Ultrasound investigation of fetal human upper respiratory anatomy

Although the human upper respiratory-upper digestive tract is an area of vital importance, relatively little is known about either the structural or functional changes that occur in the region during the fetal period. While investigations in our laboratory have begun to chart these changes through the use of postmortem materials, in vivo studies have been rarely attempted. This study combines ultrasonography with new applications of video editing to examine aspects of prenatal upper respiratory development. Structures of the fetal upper respiratory-digestive tract and their movements were studied through the use of ultrasonography and detailed frame-by-frame analysis. Twenty-five living fetuses, aged 18-36 weeks gestation, were studied in utero during routine diagnostic ultrasound examination. These real-time linear array sonograms were videotaped during each study. Videotapes were next analyzed for anatomical structures and movement patterns, played back through the ultrasound machine in normal speed, and then examined with a frame-by-frame video editor (FFVE) to identify structures and movements. Still images were photographed directly from the video monitor using a 35 mm camera. Results show that upper respiratory and digestive structures, as well as their movements, could be seen clearly during normal speed and repeat frame-by-frame analysis. Major structures that could be identified in the majority of subjects included trachea in 20 of 25 fetuses (80%); larynx, 76%; pharynx, 76%. Smaller structures were more variable, but were nevertheless observed on both sagittal and coronal section: piriform sinuses, 76%; thyroid cartilage, 36%; cricoid cartilage, 32%; and epiglottis, 16%. Movements of structures could also be seen and were those typically observed in connection with swallowing: fluttering tongue movements, changes in pharyngeal shape, and passage of a bolus via the piriform sinuses to esophagus. Fetal swallows had minimal laryngeal motion. This study represents the first time that the appearance of upper airway and digestive tract structures have been quantified in conjunction with their movements in the living fetus.