Discussion

In the embryological period, the formation of a laryngotracheal groove by four weeks is the first indication of the respiratory tract. The larynx develops from the cranial end of this groove while the trachea develops from the middle part of the groove. The laryngotracheal groove deepens to form a diverticulum anterior to the pharynx. The distal portion of this diverticulum will eventually grow into bronchial buds which further develops into lungs. Proximally, the lateral walls of the diverticulum invaginate to form tracheoesophageal folds, which eventually fuse in the midline. This fusion forms a tracheoesophageal septum which separates the primitive airway from the esophagus. The cartilages of the larynx are derived from the fourth and sixth pair of branchial arches in the fifth week of gestation. Arytenoid swellings form at the laryngeal inlet, narrowing the slit like glottis. The glottic epithelium proliferates rapidly and temporarily occludes the lumen. Recanalization of this lumen occurs at the 10th week of embryonic life. Any interruption in the embryological development during recanalization leads to congenital laryngeal and tracheal abnormalities. Any disruption in the formation of the tracheoesophageal septum leads to various types of tracheoesophageal fistula [4]. The most common variety is type C, where the proximal esophagus is dilated and blind ending is about the level of the third or fourth thoracic vertebra, with a distal esophagus which is thinner and narrower attached to the posterior wall of the trachea near the carina [2].

Overview of the triad involving polyhydramnios, gastrointestinal obstruction, and a small fetal stomach indicates a physiological disruption where the fetus cannot swallow or process amniotic fluid due to structural or neurological issues. Congenital High Airway Obstruction Syndrome (CHAOS) triggers this triad through extrinsic structural compression. A complete blockage of the fetal larynx or trachea traps lung fluid, causing the lungs to hyper-expand under high intrathoracic pressure. This expansion physically squeezes the adjacent esophagus, acting as a high GI obstruction. This compression prevents amniotic fluid from reaching the stomach, leaving the gastric walls uninflated and abnormally small on ultrasound. Because the fetus cannot swallow or recycle the fluid while urination remains normal, the unabsorbed fluid accumulates in the uterine cavity, resulting in severe polyhydramnios.

Neonatal resuscitation is performed when a newborn fails to establish effective breathing or circulation at birth. The pathophysiology underlying the need for resuscitation involves complex transitions from intrauterine to extrauterine life. When this transition is disrupted, a cascade of birth asphyxia occurs. Failure to aerate the lungs due to obstruction at any level leads to prolonged hypoxia and myocardial dysfunction. Positive Pressure Ventilation is the most critical step, as improving oxygenation typically resolves the secondary bradycardia and potentially cardiac arrest.

CHAOS is a rare congenital anomaly caused by laryngeal or tracheal atresia, tracheal stenosis, obstructing laryngeal cysts, obstructing tumors of the oropharynx and the cervical region, or compression from a double aortic arch. Immediate postnatal management is challenging with efforts to secure the airway. CHAOS should be an important diagnosis to be considered in neonates presenting with severe respiratory distress and no audible cry at birth. Endotracheal intubation cannot be accomplished because it is impossible to advance the tube beyond the vocal cords. Immediate tracheostomy can be lifesaving; however, it necessitates a patent distal tracheal lumen to be effective. If CHAOS has been antenatally identified EXIT procedure should be considered which increases the rate of survival for these patients [5]. LMA may be lifesaving if there is difficulty with intubation but ability to ventilate raises the possibility of a H type fistula with CHAOS [6]. If tracheal intubation attempts are unsuccessful, esophageal intubation could be a vital component of neonatal resuscitation to increase the chance of successfully transitioning to surgical reconstruction [7].

Prenatal ultrasound and fetal MRI are the standards for detection of CHAOS which includes laryngeal/tracheal atresia. The key findings on a prenatal ultrasound include enlarged, hyper echogenic lungs, a dilated tracheobronchial tree, a flattened or an inverted diaphragm and ascites all indicating a blockage in the upper airway of the fetus [5]. Further confirmation may be achieved with a fetal MRI to pinpoint the location of obstruction. Few such cases have been reported and some who included survival had a history of polyhydramnios and were prenatally diagnosed [8]. In our case, absence of polyhydramnios starting with ultrasound at 20 weeks, fetal MRI at 22 weeks and subsequent antenatal ultrasounds as late as 31 weeks with no evidence of hyperechogenic lungs due to TEF prevented suspicion of CHAOS. Early presence of a small stomach could have been a clue of gastrointestinal tract obstruction combined with airway obstruction. Though small stomach could also be due to physiological, structural, anatomical, or chromosomal defects, an absent stomach or a small stomach after 18 weeks gestation is associated with a guarded prognosis [9], [10], [11], [12]. The first description of tracheal atresia was described by William Payne in 1900 [13] where he describes a case with isolated tracheal atresia with no tracheoesophageal connections. Then the first case of both tracheal atresia and esophageal atresia with TEF was described by David Ashley in 1972 [14]. Successful surgical repair of TEF was not achieved until 1941, when Cameron Haight performed the inaugural procedure with tracheostomy as the mainstay of management [15]. If the trachea is palpable below the atretic area, immediate tracheostomy may be lifesaving [16]. There are recent advances in surgical techniques for management of TEF. Different reconstructive procedures using either the esophagus or synthetic material have been attempted to create an airway lumen [5], 17]. Given the variable and risk of severe presentation, early detection can be a valuable tool to ensure better prognosis. A high degree of suspicion in neonates presenting with severe respiratory distress could help guide the management. Emergency tracheotomy/tracheostomy can also be considered as an alternate airway management during neonatal resuscitation if ETT and LMA fails to achieve ventilation. In our case, findings on prenatal ultrasound failed to show any signs of upper airway or gastrointestinal obstruction except for a small stomach. There are no prior cases of CHAOS reported that are known to be associated with small stomach.