MRI在产前胎盘植入诊断的应用与进展

Application of MRI in the diagnosis of Placenta implantation before delivery

超声检查作为胎盘植入的检查方式有很多局限性,如胎盘位置太深、羊水太少、孕妇过于肥胖等条件不利于超声准确评估。MRI越来越多地应用于胎盘植入诊断中,尤其针对超声评估不佳的患者。近年来,MRI的快速扫描序列及功能成像,如SSTSE、HASTE、DWI、MRS等在胎盘植入的诊断中发挥极大作用。MRI诊断胎盘植入的直接征象包括:子宫肌层变薄,肌层不连续、胎盘子宫肌层分界不清。胎盘植入的间接征象包括:胎盘内的异质信号;T2WI像胎盘内低信号带;胎盘内异常血管分布,血管迂曲、粗大;胎盘局部膨隆;子宫局限性凸起;邻近器官受侵等。异常胎盘的可能性随着胎盘侵袭的影像学特征数量的增加而增加,并且与患者的危险因素如剖宫产、前置胎盘等因素相关。胎盘内暗带的出现是胎盘植入最强的佐证。本文就目前MRI在产前胎盘植入的应用与进展方面进行综述。

The ultrasonography,as a method of placental implantation,has many limitations,such as too deep placenta,too little amniotic fluid and too fat pregnant women.Magnetic resonance imaging is increasingly used in the diagnosis of placenta accreta,especially for patients with poor ultrasonic evaluation.In recent years,fast scanning sequences and functional imaging of MRI,such as SSTSE,HASTE,DWI and MRS,play a great role in the diagnosis of placenta accreta.The direct signs of MR diagnosis of placental implantation are:thin myometrium,discontinuous myometrium and unclear boundary between myometrium and placenta.Indirect signs of placental implantation:heterogeneous signal in placenta;T2WI like low signal band in placenta;abnormal distribution of blood vessels in placenta,tortuosity and coarseness of blood vessels;local expansion of placenta;local bulge of uterus;invasion of adjacent organs,etc.The possibility of abnormal placenta increased with the number of imaging features of placenta invasion,and was related to the risk factors of patients such as cesarean section,placenta previa and so on.Some scholars have pointed out that the occurrence of placenta dark belt is the strongest evidence of placenta implantation.This article reviews the application and progress of MRI in placenta implantation.