Chest Computed Tomography (Chest CT)
Indications
Hounsfield Units
- Low Density by Hounsfield Units Measurement: -50 to -300 HU is consistent with fat
- Pure air or emphysema: -1000 HU
- Normal lung parenchyma: -750 HU
- Normal soft tissue and parenchymal lesions: around 10-70 HU
- Calcified lesions: >100-400 HU
- Bone: 1000 HU
Chest CT Differentiation: Empyema vs Lung Abscess
Empyema
CT Features of Empyema
- Angles: “Ball Under the Carpet” Appearance: obtuse angeles between fluid collection and chest wall
- Shape: lenticular shape
- Internal Surface: typically smooth internal surface of fluid collection
- Displacement: displacement of lung and mediastinum, as empyema pushes adjacent structures toward contralateral side
- “Split Pleura” Sign: separation of parietal and visceral pleura
- Air-Fluid Level: may be seen in cases with bronchopleural fistula (Bronchopleural Fistula, Bronchopleural Fistula)
CT Features of Lung Abscess
- Angles: acute angles between fluid collection and chest wall
- Shape: typically round shape
- Internal Surface: typically thick, irregular internal surface of fluid collection
- Displacement: lack of displacement of lung and mediastinum, as abscess tends to destroy adjacent lung, rather than displace it
- Air-Fluid Level: may be seen
References
