MR Imaging of Abnormal Placentation

Imaging the Uterus in Placenta Accreta Spectrum Disorder

Antenatal diagnosis of placenta accreta spectrum (PAS) improves maternal and neonatal outcomes by allowing for multidisciplinary planning and preparedness. Ultrasound is the primary imaging tool. Simplification and standardization of placental evaluation and reporting terminology allows improved communication and understanding between teams. Prior to 10 weeks of gestation, gestational sac position and least myometrial thickness surrounding the gestational sac help PAS diagnosis very early in pregnancy. Late first-, second-, and third-trimester evaluation includes comprehensive evaluation of the placenta, transabdominal and transvaginal with partially full maternal urinary bladder, and by color Doppler. Subsequently, the sonologist should indicate whether the evaluation was optimal or suboptimal; the level of suspicion as low, moderate, or high; and the extent as focal, global, or extending beyond the uterus. Other complementary imaging modalities such as 3D-power Doppler ultrasound, magnetic resonance imaging (MRI), and vascular topography mapping strive to improve antenatal placental evaluation but remain investigational at present. KEY POINTS: · Antenatal imaging, primarily using ultrasound with partially full maternal urinary bladder, is an essential means of evaluation of those at risk for PAS.. · Simplification and standardization of placental evaluation and reporting will allow improved communication between the multidisciplinary teams.. · Gestational sac location prior to 10 weeks of gestation and four markers after that (placental lacunae and echostructure, myometrial thinning, hypoechoic zone with or without bulging between placenta and myometrium, and increased flow on color Doppler)..

Ferumoxytol-enhanced MR demonstration of changes to internal placental structure in placenta accreta spectrum: Preliminary findings

INTRODUCTION

The goal of this pilot study is to determine if ferumoxytol-enhanced MR might provide a new approach to the diagnosis of placenta accreta spectrum (PAS), and if so, to identify signs of PAS.

METHODS

Ten pregnant women were referred for MRI evaluation for PAS. MR studies consisted of pre-contrast SSFSE, SSFP, DWI, and ferumoxytol-enhanced sequences. Post-contrast images were rendered as MIP and MinIP images to separately display the maternal and fetal circulations respectively. Two readers examined the images for architectural changes to placentone (fetal cotyledon) that might distinguish PAS cases from normal. Attention was given to the size and morphology of the placentone, villous tree, and vascularity. In addition, the images were examined for evidence of fibrin/fibrinoid, intervillous thrombus, basal and chorionic plate bulges. Interobserver agreement was characterized with kappa coefficients and levels of confidence for feature identification was recorded on a 10-point scale.

RESULTS

At delivery, there were five normal placentas and five with PAS (one accreta, two increta, two percreta). The ten changes of placental architecture in PAS included: focal/regional expansion of placentone(s); lateral displacement and compression of the villous tree; disruption of a regular pattern of normal placentones; bulging of the basal plate; bulging of the chorionic plate; transplacental stem villi; linear/nodular bands at basal plate; non-tapering villous branches; intervillous hemorrhage; and dilated subplacental vessels. All these changes were more common in PAS; the first five achieved statistical significance in this small sample. The interobserver agreement and confidence for the identification of these features was good to excellent except for dilated subplacental vessels.

DISCUSSION

Ferumoxytol-enhanced MR imaging appears to depict derangements of the internal architecture of placentas with PAS, thereby suggesting a promising new strategy to diagnose PAS.

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.

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

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

Maternal Serum Placental Protein-13 Levels in the Prediction of Pregnancies with Abnormal Invasive Placentation

OBJECTIVE

To evaluate whether placental protein-13 (PP-13) measured in the serum of pregnant women could predict abnormal invasive placentation (AIP) detected by color Doppler ultrasound (US) and magnetic resonance imaging scan in addition to the routine US scan during the third trimester.

MATERIALS AND METHODS

The prospective case-control study included patients subdivided in 2 groups: 42 pregnant women with a singleton pregnancy at 28-32 weeks of gestation with only suspected AIP, and 32 healthy pregnant women. The serum PP-13 levels were measured in both groups using an enzyme-linked immunosorbent assay (ELISA) method and statistically compared. The cases of AIP were confirmed by placental histopathological examination and/or the uterus removed by hysterectomy after elective caesarean section.

RESULTS

Serum PP-13 levels of pregnant women with AIP were significantly higher (p<0.001) than those of controls (650.32±387.33 vs. 231.43±94.33). Statistical analysis of maternal serum PP-13 levels above the threshold of 312 pg/ml (measured in the early third trimester) predicted AIP with 76.2% sensitivity and 75% specificity.

CONCLUSION

Maternal serum PP-13 may have a role in the pathophysiology of AIP owing to its high serum value in the AIP group. The maternal serum dosage of PP-13 levels could improve pregnancy management in those patients suspected of having AIP.

Placenta Accreta Spectrum Disorder: Uterine Dehiscence, Not Placental Invasion

For decades, placenta accreta spectrum disorder has been classified, staged, and described as a disorder of placental invasion. In this commentary, we argue that placenta accreta spectrum exists as a disorder of defective decidua and uterine scar dehiscence, not as a disorder of destructive trophoblast invasion. Adopting this understanding of placenta accreta spectrum will help direct research efforts and clinical resources toward the prevention, accurate diagnosis, and safe treatment of this devastating-and increasingly common-disorder.

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

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