European Journal of Cardiovascular Medicine

Placenta accreta is a pathological condition characterized by the abnormal attachment of the placenta to the uterine wall, encompassing all forms within the PAS (Placenta Accreta Spectrum). This spectrum includes three categories based on the degree of placental invasion into the myometrium: placenta accretavera, where villi attach to the myometrium without invading the muscle; placenta increta, where villi partially invade the myometrium; and placenta percreta, the most severe form, in which villi penetrate through the entire myometrium and may extend beyond the uterine serosa.^[1,2]

The etiology of placenta accreta is not fully understood, though several factors contribute to its development, including trophoblast over-invasion and localized hypoxia. Additionally, a lack of decidualization can impair the usual changes in maternal arteries, further facilitating abnormal placental attachment.^[3,4,5] The main risk factors for placenta accreta are a history of LSCS (Lower-Segment Cesarean Section) and placenta previa. Other contributing factors include advanced maternal age, uterine anomalies, prior uterine surgeries, and procedures like dilation and curettage or myomectomy. Women with placental adhesion often exhibit elevated concentrations of biochemical markers such as fetoprotein and human chorionic gonadotropin during the second trimester, which are indicative of aberrant placentation.^[6-9]

The primary consequence of placenta accreta is significant maternal morbidity, with the most common intervention being a hysterectomy following delivery. Given its potentially life-threatening complications, early and accurate diagnosis is crucial. USG and MRI are the most effective diagnostic tools for placenta accrete.^[10] Timely prenatal identification allows for appropriate delivery planning, ensuring availability of blood products and specialized surgical teams. This study aims to evaluate the diagnostic accuracy of USG and MRI in detecting placenta accreta, based on postoperative outcomes.

AIMS AND OBJECTIVES

The study aimed to evaluate the accuracy of USG and MRI in diagnosing abnormal placental adherence, with reference to postoperative findings. The objectives include identifying the key ultrasound features that can predict placental invasion and outlining the specific MRI characteristics that may indicate placental invasion. By focusing on these diagnostic markers, the study seeks to enhance early detection of placental accreta and improve clinical decision-making..

Study Design

The study was a cross-sectional design conducted over a period of 24 months at the Department of Radiology, Kurnool Medical College & Hospital, Kurnool. The study population consisted of pregnant women referred for MRI with a history of previous cesarean section and suspected placental invasion from both the Department of Radio-diagnosis and Imaging at Kurnool Medical College and GGH (Government General Hospital). A convenient sampling technique was used, and the study included a total sample size of 50 participants.

Inclusion and Exclusion Criteria

The inclusion criteria for this study were pregnant women referred for MRI with a history of previous cesarean section and suspected placental invasion, who were also willing to provide informed consent. The exclusion criteria included patients with contraindications to MRI, such as metallic implants or other conditions preventing safe imaging, and those who were not willing to give informed consent.

Data Collection Procedure

Data collection was carried out prospectively on 50 patients who met the inclusion criteria and provided written informed consent. Participants were selected using a convenient sampling method, and relevant clinical and imaging data were documented using a specially designed proforma. All patients underwent ultrasonography using a GE Versana ultrasound machine and MRI using a 1.5 Tesla Philips superconducting magnet with a multichannel phased array surface coil. MRI examinations typically lasted 15–30 minutes, with second-trimester patients scanned in a supine position and third-trimester patients in a left lateral decubitus position. A moderately full bladder and breath-holding techniques were used to optimize image quality. MRI protocols included balanced turbo field echo SPAIR sequences in axial, coronal, and sagittal planes, T2-weighted axial sequences, and DWI (Diffusion-Weighted Imaging), all with a FOV (Field Of View) of 320–400 mm. Ultrasonographic features assessed for placental invasion included placental lacunae with turbulent flow, loss of retroplacental clear space, irregular bladder wall with vascularity, gaps in retroplacental blood flow, and myometrial thinning (<1 mm) or non-visualization. MRI features included dark T2 intraplacental bands, heterogeneous placenta, placental bulge, lumpy contour with rounded edges, thinning or loss of the retroplacental T2 dark zone, myometrial thinning, and bladder tenting. All findings were recorded systematically, and a comparative analysis of USG and MRI findings was conducted.

Statistical Analysis

The collected data were entered and analyzed using Microsoft Excel 2010 and Epi Info version 7.2.0. Both descriptive and inferential statistical methods were employed in the analysis. Continuous variables were expressed as mean ± SD (Standard Deviation) along with their minimum and maximum values, while categorical variables were presented as frequencies and percentages. To assess statistical significance, a 5% level of significance was used. ANOVA (Analysis of Variance) was applied to evaluate intergroup differences for continuous variables, and the chi-square test was used to compare categorical variables. A p-value of less than 0.05 was considered statistically significant.

Table 1 shows the baseline demographic characteristics including age, gravidity, and prior cesarean history, with most participants between 21 and 29 years old and having one prior C-section.

