Bronchiectasis Imaging 

Bronchiectasis is defined as localized, irreversible dilatation of part of the bronchial tree. Involved bronchi are dilated, inflamed, and easily collapsible, resulting in airflow obstruction and impaired clearance of secretions. Bronchiectasis is associated with a wide range of disorders, but it usually results from necrotizing bacterial infections, such as infections caused by the Staphylococcus or Klebsiella species or Bordetella pertussis.

Hemoptysis is common and may occur in as many as 50% of patients. Episodic hemoptysis with little to no sputum production (dry bronchiectasis) is usually a sequela of tuberculosis. However, massive hemoptysis may occur; bleeding usually originates in dilated bronchial arteries, which contain blood at systemic (rather than pulmonary) pressures.

Diagnosis of bronchiectasis is based on a clinical history of daily viscid sputum production and characteristic computed tomography (CT) scan findings. (See the images below.)

Preferred examination

Chest radiography is usually the first imaging examination, but the findings are often nonspecific and the images may appear normal.^[1] High-resolution computed tomography (HRCT) scanning has become the imaging modality of choice for demonstrating or ruling out bronchiectasis and its extent (see the images below). HRCT scanning also helps clinicians to evaluate the status of the surrounding lung tissue and exclude other lesions such as neoplasms.^[2]

Bronchography was the classic modality used and, until the advent of HRCT scanning, was the only imaging method to demonstrate bronchiectasis. Bronchography is performed by instilling an iodine-based contrast material via a catheter or bronchoscope, but it is rarely, if ever, performed today, as HRCT scanning has replaced it as the diagnostic modality of choice. HRCT scanning is noninvasive and has a sensitivity of 96% and a specificity of 93%.^[3]

Limitations of techniques

Bronchoscopy is not helpful in diagnosing bronchiectasis, but it may be used to identify underlying abnormalities, such as tumors and foreign bodies.

Chest radiographs may be negative in patients with minor to moderate disease. Many abnormal radiographic findings may be nonspecific, and confirmation using HRCT scanning may be required.

Bronchography is rarely indicated because it is invasive and is associated with allergic reactions to the contrast material. Bronchography also carries the risk of acute bronchoconstriction.

HRCT scanning is the diagnostic modality of choice and has few limitations.

Chest radiography helps to identify serious disease, and it was once the standard imaging modality.^[4] However, the radiographs may depict no abnormalities, or the findings may be nonspecific in patients with less-severe disease.^[5]

Various abnormal radiographic findings have been described as follows (see the images below):

• Parallel line opacities (tram tracks) caused by thickened dilated bronchi
• Ring opacities or cystic spaces as large as 2 cm in diameter resulting from cystic bronchiectasis, sometimes with air-fluid levels
• Tubular opacities caused by dilated fluid-filled bronchi
• Increased size and loss of definition of the pulmonary vessels in the affected areas as a result of peribronchial fibrosis
• Crowding of pulmonary vascular markings from the associated loss of volume, usually caused by mucous obstruction of the peripheral bronchi
• Oligemia as a result of reduction in pulmonary artery perfusion (severe disease)
• Signs of compensatory hyperinflation of the unaffected lungA 27-year-old man diagnosed with reactive airway disease as a child was examined because of frequent respiratory infections. The posteroanterior chest radiograph shows ill-defined pulmonary nodular opacities, mild scoliosis, and moderate overaeration. This is a close-up radiograph of the left upper lung zone in a 31-year-old woman with chronic cough since childhood. Nodules are present in the left upper lung; the right upper lung was similarly involved. A 65-year-old woman was examined for chronic cough. The lateral chest radiograph shows overaeration and increased markings over the heart. This posteroanterior chest radiograph shows overaeration and somewhat-obscured heart borders.

Bronchography

Introduced in 1922, bronchography was the investigation of choice until the introduction of HRCT scanning in the mid 1980s. Currently, bronchography is rarely used. Bronchography is performed by instilling contrast material via a catheter or bronchoscope under fluoroscopic control and plain radiographic imaging. The procedure is unpleasant for the patient and is also associated with temporary impairment of ventilation, as well as allergic and foreign body reactions to the contrast medium. In addition, interpretation of bronchographic images is difficult, owing to underfilling and retained secretions.

