Ø  History: Female came for routine anomaly scan at 20 weeks of gestation.

Ø Findings and description:

·         Both lungs appears hyperechoic & over expanded.

·         Both domes of diaphragm appears everted.

·         Visualized part of trachea-bronchial tree appears dilated.

·         Heart is seen in the midline thorax (mesocardia) and appears tubular.

·         Grossly distended fetal abdomen with gross ascites.

·         Mild oligohydramnios.

Ø  Diagnosis:   Congenital High Airway Obstruction Syndrome (CHAOS)

Ø Differential Diagnosis:

1) Bilateral congenital cystic adenomatoid malformation especially type III (CCAMIII)

In order to make a differentiation between CHAOS and CCAM type III, the obstruction site with distal airway dilatation (present in CHAOS) and the systemic arterial supply (present in CCAM type III) must be seen.

2) Extrinsic causes of tracheolaryngeal obstruction.

CHAOS should be also differentiated from extrinsic causes of tracheolaryngeal obstruction. Some of these extrinsic causes are lymphatic malformation, cervical teratoma, and vascular rings like double aortic arch.

Ø Discussion:

Congenital high airway obstruction syndrome (CHAOS) is an extremely rare congenital anomaly, caused by laryngeal or tracheal atresia, tracheal stenosis, obstructing laryngeal cysts and obstructing tumors of the oropharynx and the cervical region, or rarely by compression from a double aortic arch. Laryngeal atresia seems to be the most frequent cause . In these cases, an outflow obstruction of the fetal lung fluid leads to pulmonary hyperplasia. Prenatal ultrasound findings are very characteristic and include lungs symmetrically enlarged and highly echogenic, dilated and fluid-filled trachea and bronchi, inverted hemidiaphragms. The heart appears small compared with the enlarged lungs and positioned towards the midline of the thorax due to compression by the lungs. Fetal ascites is often present and sometimes hydrops.

Compression of the esophagus due to dilated trachea may result in polyhydramnios. The typical sonographic findings can also be recognized on MRI, which can be used to localize the exact level of obstruction if a fetal surgical intervention is planned .

There are some genetic syndromes associated with CHAOS such as Short-Rib Polydactyl Syndrome (SRPS), Shprintzen–Goldberg Omphalocele syndrome (SGOS) and VATER/VACTERL association. In addition to these syndromes, some chromosomal abnormalities (deletions of 22q11.2, deletion of chromosome 5p, 47, XXX, partial trisomy 9 and partial trisomy 16q) have been reported in association with CHAOS.

The most common associated genetic disorder with CHAOS is Fraser’s syndrome which is inherited by autosomal recessive form and characterized by tracheal or laryngeal atresia, renal agenesis, microphtalmia, and syn- or polydactyly .

Ø Conclusion:

To date literature provides very few individual case reports. So typical sonographic findings of this syndrome and it underlines the importance of early prenatal diagnosis to improve prognosis thought an ex utero intrapartum treatment, that seems to be the only chance of survival for the affected fetus.