Miscellaneous Airway Diseases

This chapter considers several disorders that affect airways, chosen because of their clinical or physiologic importance. The first of these disorders, bronchiectasis, is a disease that was much more common in the past. The availability of effective antibiotics for control of respiratory tract infections has made this problem less prevalent and diminished its clinical consequences. The second disorder, cystic fibrosis, is a genetic disease that generally manifests in childhood and is notable for the often devastating clinical consequences that ensue. Abnormalities of the upper airway (which for our purposes here includes the airway at or above the level of the trachea) are discussed briefly to acquaint the reader with the physiologic principles that allow detection of these disorders.

Bronchiectasis

Bronchiectasis is an irreversible dilation of airways caused by inflammatory destruction of airway walls. Because the most common etiologic factor is infection, which triggers the destructive inflammatory process, the extent of the bronchiectasis in a patient depends on the location and extent of the underlying infection. In some cases, bronchiectasis is localized to a specific region of the lung. In other cases, the process involves more than one area or even is diffuse, involving a large portion of both lungs.

Etiology and Pathogenesis

Infection and impairment of drainage (frequently due to obstruction) are the two underlying problems that contribute to development of dilated or bronchiectatic airways. The responsible infection(s) may be viral or bacterial. Years ago, measles and pertussis (whooping cough) pneumonia were common problems resulting in bronchiectasis. Currently, a variety of other viral and bacterial infections often are responsible; important examples are tuberculosis and Mycobacterium avium complex. At times, inflammation resulting from hypersensitivity to fungal organisms is the underlying cause, as with allergic bronchopulmonary aspergillosis. This condition, found almost exclusively in patients with clinically apparent asthma or cystic fibrosis, is characterized by colonization of airways with Aspergillus organisms and by thick mucous plugs and bronchiectasis in relatively proximal airways.

Prior infection, obstruction, or both are the most common problems leading to bronchiectasis.

When an airway is obstructed, a superimposed infection may develop behind the obstruction, causing destruction of the airway wall and leading to bronchiectasis. Tumors, thick mucus, or foreign bodies commonly cause bronchial obstruction, resulting in bronchiectasis.

Another factor that plays a role in some patients is a defect in the ability of the airway to clear itself of, or protect itself against, bacterial pathogens (see Chapter 22). Such a defect predisposes a person to recurrent infections and eventually to airway dilation and bronchiectasis. The abnormality may involve inadequate humoral immunity and insufficient antibody production (hypogammaglobulinemia) or defective leukocyte function. Another problem that has received significant attention is dyskinetic cilia syndrome, in which ciliary dysfunction affects the ability of the ciliary blanket that lines the airway to clear bacteria and protect the airway against infection. The ciliary dysfunction is not limited to the lower airways; it also affects the nasal mucosa and, in males, may affect sperm motility and hence fertility. Pathologically, the dynein arms that are a characteristic feature of the ultrastructure of cilia are frequently absent in this disorder. One specific syndrome associated with bronchiectasis and ciliary dysfunction is Kartagener syndrome, which includes a triad of sinusitis, bronchiectasis, and situs inversus (usually discovered because of the presence of dextrocardia).

Abnormalities of ciliary structure and function can result in recurrent infections and bronchiectasis.

Pathology

The primary pathologic feature of bronchiectasis is evident on gross inspection of the airways, which are markedly dilated in the involved region (Fig. 7-1). Three specific patterns of dilation have been described: cylindrical (appearing as uniform widening of the involved airways), varicose (having irregularly widened airways resembling varicose veins), and saccular bronchiectasis (characterized by widening of peripheral airways in a balloonlike fashion). These terms are still used when describing radiographic patterns but are much less relevant clinically. The dilated airways are generally filled with a considerable amount of secretions that may be grossly purulent. Microscopic changes of the bronchial wall epithelium, consisting of ulceration and squamous metaplasia, are seen.

Figure 7-1 Surgically removed specimen of lung shows extensive bronchiectasis. Some grossly dilated airways are filled with large amounts of mucoid and purulent material.

As a result of the exuberant inflammatory changes in the bronchial wall, the blood supply, provided by the bronchial arteries, is increased. The arteries enlarge and increase in number, and new anastomoses may form between the bronchial and pulmonary artery circulations. Inflammatory erosion or mechanical trauma at the site of these vascular changes is often responsible for the hemoptysis seen frequently in patients with bronchiectasis.

Vessels from the bronchial arterial circulation supplying a bronchiectatic region are often a source of bleeding and hemoptysis.

Coexisting disease in the remainder of the tracheobronchial tree is common. Other areas of bronchiectasis may be present, or generalized changes of chronic bronchitis may be seen (see Chapter 6).

High-resolution computed tomography (HRCT) provides a definitive diagnosis and is the initial procedure used to define the presence, location, and extent of bronchiectasis (Fig. 7-2). HRCT (with sections 1-2 mm thick) provides excellent detail and is particularly useful for detecting subtle bronchiectasis. In the past, the definitive diagnosis depended on bronchography, a radiographic procedure in which an inhaled opaque contrast material was used to outline part of the tracheobronchial tree (Fig. 7-3). This procedure is uncomfortable, can induce bronchospasm, and is not performed today.