The radiological diagnosis of bronchiectasis: what's in a name?

Abstract

Diagnosis of bronchiectasis is usually made using chest computed tomography (CT) scan, the current gold standard method. A bronchiectatic airway can show abnormal widening and thickening of its airway wall. In addition, it can show an irregular wall and lack of tapering, and/or can be visible in the periphery of the lung. Its diagnosis is still largely expert based. More recently, it has become clear that airway dimensions on CT and therefore the diagnosis of bronchiectasis are highly dependent on lung volume. Hence, control of lung volume is required during CT acquisition to standardise the evaluation of airways. Automated image analysis systems are in development for the objective analysis of airway dimensions and for the diagnosis of bronchiectasis. To use these systems, clear and objective definitions for the diagnosis of bronchiectasis are needed. Furthermore, the use of these systems requires standardisation of CT protocols and of lung volume during chest CT acquisition. In addition, sex- and age-specific reference values are needed for image analysis outcome parameters. This review focusses on today's issues relating to the radiological diagnosis of bronchiectasis using state-of-the-art CT imaging techniques.

FIGURE 1

a) A healthy small airway and b) an inflamed airway with a thickened wall at full inspiration. On inspiration, the mucosa of the healthy airway is only slightly folded. The inflamed airway has larger folds compared with the normal airway. Mucus fills up the gaps between the mucosal folds. On chest CT, the folds and mucus will be interpreted as a thickened airway wall. This figure also illustrates why the outer diameter is a more robust parameter for diagnosing and quantifying bronchiectasis because in contrast to the inner diameter, it is not influenced by the presence of mucus in the lumen. Image provided by, and reproduced and modified with the kind permission of, M. Meerburg (Amsterdam, The Netherlands).

FIGURE 2

A spirometer-controlled chest computed tomography of a healthy adult showing the lung in the coronal plane at a) total lung capacity (TLC) and b) after full expiration at residual volume level. a) Arrows indicate the maximal height and width of the lung at TLC. b) The same dimensions projected over the lung in expiration. Note that the largest displacement is in the cranial caudal direction. Also note the differences in lung density and the altered orientation of the left and right main stem bronchi between inspiration and expiration. Finally, at full inspiration, the pleura parietalis is bulging out between the ribs, while on expiration the pleura parietalis is bulging in.