The purpose of this study was to determine whether the pattern and distribution of bronchiectasis shown on CT scans can be used to discriminate between idiopathic cases and those with an identifiable cause.

The CT scans of 168 patients with chronic purulent sputum production and who were suspected of having bronchiectasis were analyzed (117 patients with idiopathic bronchiectasis, 15 with allergic bronchopulmonary aspergillosis, 15 with hypogammaglobulinemia, 15 with impaired mucociliary clearance, and seven with cystic fibrosis diagnosed in adult life). The scans were analyzed in random order by two observers. The extent, site, type, and lobar distribution of bronchiectasis and the severity of bronchial dilatation and bronchial wall thickening were scored. The frequency of these features in the known-cause groups was compared with that in the idiopathic group to identify any significant differences.

Compared with idiopathic bronchiectasis, no significant lobar predominance was seen in any of the known-cause groups, apart from a higher frequency of lower lobe involvement in the patients with syndromes of impaired mucociliary clearance (p < .02). The bronchiectasis of allergic bronchopulmonary aspergillosis and adult cystic fibrosis was more often widespread (five or six lobes involved (p < .001 and p < .01, respectively) than idiopathic bronchiectasis. Central bronchiectasis was more common in allergic bronchopulmonary aspergillosis (p < .005), although the sensitivity when this was used as a diagnostic feature was only 37%. In all groups, cylindrical bronchiectasis was the most common type, with varicose and cystic bronchiectasis occurring more frequently in allergic bronchopulmonary aspergillosis (p < .01). On multiple regression analysis, allergic bronchopulmonary aspergillosis and adult cystic fibrosis showed more extensive disease than idiopathic bronchiectasis (p < .0005 and p < .001, respectively), independent of other CT features. In hypogammaglobulinemia, dilatation of the bronchial lumen was less than in idiopathic bronchiectasis (p < .02) independent of disease extent and bronchial wall thickness.

Although differences in distribution and morphology of bronchiectasis may be seen on CT scans in groups of patients with bronchiectasis of different causes, CT findings applied to individual patients are of limited value in discriminating between idiopathic bronchiectasis and bronchiectasis of various known causes.