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Intercostal muscles

The intercostal muscles are three layers of muscles located in the intercostal spaces between adjacent ribs. They are arranged in three groups:

  • External intercostal muscles: Run obliquely downward and forward from the rib above to the rib below, aiding inspiration.

  • Internal intercostal muscles: Run downward and backward, deep to the external layer, and assist in forced expiration.

  • Innermost intercostal muscles: The deepest layer, parallel to the internal intercostals, stabilizing the intercostal spaces.

Together, these muscles form the muscular component of the thoracic wall, protecting the thoracic organs and assisting with respiration by controlling rib movement. They also support the intercostal spaces, preventing paradoxical movement during breathing.

Clinically, intercostal muscles are important in chest wall trauma, intercostal neuralgia, thoracic surgery, and respiratory mechanics evaluation.

Synonyms

  • Musculi intercostales

  • Thoracic wall muscles

  • Respiratory rib muscles

Function

  • External intercostals: Elevate ribs during inspiration, increasing thoracic volume

  • Internal intercostals: Depress ribs during forced expiration

  • Innermost intercostals: Assist in rib depression and stabilize intercostal spaces

  • Contribute to respiratory mechanics, chest wall stability, and protection of thoracic organs

Nerve Supply

  • Supplied by intercostal nerves (ventral rami of thoracic spinal nerves T1–T11)

Arterial Supply

  • Anterior intercostal arteries (branches of internal thoracic artery)

  • Posterior intercostal arteries (branches of thoracic aorta)

  • Small contributions from musculophrenic artery

Venous Drainage

  • Anterior intercostal veins → internal thoracic vein → brachiocephalic vein

  • Posterior intercostal veins → azygos and hemiazygos system → superior vena cava

MRI Appearance

T1-weighted images:

  • Intercostal muscles show intermediate signal intensity, with clear fascicular pattern

  • Fat between muscle layers appears hyperintense, delineating each layer

T2-weighted images:

  • Muscles appear intermediate to low signal

  • Muscle edema or strain appears as focal hyperintensity

STIR:

  • Suppresses fat, making muscle edema, trauma, or inflammatory changes hyperintense

  • Useful in detecting rib fractures with associated soft tissue injury

T1 Fat-Saturated (Pre-contrast):

  • Muscles show intermediate signal relative to surrounding suppressed fat, standing out more clearly

  • Enhances visualization of subtle asymmetry

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Normal intercostal muscles enhance mildly and homogeneously

  • Pathology (myositis, infection, tumors) shows heterogeneous enhancement

  • Useful for detecting intercostal muscle metastases or inflammatory conditions

MRI Non-Contrast 3D Imaging:

  • Allows multiplanar and 3D reconstruction of thoracic wall musculature

  • Helpful in trauma, tumor mapping, and surgical planning

CT Appearance

CT Pre-Contrast:

  • Intercostal muscles appear as soft tissue densities between ribs

  • Useful for detecting hematomas, atrophy, or disruption after trauma

CT Post-Contrast:

  • Muscles enhance uniformly

  • Pathologies (abscess, neoplasms, post-traumatic changes) show abnormal focal or diffuse enhancement

  • 3D reconstructions delineate muscle-rib relationships for thoracic surgery

CT images

Intercostal muscles CORONAL CT IMAGE

CT images

Intercostal muscles ct axial image

MRI images

Intercostal muscles MRI AXIAL image anatomy image -img-00000-00000

MRI images

Intercostal muscles MRIcoronal image anatomy image -img-00000-00000