 91/182 (50%) with 3.0-T MRI (mean age, 34.9 ± 4.9 [SD] years; mean gestational age, 32.1 weeks). 1.5-T MRI yielded 95.7% sensitivity (95% CI: 87.8-99.1) and 81.8% specificity (95% CI: 59.8) and 3.0-T MRI 93.8% sensitivity (95% CI: 86.0-97.9) and 83.3% specificity (95% CI: 48.2-97.7) for PAS identification, with no differences between the two groups (P = 0.725 and P >0.999, respectively). MRI showed excellent predictive ability for detecting extrauterine placental spread with 100% sensitivity (95% CI: 89.4-100.0), 96.7% specificity (95% CI: 88.1-99.6) for 1.5-T and 97% sensitivity (95% CI: 84.2-99.9), 96.7% specificity (95% CI: 88.1-99.6) for 3.0-T without differences between the two groups (P > 0.999). Interobserver agreement was excellent for both groups. The most frequently detected MRI signs of PAS for both 1.5-T and 3.0-T groups were placental heterogeneity (n = 85, 93.5% vs. n = 90, 98.9%; P = 0.413), and intraplacental fetal vessels (n = 64, 70.3% vs. n = 65, 71.4%; P = 0.870).

CONCLUSION

This study suggests that 3.0-T MRI and 1.5-T MRI are equivalent for the diagnosis of PAS.

Treatment of Placenta Increta With High-Intensity Focused Ultrasound Ablation and Leaving the Placenta in situ: A Multicenter Comparative Study

Objective

To explore the feasibility of simple high-intensity focused ultrasound (HIFU) ablation for placenta increta.

Methods

Ninety-five patients after a vaginal delivery were enrolled in this retrospective cohort study, 53 patients were treated with simple HIFU ablation, and 42 patients were treated with HIFU followed by uterine curettage.

Results

All 95 patients were successfully treated with a single-session HIFU procedure, and in the control group, the necrotic placental tissue was removed with curettage. Vaginal hemorrhage did not occur in either group. The duration of bloody lochia was 25.9 ± 8.6 days in the sHIFU group and 24.2 ± 8.8 days in the control group (P > 0.05). The median serum human chorionic gonadotropin (HCG) level was 3,222 mIU/mL and 2,838 mIU/mL in the sHIFU and control groups, respectively, which decreased and returned to normal within 30 days, and the differences were not significantly on comparing the blood HCG level in the two groups at 7, 15, and 30 days after HIFU (all P > 0.05). Decreased menstrual volume occurred in 85.71% of patients in the control group, which was higher than that in the sHIFU group (23.08%) (χ² = 6.839, P < 0.001). During 2–8 years of follow-up, six pregnancies occurred in the sHIFU group without any recurrence of placenta increta, three pregnancies occurred in the control group, and one patient developed a repeat placenta increta.

Conclusion

Simple HIFU treatment is safe and effective for postpartum placenta increta and leaving the placenta in situ. It is a promising option for patients who wish to preserve their fertility and conceive.

Assessment of placental abruption with diffusion-weighted imaging

AIM

To investigate whether placental abruption without fetal distress could be assessed by apparent diffusion coefficient (ADC) values in magnetic resonance imaging (MRI).

METHODS

We conducted a retrospective case-control study at a single center. ADC values at the lesions of placental abruption in the abruption group (n = 8) were compared to those in the control group (n = 32). In the abruption group, ADC values at the sites of abruption were also compared to those at the nonabruption sites within the same placenta.

RESULTS

The ADC values in the placental area above the abruption site in the abruption group showed lower values than those in the control group when the slice containing the umbilical cord insertion site was set as the reference, and those values were compared in each corresponding slice. Compared with average ADC values, those above the abruption site in the abruption group were also significantly lower than those in the control group (p < 0.001). Furthermore, ADC values at the area above abruption were lower than those at the nonabruption area of all planes in the abruption group.

CONCLUSIONS

ADC values at the lesions above the placental abruption site were reduced compared to those in the normal placenta and those in the nonabruption area. Thus, it would be helpful to understand the pathophysiology of placental abruption in expectant management, although further investigations would be needed.

Developing and Validating Nomogram to Predict Severe Postpartum Hemorrhage in Women With Placenta Previa Undergoing Cesarean Delivery: A Multicenter Retrospective Case-Control Study

Objective

Developing and validating nomogram to predict severe postpartum hemorrhage (SPPH) in women with placenta previa (PP) undergoing cesarean delivery.

