Right Middle Lobe Syndrome

General Considerations

• Definition varies
• Usually refers to any cause of recurrent or persistent atelectasis of the right middle lobe
• Occurs at all ages but most common at two peaks: in children and over 50
  • Reportedly more common in women than men
• Originally thought to be due only to bronchial obstruction, but it is more often present with non-obstructive lesions
  • Some believe the right middle lobe is more often involved because of its isolation and poor collateral flow from the upper and lower lobes
• Etiologies include
  • Inflammatory disease is the most common etiology
• In children, it is most common in association with asthma
• Malignant tumors (22%0
• Bronchiectasis (15%)
• Tuberculosis (9%)
• Benign tumors (2%)
• In most cases, the etiology is never found

Clinical Findings

• Most often asymptomatic
• Cough
• Wheezing
• Dyspnea

Imaging Findings

• Right middle lobe atelectasis is usually easier to recognize on the lateral view than the frontal view, where it may produce very subtle findings
• Silhouetting of the right heart border on the frontal view by the adjacent un-aerated medial segment of the middle lobe
  • If the atelectatic middle lobe swings upward and anteriorly, it may produce a wedge-shaped density on the frontal view with its base at the heart
• Depression of the minor fissure and elevation of the major fissure, especially well seen on the lateral view
  • On the lateral view, the atelectatic lobe forms a triangular density with its apex at the hilum and its base more peripheral in the lung
• If there is a nodular density seen at the apex of the triangle on the lateral view, suspect a mass in the hilum producing the atelectasis
• Elevation of the right hemidiaphragm may occur
• CT is useful in excluding a cause of bronchial obstruction
  • Middle lobe bronchus enters consolidated lobe in the posteromedial corner

Differential Diagnosis

• Middle lobe pneumonia

Treatment

• Depends on etiology
• Most are treated with medical therapy alone

Prognosis

• Cases in about 1/3 of pediatric patients resolve after bronchoscopy

Right Middle Lobe Syndrome. Chest images at top are taken 3 months before images on bottom. Both show middle lobe atelectasis with silhouetting of the right heart border on the frontal view (white arrows) and a wedge-shaped density on the lateral with a depressed minor fissure (yellow arrows).
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Middle Lobe Syndrome Due To Tuberculous Etiology: A Series Of 12 Cases.

Gupta1, P; Gupta, K and Agarwal, D.  Indian J Tuberc 2006; 53:104-108

Diagnostic thoracic imaging By Wallace T. Miller. McGraw-Hill Professional, 2006