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Iliocostalis muscle

The iliocostalis muscle is the most lateral column of the erector spinae group, located along the vertebral column. It runs from the iliac crest, sacrum, and lumbar vertebrae to the angles of the ribs and cervical transverse processes. It is subdivided into three regions:

  • Iliocostalis lumborum – arises from the iliac crest, sacrum, and thoracolumbar fascia, inserting onto the lower ribs.

  • Iliocostalis thoracis – extends from lower ribs to upper ribs.

  • Iliocostalis cervicis – runs from upper ribs to cervical transverse processes.

Together with longissimus and spinalis muscles, the iliocostalis helps maintain posture and allows extension and lateral flexion of the vertebral column. It is an important muscle for spinal stability, posture control, and respiratory mechanics.

Synonyms

  • Lateral erector spinae muscle

  • Iliocostalis lumborum / thoracis / cervicis

Function

  • Extension of the vertebral column (bilateral contraction)

  • Lateral flexion of the spine (unilateral contraction)

  • Maintains erect posture and stabilizes the vertebrae during movement

  • Assists in rib depression and elevation during respiration

Nerve Supply

  • Dorsal rami of spinal nerves (segmental innervation corresponding to vertebral levels)

Arterial Supply

  • Lumbar arteries (from abdominal aorta)

  • Intercostal arteries (posterior branches)

  • Deep cervical artery (for cervical region)

Venous Drainage

  • Parallels arterial supply:

    • Lumbar veins → inferior vena cava

    • Posterior intercostal veins → azygos and hemiazygos system

    • Deep cervical vein → vertebral venous plexus

MRI Appearance

T1-weighted images:

  • Muscle belly shows intermediate signal intensity with visible fascicular architecture

  • Fatty infiltration (chronic degeneration or denervation) appears hyperintense

T2-weighted images:

  • Normal muscle: intermediate-to-low signal

  • Edema, strain, or myositis: hyperintense signal changes

STIR:

  • Suppresses fat, highlighting muscle edema, trauma, or inflammation as bright hyperintensity

  • Useful in detecting acute strain, paraspinal infection, or myopathy

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Normal muscle enhances mildly

  • Myositis, infection, tumors, or metastases show heterogeneous enhancement

MRI Non-Contrast 3D Imaging:

  • Provides detailed morphology and spatial relation of iliocostalis to other erector spinae components

  • Used in spinal surgery planning and paraspinal muscle assessment

CT Appearance

Non-contrast CT:

  • Appears as a soft-tissue density lateral to vertebral spinous processes and laminae

  • Detects atrophy, calcifications, or fatty replacement

CT Post-Contrast:

  • Enhances in cases of infection, tumor, or vascular involvement

  • Useful for identifying paraspinal abscesses, infiltrative lesions, or traumatic hematomas

MRI images

Iliocostalis muscle anatomy MRI axial image -img-00000-00000

CT images

Iliocostalis muscle muscle anatomy MRI axial image -img-00000-00000