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BRONCHIECTASIS

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Bronchiectasis refers to irreversible dilation of the bronchi or bronchioles. The airway enlargement is a result of weakening of the bronchial walls in response to chronic inflammation. Impairment of the mucus transport mechanism contributes to the formation of exudative filling of the dilated bronchus. Bacterial colonization of the abnormal bronchus leads to progressive damage.

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Three forms of bronchiectasis are recognized. The cylindrical type consists of diffuse dilation of the involved bronchus (Figure 4-1). With the varicose form, the dilated bronchus has a beaded configuration. Bronchiectasis is saccular if there are bronchial cysts that are at least 1 cm in diameter.

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Figure 4–1

Cylindrical bronchiectasis.

CT of a teenager with cystic fibrosis shows cylindrical bronchiectasis in the left upper lobe.

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Radiographs and CT show bronchiectasis as airfilled dilated tubular structures, usually with thickened irregular walls. When viewed on end, the dilated bronchus appears as a ring that is larger than the accompanying pulmonary artery, producing the "signet ring sign" (Figure 4-2). When filled with fluid or mucous, the dilated bronchi may appear as linear soft-tissue density structures that are branching or finger-like. When viewed on end, they appear nodular.

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Figure 4–2

Bronchiectasis.

CT of a 17-year-old with cystic fibrosis shows the cross-sectional appearance of a dilated bronchus and its companion pulmonary artery, resulting in the signet ring sign.

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Cystic fibrosis is the most common cause of bronchiectasis. Other etiologies include dysmotile cilia syndrome, allergic bronchopulmonary aspergillosis in asthma patients, chronic infection, and immunodeficiency (Table 4-1).1

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Table 4–1.Causes of Bronchiectasis in Children
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BRONCHIOLITIS OBLITERANS

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Bronchiolitis obliterans (obliterative bronchiolitis) refers to fibrous obliteration of the small airways. The fibrosis is caused by the repair process that occurs following inflammation and damage to the bronchiolar epithelium. Potential causes of bronchiolitis obliterans include lung infection (particularly adenovirus pneumonia), chronic graft-versus-host disease in transplantation patients, Stevens-Johnson syndrome, drug reactions, connective tissue disease, and toxic gas inhalation. The most common cause of bronchiolitis in children who have not undergone transplantation is adenovirus pneumonia. Unilateral bronchiolitis obliterans caused by bronchiolitis in infancy is termed Swyer-James syndrome.2,3

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Standard chest radiographs of patients with bronchiolitis obliterans may show hyperinflation, attenuated peripheral pulmonary vascular markings, and nodular or reticulonodular opacities. However, chest radiographs are sometimes normal despite symptomatic disease. High-resolution CT typically demonstrates centrilobular branching structures and centrilobular nodules caused by thickening of the bronchial walls. Indirect signs that are sometimes present on CT ...

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