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Scalenus medius muscle (middle scalene muscle)

The scalenus medius muscle is one of the three scalene muscles (anterior, middle, posterior) in the lateral neck, located deep to the sternocleidomastoid. It originates from the posterior tubercles of the transverse processes of C2–C7 vertebrae and inserts onto the first rib, posterior to the groove for the subclavian artery.

It lies posterior to the scalenus anterior, forming part of the scalene triangle, a clinically significant space through which the brachial plexus roots and subclavian artery pass. The subclavian vein lies anterior to the scalenus anterior and does not traverse this triangle.

The scalenus medius plays an important role in respiration and neck stability. It acts as an accessory muscle of inspiration and also laterally flexes the cervical spine. Clinically, hypertrophy or anatomical anomalies of the scalenes may cause thoracic outlet syndrome (TOS) by compressing neurovascular structures.

Synonyms

  • Middle scalene muscle

  • Musculus scalenus medius

  • Lateral scalene

Function

  • Elevates the first rib during forced inspiration

  • Laterally flexes the cervical spine ipsilaterally

  • Contributes to stability of the cervical region

  • Forms part of the scalene triangle, an important anatomical passage

Nerve Supply

  • Ventral rami of cervical spinal nerves C3–C8

Arterial Supply

  • Ascending cervical artery (branch of thyrocervical trunk)

  • Contributions from vertebral artery and inferior thyroid artery

Venous Drainage

  • Drains into veins corresponding to arterial supply: ascending cervical vein, tributaries of internal jugular vein, and vertebral venous plexus

MRI Appearance

T1-weighted images:

  • Appears as intermediate signal intensity with distinct fascicular pattern

  • Surrounded by hyperintense fat, improving delineation

T2-weighted images:

  • Normal muscle: intermediate-to-low signal

  • Edema, strain, or denervation: hyperintense changes

STIR:

  • Suppresses fat to highlight muscle edema, inflammation, or trauma

  • Useful in thoracic outlet syndrome evaluation for soft tissue changes

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Mild, homogeneous enhancement in normal muscle

  • Increased heterogeneous enhancement in myositis, tumor, or inflammatory involvement

  • Helps evaluate nerve or vascular compression by hypertrophied muscle

MRI Non-Contrast 3D Imaging:

  • Provides multiplanar reconstructions of the scalene triangle and relationship with brachial plexus and subclavian artery

  • Valuable for thoracic outlet syndrome surgical planning

CT Appearance

Non-contrast CT:

  • Appears as a soft tissue density lateral to the cervical vertebrae and adjacent to the first rib

  • Useful for evaluating calcifications, trauma, or asymmetry

CT Post-Contrast:

  • Enhances muscle vascular detail and its relation to subclavian vessels and brachial plexus

  • Helpful in detecting masses, infection, or vascular anomalies

  • 3D reconstructions clarify spatial relationships in thoracic outlet syndrome

MRI images

Scalenus medius muscle mri image

CT images

Middle scalene muscle anatomy CT axial image -img-00000-00000

MRI image

Scalenus medius muscle (middle scalene muscle) MRI axial image -img-00000-00000