Methods

We conducted a multicenter retrospective case-control study in five hospitals. In this study, 865 patients from January, 2018 to June, 2020 were enrolled in the development cohort, and 307 patients from July, 2020 to June, 2021 were enrolled in the validation cohort. Independent risk factors for SPPH were obtained by using the multivariate logistic regression, and preoperative nomogram and intraoperative nomogram were developed, respectively. We compared the discrimination, calibration, and net benefit of the two nomograms in the development cohort and validation cohort. Then, we tested whether the intraoperative nomogram could be used before operation.

Results

There were 204 patients (23.58%) in development cohort and 80 patients (26.06%) in validation cohort experienced SPPH. In development cohort, the areas under the receiver operating characteristic (ROC) curve (AUC) of the preoperative nomogram and intraoperative nomogram were 0.831 (95% CI, 0.804, 0.855) and 0.880 (95% CI, 0.854, 0.905), respectively. In validation cohort, the AUC of the preoperative nomogram and intraoperative nomogram were 0.825 (95% CI, 0.772, 0.877) and 0.853 (95% CI, 0.808, 0.898), respectively. In the validation cohort, the AUC was 0.839 (95% CI, 0.789, 0.888) when the intraoperative nomogram was used before operation.

Conclusion

We developed the preoperative nomogram and intraoperative nomogram to predict the risk of SPPH in women with PP undergoing cesarean delivery. By comparing the discrimination, calibration, and net benefit of the two nomograms in the development cohort and validation cohort, we think that the intraoperative nomogram performed better. Moreover, application of the intraoperative nomogram before operation can still achieve good prediction effect, which can be improved if the severity of placenta accreta spectrum (PAS) can be accurately distinguished preoperatively. We expect to conduct further prospective external validation studies on the intraoperative nomogram to evaluate its application value.

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.

MRI based morphological examination of the placenta

Ultrasound is widely used as the initial diagnostic imaging modality during pregnancy with both high spatial and temporal resolution. Although MRI in pregnancy has long focused on the fetus, its use in placental imaging has greatly increased over recent years. In addition to the possibilities of evaluating function, MRI with a wide field of view and high contrast resolution allows characterization of placental anatomy, particularly in situations that are difficult to specify with ultrasound, especially for suspected placenta accreta. MRI also appears to be a particularly useful examination for the anatomical evaluation of the placenta independent of maternal body habitus or fetal position. Indeed, surprisingly little attention is paid to the placenta in MRI when the indication for the examination is fetal. Thus, some aspects of the placenta seem to us to be important to be recognized by the radiologist and to be described on the MRI report. In this review, we will describe MRI sequences used for, and common features seen in, imaging of i) the normal placenta, ii) abnormal aspects of the placenta that should be identified on MRI performed for fetal reason, and iii) placental anomalies for which placental MRI may be indicated.

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.

Correlation of placental MR imaging signs and pathologic diagnosis of placenta accreta spectrum: Retrospective single center case series

INTRODUCTION

Alongside initial screening obstetric US, use of placental MRI has been increasing in the last few decades to aid with antenatal diagnosis and delivery planning in Placenta Accreta Spectrum (PAS). The aim of this study was to determine if the MRI pathophysiological sign subcategories described in the current literature can predict the severity of pathologic diagnosis.

METHODS

Institutional imaging records were reviewed for placental MRIs performed for suspicion of PAS in the last decade. Electronic health records were searched for patient history and pathology. The 59 MRI studies were reviewed using the 11 MRI signs described by the SAR and ESUR joint consensus statement. Further breakdown of the signs was divided by underlying pathophysiologic subcategories including gross morphologic, interface and tissue architecture signs.

RESULTS

Pathologic diagnosis yielded 34 cases: accreta 4/34, incerta 14/34, percreta 10/34 and normal 6/34. Of the accreta cases all of them demonstrated at least two interface and half of the cases had tissue architecture signs, 13/14 increta cases demonstrated interface signs and 12/14 demonstrated tissue architecture signs, 9/10 percreta cases had two interface and at least six demonstrated three tissue architecture signs. Statistical analysis showed significant difference between pathologic diagnosis and the number of positive interface signs with p = 0.02.

DISCUSSION

Interface signs were the most objective and sensitive MRI subcategory. Statistical analysis determined there was a significant difference between PAS diagnosis and number of interface signs present. This subcategory has the most overlap with classic US signs which are traditionally used before MRI referral.