Bronchiectasis means dilatation of the airways; this occurs patchily due to scarring and is usually associated with mucosal thickening, mucus plugging and a variable degree of lung over- inflation. Bronchiectasis is associated with a range of common and rare diseases, some of which impact on mucociliary clearance and immunity. Mucus clearance and local defence mechanisms against microorganisms are critically important in keeping the lungs free of infection. When they are impaired, repeated infection causes damage which further impedes the clearance of mucus. The airway dilatation and consequent impairment of mucociliary clearance combine to further increase susceptibility to repeated infection in the lungs, resulting in chronic infection in some cases. The abnormal airway anatomy, chronic infection and mucus retention result in a slow decline in respiratory function. In the early stages of the disease, even with significant evidence of bronchiectasis on computed tomography (CT), spirometry may be normal; in advanced disease, functional evidence of airway obstruction is usual. The apparent paradox of the structural bronchodilatation of airways but functional evidence of diffuse narrowing, largely reflects the different generations of airways involved; there may be irregular bronchodilatation of medium-sized airways but airflow is determined more by the smaller airways, which are narrowed due to chronic inflammation and scarring.
As a diagnostic term, bronchiectasis is sometimes prefixed by non-cystic fibrosis (non-CF) to exclude this specific cause from that associated with another condition or in which no cause is identified. Bronchiectasis is, however, primarily a pathological description of the airways; although an aetiological diagnosis can only be established in some patients with definite CT radiological evidence of the condition, bronchiectasis is a useful diagnostic term as patients share a common symptomatology.