An infant (<12months)presentedwith a several-day history of fevers, malaise, and progressive respiratory distress associated with a worsening cough and subjective wheezing. His caretakers reported that he had previously been evaluated formild reactive airway disease initially noted several months prior that had failed to respondtosymptomatic treatmentwithanalbuterolnebulizer.Over the several daysprecedingpresentation, his baselinewheezingand workofbreathinghadacutely increased.Ofnote, a twin sibling also had symptoms of an upper respiratory illness. His birth historywas uneventful, and no further pertinent data were elicited during the initial evaluation. At the timeofpresentation, thechildwas inmild respiratorydistress with oxygen saturation levels between 90% and 92%. His examination was significant for crepitus in the anterior side of the neck, increased work of breathing with accessory muscle use, diffuse rales, and rhonchi throughout his lung fieldswith amildly prolongedexpiratoryphase.Hewasadmitted for furtherevaluationand symptomatic treatment. A viral panel was positive for human respiratory syncytial virus (RSV) typeB. The initial chest radiograph is shown inFigure, A. Progression of radiographic findings and further respiratory decompensation prompted a computed tomographic (CT) scan of the patient’s chest (Figure, B-D). Following the CT scan of his chest, he continued to slowly decompensate and develop further respiratory distress. What is your diagnosis? A