Table 2 observes gestational age distribution, placental site, and placenta previa types, with the majority presenting between 26 and 34 weeks and type IV placenta previa.

Table 3 illustrates USG findings, where most cases showed no invasion, while accreta and percreta accounted for 12%.

Table 4 shows MRI findings, with 24% of cases diagnosed as invasive (accreta/percreta).

Table 5 presents the gold standard results, confirming 20% of cases as PAS (accreta/percreta).

Table 6 shows that USG had higher sensitivity, while MRI achieved perfect specificity and PPV, highlighting complementary diagnostic roles.

Table 7 demonstrates that the most sensitive USG marker was intraplacental lacunae/retroplacental clear space loss, while MRI best detected myometrial thinning.

The present study was conducted in the Department of Radiodiagnosis, Kurnool Medical College & Hospital, Kurnool, with the objective of assessing the accuracy of USG and MRI in the antenatal detection of placental invasion spectrum and correlating the findings with postoperative histopathology.

Age Distribution

In this study, 42% of women belonged to the 21–24 years age group, followed by 36% in the 25–29 years group. Only 12% were above 30 years. These findings are comparable to Sawant et al.^[11] where the mean age was 26.67 years, and lower than Riteau et al.^[12] who reported a mean age of 34 years. This suggests that although PAS is more frequent in advanced maternal age, younger women with previous cesarean delivery are also significantly at risk.

Gestational Age at Diagnosis

Most patients (55%) were scanned between 26 and 30 weeks, followed by 34% between 31 and 34 weeks. Sawant et al.^[11] reported a mean gestational age of 30 weeks, while Riteau et al.^[12] noted mean gestational ages of 28.7 weeks for USG and 32.4 weeks for MRI. This highlights the importance of mid-trimester screening for timely identification of PAS.

History of Previous Cesarean Section

In this study, 46% of cases had one previous cesarean section, while 24% had two. Similar trends were observed by Sawant et al.^[11] where most patients had prior cesareans, and Riteau et al.^[12] who reported 88% of cases with cesarean history. These findings reaffirm that previous uterine surgery, especially cesarean delivery, remains the strongest risk factor for PAS.

Type of Placenta Previa

Type IV placenta previa was the most common (60%) in this study, consistent with the strong association between placenta previa and accreta. Sawant et al.^[11] reported placenta previa in all cases, while Riteau et al.^[12] observed varying distributions of accreta, percreta, and non-adherent placenta. This supports the established evidence that placenta previa is a key predisposing factor for PAS.

Ultrasonography Findings

USG showed no invasion in 82% of cases, while 12% were confirmed PAS (8% accreta, 4% percreta). Sawant et al.^[11] found abnormal bridging vessels (80%), myometrial thinning and lacunae (50%), and bladder wall disruption (20%) as major predictors. The sensitivity of USG in this study was 100% with a specificity of 90%, which is higher than Dahmarde et al.^[13] who reported a sensitivity of 73% and a specificity of 89%. Riteau et al.^[12] also reported high sensitivity (100%) but low specificity (37.5%). This indicates that while USG is highly sensitive, false positives can occur, warranting MRI confirmation in equivocal cases.

MRI Findings

MRI diagnosed 24% as PAS (20% accreta, 4% percreta), closely matching histopathology. In comparison, Sawant et al.^[11] reported abnormal bulge (73.3%) and heterogeneous placenta (70%) as frequent MRI features, while Riteau et al.^[12] noted uterine bulge and T2 dark intraplacental bands as reliable predictors. In the present study, MRI achieved 83% sensitivity and 100% specificity, similar to Dahmarde et al.^[13] who reported 89% sensitivity and 97% specificity. Although MRI is slightly less sensitive than USG, it provides superior specificity and anatomical detail, especially for surgical planning.

Histopathological Correlation

Histopathology confirmed 20% PAS (16% accreta, 4% percreta). Sawant et al.^[11] found higher rates of increta and percreta, while Riteau et al.^[12] demonstrated MRI accuracy in 20 of 26 cases. These differences may reflect population characteristics and referral bias.

Diagnostic Accuracy

USG showed diagnostic accuracy of 98% compared to 96% for MRI. While USG had higher sensitivity, MRI offered perfect specificity. These results align with previous reports,^[11-13] suggesting that USG should be the first-line tool, with MRI reserved for posterior placentas, inconclusive USG findings, or when surgical planning requires precise assessment of invasion depth.

The present study concluded that MRI demonstrates diagnostic findings closely correlating with those of histopathological examination, making it a reliable modality for evaluating abnormal placental adherence. However, considering economic constraints and wider accessibility, USG remains a highly effective and practical diagnostic tool. In this study, USG demonstrated 100% sensitivity in detecting placental invasion, highlighting its value as a first-line imaging modality in the evaluation of suspected cases of placenta accreta spectrum.

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