Fetal tracheolaryngeal airway obstruction: prenatal evaluation by sonography and MRI
We reviewed the sonographic and MRI findings of tracheolaryngeal obstruction in the fetus. Conditions that can cause tracheolaryngeal obstruction include extrinsic causes such as lymphatic malformation, cervical teratoma and vascular rings and intrinsic causes such as congenital high airway obstruction syndrome (CHAOS). Accurate distinction of these conditions by sonography or MRI can help facilitate parental counseling and management, including the decision to utilize the ex utero intrapartum treatment (EXIT) procedure.
KeywordsFetal tracheolaryngeal Airway obstruction Sonography MRI
Intrinsic tracheolaryngeal obstruction
Congenital high airway obstruction syndrome (CHAOS) is a rare form of intrinsic obstruction of the larynx or trachea that results in retention of bronchial secretions and subsequent pulmonary distention from the retained fluid . Obstruction of the airway in CHAOS might be related to intrinsic atresia or stenosis of the larynx or upper trachea . This obstruction leads to the constellation of pulmonary and extra-pulmonary findings. Pulmonary findings include dilated airways below the level of obstruction, hyperexpanded lungs and flattened diaphragms. Extra-pulmonary findings include fetal hydrops or ascites and placentomegaly. Although the exact etiology is not clear, it is believed that hyperexpansion of the lungs results in flattening or eversion of the diaphragm. This abnormal hyperexpansion of the lungs is believed to cause impaired venous return to the heart. It has been proposed that this impaired venous return leads to the subsequent development of fetal hydrops and ascites [4, 5].
Extrinsic tracheolaryngeal obstruction
With the use of the ex utero intrapartum treatment (EXIT) procedure, a marked improvement in survival can now be accomplished. The EXIT procedure involves partial delivery of the fetus via a hysterotomy while both the placenta and umbilical cord remain intact. Halogenated agents are administered to the mother in order to promote uterine relaxation . The fetus remains hemodynamically stable, as the uteroplacental gas exchange is maintained. Mean times of hemodynamic stability have ranged from 18 to 45 min . This allows for a controlled environment to manage the airway, as opposed to a more emergent attempt at airway access at birth . A common strategy is to first attempt intubation via direct laryngoscopy. If the airway is not adequately visualized then rigid bronchoscopy is attempted. If an endotracheal tube is unable to be passed, tracheotomy is the final option . Although the EXIT procedure was initially developed to deliver fetuses with congenital diaphragmatic hernia after tracheal occlusion , it has also demonstrated success in the treatment of fetuses with obstructing neck masses and cleft lip and palate [1, 10, 11, 12].
In a study by Wagner and Harrison , an airway was established in 79% of the 29 cases reviewed using the EXIT procedure, with an overall survival rate of 69%. Another study with 13 patients treated with the EXIT procedure for obstructive neck masses resulted in only one death . Successful management of CHAOS has been achieved with a combination of fetal tracheostomy and delivery using the EXIT procedure [3, 11]. Fetal MRI has demonstrated its value in the facilitation of treatment planning in fetal upper airway obstruction. With a large field of view and high soft-tissue contrast, MRI can produce images that are easily understood by clinicians. Prenatal MRI can be used to delineate tumor extent, evaluate facial involvement and demonstrate the relationship of the mass to the trachea. Similarly, prenatal MRI can be used to confirm the diagnosis of CHAOS prior to undertaking fetal surgery .
The accurate prenatal diagnosis of upper airway obstruction is essential in order to provide appropriate management of this condition. The use of fetal MRI allows exquisite definition of fetal anatomy and facilitates treatment planning. The EXIT procedure has also demonstrated success in the treatment of intrinsic and extrinsic airway obstruction.
Zhen J. Wang is supported by NIBIB T32 Training Grant 1 T32 EB001631.
This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.