A thick-walled cavity with an air–fluid level inside the lung: CT separates it from an empyema (lenticular, split pleura, compresses lung) because an abscess is treated with antibiotics and an empyema with drainage.
Orient first
- Abscess: spherical, thick irregular wall, acute angle with the chest wall, vessels end at it.
- Empyema: lenticular, thin smooth wall, split pleura sign, obtuse angle, displaces vessels.
- Aspiration risk (alcohol, dental disease, reduced consciousness) → posterior upper and superior lower lobe segments.
Acquire the study
- Contrast-enhanced CT chest; lung window and soft-tissue window.
The manoeuvre
- Soft-tissue window: wall thickness in mm, enhancing wall, surrounding consolidation.
- Shape and angle with the chest wall on axial and sagittal reformats.
- Split pleura sign (empyema) on the post-contrast series.
- Lung window: bronchus leading into the cavity; endobronchial obstruction (tumour).
What confirms it
- An intrapulmonary thick-walled cavity with an air–fluid level in an infected patient.
What licenses you to exclude it
- A lenticular pleural collection with a split pleura sign is empyema, not abscess.
The classic misread
- A cavitating squamous cell carcinoma called an abscess — a thick nodular wall and no resolution on follow-up.