胸腺-胸廓比评价胎儿胸腺大小及其临床意义

目的 探讨胸腺-胸廓比（T-T）评价胎儿胸腺发育的价值。方法 对317名孕18~39周健康单胎妊娠孕妇行产前超声检查,于三血管-气管（3VT）切面观察正常胎儿胸腺特征,测量胸骨后缘至主动脉前缘的距离（T1）与胸骨后缘至椎体前缘的距离（T2）,二者之比即为T-T值。绘制T-T值随孕周变化的散点图,并进行Spearman回归分析。结果 3VT切面显示胎儿胸腺位于前上纵隔内,表现为一不规则"四边形"低回声实质性结构。正常胎儿T-T平均值为（0.45±0.03）。T-T值与孕周无相关性（r_s=0.06,P=0.29）。结论 产前超声检查可清晰显示胎儿胸腺,T-T值可用以评价胎儿胸腺大小,为胎儿胸腺缺如或发育不良提供诊断依据。

Evaluation of fetal thymus size with thymic-thoracic ratio and clinical significance

Objective To explore value of detecting fetal thymus size with the thymic-thoracic ratio (TT-ratio). Methods Prenatal ultrasonography examinations were performed on totally 317 normal singleton healthy pregnancies from 18 to 39 gestational weeks. The normal thymus of fetus were observed on the three-vessel-trachea (3VT) view. The anteroposterior diameter of the thymus (T1) was measured between the anterior border of the aortic arch and posterior border of sternum. The intrathoracic mediastinal diameter (T2) was measured between the anterior border of thoracic vertebral body and posterior border of sternum. The TT-ratio was then calculated as the ratio of T1 to T2. Scatter plot between TT-ratio and gestational age was drawn. And the Spearman regression analysis was performed. Results The thymus of fetus was shown as an irregular homogenous structure in the anterior mediastinum on the 3VT view. The mean TT-ratio was 0.45±0.03. There was no correlation between TT-ratio and gestation (r_s=0.06, P=0.29). Conclusion Prenatal ultrasound can display the thymus obviously. TT-ratio could be applied to assess the fetal thymus size, which can provides clinical basis for the detection of absent or hypoplastic thymus in fetus.