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Brachial plexus

The brachial plexus is a complex network of nerve fibers formed by the ventral rami of spinal nerves C5–T1, with occasional contributions from C4 and T2. It provides motor, sensory, and autonomic innervation to the upper limb, as well as portions of the shoulder and thoracic wall.

The plexus is organized into five sequential components:

  • Roots (C5–T1)

  • Trunks (upper, middle, lower)

  • Divisions (anterior and posterior for each trunk)

  • Cords (lateral, posterior, medial — named relative to the axillary artery)

  • Terminal branches (major peripheral nerves of the upper limb)

Anatomically, the brachial plexus passes between the anterior and middle scalene muscles, through the cervicoaxillary canal, and into the axilla, where it surrounds the axillary artery.

It is clinically significant in traumatic injuries, tumors, inflammatory neuropathies, thoracic outlet syndrome, surgical procedures, and anesthetic blocks.

Detailed Anatomy

Roots (C5–T1):

  • Lie in the neck, between anterior and middle scalene muscles

  • Each root gives off branches:

    • Dorsal scapular nerve (C5) → rhomboids

    • Long thoracic nerve (C5–C7) → serratus anterior

Trunks:

  • Upper trunk (C5–C6): gives suprascapular nerve & nerve to subclavius

  • Middle trunk (C7)

  • Lower trunk (C8–T1)

Divisions:

  • Each trunk divides into anterior (flexor) and posterior (extensor) divisions

  • No named branches arise here

Cords: (named relative to axillary artery)

  • Lateral cord (C5–C7): gives musculocutaneous nerve, lateral root of median nerve

  • Posterior cord (C5–T1): gives axillary nerve, radial nerve, upper & lower subscapular nerves, thoracodorsal nerve

  • Medial cord (C8–T1): gives ulnar nerve, medial root of median nerve, medial pectoral nerve, medial cutaneous nerves

Terminal Branches:

  • Musculocutaneous nerve (C5–C7) → anterior arm muscles

  • Axillary nerve (C5–C6) → deltoid, teres minor, shoulder sensation

  • Radial nerve (C5–T1) → extensor compartment of arm & forearm

  • Median nerve (C5–T1) → most forearm flexors, thenar muscles, lateral hand sensation

  • Ulnar nerve (C8–T1) → intrinsic hand muscles, medial forearm flexors, medial hand sensation

Function

  • Provides motor innervation to all muscles of the upper limb

  • Provides sensory innervation to skin of shoulder, arm, forearm, and hand

  • Transmits autonomic fibers (sympathetic) to upper limb vasculature and sweat glands

  • Coordinates integrated function of movement, sensation, and vascular tone in the upper limb

MRI Appearance

T1-weighted images:

  • Brachial plexus roots, trunks, cords, and branches appear as intermediate signal intensity structures

  • Surrounded by hyperintense fat, which provides excellent contrast

T2-weighted images:

  • Nerves appear as low-to-intermediate signal intensity

  • Pathology (edema, inflammation, tumors) appears hyperintense relative to normal nerves

STIR:

  • Suppresses fat, improving visualization of plexus nerves against background

  • Detects inflammation, edema, or trauma-related changes

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Normal nerves enhance minimally

  • Pathology such as tumors, inflammatory neuropathy, or metastasis shows abnormal heterogeneous enhancement

  • Useful for mapping tumor infiltration or post-radiation fibrosis

CT Appearance

Non-contrast CT:

  • Limited in soft tissue resolution, but may show calcifications, trauma, or bony compression affecting the plexus

CT Post-Contrast (CT Neurography):

  • Helps identify tumor extension, extrinsic compression, or vascular involvement

  • CT angiography delineates relationships between plexus and subclavian/axillary vessels

  • Useful when MRI is contraindicated

MRI images

Brachial plexus anatomy MRI axial image -img-00000-00000

MRI images

Brachial plexus anatomy MRI axial image -img-00000-00000_00001

MRI images

Brachial plexus anatomy MRI axial image -img-00000-00000_00002

MRI images

Brachial plexus anatomy MRI coronal image -img-00000-00000

MRI images

Brachial plexus anatomy MRI coronal image -img-00000-00000_00001

CT images

Brachial plexus anatomy CT axial image

CT images

Brachial plexus anatomy CT axial image -img-00000-00000_00001

MRI image

Brachial plexus branches