Purpose or Case Report: Congenital high airway obstruction syndrome (CHAOS) is a rare but life-threatening fetal condition resulting from obstruction of the fetal upper airway, most commonly due to laryngeal or tracheal atresia. Accurate prenatal diagnosis is critical for perinatal management and potential surgical planning, including consideration of an ex utero intrapartum treatment (EXIT) procedure. While ultrasound is typically the initial modality for detection, fetal MRI provides superior anatomic detail and plays an increasingly important role in confirming the diagnosis, assessing the level and extent of obstruction, and evaluating associated anomalies.

In this case series, we present fetal MRI findings from four cases of CHAOS, each diagnosed in the second trimester. MRI demonstrated hallmark features including bilaterally enlarged, hyperintense lungs on T2-weighted images, flattened or inverted diaphragms, central compression of the heart, and dilated airways distal to the point of obstruction. Associated anomalies, including ascites and hydrops fetalis, were variably present. In all cases, MRI provided critical information for determining the severity and level of obstruction, distinguishing CHAOS from other causes of airway obstruction or other thoracic masses such as congenital pulmonary airway malformation (CPAM), and aiding multidisciplinary decision-making regarding delivery planning and neonatal resuscitation.

This case series underscores the diagnostic value of fetal MRI in the evaluation of CHAOS and highlights key imaging features that can facilitate accurate prenatal diagnosis. Early and precise recognition of this rare condition allows for appropriate counseling of expectant parents and coordination of specialized perinatal interventions that may improve neonatal outcomes.
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