【作者】 李凌；

【导师】 周启昌； Joshua A. Copel；

【作者基本信息】 中南大学 ， 影像医学与核医学， 2010， 博士

【摘要】 研究背景与目的：胸腺是一个淋巴上皮器官,在胎儿时期T淋巴细胞在胸腺内发育,胸腺为T淋巴细胞的分化和选择提供环境,且胸腺随着胎儿生长发育而不断生长。多项研究表明,胸腺发育不全或者胸腺缺如与孕妇酗酒及多种疾病相关,例如22q11微缺失综合征,DiGeorge综合征,Ellis-van Creveld综合征,重症联合免疫缺陷,HIV感染,胎儿宫内发育迟缓,急性疾病以及绒毛膜羊膜炎等。胸腺发育不全或者胸腺缺如,需要与胎儿正常胸腺大小比较,才能确立其诊断。以往的研究都是应用二维超声观测胸腺,Felker等应用前后径(APD), Jeppesen和Cho等应用横径(MTD), Zalel等应用周长(TC)评估胎儿胸腺的大小。但从解剖学角度考虑,胸腺位于前上纵隔内,其前方是胸骨,后方和腹侧是心包和心脏发出的大血管,两侧是肺脏,而且胸腺是一个不规则、分叶状的实质性器官。应用二维超声测量单个切面获得的参数,反映胸腺的大小存在局限性。随着超声技术的日益发展,三维和四维超声也随之不断发展,并且开始在多个医学领域中应用,尤其是产前诊断。三维超声中虚拟器官计算机辅助分析(VOCAL)技术,可以把胸腺作为一个整体进行分析,并整合多个二维切面的信息,重建三维模型,克服了二维超声测量只能反映单一平面信息的局限性。在胚胎发育过程中,咽器内起源于神经嵴的间充质细胞生发了心脏圆锥动脉干血管的平滑肌,以及胸腺和甲状旁腺的结缔组织。咽器各个结构的发育对于环境和基因的改变非常敏感。任何能够影响咽器发育的因素,都可能导致胎儿胸腺发育不全或者胸腺缺如和先天性的心脏畸形。22q11微缺失综合征(22号染色体长臂第11.2位点微缺失)是一类临床表现丰富多变的基因异常疾病,其与180多种表型相关联,其中心脏畸形和胸腺发育不全或者缺失是最常见的临床表现。此外,多项研究表明22q11微缺失与先天性心脏病关系最为密切。而且在引起先天性心脏病的原因中,22q11微缺失是最常见原因之一。然而,在患有先天性心脏病的高危胎儿中,22q11微缺失综合征的产前发生率并不十分清楚。本研究旨在：1.建立胎儿胸腺二维各径线和三维体积的正常值,并比较胎儿胸腺的二维、三维超声测量。2.探讨胎儿先天性心脏病和胎儿胸腺发育不全或者缺如的关联性。3.探讨胎儿先天性心脏病和22q11微缺失的关联性。方法：于2006年6月至2007年11月,应用GE公司Voluson 730彩色多普勒高分辨率超声诊断系统,二维腹部探头频率为4-6MHz,测量347例正常胎儿的胸腺周长(TC组)和28例先天性心脏病并尸解证实的胎儿(CHD组Ⅰ)的胸腺周长。于2007年12月至2010年2月,应用Philips公司IU22彩色多普勒高分辨率超声诊断系统,三维腹部探头频率为6MHz和GE公司Voluson730彩色多普勒高分辨率超声诊断系统,三维腹部探头频率为4-6MHz,测量567例胎儿胸腺最大横径(MTD组)、前后径(APD组)、上下径(SID组)和最大横截面积(MTA组)。同时应用三维超声的虚拟器官计算机辅助分析(VOCAL)技术,测量胎儿胸腺体积(TV组)。同期测量20例先天性心脏病胎儿(CHD组Ⅱ)的胸腺体积。计算TC组、TV组、MTD组、APD组、SID组、MTA组在每个孕周的均值和90%置信区间,分别将MTD组、APD组、SID组、MTA组与GA的相关性和TV组与GA的相关性相对比。比较TC组和CHD组Ⅰ胎儿胸腺周长,比较TV组和CHD组Ⅱ胎儿胸腺体积。应用队列研究回顾性分析,于1998年6月到2008年6月,在耶鲁大学医学院母胎医学中心,59例进行常规胎儿超声心动图检查且存在22q11微缺失高危因素胎儿的资料,探讨先天性心脏病与22q11微缺失的关联性。统计学分析,应用线性回归分析、Fisher’s Z值转换分析、大样本t检验。p值<0.05认为具有统计学意义。本研究均获得耶鲁大学医学院和中南大学湘雅二医院伦理委员会的批准。结果：567例正常胎儿中,成功获得541例胎儿胸腺的最大横径、前后径、上下径、最大横截面积和体积,成功测量率95.4%；347例正常胎儿中,成功获得320例胎儿的胸腺周长,成功测量率92.2%。胎儿胸腺二维各径线和三维体积均随孕周增加而增加,与孕周均呈直线相关,回归方程分别为：TC(cm)=-4.147+0.443×GA(周),r=0.980；MTD(cm)=-0.8031+0.1393xGA(周),r=0.9114；APD(cm)=-0.4808+0.0597xGA(周),r=0.8559；SID(cm)=-0.2741+0.0826×GA(周),r=0.8420；MTA(cm2)=-5.3551+0.3282×GA(周),r=0.9381；TV(ml)=-7.5098+0.4538xGA(周),r=0.9907,以上均有统计学意义,(p<0.01)。经过Fisher’s Z值转换检验,分别将MTD组、APD组、SID组、MTA组与GA的相关性,和TV组与GA的相关性进行比较,胎儿胸腺三维体积与孕周的相关性明显高于各二维径线值与孕周的相关性(p<0.05)。CHD组Ⅰ胎儿胸腺周长明显小于TC组胎儿胸腺周长(p<0.05)。28例胎儿中,13例超声检测胸腺周长小于正常参考值第五个百分位数,其中12例尸解证实胸腺明显减小,1例尸解未发现胸腺明显减小；15例超声检测胸腺周长在正常范围内,尸解证实14例胎儿胸腺无明显减小,1例胎儿胸腺左侧叶缺如。CHD组Ⅱ胎儿胸腺体积明显小于TV组胎儿胸腺体积(p<0.05)。20例胎儿中,11例胸腺体积小于正常参考值第五个百分位数,余9例胸腺体积在正常范围内。1998年6月至2008年6月,8220例在耶鲁大学母胎医学中心进行胎儿超声心动图检查的胎儿,其中59例胎儿存在22q11微缺失综合征高危因素。43例胎儿进行染色体核型和22q11微缺失检测,16例胎儿的母亲拒绝羊水穿刺术未能进行染色体核型的分析和22q11微缺失的检测。5例胎儿确诊为22q11微缺失综合征,其中2例胎儿患有法洛氏四联症,2例胎儿患有主动脉弓异常合并室间隔缺损,1例胎儿有22q11微缺失家族史。结论：1.本研究建立了胎儿胸腺二维超声面积、周长、直径、横径和三维超声体积的正常参考值。三维超声测量胎儿胸腺体积与孕周相关性更高,提示较二维超声测量更为准确。2.胎儿先天性心脏病与胎儿胸腺发育不全或胸腺缺如具有关联性。因此对超声检测发现胸腺发育不全或者胸腺缺如的胎儿,应进行详细的超声心动图检查。3.胎儿先天性心脏病与22q11微缺失具有关联性,先天性心脏病、胸腺发育不全或者胸腺缺如、22q11微缺失三者间是否具有关联性,仍需要大样本,密切追踪观察的长期研究。更多还原

【Abstract】 Background:The thymus is a lymphoepithelial organ, providing the environment for T-lymphocyte differentiation and selection, in which T-lymphocytes develop during fetal life. The thymus is believed to grow throughout the fetal life. Thymic hypoplasia or aplasia has been reported as an associated finding in various diseases, such as 22q11 micro-deletion syndrome, DiGeorge syndrome, Ellis-van Creveld syndrome, severe combined immunodeficiency, HIV infection, intrauterine growth retardation, acute illness, exposure to ethanol and chorioamnionitis ect.Assessment of thymic hypoplasia or aplasia requires normal data for thymic size at each gestational age. In previous studies, Felker et al measured the