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, in a caudocephalad direction. This demonstrated patency of the airway (Figure 1 and Videoclip S2a). Reverse navigation, from the trachea towards the oropharynx, was potentially able to demonstrate the uvula from a perspective below the palate (Videoclip S2b). Cesarean delivery was performed at 36 weeks for hydrops and breech presentation. A 2735-g male fetus was delivered with Apgar scores of 1, 6 and 7 at 1, 5 and 10 min, respectively. The neonate required continuous positive airway pressure for poor respiratory effort for the first 2 days and was discharged from hospital on day 16. Postnatal neck ultrasound examination showed macrocystic lymphangioma. In summary, to complement the work of Liberty et al.1, we have demonstrated that 3D ultrasound and Fly Thru can create a 3D model of the respiratory tract and predict airway patency in a fetus at risk for airway compromise. We wish to acknowledge the support of Mr Benoit Duchon and Ms Sandra Shannon of Toshiba Medical Systems Canada, and the RAFT (Research in Advanced Fetal Diagnosis and Therapy) Group at B.C. Women's Hospital and Health Centre. D. Pugash*†, F. K. Kozak‡ and A. Gagnon§ †Department of Radiology, University of British Columbia, Ultrasound 1T48, BC Women's Hospital, 4500 Oak St., Vancouver, British Columbia V6H 3N1, Canada; ‡Department of Surgery/ Otolaryngology, University of British Columbia, Vancouver, British Columbia, Canada; §Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, University of British Columbia, Vancouver, Canada *Correspondence. (e-mail: [email protected]) Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. The following supporting information may be found in the online version of this article: Videoclip S1 Three-dimensional volume data acquisition with manual Fly Thru navigation in a normal fetus at 20 weeks' gestation. Navigation proceeds from the oropharynx, to the adducted vocal cords. Since Fly Thru cannot navigate tubular structures < 2 mm in diameter, it is not possible to visualize the subglottic trachea. Videoclips S2a and S2b Three-dimensional volume data acquisition with Fly Thru reconstruction using both automatic and manual navigation, in a fetus with a large nuchal macrocystic lymphangioma revealed on sonographic examination at 28 weeks' gestation. (a) Navigation from the uvula to the epiglottis and through the vocal cords into the subglottic trachea, demonstrating patency of the airway. (b) Navigation in reverse caudocephalad direction, from the trachea toward the oropharynx, potentially demonstrating the uvula from a perspective below the palate.

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