Retrosternal space

The retrosternal (prevascular) space is the space between the posterior surface of the sternum and the anterior pericardium/great vessels. It normally contains thymic tissue (especially in children), fat, and internal mammary vessels.

Boundaries:

• Anteriorly: The posterior surface of the sternum and costal cartilages

• Posteriorly: The anterior surface of the pericardium (fibrous pericardium), which is attached to the sternum by the sternopericardial ligaments

• Laterally: The mediastinal pleura on each side

• Superiorly: Continuous with the superior mediastinum

• Inferiorly: The diaphragm

Contents:

The retrosternal space normally contains mediastinal adipose tissue (fat), the thymus (or thymic remnant in adults), lymph nodes, and the internal thoracic (mammary) vessels. The amount of mediastinal adipose tissue in this space varies by level it is more abundant superiorly and becomes thinner at lower levels near the ventricles.

Clinical significance:

• On the lateral chest radiograph, the retrosternal space appears as a radiolucent (dark) area between the sternum and the cardiac silhouette. Loss of this normal lucency (retrosternal opacification) may indicate an anterior mediastinal mass (e.g., thymoma, lymphoma, teratoma, or thyroid goiter).

• The modern CT-based mediastinal classification adopted by the International Thymic Malignancy Interest Group defines this region as the prevascular compartment, which is the preferred terminology for standardized reporting.

• This space is surgically accessible via subxiphoid videomediastinoscopy through the retrosternal plane, which can be used for diagnostic biopsy of anterior mediastinal masses or to facilitate transcervical thymectomy.