Congenital Lobar Overinflation (CLO), formerly known as Congenital Lobar Emphysema, is a rare respiratory malformation characterized by the hyperinflation of one or more pulmonary lobes. Despite the old nomenclature, there is no actual destruction of alveolar walls; rather, it is a functional “air-trapping” mechanism, often due to bronchial cartilage deficiency.
Quick Clinical Summary for Radiologists
- Most Common Site: Left Upper Lobe (approx. 40-50%).
- Key Finding: Hyperlucency of the affected lobe with mass effect (mediastinal shift).
- Primary Differential: Pneumothorax (Look for the presence of lung markings!).
1. Pathophysiology and Epidemiology
CLO is typically diagnosed in the neonatal period, though mild cases may appear in older infants. It is twice as common in males. The condition arises from a “check-valve” mechanism: air enters during inspiration but cannot escape during expiration, leading to progressive lobar distension.
- Left Upper Lobe (LUL): 42%
- Right Middle Lobe (RML): 35%
- Right Upper Lobe (RUL): 21%
2. Radiographic Features: What to Look For
The imaging appearance of CLO evolves depending on the age of the patient and the timing of the scan.
Chest X-ray (CXR) Findings
- Early Phase (Birth): The affected lobe may appear opaque or hazy because it is still filled with fetal lung fluid that hasn’t cleared.
- Classical Phase: A hyperlucent, overdistended lobe.
- Mass Effect: Look for depression of the ipsilateral diaphragm and herniation of the lung across the midline (mediastinal shift).
- Vascularity: Unlike a pneumothorax, bronchovascular markings are visible within the hyperlucent area, extending to the periphery.
Computed Tomography (CT) Features
CT is the gold standard for surgical planning and confirming the diagnosis.
- Lobar Expansion: Identifying exactly which lobe is affected.
- Vessel Attenuation: Pulmonary vessels in the affected lobe appear small and stretched.
- Etiology Check: CT can identify extrinsic causes like a bronchogenic cyst or anomalous vessel (e.g., pulmonary artery sling) compressing the bronchus.
3. Differential Diagnosis Table
To rank for “CLO vs Pneumothorax,” this structured comparison is essential:
| Feature | Congenital Lobar Overinflation | Tension Pneumothorax |
| Lung Markings | Present (stretched/thin) | Absent |
| Edge of Lung | No visible pleural line | Visible visceral pleural line |
| Heart/Mediastinum | Shifted away from the lesion | Shifted away from the lesion |
| Diaphragm | Flattened or inverted | Flattened or inverted |
Pro Tip: In the neonatal ICU, mistaking CLO for a tension pneumothorax can lead to the dangerous insertion of a chest tube into healthy lung tissue. Always check for those fine vascular markings.
4. Antenatal Ultrasound and MRI
With advances in fetal imaging, CLO is increasingly picked up in utero.
- Ultrasound: Appears as a hyperechoic mass within the fetal lung.
- Fetal MRI: Useful for calculating the Lung-to-Head Ratio (LHR) to predict neonatal respiratory distress severity.
5. Management and Prognosis
Management ranges from “watchful waiting” in asymptomatic cases to lobectomy for infants with severe respiratory distress. Most patients have an excellent prognosis following the removal of the affected lobe, as the remaining lung tissue undergoes compensatory growth.
