BACKGROUND: In this study we aimed to describe the morphological and pathogenetic differences between tracheal agenesis and tracheal atresia, which are not clearly distinguished from each other in the literature, and to contribute thereby to the understanding and management of these conditions. Both tracheal agenesis and tracheal atresia represent rare disorders of still unknown aetiology that cannot be detected by prenatal ultrasound. If the affected foetuses survive until birth these conditions result in respiratory failure and in futile attempts to rescue the infant\'s life.
RESULTS: Autopsies and genetic analyses, including singleton or trio exome sequencing, were performed on five neonates/foetuses with tracheal agenesis and three foetuses with tracheal atresia. Tracheal agenesis was characterized by absence of the sublaryngeal trachea and presence of a bronchooesophageal fistula and by pulmonary isomerism and occurred as an isolated malformation complex or as part of a VACTERL association. Special findings were an additional so-called \'pig bronchus\' and a first case of tracheal agenesis with sirenomelia. Tracheal atresia presenting with partial obliteration of its lumen and persistence of a fibromuscular streak resulted in CHAOS. This condition was associated with normal lung lobulation and single, non-VACTERL type malformations. Trio ES revealed a novel variant of MAPK11 in one tracheal agenesis case. Its involvement in tracheooesophageal malformation is herein discussed, but remains hypothetical.
CONCLUSIONS: Tracheal agenesis and tracheal atresia represent different disease entities in terms of morphology, pathogenesis and accompanying anomalies due to a primary developmental and secondary disruptive possibly vascular disturbance, respectively.

Tracheal atresia is an extremely rare condition whereby a partial or total obstruction of the trachea is seen. It is almost always lethal, with just a handful of cases that ended with a good outcome. In this study we report on a 15-week male fetus, diagnosed with hyperechogenic lungs, midline heart position and inverted diaphragm. Sonographic findings suggest congenital High Airway Obstruction Syndrome (CHAOS) An ultrasound scan and fetal MRI were not able to point out the exact obstruction level. In spite of extensive counselling, the parents opted to carry on with the pregnancy. Fetal demise was noted on a scan at 19 weeks gestation. After the elective termination of pregnancy, a post-mortem examination showed partial tracheal atresia with no other anomalies. Despite technological progress in CHAOS syndrome, a precise diagnosis and accurate prognosis remain elusive.

BACKGROUND: Tracheal atresia causes some secondary changes (dilated trachea, flattened/inverted diaphragm, hyperintense and hyperinflated lungs). They can be reduced if a high airway fistula is present.
OBJECTIVE: This study evaluated fetal MR images of tracheal atresia and the secondary changes, focusing on the presence of a fistula.
METHODS: We assessed fetal MR images of tracheal atresia without fistula (n=4, median 26 weeks), tracheal atresia with fistula (n=4, median 33 weeks) and controls (n=30, median 32 weeks). We evaluated airway obstruction using true-positive rate in tracheal atresia and false-positive rate in controls indicating they are likely normal variants. Tracheal diameter, craniocaudal-anteroposterior ratio of the right hemidiaphragm, lung-to-liver signal intensity ratio, and cardiothoracic ratio were compared among the three groups using the Kruskal-Wallis test followed by pairwise comparison using the Mann-Whitney U test.
RESULTS: True-positive rate was 100% in tracheal atresia, while false-positive rate was 20% in controls. The Kruskal-Wallis test showed differences among groups in craniocaudal-anteroposterior ratio and cardiothoracic ratio (P<0.001) but not in tracheal diameter (P=0.256) or lung-to-liver signal intensity ratio (P=0.082). The pairwise comparison in craniocaudal-anteroposterior ratio and cardiothoracic ratio showed differences between controls and tracheal atresia without fistula (P<0.01) and with fistula (P<0.05).
CONCLUSIONS: Fetal MRI is useful for the diagnosis of tracheal atresia, and detection of airway obstruction is essential. Lower craniocaudal-anteroposterior ratio and cardiothoracic ratio might be reliable measures even if a fistula is present.

Congenital high airway obstruction syndrome (CHAOS) is a rare life-threatening fetal condition resulting from obstruction of the upper fetal airway which may be partial or complete. Prenatal diagnosis is crucial as it usually results in stillbirth or death after delivery if unrecognized. We report a case of CHAOS that was diagnosed prenatally due to characteristic ultrasound features. We also briefly review literature in light of current management options.

Described here are a series of four cases of congenital high airway obstruction in the fetus. All of the patients presented in the second trimester and all had hydrops fetalis. Three cases had bilateral hyperinflated lungs, midline shift of heart, flattening or inversion of the diaphragm, and fetal ascites. Autopsy was performed in one of these three and showed laryngeal atresia. In one fetus, there was only a unilateral huge enlargement of the lung with mediastinal shift. On autopsy, this fetus had atresia of right main bronchus. All parents had terminated the pregnancy following the prenatal diagnosis. Laryngeal atresia is an extremely rare fetal anomaly with dismal prognosis. It is important to differentiate the condition from other lesions with a more favorable prognosis, such as congenital adenomatoid malformation of the lung. Much research is needed in the future to explore the therapeutic options, including fetoscopic intervention or transplantation of stem cell-derived airways.