Bronchiectasis
| Overview |
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- Bronchiectasis refers to an irreversible dilation of airways,typically involving medium-sized bronchi which can become dilated several times their normal diameter.
| Pathogenesis |
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- Bronchiectasis is caused by long-term inflammatory weakening of the bronchial wall combined with obstruction of the airway, leading to its gradual and irreversible dilation. Inflammation is typically characterized by neutrophils which release a wide variety of destructive factors, such as proteases, that weaken the bronchial wall. A thick purulent mucous accumulates behind the obstruction and eventually expands the weakened airway, leading to dilation.
- The source of the purulent mucous is a combination of dead inflammatory neutrophils along with normally-produced mucous which can no longer be cleared by the action of the mucociliary elevator, defective from the inflammation as well as the physical presence of the obstruction. Inflammation may also cause desquamation of the respiratory epithelium, resulting in its ulceration. Over time, the dilated airway may undergo a healing process characterized by progressive fibrosis. Although the respiratory epithelium may regenerate, the airway will remain dilated and scarred for the remainder of the individual's life. In some cases, healing does not occur and the dilated airway evolves into a full-blown lung abscess.
| Etiology |
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- The initiating cause of bronchiectasis may be either an airway obstruction or a pulmonary infection. Examples of initiating airway obstructions are lung tumors, aspirated foreign bodies, or a mucous plug secondary to a genetic abnormality such as Cystic Fibrosis or Kartagener Syndrome. Alternatively, the initiating cause might be a primary pulmonary infection due to either a viral or bacterial cause
- In general, the risk for bronchiectasis is higher in those who undergo repeated severe pulmonary infections such as patients with a variety of immunodeficiency diseases.
- Whatever the initiating injury, obstruction or infection, the functioning of the mucociliary elevator is compromised, leading to accumulation of mucous which is highly prone to microbial infection. Infection with microbes leads to generation of further mucous which consequently initiates or aggravates the obstruction. Consequently, a vicious circle of obstruction and infection follows, ultimately leading to dilation of inflammitorily weakened bronchi by accumulating purulent mucous.
| Clinical Consequences |
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- Bronchiectasis is typically heralded by a productive, purulent cough which can be complicated by hemoptysis if there are widespread ulcerations of the inflamed airway. Symptoms may develop insidiously if the cause is a slow-growing obstruction or may manifest rapidly following a bout of severe pneumonia. Pulmonary function tests may be abnormal in bronchiectasis and if so typically follow an obstructive pattern characteristic of obstructive lung disease.