Bronchiectasis represents irreversible dilation of the airway due to infection, obstruction, or congenital abnormalities. The three types of bronchiectasis are cylindrical (smooth, tubular), varicose (undulating, irregular), and cystic (saccular dilation). In this case, there is diffuse cystic bronchiectasis with a central predominance. The differential diagnosis would be allergic bronchopulmonary aspergillosis (ABPA), Mounier-Kuhn syndrome (tracheobronchomegaly), and Williams-Campbell (WC) syndrome. ABPA results in mucoid impactions and a characteristic "finger in glove" appearance with areas of bronchiolitis distally. Mounier-Kuhn syndrome affects the trachea, mainstem bronchi, and distal airways. WC is a congenital cartilage disorder mostly affecting the mid-bronchi (4th-6th order).

The dramatic appearance of the bilateral, diffuse, central cystic bronchiectasis with air-mucus levels could be mistaken for cystic lung disease. Given the extensive nature of the disease, a congenital cause is most likely. The trachea is narrowed (saber sheath appearance) rather than dilated, which would be the major feature of Mounier-Kuhn syndrome. There is some enlargement of the mainstem bronchi; however, the predominant feature in this case is dilation of the middle (4th-6th order) bronchi, making WC the most appropriate diagnosis. There may be some overlap in the spectrum of the underlying cartilage deficiency resulting in this appearance, or perhaps multiple bouts of infection and inflammation have further exacerbated his imaging findings. Surprisingly, the patient was not aware of this diagnosis prior to this study despite his later age of presentation.