What are the typical CT (Computed Tomography) scan findings in a patient with suspected aspergilloma, particularly in those with pre-existing lung disease or an immunocompromised state?

CT Scan Findings in Aspergilloma

The classic CT finding of aspergilloma is a mobile mass with soft-tissue attenuation within a pre-existing lung cavity, separated from the cavity wall by an airspace creating the characteristic "air crescent sign" or "meniscus sign." 1, 2

Primary Imaging Modality

• CT scan (preferably high-resolution CT with contrast) is the imaging modality of choice for diagnosing aspergilloma, providing superior definition and localization compared to chest radiographs 1, 2
• Intravenous contrast administration (CT-angiography) is required at baseline, particularly to evaluate vascular structures and is essential if hemoptysis is present 1, 2
• Chest radiographs remain useful for initial suspicion but have limited sensitivity for definitive diagnosis 2

Classic CT Findings

The Mobile Aspergilloma

• Round or oval mass with soft-tissue attenuation within a pre-existing lung cavity 3, 4
• Air crescent sign (meniscus sign): airspace of variable size and shape separating the fungal mass from the cavity wall 3, 4, 5
• Mobility is easily demonstrated by obtaining images in both supine and prone positions, confirming the mass moves with gravity 5
• Thickening of the cavity wall and adjacent pleura is commonly associated 3

The Fixed Aspergilloma

• Irregular spongework pattern containing multiple air spaces filling the cavity, which obliterates the classic air crescent sign 5
• This appearance represents a fixed, immobile fungus ball 5
• Forming aspergillomas show fungal strands falling into the cavity lumen, trapping air and creating the initial sponge-work appearance 5

Technical Imaging Parameters

• Use narrow (3-5 mm) sections with a bone algorithm and wide window settings to accurately identify both forming and mature aspergillomas 5
• Sections should be obtained every 5-10 mm through the thorax 6
• Lateral mobilizations (prone and supine positioning) help demonstrate mobility of the fungal ball 6, 5

Associated Findings

• Pre-existing cavitary lung disease is almost always present (from tuberculosis, sarcoidosis, COPD, prior pneumothorax, or treated lung cancer) 1
• Pleural thickening adjacent to the cavity 3
• Upper lobe predominance is common, reflecting the typical location of underlying cavitary disease 1
• Small aspergillomas can be identified that may be missed on conventional radiography 6

Important Caveats

• The air crescent sign is not specific for aspergilloma and can be mimicked by pulmonary hydatid cyst, Rasmussen aneurysm, pulmonary gangrene, intracavitary clot, textiloma, lung cancer, metastasis, and teratoma 4
• CT can help rule out fibrotic lesions previously attributed to mycetomas on conventional X-ray 6
• The classic mobile fungus ball appearance is not the only definitive criterion—fixed sponge-work patterns are equally diagnostic in the appropriate clinical context 5
• No CT technique is 100% sensitive or specific, and correlation with Aspergillus IgG antibodies (positive in >90% of cases) is essential for confirmation 1, 2

Diagnostic Confirmation

• CT findings must be combined with positive Aspergillus IgG or precipitins testing for definitive diagnosis 1, 2
• Virtually all patients with aspergilloma have serum precipitating antibodies to Aspergillus antigens 7
• Bronchoscopy with bronchoalveolar lavage should be performed if clinically indicated, with samples sent for culture and galactomannan testing 2

Follow-up Imaging

• Follow-up CT scans should be obtained after a minimum of 2-3 months of treatment to assess response 2
• Low-dose CT protocols should be used for serial imaging to minimize radiation exposure 1