thymic anterior-posterior diameter (APD), Jeppesen and Cho et al measured the thymic maximum transverse diameter (MTD), Zalel et al measured the thymic circumference (TC) to assess the size of the fetal thymus. However, in anatomy, the thymus occupies anterior-superior mediastinum, behind the sternum, in front of and ventral to the pericardium and great vessels of the heart (pulmonary artery, aorta and superior vena cava), between the lungs, which is asymmetric lobulated parenchymatous organ. Utility of 2DUS (two-dimensional Ultrasound) to assess the size of the fetal thymus might get limitation. With the development and application of 3DUS (three-dimensional Ultrasound) and 4DUS (four-dimensional Ultrasound) in medical field, especially in prenatal diagnosis, VOCAL (Virtual Organ Computer-Aided Analysis) from 3DUS, could globally analyze and measure the whole fetal thymus and reconstruct 3D model from multiple 2D plans, which conquers the limitation of single plan information from 2DUS.During the embryo development, the pharyngeal arches, mesenchymal cells which derived from neural crest give rise to smooth muscles of the conotruncal vessels and connective tissue of the thymus and the parathyroid gland. The development of the derivatives of the pharyngeal apparatus is highly sensitive to environmental and genetic insults. Any cause affects pharyngeal apparatus fail to develop, which could result in abnormal thymus growth and congenital heart defects. The 22q11 micro-deletion (del22q11.2) is the most common micro-deletion syndrome, associate with a markedly variable phenotypic expression, more than 180 clinical findings, in which congenital heart defects and thymic hypoplasia or aplasia are the most common clinical expression.Moreover, a great deal of studies show that micro-deletion at the 22q11 position is strongly associated with congenital heart defects (CHD). The 22q11 micro-deletion is the second most common chromosomal cause of congenital heart defects after trisomy 21. However, prenatal frequency of the micro-deletion in the fetuses with increased risk for congenital heart defects has not been completely elucidated. Aim:1. Establishing the normative data of the 2DUS and 3DUS measurements of the developing fetal thymus and comparing the 2DUS and 3DUS measurements of the fetal thymus.2. Discussing the relevance between congenital heart defects and thymic hypoplasia or aplasia3. Discussing the relevance between congenital heart defects and 22q11 micro-deletion.Material & Methods:Between June 2006 and November 2007, applying GE Voluson 730 high-resolution color Doppler ultrasound diagnose system,4-6 MHz transabdominal probe, measured the fetal thymic circumference (TC) in 347 normal singletons (TC group) and 28 singletons with CHD and proved by autopsy (CHD I group).Between December 2007 and February 2010, applying Philips IU22 high-resolution color Doppler ultrasound diagnose system,6 MHz transabdominal probe, measured the fetal thymic maximum transverse diameter (MTD group), anterior-posterior diameter (APD group), superior-inferior diameter (SID group) and maximum transverse area (MTA group), meantime utilizing 3DUS VOCAL technique to measure the thymic volume (TV group) in 567 normal singletons. During the same period, the thymic volumes of 20 singletons with CHD (CHD II group) were measured.The predicted mean and 90% confidence interval of 2DUS and 3DUS measurements were calculated at each gestational week, compared the correlation of thymic MTD, APD, SID, MTA measurements and GA with that of TV and GA. Between TC