What are the divisions of the mediastinum?

Divisions of the Mediastinum

The mediastinum is divided into three compartments according to the American College of Radiology: prevascular (anterior), visceral (middle), and paravertebral (posterior) compartments, which better reflect anatomical relationships visible on cross-sectional imaging. 1

Modern Three-Compartment Classification

• The prevascular (anterior) compartment contains the thymus gland and is the primary site for thymic epithelial tumors, germ cell tumors, and lymphomas, with thymomas being the most common lesion (28%) 1
• The visceral (middle) compartment contains vital structures including the heart, great vessels, trachea, esophagus, and lymph nodes 1
• The paravertebral (posterior) compartment is located posterior to the posterior axillary line and can be defined as 2/3rds of the circumference between the costochondral junction and the costotransverse joint 1

Surface Landmarks and Boundaries

• The visceral (middle) compartment is located between the anterior and posterior axillary lines 1
• The anterior axillary line is marked by the intersection of the posterior border of Pectoralis Major and the 2nd rib 1
• The posterior axillary line is marked by the posterior border of Pectoralis Major 1
• There is no universally accepted nomenclature to describe the exact borders of each region of the mediastinum 1

Traditional Four-Compartment Classification

While the three-compartment model is now preferred, some sources still reference the traditional four-compartment model:

• Superior mediastinum: located above the upper level of the pericardium 2
• Anterior mediastinum: region posterior to the sternum and anterior to the heart and brachiocephalic vessels 2
• Middle mediastinum: contains the heart, great vessels, trachea, and esophagus 3
• Posterior mediastinum: extends from the posterior pericardium to the vertebral column 3

Clinical Significance

• The superior mediastinum contains vital structures including the thymus gland, great vessels, trachea, esophagus, thoracic duct, vagus and phrenic nerves, and lymph nodes 4
• Understanding mediastinal compartments is crucial for:
  • Differential diagnosis of mediastinal masses 5
  • Planning surgical approaches 6
  • Accurate staging of lung cancer 7
  • Avoiding damage to vital structures during interventions 1

Imaging Considerations

• CT chest with contrast is the primary imaging modality for evaluating mediastinal masses 1, 4
• MRI provides superior soft tissue contrast for assessing invasion of mediastinal structures 4
• PET-CT helps in metabolic assessment of mediastinal masses and lymph nodes 4

Surgical Approaches

• Mediastinoscopy provides access to lymph nodes in the visceral compartment but cannot access the paravertebral compartment or anterior mediastinal (station 6) nodes 1
• Complete resection with appropriate lymphadenectomy is crucial for optimal outcomes in mediastinal tumors 4
• Surgical approaches trend toward minimally invasive, video- or robotic-assisted techniques 6

The three-compartment classification (prevascular, visceral, and paravertebral) is increasingly preferred over the traditional four-compartment model as it better aligns with modern cross-sectional imaging techniques and promotes standardized communication between specialists 8.