MAGNETIC RESONANCE EVALUATION OF INVASIVE PLACENTA – OUR EXPERIENCE

and mortality. The availability of conservative treatment modalities for the management of post partum hemorrhage arising from the same mandates the use of magnetic resonance imaging (MRI) to precisely evaluate the degree of placental invasion so as to further guide the treatment options. Materials and Methods: In two years observational cross sectional study, 18 pregnant females between age group 15-40 years were subjected to MRI pelvis and MRI ndings were noted. Result : Placenta accrete vera was the most common type found in our study. Patients with placenta previa and previous Caesarean section were at highest risk. Intraplacental bands, heterogenous placenta, lumpy placental contour were the most commonly observed ndings. Conclusion: MRI is very useful for accurate evaluation of placenta accreta particularly when USG ndings are ambiguous or when there is a posterior placenta. There is increased incidence of placenta accreta with multiparity, placenta previa and history of previous Caesarean sections.


INTRODUCTI0N
Placenta Accreta (PA) occurs due to abnormal invasion of the chorionic villi (CV) into the myometrium due to defect in the decidua basalis. PA is classied on the basis of the degree of myometrial invasion as 1)placenta accreta vera-chorionic villi are in contact with the myometrium without myometrial invasion(incidence 75-78%) ; 2)placenta increta-placenta partially invades the myometrium (incidence 15-17%); 3)placenta percreta-CV penetrate through entire [1] myometrial thickness or beyond serosa (5%incidence) . PA can lead to severe post partum hemorrhage and maternal mortality. History of lower segment Caesarean section (LSCS) and placenta previa are the commonest predisposing factors whereas uterine curettage and [2,3] multiparity are less common risk factors . High-resolution greyscale ultrasound (USG) with colour Doppler is widely used for antenatal diagnosis of invasive placenta. Irregularly shaped placental lacunae with turbulent ow and abnormal areas of hypervascularity with dilated blood vessels at the placenta-myometrial interphase are [4,5] the most useful USG markers for PA .
Magnetic resonance imaging (MRI) is indicated in the diagnostic workup when the ultrasound evaluation is equivocal or for patients with high clinical risk factors for placenta accreta. MRI achieves better soft tissue contrast than ultrasonography in posteriorly situated placenta accreta where the foetal head impedes the ultrasound beam . [6] and in prior myomectomy cases because it is blocked by scar tissue The purpose of this article is to prime radiologists performing MRI for suspected placenta accreta, illustrating abnormal ndings and diagnostic pitfalls so that they are familiar with the recommended MRI protocols and implications of examination ndings for planning appropriate management strategy and thus contribute towards an improved maternal and fetal outcome.
In this study, all women who were antenatally diagnosed by ultrasound to have invasive placenta underwent MRI and observations were noted.

AIMS AND OBJECTIVES:
Ÿ To study the MRI ndings of invasive placenta. Ÿ To formulate an optimum reporting template for accurate MRI diagnosis of invasive placenta.

MATERIALS AND METHODS:
This cross sectional observational study was conducted in our institute between January 2019 to January 2020. Eighteen patients referred From Department Of Obstetrics and Gynaecology with antenatal sonographic diagnosis of invasive placenta were evaluated with MRI pelvis. Post partum patients with retained placenta were excluded from the study. All patients underwent non contrast MRI pelvis on 1.5-T Philips Achieva machine using a multi channel phased-array surface coil without respiratory gating as per the MRI protocol mentioned (Table 1). Scan was done with patient in supine position with moderately distended urinary bladder for better assessment of potential bladder invasion.

Table 1 -MRI scanning Protocol
Fast sequences like T2-weighted HASTE and BTFE needed to minimize fetal motion artefact. T1-weighted gradient-echo sequence in any one plane to look for subchorionic hemorrhage.
Optimum knowledge about the normal changes in placental morphology throughout pregnancy is essential for differentiating them with changes seen in PA. Normal placental morphology and abnormal changes in PA are tabulated in Table 2. There is a rising trend of placenta accreta owing to increased number of primary and repeat Caesarean sections. Accurate and timely identication of affected pregnancies allows optimal obstetric management to reduce maternal morbidity and mortality. The availability of conservative treatment modalities for the management of post partum hemorrhage arising from the same mandates the use of magnetic resonance imaging (MRI) to precisely evaluate the degree of placental invasion so as to further guide the treatment options.

Materials and Methods:
In two years observational cross sectional study, 18 pregnant females between age group 15-40 years were subjected to MRI pelvis and MRI ndings were noted. Result : Placenta accrete vera was the most common type found in our study. Patients with placenta previa and previous Caesarean section were at highest risk. Intraplacental bands, heterogenous placenta, lumpy placental contour were the most commonly observed ndings. Conclusion: MRI is very useful for accurate evaluation of placenta accreta particularly when USG ndings are ambiguous or when there is a posterior placenta. There is increased incidence of placenta accreta with multiparity, placenta previa and history of previous Caesarean sections. Prominent intraplacental vascularization, protrusion of placenta within the cervix, irregularity or disruption of the normal T2 hypointense bladder wall, vessels from placenta extending into the vesical wall and within the parametrium are other features in placenta percreta. Methodical image evaluation and interpretation is crucial as, occasionally, presentation can be quite subtle, with placenta accreta exhibiting only one or two of the aforementioned features.

