Bronchiectasis is a relatively frequent condition in the United States, with an estimated prevalence of 4.2 per 100,000 persons 18–34 years old and 272 per 100,000 persons 75 years or older. It is defined as an “irreversible localized or diffuse dilatation, usually resulting from chronic infection, proximal airway obstruction, or congenital bronchial abnormality.” On chest radiographs, bronchiectasis manifests as tram tracks, parallel line opacities, ring opacities, and tubular structures. However, chest radiographs lack sensitivity for detecting mild or even moderate disease. CT is substantially more sensitive than chest radiography for showing bronchiectasis, which is characterized by lack of bronchial tapering, bronchi visible in the peripheral 1 cm of the lungs, and an increased bronchoarterial ratio producing the so-called signet-ring sign. According to appearance and severity, bronchiectasis can be classified as cylindric, varicose, or cystic (Figs. 1A, 1B, 1C, and 1D). The wide differential diagnosis of bronchiectasis can be substantially narrowed by considering both the anatomic location and the distribution of this pathology (Fig 2).
Any cause of airway obstruction can lead to focal bronchiectasis (Fig. 3). In contrast to diffuse bronchiectasis, focal bronchiectasis requires diagnostic bronchoscopy in almost all patients.
The most common cause of congenital focal bronchiectasis is bronchial atresia, characterized by obliteration of a bronchus with distal bronchiectasis, mucoid impaction, and air trapping that is most commonly seen in the left upper lobe (Figs. 4A and 4B). In this rare lesion, the bronchial tree peripheral to the point of obliteration is patent and the lung parenchyma is overinflated because of collateral air drift.
Extrinsic compression is an acquired cause of focal bronchiectasis, most commonly caused by lymphadenopathy, usually from previous granulomatous exposure. Less frequent causes include sarcoidosis, hilar mass, and metastatic lymphadenopathy.
Endoluminal Obstruction by Tumor
Most carcinoid tumors are primarily endobronchial lesions, occurring in the central, main, or segmental bronchi (Figs. 5A, 5B, 5C, and 5D). Some small tumors are located entirely within the lumen. However, some display a dominant extraluminal component with only a small part of the tumor lying within the airway (iceberg lesion). A variety of other benign and malignant neoplasms can also result in obstruction leading to focal bronchiectasis.
Aspirated foreign material can result in focal bronchiectasis. Persistence of a noncalcified foreign body, such as a vegetable fiber, within a bronchus for a prolonged period of time can serve as a nidus for calcium deposition.
Calcified or ossified material within the bronchial lumen can cause focal bronchiectasis. By far the most common cause of broncholithiasis is erosion by and extrusion of a calcified adjacent lymph node, usually associated with a long-standing focus of necrotizing granulomatous lymphadenitis, especially after tuberculosis (Figs. 6A, 6B, and 6C). Nevertheless, the frequency of broncholithiasis complicating granulomatous infection is quite low. The most common sites are the proximal right middle lobe bronchus and the origin of the anterior segmental bronchus of the upper lobes because of airway anatomy and lymph node distribution.
Airway stenosis causing focal bronchiectasis (Figs. 7A, 7B, and 7C) can result from a broad spectrum of entities including infection, intubation stricture, healing of a tracheostomy stoma, tracheobronchopathia osteochondroplastica, amyloidosis, relapsing polychondritis, sarcoidosis, and fibrosing mediastinitis.
Diffuse Bronchiectasis: Upper Predominance
The most common cause of congenital upper-lung-predominant bronchiectasis is cystic fibrosis, commonly associated with enlarged lung volumes and interstitial alterations (Figs. 8A and 8B). An autosomal recessive genetic disorder causing ineffective clearance of secretions, cystic fibrosis presents with recurrent pneumonias, sinusitis, pancreatic insufficiency, and infertility. Milder forms of cystic fibrosis, however, can remain unrecognized until adulthood (Fig. 9).
Parenchymal involvement by sarcoidosis can lead to upper and mid lung fibrosis and traction bronchiectasis, typically associated with multiple nodules in a perilymphatic distribution (Figs. 10A and 10B). Mediastinal and bilateral symmetric lymphadenopathy is common, although it can regress as the interstitial disease worsens.
