41 Right Middle Lobe Syndrome

Clinical Presentation

An elderly woman with persistent cough and wheezing

Radiologic Findings

PA (Fig. 41.1A) chest exam demonstrates a vague opacity in the lower right thorax that obscures the heart border. The horizontal fissure is inferiorly displaced and the ipsilateral diaphragm is elevated. Subtle bronchiectasis is seen in the infrahilar region paralleling the right heart border. The cardiac silhouette is poorly defined on the lateral exam (Fig. 41.1B). A small pleural effusion blunts the posterolateral sulcus. The lungs are hyperexpanded, consistent with underlying obstructive lung disease. PA (Fig. 41.1C) and lateral (Fig. 41.1D) chest radiographs from two years earlier demonstrate similar imaging findings with respect to the right thorax. Contrast-enhanced chest CT (Figs. 41.1E, 41.1F, 41.1G; mediastinal window) reveal a triangular focal area of consolidated lung in the right middle lobe. The proximal bronchi are patent but irregular and distorted. The visualized middle lobe segmental bronchi are also bronchiectatic.

Diagnosis

Right Middle Lobe Syndrome (RMLS) Synonyms

• Brock Syndrome

• Middle Lobe Syndrome

• Shrunken Middle Lobe

Differential Diagnosis

• Middle Lobe Pneumonia

• Middle Lobe Obstruction Secondary to Primary or Secondary Endobronchial Neoplasia

Discussion

Background

Middle lobe syndrome is an uncommon lung disorder associated with recurrent atelectasis, pneumonias, or bronchiectasis of the right middle lobe, lingula, or both. It was originally thought that bronchial compression by inflamed peribronchial lymph nodes (e.g., tuberculous lymphadenitis) was responsible for the development of this syndrome. That theory has since been rejected. Most authors now believe this syndrome is related to relative isolation of the middle lobe from the remainder of the lung, especially in patients with a complete

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