Bronchiectasis.

Bronchiectasis is defined as irreversible bronchial dilatation, leading to chronic cough, sputum formation, and recurrent infections. HRCT plays a major role in diagnosis of bronchiectasis. Most bronchiectasis is either idiopathic or a result of prior infections. Cystic fibrosis, allergic bronchopulmonary aspergillosis, and traction bronchiectasis caused by prior tuberculosis, sarcoidosis, and silicosis with progressive massive fibrosis have an upper lobe distribution. A lower lobe distribution is mostly seen in chronic aspiration, hypogammaglobulinemia, Mounier-Kuhn syndrome, primary ciliary dyskinesia, and traction bronchiectasis caused by usual interstitial pneumonitis and nonspecific interstitial pneumonitis. The right middle lobe and lingula are preferentially involved in atypical mycobacterial infections and sometimes in primary ciliary dyskinesia and Kartagener syndrome. A location-based approach may help lead to a specific diagnosis.