Topics

Topic

design image
Longissimus muscle

The longissimus muscle is the intermediate and largest component of the erector spinae group, positioned between the spinalis (medial) and iliocostalis (lateral) muscles. It extends from the sacrum and lumbar vertebrae to the skull, forming a major portion of the deep paraspinal muscles.

It is divided into three main parts:

  • Longissimus thoracis: the largest part, originating from the sacrum, iliac crest, and lumbar vertebrae, inserting onto thoracic transverse processes and adjacent ribs.

  • Longissimus cervicis: arising from upper thoracic transverse processes, inserting on cervical transverse processes.

  • Longissimus capitis: the most superior part, originating from upper thoracic and lower cervical transverse processes, inserting on the mastoid process of the temporal bone.

The longissimus functions in extension, lateral flexion, and stabilization of the vertebral column, as well as head extension and rotation (via longissimus capitis).

Synonyms

  • Musculus longissimus

  • Middle erector spinae muscle

  • Intermediate column of erector spinae

Function

  • Bilateral contraction: extends vertebral column and head

  • Unilateral contraction: laterally flexes spine, rotates head ipsilaterally (capitis)

  • Stabilizes the vertebral column during posture and movement

Nerve Supply

  • Dorsal rami of spinal nerves at each segmental level

Arterial Supply

  • Segmental supply from:

    • Posterior intercostal arteries (thoracic region)

    • Lumbar arteries (lumbar region)

    • Lateral sacral arteries (sacral region)

    • Occipital artery and deep cervical artery (cervical region)

Venous Drainage

  • Mirrors arterial supply:

    • Posterior intercostal veins → azygos/hemiazygos system

    • Lumbar veins → ascending lumbar and IVC

    • Deep cervical and occipital veins → vertebral venous plexus

MRI Appearance

T1-weighted images:

  • Normal muscle shows intermediate signal intensity with visible fascicular structure

  • Fat infiltration (degenerative atrophy, chronic denervation) appears as high signal intensity

T2-weighted images:

  • Muscle shows intermediate to low signal

  • Edema, inflammation, or acute injury appears as hyperintense signal

STIR:

  • Fat suppression highlights acute muscle edema, inflammation, or trauma

  • Useful in myositis, infection, and paraspinal muscle injury

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Normal muscle enhances mildly and diffusely

  • Pathological enhancement suggests infection, tumors, or inflammatory changes

MRI Non-Contrast 3D Imaging:

  • Provides 3D reconstruction of erector spinae muscles relative to vertebrae and ribs

  • Important for pre-surgical planning, scoliosis evaluation, and paraspinal tumor assessment

CT Appearance

Non-contrast CT:

  • Longissimus appears as paraspinal soft tissue mass lateral to spinous processes

  • Can demonstrate calcifications, fatty replacement, or muscle atrophy

CT Post-Contrast:

  • Enhances visualization of vascular structures and pathological infiltration

  • Useful in detecting abscesses, tumors, or extension of spinal disease into paraspinal muscles

MRI image

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

CT image

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