CT Findings of Aspergilloma
The classic CT finding of aspergilloma is the "air-crescent sign" – a solid, round or oval intracavitary mass partially surrounded by a crescent of air, typically in the upper lobes 1.
Key Diagnostic Features
Primary CT Characteristics
The aspergilloma appears as:
- Solid mass with soft-tissue attenuation within a pre-existing lung cavity
- Upper lobe predominance (most common location)
- Mobile on positional changes (prone vs. supine imaging) when the classic air-crescent is present 1
- No contrast enhancement after IV contrast administration 1
Additional CT Findings
Beyond the classic air-crescent sign, aspergillomas demonstrate several other patterns:
Alternative Appearances:
- Fixed, immobile irregular sponge-work filling the cavity with air spaces (not the classic mobile ball) 1, 2
- Coarse irregular network of fungal strands with interstices, representing mats of fungal growth detached from the cavity interior 1
- Calcification within the fungal ball (flecks, dense nodules, or extensive throughout) 1
Associated Features:
- Adjacent pleural thickening (frequently observed) 1
- Thick-walled cavity with slightly irregular margins 1
- Dense extrapleural fat 1
Important Distinction: Halo Sign vs. Air-Crescent Sign
Critical caveat: The "halo sign" is NOT characteristic of aspergilloma. The halo sign (nodule surrounded by ground-glass attenuation) is a finding of invasive pulmonary aspergillosis in immunocompromised patients, representing hemorrhage around the nodule 3, 4, 5, 6. This is a completely different entity from aspergilloma.
The Two Signs:
- Air-crescent sign = aspergilloma (chronic pulmonary aspergillosis)
- Halo sign = invasive aspergillosis (acute, in immunocompromised hosts)
Diagnostic Approach
CT technique recommendations 1:
- Use narrow (3-mm) sections
- Apply bone algorithm
- Use wide window settings
- Obtain prone and supine positions to demonstrate mobility of the fungal ball
Early/forming aspergillomas show 1:
- Bumpy or irregular interior cavity appearance
- Fungal strands falling into the cavity lumen
- Initiating sponge-work pattern before mature ball formation
Differential Diagnosis Pitfalls
Aspergilloma can mimic:
- Necrotic lung carcinoma (most important mimic) 1
- Other intracavitary masses
The absence of contrast enhancement helps distinguish aspergilloma from vascular tumors 1.