What are the divisions of the mediastinum and their corresponding surface landmarks?

Divisions of the Mediastinum and Surface Landmarks

The mediastinum is best divided into three compartments (prevascular, visceral, and paravertebral) based on cross-sectional imaging, which better reflects anatomical relationships visible on modern imaging techniques. 1

Modern Three-Compartment Classification

• Prevascular (Anterior) Compartment:

  • Located posterior to the sternum and anterior to the heart and brachiocephalic vessels 2
  • Extends from thoracic inlet to diaphragm 2
  • Contains thymus gland, fat, and lymph nodes 2
  • Primary site for thymic epithelial tumors, germ cell tumors, and lymphomas 1
  • Surface landmarks: Posterior to sternum, anterior to pericardium 2

• Visceral (Middle) Compartment:

  • Contains vital structures including heart, great vessels, trachea, and esophagus 1
  • Most common lesions are benign cysts 1
  • Surface landmarks: Between anterior and posterior axillary lines 3
  • The anterior axillary line is marked by the intersection of the posterior border of Pectoralis Major and the 2nd rib 3
  • The posterior axillary line is marked by the posterior border of Pectoralis Major 3

• Paravertebral (Posterior) Compartment:

  • Located adjacent to the vertebral column 4
  • Surface landmarks: Posterior to posterior axillary line 3
  • Can be defined as 2/3rds of the circumference between the costochondral junction and the costotransverse joint 3

Traditional Classification Systems

• Four-Compartment Model (still commonly used):

  • Superior mediastinum: Above the upper level of the pericardium 4
  • Anterior mediastinum: Below the superior mediastinum and anterior to the pericardium 4
  • Middle mediastinum: Contains heart and great vessels 4
  • Posterior mediastinum: Behind the heart to the vertebral column 4

• Surface Landmarks for Traditional Model:

  • Superior mediastinum: From thoracic inlet to the upper level of pericardium 2
  • Anterior mediastinum: From sternal angle to xiphoid process, anterior to heart 2
  • Middle mediastinum: Between anterior and posterior mediastinum, contains heart 5
  • Posterior mediastinum: From posterior heart to vertebral column 5

Clinical Significance of Mediastinal Divisions

• The traditional compartmentalization based on projection radiographs can lead to confusing interdisciplinary communication 6
• The three-dimensional classification proposed by ITMIG (International Thymic Malignancy Interest Group) better suits modern clinical workflow and promotes standardization 6
• Knowledge of mediastinal compartments is essential for diagnostic imaging interpretation and surgical approaches 4

Important Anatomical Landmarks for Mediastinal Access

• Suprasternal Notch View: Placing the probe in the suprasternal notch, directed inferiorly into the mediastinum allows visualization of the aortic arch and great vessels 3
• Parasternal Approach: Awareness of internal mammary vessels is crucial for safely performing this approach 3
• Mediastinoscopy Access: Provides access to lymph nodes in the visceral compartment but cannot access the paravertebral compartment or anterior mediastinal (station 6) nodes 3

Imaging Considerations for Mediastinal Assessment

• CT chest with contrast is the primary imaging modality for evaluating mediastinal masses 1
• MRI provides additional tissue characterization that may prevent unnecessary biopsies 1
• PET-CT can help differentiate between benign and malignant disease 1

Common Pitfalls and Caveats

• There is no universally accepted nomenclature to describe the exact borders of each region of the mediastinum 3
• The CWIS (Chest Wall Injury Society) has proposed various methods for defining boundaries, but standardization is still needed 3
• Muscle markings used as landmarks do not run in vertical lines and may be difficult to visualize on CT scans, particularly at the lower chest 3
• For surgical approaches, understanding the relationship between surface landmarks and underlying structures is crucial to avoid damage to vital structures 3