Allergic Bronchopulmonary Aspergillosis

Gerald F. Abbott, MD

Key Facts

Terminology

Chronic airway inflammation and injury from colonization and sensitization by Aspergillus fumigatus and related species

Imaging Findings

Central bronchiectasis and mucoid impaction in asthmatic patient
Mucoid impaction may have higher attenuation than soft tissue in 30%
Migratory fleeting pulmonary opacities may be seen early, before development of bronchiectasis
Bronchiectasis in 3 or more lobes in asthmatics highly suggestive of ABPA
Confident diagnosis of ABPA in 90% of patients with eosinophilic lung disease

Top Differential Diagnoses

Cystic Fibrosis
Asthma
Congenital Bronchial Atresia

Pathology

1-2% of asthmatic patients have ABPA
10% of patients with cystic fibrosis have ABPA

Clinical Issues

Recurrent ABPA may result in widespread bronchiectasis and fibrosis
Oral corticosteroids treatment of choice
Serial measurement of serum IgE useful to monitor response to therapy
ABPA may recur in patients with cystic fibrosis who have had lung transplantation

Axial HRCT shows cylindrical bronchiectasis of the segmental and subsegmental bronchi of the right upper lobe and mucoid impaction manifesting as a nodular opacity

Axial HRCT shows cylindrical and mild varicose bronchiectasis of the segmental and subsegmental bronchi of the right upper lobe with airway wall thickening

TERMINOLOGY

Abbreviations and Synonyms

Allergic bronchopulmonary aspergillosis (ABPA)

Definitions

Chronic airway inflammation and injury from colonization and sensitization by Aspergillus fumigatus and related species
Hypersensitivity reaction that occurs almost exclusively in patients with asthma and cystic fibrosis

IMAGING FINDINGS

General Features

Best diagnostic clue: Central bronchiectasis and mucoid impaction in asthmatic patient
Patient position/location
- Central bronchiectasis (may spare peripheral airways)
- Predominantly upper lobes

CT Findings

Bronchiectasis (95%)
- Bronchiectasis ranges from cylindrical (early) to saccular (advanced)
- May be air-filled or filled with soft tissue (mucoid impaction)
- Y- or V-shaped tubular opacities emanating from hilum
Mucoid impaction (70%)
- Homogeneous tubular &/or branching “finger-in-glove” opacities
- Mucoid impaction may have higher attenuation than soft tissue (30%)
- Centrilobular nodules, tree-in-bud opacities in distal lung (90%)
- May contain air-fluid levels
- Distal lung (curiously) usually remains aerated rather than collapsed
Eosinophilic pneumonia
- Migratory fleeting pulmonary opacities may be seen early, before development of bronchiectasis
Associated findings
- Areas of consolidation, ground-glass opacity due to pneumonia or atelectasis distal to airway obstruction
- Pleural effusions absent
- Lymphadenopathy, mild in 5%
Location
- Zonal distribution of bronchiectasis
  - Upper lobes (50%)
  - Lower lobes (20%)
  - Random (30%)
- Axial distribution of bronchiectasis
  - Central (60%)
  - Random (30%)
  - Peripheral (10%)
- Mainly involves segmental and subsegmental bronchi
- Bronchiectasis in 3 or more lobes in asthmatics highly suggestive of ABPA
Observer accuracy
- Confident diagnosis of ABPA in 90% of patients with eosinophilic lung disease

Radiographic Findings

Radiography: May be normal

Imaging Recommendations

Best imaging tool: CT much more sensitive for bronchiectasis

DIFFERENTIAL DIAGNOSIS

Cystic Fibrosis

ABPA seen in 10% of patients with cystic fibrosis
Usually younger
Positive sweat chloride skin test
Distribution of bronchiectasis identical

Asthma

Mucoid impaction may be seen in absence of ABPA
Mild cylindrical bronchiectasis may also be seen in asthma alone
ABPA needs to be excluded

Endobronchial Neoplasm

Mucoid impaction usually seen only with slow-growing tumors
- Carcinoid or benign tumors such as hamartomas
Usually unilateral in single lobar or segmental distribution

Congenital Bronchial Atresia

Likely sequela of vascular insult to lung during early fetal development
Thin membranous point of atresia; normal airway distal to atresia
Segmental bronchus does not communicate with central airway
Mucocele develops distal to point of obstruction; round, ovoid, or tubular opacity that may be branching
Often misdiagnosed as arteriovenous malformation
Apical posterior segment of left upper lobe most common but may occur in any part of lung
Difficult to distinguish from ABPA
- Look for
  - Wedge-shaped area of hyperinflation of lung with decreased vascular markings surrounding mucocele
  - No history of allergies or cystic fibrosis

Primary Ciliary Dyskinesia

Characterized by immotile or dyskinetic cilia; leads to poor mucociliary clearing and development of bronchiectasis
Other manifestations include hearing loss and male infertility
Dextrocardia in patients with Kartagener syndrome

Airway Obstruction from Foreign Body

Look for radiopaque foreign body or broncholith
Unilateral distribution in single segment or lobe

Bronchocentric Granulomatosis

Rare hypersensitivity lung disease may be caused by Aspergillus species
Can be seen with ABPA or separate from it as response to infection with Mycobacterium, other fungi, or Echinococcus
Distal airway lumen replacement by necrotizing granulomas
Imaging similar to ABPA, may predominantly affect more distal airway
Can have focal mass or lobar consolidation with atelectasis