OBSERVATIONS AND RESULTS
Our study included 18 patients of which 13 were less than 30 years old and 5 were more than 30 years old. Nine out of 18 patients were second gravida while 6 out of 18 patients were third gravida. Fourteen of 18 patients had history of previous LSCS, 2 patients had history of abortions with curettage, 1 patient had history of hystorotomy while 1 patient had no operative history.
Twelve out of 18 patients had placenta previa.
There were 10 patients with placenta acreta vera, 5 with placenta increta and 3 patients with placenta percreta. Succenturiate lobe was present in one patient. MRI features were documented as seen in Table 3 Table 3-MRI features of invasive placenta

DISCUSSION:
In this study, 72.2% patients were aged between 20-29 years, median age being 27.5 years, 27% aged more than 30 years, 95.45% patients were second gravida or higher. In a similar study by Umezurike C et al, median age was 30 years and 82% patients were second gravida or [7] more with a median parity of 3 .
History of at least one LSCS was present in 77.7%, and 70.58% patients had an associated placenta previa. In the 2008 study by Dwyer et al, 81% of patients with PA had history of previous LSCS and 66% [8] patients had placenta previa.
The most consistently observed features were heterogenous placental intensity with lumpy contour, rounded edges and irregularly distributed thick intraplacental bands (100%) (Fig.1). These result due to tethering of placental tissue and are more pronounced in placenta percreta as compared with placenta accreta or placenta increta. These [9] are consistent with the study conducted by Lax A et al . Less frequently documented ndings included myometrial thinning ( Fig. 2 and 3) /increased vascularity at utero-placental interface (55.5%) (Fig.4).    9 Lobulated outer uterine contour 3 5.5% 10 Protrusion of placenta within the cervix 0 0% In general, no attempt is made to distinguish placenta accreta from placenta increta, because the treatment plan does not differ between the two. However, with placenta percreta, invasion of bladder, rectum, or abdominopelvic wall muscles, does affect the surgical management, and an attempt should be made to identify involved structures on MRI.
In cases of placenta percreta, all adjacent involved structures should be identied so that, if necessary, the relevant surgical expertise (e.g., urology, vascular, colorectal, or plastic surgery) can be recruited [10,11,12 to 16] before the procedure. Limitations: Before week 24, the placenta is immature and vascularity at the placental-myometrial interface cannot be differentiated from signs of invasion. After 30 weeks, the aging placenta appears more heterogeneous and can be mistaken for an invasive placenta. Thus, to minimize false positive results, MRI placenta needs to be performed at 24-30 weeks when normal placenta exhibits homogeneous intermediate signal and is distinct from the more heterogeneous and [17].
hyperintense myometrium Dark intraplacental bands are also seen in placental infarction and intervillous thrombus. Even though abnormal intraplacental vascularity denotes placental invasion, the increased pelvic vascularity is not a reliable indicator of invasive placentation. Additional imaging perpendicular to the suspicious interphase and localization of abnormality in at least two orthogonal planes are suggested to avoid pseudo -impressions regarding signs due to [18].
obliquity of imaging planes. Rapid imaging is available with both gradient-echo which better delineates the placental contour and placenta-myometrial interface and spin-echo sequences reliably depicts placental signal heterogeneity and intraplacental bands. Fast spin-echo sequences yield greater tissue contrast and signal-to-noise [18].
ratios than does single-shot imaging We recommend the use of a reporting template (Table 4) for the MRI diagnosis of PA so as to follow a detailed check list for comprehensive evaluation of each patient and reduce inter-observer variation in standard of reporting.

SUMMARY AND CONCLUSION
Invasive placenta is one of the most feared complications in obstetrics. The diagnosis of invasive placenta is usually made based on clinical history, imaging ndings and histological features. Antenatal imaging assessment using ultrasonography or MRI in high risk patients is the main stay for antenatal diagnosis. Early diagnosis is important so that the patient can be prepared and adequately counselled with regard to treatment options and their possible consequences. Increased placental lacunae and increased vascularity at the placenta-myometrial interface are the most common US features.
MRI examination is needed not only to diagnose or conrm PA when USG is inconclusive or incomplete but also to guide operative management. The most consistently observed features are heterogenous placental intensity with lumpy contour, rounded edges and irregularly distributed thick intraplacental bands. Less frequent ndings are interrupted vesical wall, trans serosal extension of placenta into the parametrium. Familiarity with MRI technique to assess the placenta and experience with imaging appearances of normal and invasive placentation will help the radiologist in contributing to an optimal outcome. MRI increases the accuracy of the workup of high-risk patients and aids in multidisciplinary delivery planning to improve maternal outcome.