Lingula

1. Overview

The lingula is a tongue-like projection of the left upper lobe of the lung. It is considered the functional equivalent of the right middle lobe and plays a key role in facilitating lung movement and ventilation within the left hemithorax. Although small, the lingula contains its own bronchopulmonary segments and is clinically significant in infections and diagnostic imaging.

2. Location

The lingula is located in the left lung, specifically:

• As an anteroinferior extension of the superior (upper) lobe

• Inferior to the cardiac notch, adjacent to the heart

• Anterior to the oblique fissure

It lies just above the left lower lobe, and during respiration, it moves within the costomediastinal recess of the pleura.

3. Structure

The lingula consists of two distinct bronchopulmonary segments:

• Superior segment of the lingula

• Inferior segment of the lingula

These segments are supplied by:

• A lingular bronchus—a branch of the left upper lobe bronchus

• Branches of the pulmonary artery and vein that are segmental in nature

The lingula is lined by respiratory epithelium and shares the same histological features as the rest of the lung parenchyma, including alveoli, bronchioles, and capillary networks.

4. Function

While the lingula does not serve a separate function from the rest of the lung, it contributes to:

• Gas exchange: Participates in oxygen and carbon dioxide exchange through its alveolar surfaces

• Lung expansion: Its shape allows for increased flexibility and movement of the left lung during breathing

• Compensatory lobe function: Functionally mimics the right middle lobe, which is absent on the left side due to the position of the heart

5. Physiological Role(s)

The lingula plays a supportive role in pulmonary physiology:

• Ventilation-perfusion matching: Like other lung segments, the lingula maintains local airflow and blood flow balance

• Dynamic expansion: Its location near the cardiac notch allows the lingula to move freely during inspiration, helping to fill anterior thoracic space

• Mucociliary clearance: Helps eliminate mucus and debris via ciliary action, just like other bronchopulmonary segments

6. Clinical Significance

Lingular Pneumonia

Due to its dependent location and relatively narrow bronchial opening, the lingula is susceptible to infection and consolidation. Lingular pneumonia may present similarly to middle lobe pneumonia on the right, with:

• Cough

• Pleuritic chest pain

• Localized crackles or diminished breath sounds

Chest X-ray or CT scan confirms the diagnosis.

Atelectasis

The lingula may be involved in segmental atelectasis due to poor ventilation, mucus plugging, or external compression (e.g., from cardiomegaly). This can present with:

• Reduced breath sounds

• Volume loss on imaging

• Dyspnea if significant

Lingular Masses or Nodules

Pulmonary nodules or tumors in the lingula may mimic left lower lobe pathology and require careful imaging to localize. Biopsy or bronchoscopy may be needed for diagnosis.

Bronchiectasis

The lingula is a common site of localized bronchiectasis, especially in chronic inflammatory or infectious conditions such as:

• Cystic fibrosis

• Non-tuberculous mycobacterial infections

CT scan typically shows dilated bronchi with thickened walls in lingular segments.

Surgical Resection

Lingular segmentectomy may be performed for localized disease. It’s surgically treated like a lobe and is important in lung-sparing procedures.