Degree of confidence

The accuracy of plain radiographic findings in the diagnosis of bronchiectasis is unknown, because the findings are variable and nonspecific and depend on the severity and extent of the bronchiectasis. However, good correlation exists between the severity of disease as seen on plain images and HRCT scans. Chest radiographic findings may be normal or nonspecific in patients with less-severe disease.

False positives/negatives

Many plain radiographic findings are nonspecific and may be seen in patients with idiopathic pulmonary fibrosis, sarcoidosis, histiocytosis X, rheumatoid lung, and other chronic interstitial lung disorders.

The HRCT imaging technique consists of obtaining 1-2 mm collimation scans at 10 mm intervals through the chest with a window level (WL) of –700 Hounsfield units (HU) and a window width (WW) of –1000 HU. The right middle lobe and lingular bronchi cross obliquely and are not optimally depicted on axial HRCT scans; as a result, a gantry angulation of 20° may be required.^{[6, 7, 8, 9, 10, 11, 12, 13, 14, 15]}

On HRCT scans in patients with bronchiectasis, the internal bronchial diameter may be greater than that of the adjacent artery, and there may be a lack of bronchial tapering (the same diameter as the parent branch for >2 cm). The bronchi may be within 1 cm of costal pleura or abut the mediastinal pleura (more specific but less sensitive than an increased ratio), and bronchial wall thickening may be seen (in 68% of patients). A cystic cluster of thin-walled cystic spaces may be present, often with air-fluid levels. (See the image below.)

In cylindrical bronchiectasis, bronchi coursing horizontally are seen as parallel lines, and vertically oriented bronchi are seen as circular lucencies that are larger than the adjacent pulmonary artery (signet-ring appearance). (See the image below.)

Varicose bronchiectasis may be seen as nonuniform bronchial dilatation. Other findings include the following:

• Areas of increased and decreased perfusion and attenuation
• Tracheomegaly
• Enlarged mediastinal nodes

Fluid-filled bronchi are revealed as tubular or branching structures when they course horizontally or are revealed as nodules when they are perpendicular to the plane of the CT scan section (see the image below).

Degree of confidence

HRCT scanning has a sensitivity of 96% and a specificity of 93%,^[3] as compared with bronchography, the previous criterion standard.

Bronchial measurements may vary with the use of different WLs and WWs.^[16]

Some patients without bronchiectasis have a 1.49:1 bronchus-to-artery ratio; however, the ratio is reliable only if it is greater than 1.5. If the ratio is less than 1.5, other signs, such as bronchial wall thickening and lack of tapering, should be present for the diagnosis of bronchiectasis.

Bronchial wall thickening is optimally seen with a WW of –1000 HU and a WL of –700 HU; higher WL and other WW readings are associated with artifactual wall thickening.^[17] This finding is not specific and is also seen in patients with asthma and in those who smoke.

False positives/negatives

The variability of the bronchus-to-artery ratio at high altitudes and in patients with pulmonary hypertension may result in an overdiagnosis because of vasoconstriction in these conditions.

In patients with consolidation, dilated bronchi may not be seen. Cardiac and respiratory artifacts may obscure the results or mimic subtle bronchiectasis in the left lower lobe. Rarely, histiocytosis X and cavitating pulmonary masses mimic cystic bronchiectasis. Traction bronchiectasis occurs in patients with interstitial fibrosis and results from fibrous tethering of the bronchial wall. Traction bronchiectasis is not a true bronchial disorder.

Hemoptysis is symptomatic of a potentially life-threatening condition and warrants urgent and comprehensive evaluation of the lung parenchyma, airways, and thoracic vasculature.

Multidetector-row CT angiography permits noninvasive, rapid, and accurate assessment of the cause and consequences of hemorrhage into the airways and helps guide subsequent management. The combined use of thin-section axial scans and more complex reformatted images allows clear depiction of the origins and trajectories of abnormally dilated systemic arteries that may be the source of hemorrhage and that may require embolization.

Bronchiectasis, chronic bronchitis, lung malignancy, tuberculosis, and chronic fungal infection are some of the most common underlying causes of hemoptysis and are easily detected with CT angiography.