Another important cause of upper-lung-predominant bronchiectasis is postradiation fibrosis, in which traction bronchiectasis is usually limited to the radiation port (Figs. 11A and 11B). A straight interface between the irradiated field and normal lung is often seen. This does not respect anatomic borders, such as fissures and lobes. Postradiation fibrosis may also be bilateral after mediastinal radiation for lymphoma.
Diffuse Bronchiectasis: Lower Predominance
Lower-lung-predominant bronchiectasis, which is the most frequent pattern, is most commonly idiopathic (Figs. 12A and 12B). However, some cases have known causes.
Recurrent Childhood Infections
Postinfectious bronchiectasis is a frequent cause of lower-lung-predominant bronchiectasis. It is less seen today because of better control of tuberculosis, earlier treatment of pneumonia, and immunization. However, recurrent infections still remain a frequent cause of bronchiectasis in immune-suppressed patients.
Any predisposition for repeated aspiration is associated with an increased risk of developing bibasilar bronchiectasis. Common causes include a large hiatal hernia with gastroesophageal reflux, scleroderma (Fig. 13) and other causes of a patulous esophagus, and esophageal motility disorders.
Fibrotic Lung Disease
Bronchiectasis predominantly involving lung bases is a common finding in fibrotic lung disease. In usual interstitial pneumonia (UIP), coarse reticulation, honeycombing, parenchymal distortion, and traction bronchiectasis are typically predominant in a subpleural and bibasilar distribution with geographic heterogeneity (Fig. 14). Although often idiopathic, UIP occurs in asbestosis, drug toxicity, and collagen–vascular disease. Nonspecific interstitial pneumonia has almost the same differential diagnosis but typically occurs in younger patients and carries a better prognosis. Ground-glass opacity is more frequent than in UIP and honey-combing usually remains minimal.
Bronchiolitis obliterans from posttransplantation rejection is a rare cause of bronchiectasis associated with patchy mosaic perfusion, air trapping, and bronchiolar obstruction (Figs. 15A and 15B). Hypogammaglobulinemia can also be a cause of lower-lung-predominant bronchiectasis, most often caused by recurrent infections.
Diffuse Bronchiectasis: Middle Lobe and Lingula Predominance
Nontuberculous Mycobacterial Infection
The most common acquired cause of bronchiectasis predominantly involving the right middle lobe and lingula is nontuberculous mycobacterial infection, such as Mycobacterium avium-intracellulare (MAI). This infection, typically seen in women over 60 years old, presents with chronic infection, bronchiectasis, mucoid impaction, and bronchiolitis (Fig. 16). The disease often has an indolent but progressive course requiring long-term antibiotics.
Immobile Cilia Syndrome
This rare congenital cause of bronchiectasis, which primarily involves the middle lung, is characterized by ineffective clearing of secretions, causing bronchiectasis, recurrent pneumonias, sinusitis, and infertility. In 50% of cases, total situs inversus is present, a condition known as Kartagener's syndrome (Figs. 17A and 17B).
Diffuse Bronchiectasis: Central Predominance
Allergic Bronchopulmonary Aspergillosis
Allergic bronchopulmonary aspergillosis is an immune reaction to Aspergillus species that damages the bronchial wall, causing central bronchiectasis and mucous plugs that contain fungus and inflammatory cells. On chest radiography, this produces a characteristic finger-in-glove appearance. On CT, central bronchiectasis and mucoid impactions are often associated with areas of peripheral bronchiolitis, manifesting as bronchiolar nodules or tree-in-bud opacities (Figs. 18A and 18B).
Several rare disorders characterized by cartilage deficiency can cause bronchiectasis that primarily involves the central regions of the lung. One is tracheobronchomegaly, also known as Mounier-Kuhn's syndrome, which manifests as diffuse enlargement of the trachea and mainstem bronchi with more distal bronchiectasis (Figs. 19A and 19B).
An even rarer cartilage deficiency disorder is the Williams-Campbell syndrome, in which central bronchiectasis, mimicking the appearance of parenchymal cysts, is associated with widespread air trapping (Fig. 20).