Bronchiectasis

Jud W. Gurney, MD, FACR

Key Facts

Terminology

Irreversible bronchial dilatation usually associated with inflammation of bronchial wall

Imaging Findings

↑ Bronchoarterial ratio (signet-ring sign)
- B/A > 1 not specific, seen in elderly (> 65 years old) or those at high altitude (due to mild hypoxia that dilates bronchi and causes vasoconstriction)
Lack of bronchial tapering: Earliest and most sensitive sign of bronchiectasis
Acute pneumonia may result in pseudobronchiectasis (functional bronchiectasis)

Top Differential Diagnoses

Pneumonia
Chronic Bronchitis

Pathology

Integrity of bronchial wall dependent on normal immune system, normal structural integrity of airways (normal cartilage), and normal ciliary function
- Infection (most common etiology)
- Cystic fibrosis
- Allergic bronchopulmonary aspergillosis
- Chronic aspiration
- Toxic fume inhalation, especially ammonia
- Obstruction: Tumor, foreign body, or lymph node enlargement

Diagnostic Checklist

Central bronchial obstruction in patients with focal bronchiectasis

Axial graphic shows the major features of bronchiectasis, including bronchial dilatation and

bronchial wall thickening

Coronal HRCT shows saccular bronchiectasis

, more severe in the left lower lobe in this patient with postinfectious bronchiectasis.

TERMINOLOGY

Definitions

Irreversible bronchial dilatation usually associated with inflammation of bronchial wall

IMAGING FINDINGS

General Features

Best diagnostic clue: Bronchi diameter larger than adjacent pulmonary artery
Size: Cylindrical to varicose to saccular
Morphology: Bronchi can be filled with air, fluid, or mucus

CT Findings

Morphology: Direct
- Bronchial dilatation
  - ↑ Bronchoarterial ratio (signet-ring sign)
  - Normal bronchoarterial ratio (B/A) = 0.65-0.70
  - B/A > 1 not specific, seen in elderly (> 65 years old) or those at high altitude (due to mild hypoxia that dilates bronchi and causes vasoconstriction)
  - B/A > 1.5 indicative of bronchiectasis
- Contour abnormality: Cylindrical, varicose, saccular
  - Cylindrical bronchiectasis: Uniform diameter
  - Varicose bronchiectasis: “String of pearls,” alternating dilatation & narrowing
  - Saccular or cystic bronchiectasis: “Cluster of grapes,” marked dilatation, rounded
- Lack of bronchial tapering
  - Length of 2 cm distal to bifurcation
  - Earliest and most sensitive sign of bronchiectasis
- Visibility of peripheral airways within 1 cm of costal pleura
  - Normal airways may be visible within 1 cm of mediastinal pleura
Morphology: Indirect
- In bronchiectatic airways
  - Bronchial wall thickening
  - Mucoid impaction or fluid-filled bronchi
  - Bronchial artery hypertrophy
- Distal to bronchiectatic airways
  - Centrilobular nodules or tree-in-bud opacities
  - Mosaic perfusion (air-trapping on expiratory scan)
  - Atelectasis or pneumonia distal to bronchiectasis
  - Interlobular septal thickening (60%)
Distribution
- Focal or diffuse
  - Focal: Confined to 1 lobe, usually postinfectious or secondary to aspiration
  - Focal: May be due to central obstructive lesion (slow-growing tumor, broncholith, foreign body)
- Central bronchiectasis (normal peripheral airways)
  - Allergic bronchopulmonary aspergillosis
  - Tracheobronchomegaly
  - Williams-Campbell syndrome
- Upper lobe predominant bronchiectasis
  - Cystic fibrosis
  - Allergic bronchopulmonary aspergillosis
  - Tuberculosis
- Ventral bronchiectasis
  - Mycobacterial avium complex (Lady Windermere syndrome)
- Postinfectious (childhood)
  - Most commonly basilar segments of lower lobes, with relative sparing of superior and anterior basilar segments
  - Left lower lobe involved 2x as often as right lower lobe
Correlation with pulmonary function
- Extent of decreased attenuation most strongly correlated with decline in FEV₁
- Degree of bronchial wall thickness and extent of bronchiectasis also correlated with obstruction
- Degree of bronchial wall thickening main indicator of declines in pulmonary function over time
Accuracy of CT in determining etiology
- Correct diagnosis > 50% for cystic fibrosis, allergic bronchopulmonary aspergillosis, and tuberculosis

Radiographic Findings

Radiographic findings can be normal or nonspecific

Imaging Recommendations

Best imaging tool: CT much more sensitive than chest radiography
Protocol advice
- Acute pneumonia may result in pseudobronchiectasis (functional bronchiectasis)
  - Bronchi dilated but not destroyed in response to acute inflammation
  - Bronchial dilatation may persist for 3-4 months after acute pneumonia
  - CT investigation for bronchiectasis should be delayed 6 months following pneumonia to avoid pitfall of pseudobronchiectasis

Other Modality Findings

Bronchography obsolete

DIFFERENTIAL DIAGNOSIS

Pneumonia

Bronchi often dilated in consolidated lung from acute pneumonia
- Not true bronchiectasis; known as pseudobronchiectasis or functional bronchiectasis
- Bronchi will return to normal in 3-4 months

Chronic Bronchitis

Bronchial wall thickening, but morphology normal
May be precursor to bronchiectasis

Bronchial Atresia

Dilated, mucous-filled bronchus distal to atretic segment (bronchocele)
Associated with marked hyperlucency & hypoperfusion of involved segment
Interestingly, even though airway obstructed, distal airways are usually not bronchiectatic

Cystic Lung Disease

Bronchiectasis maybe confused for cystic lung disease
Tracing cysts, in continuity with airways, helps to differentiate the 2
Langerhans cell histiocytosis
- Irregular cysts can simulate bronchiectasis
- Predominantly located in upper lung zones
- Usually associated with solid nodules
Lymphangioleiomyomatosis
- Uniform distribution of cysts in young women
Laryngeal papillomatosis
- Airway nodules
- Combination solid & cystic lung nodules
- Cystic nodules may communicate with airways