MRI Study Of Placenta Accreta Spectrum In The Second And Third Trimesters

Background:The placental villi directly adhere to or invade the myometrium when the decidua of the uterus is poorly developed and then placenta accreta spectrum(PAS)occurss.In some severe cases,it can penetrate the uterine serosa and some even invade the para-uterine tissue.According to the depth of PAS,it can be divided into placenta accreta(PA),placenta increta(PI)and placenta percreta(PP).At present,the term placenta accreta spectrum is commonly referred to as the above-mentioned pathological changes of different degrees and extents.The history of cesarean section and placenta previa are two risk factors for PAS.The incidence of PAS is positively correlated with history of cesarean section.The increased incidence of PAS also increases the rate of intraoperative or postpartum hemorrhage and perinatal emergency hysterectomy for gravida.Ultrasound is still the first-line imaging method for screening and preliminary diagnosis of PAS.Magnetic resonance imaging(MRI)is an important supplementary examination.MRI is often used when diagnosis of clinically suspected PAS can not be established on ultrasound.Due to its high resolution of soft tissue,the optimized protocol and its advantages in depicting the depth and location of PAS,it is playing a more and more important role in prenatal diagnosis.At present,a series of MRI diagnostic criteria had been summarized to diagnose PAS.But there were rare studies which explored the differences of PAS between the second and third trimester.Therefore,this study intends to explore the valuable MRI signs of PAS in the second trimester,and further explore the differences in MRI signs of PAS between the second trimester and the third trimester.The paper consists of two parts.The first part is the MRI sign study of PAS in the second trimester,and the second part is the comparative study of MRI signs of PAS between the second trimester and the third trimester.Part 1.MRI signs of placenta accreta spectrum in the second trimesterPurposeTo explore the valuable MRI signs for the diagnosis of placenta accreta spectrum in the second trimester.Materials and methodsPatients:Thirty-six patients with clinically suspected PAS and underwent MRI examination at the preoperative stage were included in the study,including 16 patients proved to be PAS via operation or pathological diagnosis(mean age:32.8±3.8 years,mean gestational age:18.7±5.1 weeks),including 5 cases of PP(mean age:34.4±2.7 years,mean gestational age:18.8±5.4 weeks).20 cases without PAS(mean age:32.7±4.5 years,mean gestational age:19.6±4.5 weeks)were also included.MRI examination:All patients underwent pelvic MRI examination,and 10 of them also underwent an enhanced examination at the same time.The scanning sequence includes T2WI,T1WI and DWI sequences.The T2WI sequence was scanned in different devices including HASTE sequence(n=4),SSFSE sequence(n=10)or conventional T2WI sequence(n=22).The scanning orientation included sagittal,coronal and horizontal planes.Image analysis:Two radiologists who were blinded to the diagnosis evaluated the MRI images randomly.The incidence of the following 16 signs were recorded:placenta previa,loss of the placental-myometrial interface,local myometrial thinning,local interrupted myometrium,dark intraplacental band,marked placental heterogeneity,abnormal intraplacental vascularity,intraplacental hemorrhage,abnormal uterine bulging,placental bulging,extrauterine placental extension,uterine serosal hypervascularity,interrupted uterine serosa,tenting of the bladder,interrupted bladder wall and intrauterine or intracerebral hemorrhage.The gold standard for the presence or absence of a sign is determined by consensus of the three radiologists according to the final clinical and imaging results.Statistical analysis:The Kappa consistency test was used to calculate the consistency of the various signs interpreted between the two readers.Kendall correlation coefficient was used to analyze the correlation between MRI signs of ?>0.4 and surgical/pathological diagnosis,and the chi-square test was performed at the same time.Two parts were calculated.The first was the correlation between the appearance of each sign and existence of PAS.The second was the correlation between the presence or absence of each sign and the extent of PAS(including placenta percreta and placenta acreta,non-percreta acreta).P<0.05 was considered to be statistically significant.ResultsNine of the scored features had an interobserver agreement of ?