Findings: chest radiographs show an RUL lesion with an air-fluid level. The lesion is clearly intrapulmonary because it has an upper wall (arrows) and the air-fluid level is about the same size in both projections. The main finding is an irregular mass protruding from the lateral wall of the cavity (red arrow). This finding strongly suggests a malignant process.
CT confirms the wall mass (red arrow). Additional criteria of malignancy are the numerous Kerley lines around the lesion. PET-CT images show enhancement of the wall and mediastinal lymph nodes (arrows).
Final diagnosis: infected squamous-cell carcinoma.
Congratulations to Dr. Amutha, who was the first to suggest the right diagnosis.
Teaching point: cavitated inflammatory masses may have irregular walls, but a localised wall mass is highly suspicious of malignancy.