Presentation
An incidental CT scan finding.
Patient Data
Although slightly distorted by motion artifact, these images show a well formed cavitary lesion at the left lower lung lobe, at the dependent portion of which lies a soft tissue mass. A rim of gas is seen around the lesion and fibrotic changes surround the cavity.
A nodule is seen at the right middle lung lobe.
Both lungs show diffuse ground glass opacity.
Case Discussion
Aspergilloma (fungus ball) is what Aspergillus fumigatus causes in the immunocompetent individual with abnormal lungs, whether it is due to a cavity of previous TB, sarcoidosis, bronchiectasis, etc.
Monad sign is what describes the air that surrounds the soft tissue mass. Remember that the fungus ball is mobile, so that on an erect chest x-ray, the mass will be inferior and the gas rim is superior.