A hyperlucent hemithorax refers to increased radiolucency (blackness) of one side of the chest compared with the other. It’s a descriptive finding, not a diagnosis, and may result from technical, pulmonary, or vascular causes.
⚙️ Step 1: Confirm It’s Real — Technical Factors
Before labeling a true hyperlucency, rule out artifacts.
- Rotation – Apparent hyperlucency on the side turned closer to the film.
- Underexposure/overexposure – May falsely alter lucency.
- Unilateral mastectomy – Loss of soft tissue shadow increases apparent lucency.
🫧 Step 2: Classify True Hyperlucency Causes
A. Pulmonary Causes
➡️ Unilateral emphysema / bullous disease
- Hyperexpanded lung, ↓ vascular markings, flattened diaphragm.
➡️ Swyer–James–MacLeod syndrome (post-infectious bronchiolitis obliterans)
- Small lung, ↓ vascularity, air trapping on expiratory film.
- Often follows childhood infection.
➡️ Pneumothorax
- Absence of lung markings beyond visceral pleural line.
- May show mediastinal shift if tension pneumothorax.
➡️ Obstructive hyperinflation (check-valve mechanism)
- Mediastinal shift to opposite side, depressed ipsilateral diaphragm, ↑ intercostal spaces.
- Seen in foreign body bronchial obstruction, mucus plug, or tumor.
B. Vascular Causes
➡️ Pulmonary artery hypoplasia or thrombosis
- Normal lung volume but decreased vascular markings.
- No evidence of air trapping.
C. Chest Wall Causes
➡️ Poland syndrome – Absence of pectoralis muscles.
➡️ Mastectomy / large breast asymmetry – Less overlying soft tissue increases lucency.
📊 Summary Table
| Category | Example | Key CXR Finding |
|---|---|---|
| Technical | Rotation, exposure | Apparent difference only |
| Pulmonary | Emphysema, pneumothorax, Swyer-James | Reduced vascularity, air trapping |
| Vascular | Pulmonary hypoplasia/thrombosis | Decreased vessel markings, normal volume |
| Chest wall | Mastectomy, Poland syndrome | Soft tissue loss increases lucency |
🧠 Teaching Pearls
- Always compare lung volumes, vascularity, and mediastinal position.
- A true hyperlucent lung will have fewer vascular markings.
- Use expiratory films or CT to confirm air trapping.
