Findings, Diagnosis & Discussion

Findings:
1. Central bronchiectasis with peribronchial thickening.
2. "Finger-in-glove" mucous plugging.
3. Alveolar infiltrates, right upper lobe.

Diagnosis: Allergic Bronchopulmonary Aspergillosis (ABPA)

Discussion: Aspergillus fumigatus is a ubiquitous saprophyte that causes a wide array of diseases in humans, including infestations (aspergillomas), allergic reactions, and invasive disease. Pulmonary involvement classically occurs in four forms:

1. Allergic bronchopulmonary aspergillosis.
2. Saprophytic aspergillosis: noninvasive aspergillomas that colonize pre-existing cavities.
3. Chronic Necrotizing Aspergillosis: chronic cavitary infection most often affecting patients with chronic lung disease. Also called airway-invasive or semi-invasive aspergillosis.
4. Angioinvasive aspergillosis: Affects immunocompromised hosts, often fatal.

ABPA differs from other forms of pulmonary aspergillosis in that the organism remains confined within the bronchial lumen. Presence of the organism in susceptible individuals incites a complex immune response, with Type I, type III, and type IV hypersensitivity reactions believed to be involved. Immune complexes are deposited within the bronchial mucosa, leading to bronchial damage, bronchiectasis, and mucous plugging.

ABPA typically occurs in patients with asthma or cystic fibrosis. Prompt diagnosis is essential, as delay in diagnosis can lead to irreversible lung damage and fibrosis. Diagnostic criteria include asthma, peripheral eosinophilia, elevated IgE, positive skin test results for A fumigatus, elevated IgE and IgG specific for A fumigatus, and precipitating antibodies to A fumigatus. Treatment is with oral corticosteroids.

Chest radiographs in patients with ABPA may demonstrate fleeting alveolar infiltrates, usually bilateral and predominantly in the upper lobes. Central bronchiectasis and bronchial wall thickening may be evident on plain radiographs, and are the most common findings on CT. High attenuating mucoid impaction is a more specific finding, seen in 30% of patients. Mucoid plugging has been described as "finger-in-glove", rabbit ears, or Mickey Mouse opacities. High resolution CT may demonstrate a tree-in-bud appearance, representing mucous plugging of small airways.

References

1. Prachi, P et al. Answer to Case of the Month #108, Allergic Bronchopulmonary Aspergillosis. JACR April 2006; vol 57, no 2: 120-123

2. Khan, Ali Nawaz. Aspergillosis, Thoracic. E-Medicine, http://www.emedicine.com/radio/topic55.htm. July 28, 2005.

3. Webb, W. Richard. Thoracic Imaging: Pulmonary and Cardiovascular Radiology. Lippincott Williams & Wilkins. 2004.

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