青木 昭和, 原田 崇, 宮崎 康二

Showa AOKI, Takashi HARADA, Kohji MIYAZAKI

島根大学医学部産科婦人科

Department of Obstetrics and Gynecology, Shimane University School of Medicine

キーワード : trachea, bronchus, fetus, ultrasonography

目的：心臓・大血管との解剖学的位置関係に注目し，胎児気管・気管支の描出および観察することを目的とした．対象・方法：対象は妊娠26週から41週までの正常胎児50例とした．胎児頸部横断面にて両頸動脈の間にある気管を同定し，それを尾側にたどる事で気管・気管支を確認した．その後，心臓・大血管と気管・気管支との位置関係を観察し，容易に描出出来る断面を明らかにした．さらに気管分岐部の内径を計測し週数別に検討した．成績：気道は喉頭以下の部位で描出可能であり，three-vessel tracheal viewで横行大動脈の中央右背側に気管の短軸像が認められた．左気管支横断面は大動脈アーチ内側で右肺動脈のやや頭側後方に確認出来た．肺動脈・動脈管アーチ断面では，右肺動脈と動脈管に挟まれた位置に左気管支を認めた．three-vessel viewでは上行大動脈の右後方に右気管支の断面が描出された．その他にも気管支が描出されやすい断面が幾つか確認された．一方，奇静脈は右気管支に騎乗することより，右気管支の確認に役立った．気管，左・右気管支の内径は，妊娠26‐27週の平均でそれぞれ2.9mm，2.0mm，1.9mmであり，妊娠40‐41週では，6.0mm，4.7mm，4.6mmであった．結論：胎児心エコー検査の中で気管・気管支が比較的容易に観察可能であった．よって胎児気道の出生前スクリーニングも可能であると思われた．

Objectives and methods: Fifty normal pregnant women ranging from 26 to 41 weeks of gestation underwent ultrasonographic examination. First, we identified the trachea between both bilateral carotid arteries in the cross-section of the fetal neck. We then traced the trachea up to the bilateral bronchi, observed the spatial correlation to the heart and great vessels, and clarified the optimal section for identifying the respiratory tract image. Last, we measured the inside diameters of the trachea and bronchi. Results: The fetal respiratory tract could be identified below the larynx. In the three-vessel tracheal view, the cross-sectional image of the trachea was most easily seen behind the middle portion of the transverse aorta. When the aortic arch was clearly depicted, the cross-sectional image of the left bronchus was confirmed slightly occipito-posteriorly to the right pulmonary artery and inside the arch. In addition, bifurcation of the tracheae and bilateral bronchi were easily described by tracing the left bronchus medially. The ductal arterial arch view provided a cross-sectional image of the left bronchus between the right pulmonary artery and the ductal artery. Further, several other standard views obtained in cardiac screening also provided distinct images of the respiratory tract. The azygos vein was the landmark of the right bronchus. The fetal trachea and bronchi were measurable after the 26th week of gestation. Average inside diameters of the trachea and the right and left bronchi increased gradually from 2.9 mm, 2.0 mm, and 1.9 mm, respectively, at 26-27 weeks to 6.0 mm, 4.7 mm, and 4.6 mm, respectively, at 40-41 weeks of gestation. After week 36, the inside diameters of the trachea, and the right and left bronchi exceeded 4.5 mm and 3.0 mm, respectively, in all cases. Conclusion: The fetal respiratory tract can be observed concurrently with the cardiac screening examination of the fetus. This makes prenatal screening of pathologic condition of the fetal respiratory tract possible.