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Retrosternal space

The retrosternal space, also called the anterior mediastinal prevascular space, is the anatomical area located directly posterior to the sternum and anterior to the pericardium and great vessels. It forms the most anterior compartment of the mediastinum and contains fat, thymic tissue (more prominent in children), lymphatic channels, small vessels, and connective tissue.

In adults, this space primarily consists of low-density fat, with minimal residual thymic tissue. Its appearance on imaging provides important landmarks for evaluating the mediastinum, sternum, chest wall, and pericardial surfaces.

Synonyms

  • Prevascular space

  • Anterior mediastinal space

  • Retrosternal clear space (radiographic term)

Location and Structure

  • Position: Immediately behind the sternum, extending from the thoracic inlet to the diaphragm.

  • Boundaries:

    • Anterior: Posterior surface of the sternum

    • Posterior: Pericardium, ascending aorta, and superior vena cava

    • Superior: Thoracic inlet

    • Inferior: Diaphragmatic surface

    • Lateral: Mediastinal pleura of both lungs

  • Contents:

    • Mediastinal fat

    • Thymus or thymic remnants

    • Small lymphatic channels

    • Loose connective tissue

    • Small arterial and venous branches

Relations

  • Anteriorly: Sternum, costal cartilages, internal thoracic vessels

  • Posteriorly: Pericardium covering right ventricle, ascending aorta, SVC

  • Laterally: Mediastinal pleura and medial lung surfaces

  • Superiorly: Thoracic inlet structures (trachea, brachiocephalic vessels)

  • Inferiorly: Diaphragm and anterior diaphragmatic fat pad

Function

  • Provides cushioning and separation between sternum and major mediastinal organs

  • Allows movement of heart and vessels during respiration and cardiac motion

  • Serves as a conduit for small vessels, lymphatics, and thymic tissue

  • Acts as a radiological window for assessing mediastinal width and fat distribution

MRI Appearance

T1-weighted images

  • Fat in retrosternal space: Bright, homogeneous high signal intensity

  • Thymic tissue (if present): Intermediate signal relative to fat

  • Muscle and sternum: Lower signal intensity

  • Pericardium: Thin low-signal line deep to retrosternal space

  • Vessels: Flow voids or intermediate signal depending on technique

T2-weighted images

  • Fat: Intermediate-to-bright signal, slightly brighter than on T1

  • Thymic tissue: Appears intermediate-to-high signal

  • Pericardium and sternum: Dark, low-signal structures

  • Adjacent lungs: Very high signal at interfaces (motion-dependent)

STIR

  • Fat: Suppressed, appearing dark

  • Thymic tissue: Intermediate bright signal due to its soft tissue nature

  • Sternum and pericardium: Low signal

  • Normal vessels: Contain dark flow voids

T1 Fat-Saturated Post-Contrast

  • Fat: Fully suppressed

  • Small vessels: Enhance brightly

  • Thymic tissue (if present): Mild homogeneous enhancement

  • Pericardial surface: Thin smooth enhancement pattern, consistent with normal pleuropericardial reflections

  • Sternum: No internal enhancement

CT Appearance

Non-Contrast CT

  • Fat: Low attenuation (−80 to −120 HU) occupying most of retrosternal space

  • Thymus (in children/young adults): Soft-tissue triangular structure with homogeneous density

  • Sternum: High-density cortical margins with cancellous center

  • Pericardium: Thin soft-tissue line separating space from heart

  • Lungs: Laterally adjacent low-density aerated lung fields

Post-Contrast CT

  • Fat: Remains low density

  • Small vessels: Demonstrate mild enhancement

  • Thymic remnants: May show subtle uniform enhancement

  • Pericardial reflections: Mild linear enhancement

  • Sternum: No enhancement of bone cortex; marrow shows mild internal contrast mixing

MRI images

Retrosternal space coronal mri image

MRI images

Retrosternal space mri sagittal image