An unusual cause of stridor

A 12-month-old infant was referred with a 6-week history of recurrent admissions with worsening stridor. On each previous admission, the stridor responded well, but transiently, to oral dexamethasone. At this presentation, he required high-dependency unit care with high flow oxygen due to marked increased work of breathing.He was born at term, previously well, and up to date with immunisations. There was no significant family history. There were no smokers and two cats at home.He was afebrile with moderate subcostal recession and tracheal tug. On auscultation, breath sounds were normal with transmitted sounds of inspiratory and expiratory stridor. The rest of his examination was normal.He commenced dexamethasone 0.15 μg/kg three times a day, which was weaned as his clinical status improved.Blood tests showed total white cell count 9 x 10ˆ9/L, CRP <1 mg/L, lactate dehydrogenase level and blood film normal. Chest radiograph showed left lung hyperexpansion and apparent right-sided bronchial narrowing (figure 1). Flexible nasendoscopy was unremarkable. Microlaryngoscopy and bronchoscopy showed external airway compression at the level of the carina (figure 2). CT thorax demonstrated a non-enhancing mediastinal mass extrinsic to the airway, approximately 3cmx2.5cmx1.5cm, compressing the carina and main-stem bronchi (figure 3).