Chest ImagingBronchiectasis
chronic irreversible dilatation of diseased bronchi. The prevalence of bronchiectasis depends on the socioeconomic conditions of the population. Bronchiectasis remains a major cause of morbidity in less developed countries where access to immunization and antibiotics is limited. There are many causes of and conditions associated with bronchiectasis (Table 1), and several other conditions are associated (Table 2).
Bronchiectasis, Table 1. Causes of bronchiectasis.
| Postinfectious: | bacteria, viruses, protozoa |
| Mechanical obstruction: | |
| intrinsic: foreign body, mucoid impaction, inflammatory stenosis, broncholithiasis, tumour |
| extrinsic: lymphadenopathy, tumour |
| Congenital: | |
| bronchial atresia |
| bronchopulmonary sequestration |
| Inflammatory: | |
| aspiration |
| inhalation of hot or toxic gases |
| Immunological overresponse: | |
| allergic bronchopulmonary aspergillosis |
| post lung transplant resection |
| Immunodeficiency: | |
| panhypogammaglobulinaemia |
| selective immunoglobulin deficiencies |
| secondary (AIDS), malignancy |
| Defects of mucus transport: | |
| genetic: primary ciliary dyskinesia syndrome with or without Kartageners syndrome, cystic fibrosis |
| acquired: Youngs syndrome, secondary ciliary dyskinesia |
| Granulomas and fibrosis: | |
| tuberculosis |
| sarcoidosis |
| Idiopathic | |
Modified from Hansell. Bronchiectasis. Radiol Clin North Am 1998;36:107-128.
Bronchiectasis, Table 2. Conditions associated with bronchiectasis
Modified from Hansell. Bronchiectasis. Radiol Clin North Am 1998;36:107-128.
Pathologically, mononuclear cell infiltration is present in the bronchial wall. In more severe bronchiectasis there is degeneration of ciliated epitheli a balloon-like appearance.
Cystic bronchiectasis represents the most advanced disease.
Currently, the classical features of patients with bronchiectasis reflecting severe disease and including production of large volumes of purulent sputum, finger clubbing, frequent infective exacerbation and recurrent haemoptysis are rarely observed. Most patients now have mild bronchiectasis with few or any physical signs. Therefore the diagnosis is usually made by a high resolution CT examination requested because of persistent cough producing infected sputum. The identification of an underlying cause may result in specific treatment instituted in addition to measures including antibiotics, partial drainage and inhaled steroid treatment. The indication for surgical excision of the disease is localized disease with no underlying identifiable cause for recurrence.
Currently radiographic abnormalities are present in less than 50% of patients with bronchiectasis. Peribronchial inflammation may make the margins of pulmonary vessels indistinct, particularly in the lower lobes. With more severe bronchial inflammation and fibrosis, the bronchial walls themselves become visible as tramlines most obvious in the lower lobes, in the middle lobe or lingula. When seen end on, dilated bronchi may appear as ill-defined ring opacities, notably in the mid and upper zones. Dilated bronchi filled with pus and mucus lead to tubular and ovoid opacities sometimes assuming a gloved finger appearance (see mucoid impaction). Cystic bronchiectasis results in multiple thin-walled ring opacities that may contain fluid levels. In advanced disease, the radiographic distinction from a coarse honeycombing pattern due to end-stage fibrotic disease may be difficult. Patchy peribronchial consolidation and focal areas of subsegmental collapse are commonly seen in diffuse disease. A lobe affected by bronchiectasis may be either overinflated or relatively collapsed (see lobar atelectasis).
HRCT is currently the imaging technique of choice for the detection of bronchiectasis. It replaced bronchography which has become obsolete. The most widely used protocol for bronchiectasis consists of 1 - 1.5 mm collimation scans every 10 mm from the lung apex to the diaphragm. For areas regarded as suspicious for bronchiectasis such interspacing can be reduced to 5 mm. Helical CT with thin collimation offers potential advantages including improved detection of subtle bronchiectasis missed between HRCT sections and reduced motion artefact. As compared to HRCT, helical CT has proven able to reduce interobserver variability and to improve the accuracy of diagnosis of the segmental and subsegmental distribution of bronchiectasis. However, this improvement is obtained at the price of a greater radiation dose delivered to the skin. Helical CT is only recommended in equivocal cases, in patients being assessed for surgery and in case of unexplained haemoptysis since in such a situation both bronchial tumour and bronchiectasis must be looked for. The cardinal sign of bronchiectasis is dilatation of the bronchi with or without bronchial wall thickening. CT findings of bronchiectasis depend on the orientation of the bronchus to the scan plane and the morphological type. For bronchi running parallel to the scan plane, cylindrical bronchiectasis is recognized where the ratio of the cross-sectional diameter of the bronchus to that of the homologous pulmonary artery is greater than one. When bronchial dilatation is marked, the cross-sectional appearance of the combined bronchus and artery resembles a signet ring (Fig.1). Minor discrepancies in the bronchoarterial diameter ratio may, however, be seen in normal individuals. In addition, many factors may cause transient or permanent changes in diameter of the relatively compliant pulmonary arteries. As a result, bronchial dilatation in isolat cystic spaces grouped along a fissure or the mediastinum pleura (Fig.5). CT may readily show completely collapsed lobes or segments containing bronchiectatic airways. It may also show subtle degrees of volume loss of lung parenchyma on the association of crowding of mildly dilated airways and displacement of the fissure. Accumulation of secretions within bronchiectatic airways is generally easily recognizable as lobulated glove-finger, V- or Y-shaped densities. When orientated obliquely or perpendicular to the scan plane, filled ectatic bronchi are visualized as nodular or oval-shaped densities that can be followed on successive CT sections (Fig.6). HRCT findings of cellular bronchiolitis or Constrictive bronchiolitis may be present in the same areas as bronchiectasis or within the other territories.
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