CHAOS

Abstract

Introduction: Congenital high airway obstruction syndrome (CHAOS) is a rare, usually lethal abnormality characterized by complete or near-complete intrinsic obstruction of the fetal airway. Laryngeal atresia is the most frequent cause, but other etiologies include laryngeal or tracheal webs, laryngeal cyst, subglottic stenosis or atresia, tracheal atresia and laryngeal or tracheal agenesis. When antenatal diagnosis of possible upper airway obstruction is made, specific type of obstruction is rarely determined making the term CHAOS introduced by Hedrick et al in 1994 more appropriate.

Usg characteristics: Sonographic findings in CHAOS are characteristic and are secondary to high airway obstruction. The lungs are symmetrically enlarged, echogenic and homogenous. The distended lungs have mass effect on the diaphragm, which appears flattened or inverted, and the heart is displaced anteriorly in the midline. The heart often appears dwarfed by the surrounding enlarged lungs.

Discussion: The primary abnormality is an intrinsic obstruction of the upper airway. Normal lung development involves a continuous efflux of fluid from the fetal lungs. Laryngeal atresia/CHAOS stops the efflux of this fluid, and this retained fluid distends the alveoli with fluid giving the lungs voluminous echogenic appearance and inverting the diaphragm. Isolated airway obstruction without hydrops has a relatively favorable prognosis. CHAOS with associated anomalies and with early presentation of hydrops is an ominous sign with a high rate of fetal demise and a poor survival rate even with the ex utero intrapartum treatment (EXIT) procedure.

Keywords: Antenatal; Laryngeal atresia; Sonography.

Fig. 1

a, b (Axial and coronal)Echogenic voluminous lungs with flattening of diaphragm. Heart is in midline, compressed and displaced anteriorly

Fig. 2

a, b (Sagittal and coronal)Dilated trachea and lower esophagus with tracheo-esophageal fistula

Fig. 3

a (Coronal) Dilated lower esophagus and ‘double bubble sign’ in upper abdomen. b (Axial) Continuity of stomach with duodenum confirming duodenal atresia

Fig. 4

a, b Placentomegaly (4.8 cm in thickness) and single umbilical artery (two-vessel cord)

Fig. 5

a Dilated trachea and bronchi with echogenic voluminous lungs causing mass effect on diaphragm leading to eversion. b Zoomed view of trachea and bronchi

Fig. 6

a, b (Axial sections) c, d (sagittal sections) Normal-appearing orbits and face but with absence of calvarium, marked retroflexion at neck and disorganized brain tissue displaced caudally and seen overlying upper torso

Fig. 7

a (Coronal section spine), b (7d Image), c and d (Radiograph spine AP and Lat.) Absence of cervical vertebrae and rachischisis of upper thoracic vertebrae

Fig. 8

a, b Post-abortion 18-week fetus showing features of iniencephaly and anencephaly. c Autopsy specimen showing hyperinflated lungs with costal impressions