Evaluation of fetal thymus size with thymic-thoracic ratio and clinical significance / 中国医学影像技术

ABSTRACT

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 (rs =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.