MR在妊娠中晚期正常胎儿及胎盘检查中的应用价值

Magnetic Resonance Imaging of the Normal Fetus and Placenta in Medium to Late Pregnancy

目的了解正常胎儿主要器官及胎盘的MRI表现。资料与方法对36例孕20周以上正常胎儿行MRI检查,采用单次激发快速自旋回波序列(SSFSE),从胎儿头颅、躯干轴位、冠状位、矢状位等多体位观察胎儿各系统主要器官,包括脑、肺、心脏、肝、脾、胃肠道等和胎盘的解剖和MRI表现。结果 36例胎儿MRI检查结果表明:中枢神经系统:孕20周以后大脑三层结构在SSFSE上已经可以辨别,皮质与脑室周围的生发层呈稍低信号,中间白质为高信号。双侧侧脑室在25周前呈生理性扩大状态,枕角明显,25周后逐渐缩小;孕20周时,两侧大脑皮层光滑,无明显沟回形成;孕23周时,仅见双侧侧裂池初具形态;23～30周,两侧大脑皮质主要沟回逐渐形成;30～37周,两侧脑皮质脑沟、回形成明显增多。呼吸循环系统:两肺呈高信号,纵隔内心脏、大血管及两肺纹理呈低信号。消化系统:胃泡、胆囊呈高信号,肠管不扩张时呈等低信号,部分肠管内见低信号胎粪影。肝脏、脾脏呈等低信号位于上腹部两侧。泌尿系统:双侧肾脏呈卵圆形等低信号,膀胱呈囊性高信号位于盆腔内。骨骼、肌肉系统:脊柱、四肢呈低信号,肌肉呈等信号。胎盘信号从均匀、稍高信号向不均匀、稍低信号过渡,胎盘边缘也从平滑向分叶状过渡。结论快速MRI能清楚显示胎儿各主要器官正常解剖和发育变化,同时可以对胎盘成熟度进行准确判断。

Objective To investigate normal MR anatomy and findings of fetus and placenta in medium and late pregnancy.Materials and Methods Thirty six pregnancy women underwented MR examination.Coronal,sagital and axial plane MR SSFSE sequence was performed.The normal MR anatomy of fetus and placenta,including brain,lungs,heart,liver,spleen,gastrointestinal tract,urinary collecting systems,bladder,bones,spine and placenta,was observed in different gestational age.Results MR findings of fetus showed that the main organs had developed at 20 weeks.（1）Central nervous system： at 20 weeks gestation,the three layers of the cerebrum were identified including the hyperintense white matter,the hypointense cortical gray matter,and the lower signal intensity germinal matrix.The ventricular system demonstrated physiologic enlargement until 25 weeks gestation.Before 20 weeks,the surface of the fetal brain was smooth.The sylvian fissure demonstrated a squared appearance at 23 weeks.At 23 to 30 weeks of gestation,the primary fissure developed slowly,until by 30 to 37 weeks,the remainder of the hemispheric fissures were developed.（2）Respiratory and circulation system： The lungs showed high signal intensity,the heart and great vessels appeared hypointense.（3）Digestive system： stomach bubble,the gallbladder showed as high signal.The intestine showed low signal and meconium showed as low signal in part of the intestine.Liver and spleen showed low signal located in right and left side of the abdomen.（4） Urinary system： kidneys showed oval shape with low signal and bladder showed high signal in pelvic cavity.（5）Skeletal,muscular system： spine,limbs showed low signal,and muscle showed equal signal.（6）The placenta signal changed from uniform,slightly higher signal to the uneven,slightly lower signal with the gestational age,and the edge of the placenta changed from the smooth to lobulated shape.Conclusion Normal anatomy and MR findings of fetal main organs and placenta were clearly showed on fast MR imagings.