Topics

Topic

design image
Scalenus anterior muscle (Anterior scalene muscle)

The scalenus anterior muscle, or anterior scalene, is one of the three paired scalene muscles of the lateral neck. It originates from the anterior tubercles of the transverse processes of cervical vertebrae C3–C6 and inserts onto the scalene tubercle of the first rib, located between the grooves for the subclavian artery and subclavian vein.

The muscle lies deep to the sternocleidomastoid and is an important anatomical landmark in the root of the neck. The phrenic nerve descends obliquely along its anterior surface, while the subclavian vein passes anterior to it, and the subclavian artery and brachial plexus trunks pass posterior to it (through the scalene triangle).

Clinically, the anterior scalene is important in thoracic outlet syndrome, nerve entrapment, and as a landmark in regional anesthesia (scalene block) and neck dissections.

Synonyms

  • Anterior scalene muscle

  • Scalenus anticus

Function

  • Elevates the first rib during inspiration, aiding in breathing

  • Flexes the cervical spine laterally (unilateral contraction)

  • Flexes the neck forward (bilateral contraction)

  • Provides important anatomical relations for neurovascular structures of the neck

Nerve Supply

  • Direct muscular branches from the cervical spinal nerves C4–C6

Arterial Supply

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

  • Small contributions from vertebral artery and inferior thyroid artery

Venous Drainage

  • Veins drain into the inferior thyroid vein and adjacent venous plexuses of the neck

MRI Appearance

T1-weighted images:

  • Appears as an elongated muscle of intermediate signal intensity lateral to cervical vertebrae and anterior to brachial plexus

  • Surrounded by hyperintense fat, which aids in delineation

T2-weighted images:

  • Muscle belly: intermediate-to-low signal

  • Acute injury or edema: hyperintense signal compared to surrounding structures

STIR:

  • Fat suppression highlights inflammatory changes, edema, or trauma within or around the muscle

  • Useful in detecting nerve entrapment or vascular compression syndromes

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Normal muscle shows mild uniform enhancement

  • Abnormal enhancement indicates myositis, tumor infiltration, or inflammatory changes

  • Helps evaluate phrenic nerve course along its anterior surface

MRI Non-Contrast 3D Imaging:

  • Provides high-resolution mapping of scalene triangle and relations to subclavian vessels and brachial plexus

  • Valuable in thoracic outlet syndrome evaluation and pre-surgical planning

CT Appearance

Non-contrast CT:

  • Appears as a soft-tissue density lateral to the cervical spine and anterior to the middle scalene muscle

  • Useful in identifying calcifications, hypertrophy, or anatomical variants

CT Post-Contrast:

  • Highlights adjacent vascular relations (subclavian artery and vein, brachial plexus)

  • Defines space-occupying lesions, tumors, or inflammatory changes affecting the muscle and surrounding structures

  • 3D reconstructions delineate scalene triangle and surgical anatomy

MRI images

Scalenus anterior muscle mri axial image

CT images

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

CT image

Anterior scalene muscle CT axial image-img-00000-00000