Radiological Evaluation for ABPA
Perform thin-section chest CT (1.25-1.5 mm slice thickness) at baseline for all suspected ABPA cases to identify bronchiectasis, mucus plugging, and high-attenuation mucus, then use chest radiographs—not repeat CT scans—for treatment monitoring. 1
Baseline Imaging: Thin-Section Chest CT
Thin-section CT is mandatory at baseline with the following specifications: 1
- Slice thickness: 1.25-1.5 mm 1
- Contrast administration: CT angiography (with intravenous contrast) is recommended at baseline to visualize vessels and assess bronchiectasis extent 1
- Radiation consideration: In children, carefully weigh radiation exposure against diagnostic necessity 1, 2
Key CT Findings to Identify
Central bronchiectasis (bilateral, predominantly upper and middle lobes) is the hallmark finding: 1, 3
- Cylindrical or cystic bronchiectasis involving central airways 1
- Isolated central bronchiectasis is highly specific—seen primarily in ABPA and tracheobronchomegaly 1
- Present in approximately 78% of ABPA patients 3
High-attenuation mucus (HAM) is pathognomonic when present: 1
- Mucus visually denser than paraspinal muscles on non-contrast CT 1
- Sensitivity: 35%, Specificity: 100% 1
- Confirms ABPA diagnosis even if other criteria are incomplete 1, 4
- Must be assessed on mediastinal windows, not just lung windows 1
Mucus plugging (non-hyperattenuating): 1
- Seen in 59% of patients 3
- Associated with eosinophilic inflammation and immunologically severe ABPA 1
- "Finger-in-glove" appearance or mucoceles 1, 3
Additional findings that support diagnosis: 1, 3
- Centrilobular nodules with tree-in-bud pattern (86% of patients) 3
- Consolidation or fleeting opacities 1
- Atelectasis and mosaic attenuation 1
- Band shadows or parallel "tram lines" 2
Prognostic Value of Baseline CT
CT findings predict disease course: 1
- Extent of bronchiectasis independently predicts recurrent exacerbations 1
- Presence of HAM predicts recurrent exacerbations 1
- Fungal ball formation indicates higher risk of complications 1
Radiological Classification System
The 2024 ISHAM-ABPA Working Group established five CT-based categories: 1
- ABPA-S (Serological): No bronchiectasis 1
- ABPA-B (Bronchiectasis): Bronchiectasis present 1
- ABPA-MP (Mucus Plugging): Non-hyperattenuating mucus plugs; if both bronchiectasis and mucus plugging present, classify as ABPA-MP due to greater immunological severity 1
- ABPA-HAM: High-attenuation mucus present 1
- ABPA-CPF (Chronic Pleuropulmonary Fibrosis): Two or more of: pulmonary fibrosis, fibro-cavitary lesions, fungal ball, pleural thickening 1
Critical caveat: In ABPA-CPF, exclude chronic pulmonary aspergillosis complicating ABPA 1
Follow-Up Imaging Strategy
Use chest radiographs, not CT, for treatment monitoring: 1
- Chest radiographs assess treatment response adequately 1
- Minimizes cumulative radiation exposure, especially with multiple follow-ups 1
- Repeat CT only for: new hemoptysis, suspected treatment failure, or significant clinical deterioration 1
Timing of follow-up imaging: 1
Imaging Modalities NOT Recommended
Magnetic resonance imaging (MRI): 1
- Not routinely recommended despite being radiation-free 1
- No significant diagnostic advantage over readily available chest CT 1
PET scanning: 1
Common Pitfalls to Avoid
- Don't rely on chest radiographs for initial diagnosis—they miss bronchiectasis and mucus plugging that CT readily identifies 1
- Don't order serial CT scans for routine monitoring—this unnecessarily increases radiation exposure 1
- Don't overlook HAM on lung windows alone—always review mediastinal windows where HAM is best visualized 1
- Don't misinterpret central bronchiectasis as infectious—consider ABPA when central distribution is prominent 1
- Don't forget to assess for chronic pulmonary aspergillosis in patients with ABPA-CPF, as this changes management 1