>0.4:placenta previa(?=0.683,P<0.001),local myometrial thinning(?=0.506,P=0.002),local interrupted myometrium(?=0.563,P<0.001),dark intraplacental bands(?=0.585,P<0.001),abnormal intraplacental vascularity(?=0.611,P<0.001),uterine serosal hypervascularity(?=0427,P=0.005),interrupted uterine serosa(?=0.484,P=0.003),intraplacental hemorrhage(?=0.484,P=0.003)and intrauterine or intracerebral hemorrhage(?=0.416,P=0.008).The correlation coefficient between the following MRI signs and PAS in the second trimester were r>0.3:local myometrial thinning(r=0.605,P<0.001),local interrupted myometrium(r=0.387,P=0.022),dark intraplacental bands(r=0.463,P=0.006),abnormal intraplacental vascularity(r=0.510,P=0.003),interrupted uterine serosa(r=0.500,P=0.003)and intraplacental hemorrhage(r=0.568,P=0.001).Local interrupted myometrium(r=0.510,P=0.003),dark intraplacental bands(r=0.558,P=0.001)and intraplacental hemorrhage(r=0.568,P=0.001)were significantly correlated with placenta percreta in the second trimester,(r>0.5).None of these signs has a correlation with non-percreta percreta(r<0.3).ConclusionsLocal myometrial thinning,local interrupted myometrium,dark intraplacental bands,abnormal intraplacental vascularity,interrupted uterine serosa and intraplacental hemorrhage have a good inter-rater agreement,and also have correlation with occurrence of PAS in the second trimester.They may have a good predictable value for the diagnosis of PAS.Local interrupted myometrium,dark intraplacental bands,and intraplacental hemorrhage have a better correlation with occurrence of placenta percreta in the second trimester.Part 2.Comparative study of MRI signs of placenta accrete spectrum between the second and third trimesterPurposeTo explore the diagnostic efficacy of MRI of PAS in the second and third trimester and to compare the differences in the rates of MRI signs between the second and third trimester.Materials and MethodsPatients:ninety-one patients who underwent pelvic MRI before surgery or labor with clinically suspected placenta were included in the study.There were 36 women in the second trimester(mean age:32.7±4.2 years mean gestational age:19.2±4.8 weeks),and 55 women in the third trimester(mean age:34.2±4.6 years,mean gestational age:33.7±2.4 weeks).MRI examination:All patients underwent pelvic MRI examination.The fundamental scanning sequence includes T2WI,T1WI and DWI sequences.The T2WI sequence was scanned in different devices including HASTE sequence(n=20),SSFSE sequence(n=26)or conventional T2WI sequence(n=45).Image analysis:The same as the first part.Statistical analysis:The diagnostic accuracy of MRI for the second trimester and third trimester was calculated,including sensitivity,specificity,negative predictive value,and positive predictive value.Chi-square test was used to compare the differences in the presence of MRI signs between the second and third trimester PAS.ResultsThe diagnostic sensitivity,specificity,negative predictive value and positive predictive value of MRI for PAS in the second trimester were 88%,90%,90%,and 88%,respectively.The diagnostic sensitivity,specificity,negative predictive value and positive predictive value of MRI for PAS in the third trimester were 83%,85%,91%,and 74%,respectively.The rates of abnormal uterine bulging,placental bulging,intraplacental hemorrhage and tenting of the bladder in the PAS in the second were higher than PAS in the third trimester.The rates were 75%vs 25.7%(P=0.002),81.2%vs 48.6%(P=0.035),62.5%vs 28.6%(P=0.031),25%vs 0(P=0.007)repectively.The rates of abnormal uterine bulging for non-percreta accreta between the second trimester and third trimester was 72.7%and 15.3%,respectively.There was statistical significance.The rate of tenting of the bladder in placenta percreta between the second trimester and third trimester was 60%and 0,respectively,and there was a statistically significant difference(P=0.001).ConclusionsMRI is equally competent in the diagnosis of PAS in the second and third trimester.For PAS,there are 4 MRI signs including abnormal uterine bulging,placental bulging,intraplacental hemorrhage and tenting of the bladder which occur more frequently in the second trimester.Radiologists should rely more on the 4 MRI signs when making diagnosis of PAS in the second trimester.While in the third trimester,sign of tenting of the bladder was not a reliable indicator for diagnosis of placenta percreta.