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Virtual fetal laryngoscopy

In a recent publication, Liberty et al.1 visualized fetal oropharyngeal and laryngeal structures successfully in 37% of fetuses examined between 11 and 24 weeks using two(2D) and three-dimensional (3D) ultrasound. We believe that interpretation of such 2D and 3D images should be made with caution due to the proximity of the fetal uvula and epiglottis; the uvular ‘equals sign’ can be easily confused with the epiglottis. We are aware that the fetal epiglottis is elongated and omega-shaped2. We wonder whether the structure labelled ‘uvula’ in Figures 5, 6 and 8 in their publication might actually depict the epiglottis, which appears to have been included in the volume acquisition. Furthermore, we are not convinced that the location of the piriform recesses as indicated in their Figures 5 and 6 corresponds with anatomical studies which show that the piriform sinuses do not extend below the level of the vocal cords2. We recognize that sonography of the fetal oropharynx and larynx is a relatively new technique and will continue to evolve. In addition, we would like to report the complementary use of sonographic 3D volume acquisition and ‘Fly Thru’ technology (Toshiba Medical Systems, Tochigi-ken, Japan) for imaging the fetal airway. Fly Thru provides reconstruction and display by navigating through tubular anechoic structures as small as 2–3 mm in diameter. It provides virtual endoscopic images of the fetal larynx that are similar to those achieved by real laryngoscopy. Prenatal imaging of the fetal airway is particularly important in conditions in which the airway could be compromised by a facial or neck abnormality. Technology that helps to confirm airway patency could prevent unnecessary ex-utero intrapartum treatment (EXIT)3. Virtual 3D imaging from the ‘inside’ could also potentially assist in the diagnosis of congenital abnormalities of the posterior palate and larynx. To illustrate this technique, we acquired 3D ultrasound datasets in a normal fetus at 20 weeks, using an Aplio 500 system (Toshiba Medical Systems) equipped with a PVT-675MV 2.8–7.2-MHz probe. Fly Thru reconstruction was performed using manual navigation through the oropharynx (Videoclip S1). However, since the vocal cords were adducted, navigation into the subglottic trachea was not possible. Sonographic examination of a 37-year-old woman, gravida 2 term 1 liveborn 1, at 28 weeks’ gestation revealed a large nuchal macrocystic lymphangioma and mild hydrops. Fly Thru reconstruction was performed using both automatic and manual navigation in two directions: from the uvula, past the epiglottis, and through the vocal cords into the subglottic trachea, and the reverse, Figure 1 Three-dimensional volume data acquisition with Fly Thru navigation through the abducted vocal cords in a 28-week fetus with cervical macrocystic lymphangioma and hydrops. Our interpretation of these images suggests that the abducted vocal folds (white arrow) are shown below the false cords (black arrows). The subglottic trachea with its surrounding tracheal ring (*) is indicated.