What are the divisions of the mediastinum?

Divisions of the Mediastinum

The mediastinum is currently divided into three compartments: prevascular, visceral, and paravertebral—these modern terms have replaced the traditional anterior, middle, and posterior designations to better reflect anatomical relationships visible on cross-sectional imaging.1, 2

Modern Three-Compartment Classification

Prevascular (Anterior) Compartment

• Located posterior to the sternum and anterior to the heart and brachiocephalic vessels 3
• Extends from the thoracic inlet to the diaphragm 3
• Contains the thymus gland, fat, and lymph nodes 3
• Most common lesions include thymomas (28%), benign cysts (20%), and lymphomas (16%) 1
• Primary site for thymic epithelial tumors, germ cell tumors, and lymphomas 4

Visceral (Middle) Compartment

• Contains vital structures including the heart, great vessels, trachea, and esophagus 5
• Benign cysts are the most common lesions in this compartment 1
• Includes lymph node stations accessible via mediastinoscopy (stations 2R, 2L, 4R, 4L, 7) 1
• Contains important vascular junctions such as the internal jugular-subclavian venous junction and left-right brachiocephalic venous junction 5

Paravertebral (Posterior) Compartment

• Located adjacent to the vertebral column 1
• Neurogenic tumors are the most common lesions in this compartment 1
• Contains sympathetic chain, intercostal nerves, and vessels 5

Clinical Significance of Mediastinal Compartments

• Localization of a mediastinal mass to one of these three compartments can significantly narrow the differential diagnosis 1
• Cross-sectional imaging (CT/MRI) is more accurate than chest radiography for defining mediastinal compartments 1, 6
• The International Thymic Malignancy Interest Group (ITMIG) developed this three-compartment classification to improve interdisciplinary communication and standardization 2
• This classification system better suits modern clinical workflow and three-dimensional imaging 2

Diagnostic Approach to Mediastinal Masses

• CT chest with contrast is the primary imaging modality for evaluating mediastinal masses 1, 4
• MRI provides additional tissue characterization that may prevent unnecessary biopsies 1
• PET-CT is optional but can help differentiate between benign and malignant disease 1, 6
• Specific serum markers (beta-HCG, AFP) may help identify germ cell tumors 1, 4

Surgical Approaches

• Surgical approach varies based on the compartment involved and suspected pathology 7
• Minimally invasive approaches are increasingly used but may not be appropriate for all cases 1
• 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 is the goal for mediastinal tumors, particularly thymic epithelial tumors 1

Common Pitfalls

• Traditional compartmentalization based on projection radiographs can lead to confusing interdisciplinary communication 2
• Relying solely on chest radiography is rarely diagnostic for mediastinal masses 6
• Failure to perform appropriate lymphadenectomy during resection of thymic tumors may affect staging accuracy 1
• Minimally invasive approaches should not compromise oncologic principles, especially complete resection 1