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Transversus thoracis muscle

The transversus thoracis muscle is a thin, flat muscle of the anterior thoracic wall, located on the inner surface of the chest. It originates from the posterior surface of the lower third of the sternum, the xiphoid process, and the adjacent costal cartilages. From there, it runs superolaterally to insert into the internal surfaces of the costal cartilages of the 2nd to 6th ribs.

It lies deep to the sternum and costal cartilages, immediately posterior to the internal thoracic vessels, and is continuous inferiorly with the transversus abdominis muscle.

Functionally, the transversus thoracis assists in depressing the ribs during forced expiration, thereby helping to reduce the thoracic cavity volume. It also serves as a landmark in cardiothoracic surgery and interventional procedures, since the internal thoracic arteries and veins course along its posterior surface.

Synonyms

  • Sternocostalis muscle

  • Triangularis sterni muscle

  • Musculus transversus thoracis

Function

  • Depresses the ribs during forced expiration

  • Stabilizes costal cartilages and sternum during respiration

  • Provides protective coverage for internal thoracic vessels

  • Acts as a surgical landmark in coronary artery bypass grafting (CABG), where the internal thoracic artery is harvested

Nerve Supply

  • Intercostal nerves (T2–T6)

Arterial Supply

  • Internal thoracic artery and its branches

  • Anterior intercostal arteries

Venous Drainage

  • Internal thoracic vein → brachiocephalic vein

  • Anterior intercostal veins → internal thoracic vein

MRI Appearance

T1-weighted images:

  • Muscle appears as intermediate signal intensity between sternum and internal thoracic vessels

  • Surrounded by high-signal mediastinal fat for contrast

T2-weighted images:

  • Normal muscle: intermediate to low signal intensity

  • Edema or inflammation appears hyperintense

STIR:

  • Fat suppression highlights muscle edema, trauma, or inflammatory changes

  • Helps differentiate muscle from adjacent fat and vessels

T1 Fat-Saturated (Pre-contrast):

  • Muscle fibers: intermediate signal standing out against suppressed fat planes

  • Useful for evaluating thickness and continuity

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Normal muscle enhances mildly and homogeneously

  • Pathology (myositis, tumor infiltration, post-surgical change) shows heterogeneous or abnormal enhancement

MRI Non-Contrast 3D Imaging:

  • Provides 3D view of anterior thoracic wall, sternum, ribs, and internal thoracic vessels

  • Useful in surgical planning and vascular mapping

CT Appearance

CT Pre-Contrast:

  • Thin muscle layer visible along the posterior sternum

  • Appears as a flat soft-tissue density anterior to internal thoracic vessels

CT Post-Contrast:

  • Muscle enhances mildly

  • Vessels on its deep surface (internal thoracic arteries/veins) enhance brightly, making it a useful anatomical landmark

  • Pathology (trauma, tumor invasion, or post-surgical scarring) becomes more conspicuous

CT images

Transversus thoracis muscle CT axial image 1

CT images

Transversus thoracis muscle CT axial image

MRI image

Transversus thoracis muscle CT axial image MRI axial image anatomy image -img-00000-00000