Bronchiectasis is the permanent dilation of bronchi and bronchioles caused by destruction of smooth muscle and the supporting elastic tissue; it typically results from or is associated with chronic necrotizing infections. It is not a primary disorder, as it always occurs secondary to persistent infection or obstruction caused by a variety of conditions. Bronchiectasis gives rise to a characteristic symptom complex dominated by cough and expectoration of copious amounts of purulent sputum. Diagnosis depends on an appropriate history and radiographic demonstration of bronchial dilation. The conditions that most commonly predispose to bronchiectasis include:
Bronchial obstruction. Common causes are tumors, foreign bodies, and impaction of mucus. In these conditions, bronchiectasis is localized to the obstructed lung segment. Bronchiectasis also may complicate atopic asthma and chronic bronchitis.
Congenital or hereditary conditions—for example:
Cystic fibrosis, in which widespread severe bronchiectasis results from obstruction caused by abnormally viscid mucus and secondary infections (Chapter 7).
Immunodeficiency states, particularly immunoglobulin deficiencies, in which localized or diffuse bronchiectasis often develops because of recurrent bacterial infections.
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Primary ciliary dyskinesia (also called the immotile cilia syndrome). This is a rare autosomal recessive disorder that is frequently associated with bronchiectasis and with sterility in males. It is caused by inherited abnormalities of cilia that impair mucociliary clearance of the airways, leading to persistent infections.
Necrotizing, or suppurative, pneumonia, particularly with virulent organisms such as Staphylococcus aureus or Klebsiella spp., predispose affected patients to development of bronchiectasis. Posttuberculosis bronchiectasis continues to be a significant cause of morbidity in endemic areas.
Two intertwined processes contribute to bronchiectasis: obstruction and chronic infection. Either may be the initiator. For example, obstruction caused by a foreign body impairs clearance of secretions, providing a favorable substrate for superimposed infection. The resultant inflammatory damage to the bronchial wall and the accumulating exudate further distend the airways, leading to irreversible dilation. Conversely, a persistent necrotizing infection in the bronchi or bronchioles may lead to poor clearance of secretions, obstruction, and inflammation with peribronchial fibrosis and traction on the bronchi, culminating again in full-blown bronchiectasis.
MORPHOLOGYBronchiectasisusuallyaffectsthelowerlobesbilaterally,particularlythoseairpassagesthataremostvertical.Whencausedbytumorsoraspirationofforeignbodies,theinvolvementmaybesharplylocalizedtoasinglesegmentofthelungs.Usually,themostsevereinvolvementisfoundinthemoredistalbronchiandbronchioles.The airways may be dilated to as much as four times their usual diameter andcanbeseenongrossexaminationalmostouttothepleuralsurface(
Fig.13.12 ).Bycontrast,innormallungs,thebronchiolescannotbefollowedbyeyebeyondapoint2to3cmfromthepleura.
Thehistologicfindingsvarywiththeactivityandchronicityofthedisease.Infull-blownactivecases,anintenseacuteandchronicinflammatoryexudatewithinthewallsofthebronchiandbronchiolesleadstodesquamationofliningepitheliumandextensiveareasofulceration.Typically,mixedfloraareculturedfromthesputum.Theusualorganismsincludestaphylococci,streptococci,pneumococci,entericorganisms,anaerobicandmicroaerophilicbacteria,and(particularlyinchildren)Haemophilus influenzae andPseudomonas aeruginosa.