1.4: Bronchiectasis

This section will address bronchiectasis, a form of airway obstruction that is often a manifestation of chronic airway inflammation. Bronchiectasis involves a permanent dilation of a bronchi or bronchiole—think of bronchiectasis as the airway equivalent of an aneurysm.

A bronchiectasis starts with a section of airway wall becoming inflamed (figure 1.24), disrupting and weakening its structure. This weakening leads to a permanent dilation of the airway that impairs the clearance of secretion. Because the airway is inflamed, the amount of secretion may be significant and it begins to accumulate.

The stagnant secretion promotes a secondary infection that leads to further inflammation, wall disruption, and dilation. Thus the airway has entered a vicious cycle that causes the dilation and retention of mucus to perpetuate (figure 1.24).

Figure 1.24: Pathophysiology of bronchiectasis.

The establishing of a bronchiectasis has an initial phase leading to persistent inflammation, desquamation (which worsens the mucus clearance), and the ulceration. In what is probably a familiar story, the continued inflammation leads to fibrosis in the chronic phase of development, and this can lead to airway destruction and perhaps the condition of bronchiolitis obliterans.

Let us look at how this process can get started.

Pathogenesis of Bronchiectasis

There are some common culprits for initiating bronchiectasis (figure 1.25). Most start with either a decline in mucus clearance and the associated inflammation or damage to the airway wall.

About 50 percent of bronchiectasis cases are associated with cystic fibrosis where the genetic condition causes production of copious, thick mucus that is difficult to clear and often results in infection (commonly caused by Staphylococcus aureus).

Conditions causing cillary dyskinesia, as seen in Kartagener’s syndrome, also disrupt the mucocillary escalator.

Another common cause of bronchiectasis is an allergy to Aspergillus fumigatus, a common fungus. In hypersensitive or immune-compromised individuals, chronic exposure can lead to allergic bronchopulmonary aspiragillosis.

Figure 1.25: Instigating factors for bronchiectasis.

Bronchiectasis can be initiated in the vicinity of tuberculosis or other necrotizing infections that damage and weaken airway walls.

Obstruction of the bronchioles or bronchi by inhaled foreign objects, tumors, or compacted mucus can also initiate bronchiectasis through local inflammation and by preventing mucus clearance. The dilation of the airway can be worsened further by distal atelectasis that produces a negative pressure around the affected airway.

As you might have gather by now, repeated local infection or inflammation has the potential to initiate bronchiectasis, so it is perhaps not surprising that with the advent of high resolution computed tomography (CT) imaging, bronchiectasis has also been found in association with AIDS, transplant rejection, and rheumatoid lung disease.

We will now examine the results of these instigating factors.

Pathology of Bronchiectasis

The outcomes of bronchiectasis are seen in the histology slide in figure 1.26, with the affected airway lumen filled with mucus and pus, and the airway walls exhibiting fibroglandular tissue and infiltration by inflammatory cells (outer red circle).

The gross view (right panel, figure 1.26) shows severely dilated bronchi and noticeable thickening of their walls.

Figure 1.26: Histological and gross changes associated with severe bronchiectasis.

There are different forms of bronchiectasis; these are classified by their shape (figure 1.27). A bronchiectasis can be cylindrical, varicose (also known as fusiform), or cystic (also known as saccular). The shape is relevant to their effect on the efficacy of coughing; cylindrical form has very little effect on cough’s ability to clear mucus, whereas varicose and cystic forms tend to disproportionately collapse during cough and reduce its effectiveness at moving mucus up the airway.

Figure 1.27: Forms of bronchiectasis.

As shown in figure 1.28 an x-ray shows the presence of bronchiectasis, but it can be difficult to ascertain the form. High resolution CT (figure 1.28) is better at determining the form and has all but replaced the much more invasive bronchography, which involves instillation of radiopaque medium into the tracheobronchial tree.

Figure 1.28: Chest x-ray and CT of severe bronchiectasis. In the x-ray there are clear markings in the right lung that follow the path of affected bronchi. The distinctly widened airways on the right of the CT are consistent with severe bronchiectasis.

Where the bronchiectasis occurs in the lung is somewhat dependent on the cause. The segmental and subsegmental bronchi are the airway types most commonly affected, and the basilar segments of the lower lobes are the most frequent region in the lung. The second most common locations are the right middle lobe and lingual segments, while bronchiectasis caused by primary tuberculosis (TB) and other infections tend to occur in the upper lung fields where the infection is located (see figure 1.29).

Figure 1.29: Common locations of the segmental and subsegmental broncho affected by bronchiectasis.

So, how does bronchiectasis present, and what are the results of diagnostic tests?

Clinical Presentation of Bronchiectasis

The initial complaint is usually a persistent cough with copious expectoration. The amount of mucus the cough produces varies and can be as high as several hundred milliliters per day, particular when the dependent airways are involved. However, it is worth noting here that bronchiectasis in the upper lobes (usually associated with infection) may be dry with little or no mucus expectoration.

Generally though there is mucopurulent expectorate, and if it is associated with an anerobic infection it will likely have a foul odor. Sputum smears are loaded with white blood cells and can contain both gram-positive and -negative organisms.

The patient will likely have a history of recurrent pneumonia, the site of the pneumonia being consistent with locality of the bronchiectasis.

The expectorate may also contain blood. The degree and frequency of hemoptysis is variable and unpredictable, but occasionally it can be massive and life threatening.

The standard diagnostic tests may not be helpful in early stages, but typical signs appear with worsening airway involvement. In the early stages the patient will likely appear normal on a physical exam and have normal spirometry and arterial blood gas values. With more significant bronchiectasis, rales and rhonchi over the affected site can be heard.

Later signs with long-standing bronchiectasis include finger clubbing, but this is not exclusive to the condition.

A chest x-ray will show the peribronchial fibrosis and any atelectasis. But, as mentioned earlier, a high-resolution CT is much more effective at determining the degree and type of airway changes.

References, Resources, and Further Reading

Text

Farzan, Sattar, with Doris L. Hunsinger and Mary L. Phillips. "Chapters 8–11." In A Concise Handbook of Respiratory Diseases. Reston, VA: Reston Publishing Company, 1978.

Husain, Aliya N. "Chapter 15: The Lung." In Robbins and Cotran Pathologic Basis of Disease, 9th ed., edited by Vinay Kumar, Abul K. Abbas, and John C. Aster. Philadelphia: Saunders, an imprint of Elsevier Inc., 2015.

West, John B. "Chapter 4: Obstructive Diseases." In Pulmonary Pathophysiology: The Essentials, 7th ed. Baltimore: Lippincott Williams & Wilkins, a Wolters Kluwer business, 2008.

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