Right Middle Lobe Syndrome

Jonathan H. Chung, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Recurrent or chronic atelectasis of right middle lobe &/or lingula
Due to extrinsic compression, central obstruction, or peripheral obstruction
- Peripheral obstruction from lack of collateral ventilation due to complete fissures hampering clearance of secretions during coughing
60% benign etiology (e.g., tuberculous stricture, nodal compression)

Helpful Clues for Common Diagnoses

Middle Lobe Syndrome
- Chronic or recurrent volume loss in right middle lobe or lingula; often associated with bronchiectasis
- Triangular opacity, which silhouettes right heart border on frontal chest radiograph
- Wedge-shaped opacity overlying heart on lateral chest radiograph
- CT may demonstrate endobronchial mass, lymph node, or broncholithiasis obstructing proximal bronchus
Pneumonia (Mimic)
- Ground-glass opacities to dense consolidation within right middle lobe or lingula
- Reactive lymphadenopathy; very large lymph nodes unusual
- Parapneumonic pleural effusion or empyema
Atelectasis (Mimic)
- Volume loss in right middle lobe or lingula
- In acute setting, most often due to central mucous plugging or aspirated material
- Similar imaging findings as in middle lobe syndrome
- Mild reversible dilation of airways; not as severe as bronchiectasis in middle lobe syndrome

Helpful Clues for Less Common Diagnoses

Pectus Excavatum (Mimic)
- Sternum depressed posterior to anterior ribs
- Right heart border obliterated as sternum displaces lung from right heart border
- Cardiac displacement and rotation may give false appearance of cardiomegaly