ROLE OF MRI IN DETECTING ABNORMAL PLACENTATION IN PATIENTS WITH STRONG ULTRASOUND CONCERN FOR MYOMETRIAL INVASION

Abstract

BACKGROUND:Placenta accreta is a severe pregnancy complication which occurs when the chorionic villi invade the myometrium abnormally. Its increasing incidence has greatly increased the risk of a possible threat to life. Previous damage to myometrial wall, through prior cesarean section is the most important risk factor for the development of placenta accreta. MRI increases the accuracy of the workup of high-risk patients and aids in multidisciplinary delivery planning to improve maternal outcome. PURPOSE: The purpose of this study was to identify the role of MRI for diagnosis of morbidly adherent placenta and to assess its depth of invasion in patients with ultrasound suspicion of accreta. The other purpose was to establish the ideal MR sequence perfect for diagnosing placental invasiveness.  PATIENTS AND METHODS: This is a prospective cross sectional analysis to identify morbidly adherent placenta, in patients who presented for MRI placenta from 1st January 2016 to 30 May 2017 at Radiology department of Rehman Medical Institute Peshawar. 14 patients were included with age range of 20-38 years and mean gestational age of 36 weeks. Included patients had sonographic findings suspicious for placenta accreta and were referred for MRI to confirm the diagnosis. The other indications for MR evaluation of the placenta included a lack of adequate visualization of the placenta on prenatal sonography; multiple previous cesarean deliveries with or without concomitant vaginal bleeding; anterior placenta with poor visualization of the region of the cesarean scar on sonography; multiple cesarean deliveries with anterior or low lying placenta and advanced maternal age; and anterior placenta with focal loss of the retroplacental myometrial zone on ultrasound, raising concern for placenta accreta.  MRI was performed on 1.5 tesla GE machine. Multiplanar T2 PROP, T2 FATSAT, T1 and T2 2D FISETA images were acquired. MR images were assessed and re-evaluated by two radiologists with experience in reading pelvic MRI who were blinded to the final diagnosis, especially the site suspicious for placental adhesion. MRI diagnostic criteria for morbidly adherent placenta were established with consensus.  In patients who were operated at our institute, the surgical findings were correlated retrospectively with the MRI findings. RESULTS: MRI confirmed morbidly adherent placenta in 93% of pregnant females with ultrasound suspicion of accreta. Placenta previa was seen in 92%. Placenta was anterior in 42%, Completely low lying in 28.5% and posterior in 28.5%. The most common type of placental invasiveness grade was Increta. MRI was more sensitive than US for the detection of depth of myometrial invasion and the type of abnormal placentation. MRI findings favoring placental invasiveness included: Placental heterogeneity, T2 low bands, Loss of placental - myometrial interface, Traversing vessels, Bulging placenta / uterine bulge, Thin bulging serosa, Direct invasion into or beyond the serosa or Bladder tenting. CONCLUSION: We conclude from our results that MRI confirmed morbidly adherent placenta in 93% patients. The most common grade of invasive placenta on MRI was Increta. T2-PROP is the imaging sequence of choice for Percreta and Increta and T2-FIESTA was found to be useful for Accreta. KEYWORDS: Magnetic Resonance Imaging (MRI), Ultrasound, Placenta percreta, increta, accreta, Morbidly adherent Placenta (MAP).