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Scalenus posterior muscle (Posterior scalene muscle)

The posterior scalene muscle is the smallest and most posterior of the scalene group (anterior, middle, posterior). It arises from the posterior tubercles of the transverse processes of cervical vertebrae C4–C6 and descends inferiorly and laterally to insert into the second rib, posterior to the serratus anterior tuberosity.

It lies posterior to the middle scalene muscle, separated by the brachial plexus trunks and subclavian artery, which pass between the anterior and middle scalenes. The posterior scalene is part of the lateral cervical region and forms a key landmark in neck dissections, thoracic outlet evaluation, and cervical plexus mapping.

Functionally, it acts as an accessory muscle of inspiration by elevating the second rib, and it also contributes weakly to lateral flexion of the neck.

Synonyms

  • Scalenus posterior

  • Posterior scalene muscle

Function

  • Elevates the second rib during inspiration (accessory respiratory function)

  • Weakly assists in lateral flexion of the cervical spine

  • Contributes to stabilization of the cervical region during respiration and motion

Nerve Supply

  • Direct muscular branches from the cervical spinal nerves C6–C8 (cervical plexus)

Arterial Supply

  • Ascending cervical artery (branch of inferior thyroid artery, thyrocervical trunk)

  • Branches of subclavian artery (dorsal scapular or superficial cervical branches may contribute)

Venous Drainage

  • Parallels arterial supply:

    • Ascending cervical vein → inferior thyroid vein → brachiocephalic vein

    • Tributaries drain into the subclavian vein

MRI Appearance

T1-weighted images:

  • Normal muscle shows intermediate signal intensity with distinct fascicular architecture

  • Surrounded by hyperintense fat planes separating it from the middle scalene

T2-weighted images:

  • Muscle: intermediate to low signal

  • Edema, inflammation, or strain appears hyperintense relative to normal tissue

STIR:

  • Suppresses fat, highlighting muscle edema, infection, or trauma

  • Excellent for detecting subtle signal changes in cervical soft tissues

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Mild homogeneous enhancement in normal state

  • Abnormal heterogeneous enhancement suggests myositis, tumor infiltration, or abscess

MRI Non-Contrast 3D Imaging:

  • Provides 3D views of scalene muscle relationships with brachial plexus and subclavian vessels

  • Valuable in mapping anatomy for thoracic outlet syndrome evaluation

CT Appearance

Non-contrast CT:

  • Appears as a soft tissue density muscle posterior to the middle scalene, inserting into the second rib

  • Useful for anatomical mapping in trauma or pre-surgical planning

CT Post-Contrast:

  • Provides excellent contrast for vascular structures around the posterior scalene

  • Demonstrates muscle pathology, tumors, or inflammatory changes

  • Key in evaluating thoracic outlet syndrome by showing spatial relation to subclavian artery and brachial plexus

MRI images

Scalenus posterior muscle mri image

MRI image

Posterior scalene muscle MRI axial image -img-00000-00000