What is a left hemithorax?

Left Hemithorax: Anatomical Definition and Clinical Significance

The left hemithorax refers to the left half of the thoracic cavity, containing the left lung, pleural space, and associated structures on the left side of the chest wall.

Anatomical Components

The left hemithorax consists of several key anatomical structures:

• Boundaries:

  • Anteriorly: Sternum and costal cartilages
  • Posteriorly: Vertebral column
  • Laterally: Ribs and intercostal muscles
  • Inferiorly: Left hemidiaphragm
  • Medially: Mediastinum
  • Superiorly: Thoracic inlet/superior thoracic aperture

• Contents:

  • Left lung (typically with 2 lobes, unlike the right with 3)
  • Left pleural space (potential space between visceral and parietal pleura)
  • Left side of the heart and great vessels
  • Left phrenic nerve
  • Left vagus nerve
  • Left pulmonary vessels
  • Thoracic duct (in parts)

Clinical Significance

Imaging Assessment

1. Ultrasound Evaluation:

   • Used to assess for pleural effusion, hemothorax, or pneumothorax
   • In the left upper quadrant view (perisplenic view), four potential spaces are examined: pleural space, subphrenic space, splenorenal space, and inferior pole of the kidney 1
   • Provides a more limited window than the right side due to the smaller size of the spleen compared to the liver 1

2. CT Imaging:

   • For optimal imaging of the left hemithorax, thin-section (1-2 mm) reconstructions in axial, coronal, and sagittal planes are recommended 1
   • The entire chest wall and complete pleural spaces should be included in the field of view, extending caudally to at least L3 level to ensure coverage of the posterior costophrenic sulcus 1

Pathological Conditions

1. Hemothorax:

   • Collection of blood in the left pleural space, often due to trauma
   • Visualized on imaging as anechoic or hypoechoic collections above the diaphragm 1
   • May require tube thoracostomy for drainage 2

2. Pneumothorax:

   • Air in the pleural space causing lung collapse
   • Absence of pleural sliding on ultrasound indicates pneumothorax 1

3. Malignancy:

   • Malignant pleural mesothelioma may involve the left hemithorax
   • Can present with direct extension into chest wall, invasion of diaphragm, or pleural effusion 1
   • CT imaging with IV contrast is essential for evaluation 1

4. Cardiac Trauma:

   • Left hemithorax injuries may involve cardiac structures due to proximity
   • CT chest with IV contrast can identify cardiac injuries such as chamber rupture or pericardial effusion 1

Clinical Evaluation

When examining the left hemithorax:

• Physical examination: Assess for decreased breath sounds, dullness to percussion, or asymmetric chest wall movement
• Imaging: Start with chest radiography, followed by more detailed imaging as needed:
  • Ultrasound: Particularly useful for fluid collections and real-time assessment 1, 3
  • CT: Gold standard for comprehensive evaluation of the hemithorax 1

Interventional Considerations

• Pleural procedures: When performing procedures on the left hemithorax (biopsies, drainage):

  • Position the patient appropriately (prone or supine) to reduce risk of air embolism 1
  • Be aware of the anatomical differences from the right side, including heart proximity
  • Monitor for complications including pneumothorax, hemothorax, and air embolism 1

• Surgical approaches: May require specific considerations for left-sided thoracic procedures:

  • Single-lung ventilation with a double-lumen endotracheal tube may facilitate surgical exposure 1
  • Left main bronchus may be compressed by large descending thoracic aortic aneurysms 1

Understanding the anatomy and pathology of the left hemithorax is essential for accurate diagnosis and management of thoracic conditions.