group and CHDⅠgroup, fetal thymus circumferences were compared, and between TV group and CHDⅡgroup, fetal thymus volumes were also compared.Then, a retrospective cohort study of 59 consecutive patients undergoing fetal echocardiogram and evaluation for 22q11 micro-deletion at the department of Maternal-Fetal Medicine of Yale University Medical School from June 1998 to June 2008, was done to discuss the relevance between CHD and 22q11 micro-deletion.Linear regression analysis, correlation coefficients comparison after Fisher’s Z-transformation and large sample t test were used where appropriate. A p value<0.05 was considered statistically significant. Institutional review board approval was obtained from Yale University, School of Medicine, Maternal-Fetal-Medicine and Central South University, The Second Xiangya Hospital prior to the study.Results:2DUS,3DUS assessments of the fetal thymic MTD, APD, SID, MTA and TV were possible in 95.8% of 567 normal singletons and 2DUS assessment of the fetal circumference was possible in 92.2% of 347 normal singletons. The fetal thymic 2D diameters/area and 3D volume grow with the GA in linear correlation, regression equations are:TC (cm) =-4.147+0.443×GA (week), r=0.980; MTD (week)=-0.8031+0.1393×GA (week), r=0.9114; APD (cm)=-0.4808+0.0597×GA (week), r=00.8559; SID (cm)=-0.2741+0.0826×GA (week), r=0.8420; MTA (cm2)=-5.3551+0.3282×GA (week), r=0.9381; TV (ml)=-7.5098+0.4538×GA (week), r=0.9907, (all p<0.01). After Fisher’s Z-transformation the correlation between the 3D-US thymus volume measurements and GA was significantly higher than that of any individual 2D-US measurements and GA (p<0.05).Thymus circumference of CHDⅠgroup was significantly lower than that of TC group (p< 0.05).28 cases of CHDⅠgroup,13 cases of them were lower than 5th percentile of normal range. The fetal thymus significantly decreased in 12 cases, and no significant decrease in 1 case, which were proved by autopsy. Thymus circumference was in normal range in another 15 cases,14 cases of them were no significant decrease, and 1 case was one lobe of thymus aplasia. Thymus volume of CHDⅡgroup was significantly lower than that of TV group (p< 0.05).20 cases of CHDⅡgroup,11 cases of them were lower than 5th percentile of normal rang, another 9 cases were in normal range. Between June 1998 and June 2008, of 8220 fetal echocardiograms performed,59 singleton fetuses were identified as being high risk for 22q11 micro-deletion.43 fetal karyotypes and FISH (Fluorescence In Situ Hybridization) tests were obtained. Sixteen mothers declined amniocentesis.5 of 43 fetuses were discovered to have the 22q11 micro-deletion. Fetuses diagnosed with 22q11 micro-deletion,2 of them had tetralogy of Fallot,2 of them had aorta arch abnormality with ventricular septal defects, and one case had positive family history.Conclusion:①This study presents the normative data of the 2DUS and 3DUS measurements of the developing fetal thymus.3DUS fetal thymus volume is more significantly correlated to GA than the other 2DUS measurements, which indicates 3DUS measurement of the fetal thymus is more accurate than that of 2DUS.②Thymic aplasia or hypoplasia is associated with congenital heart defect. Therefore, when detecting thymic aplasia or hypoplasia in fetus, the detail fetal echocardiogram is really necessary.③Congenital heart defect is associated with 22q11 micro-deletion. The relevance among the fetal thymic hypoplasia or aplasia, congenital heart defect and 22q11 micro-deletion should further study, because of the limitation of sample quantity.更多还原