Congenital High Airway Obstruction Syndrome (CHAOS) � A Rare Fetal Malformation Diagnosed on Antenatal Ultrasonography

Abstract

Introduction Congenital high airway obstruction syndrome is rare fetal malformation caused by obstruction of fetal airway because of laryngeal or tracheal atresia, subglottic stenosis, laryngeal cyst or laryngeal web. This clinical condition was brought into notice first by Hedrick in the late 1900 [1]. CHAOS is usually caused by atresia or stenosis of the larynx or trachea. The true incidence of CHAOS is unknown. It is important to diagnose it antenatally as it is uniformly lethal. If the syndrome is unrecognized during the prenatal period, it usually results in stillbirth or death shortly after delivery [2]. The prenatal ultrasound findings of CHAOS include large echogenic lungs, flattened or inverted diaphragms, dilated airways distal to the obstruction, and fetal ascites and/or hydrops [3]. Here we present a rare case of CHAOS diagnosed on the antenatal scan. Case Blog A 22 year old primi-gravida was referred for routine anomaly scan at 18 weeks of gestation. There was no history of consanguinity and the family history was unremarkable. Ultrasound examination revealed a single live intrauterine fetus corresponding to a gestational age of 18 weeks. Amniotic fluid was within normal limits. Bilateral lungs were echogenic and enlarged with small heart compressed in between the lungs (Figure 1), dilated bronchi and trachea (Figure 2), mild ascites (Figure 3), and flattened diaphragm (Figure 4). Based on these findings, the diagnosis of CHAOS was made. Patient and her family members were counselled regarding the possible unfavourable outcome of the pregnancy. The patient opted for termination of pregnancy.