What is the anatomy of the brachial plexus?

Brachial Plexus Anatomy

I cannot provide you with a picture, but I can describe the anatomical structure of the brachial plexus in detail to help you understand its organization.

Structural Organization

The brachial plexus is organized into five sequential anatomical levels: roots, trunks, divisions, cords, and terminal branches 1, 2, 3.

Roots

• The plexus is formed from the ventral rami of C5-T1 nerve roots, with occasional contributions from C4 and/or T2 1, 2, 4.
• The nerve roots pass between the anterior and middle scalene muscles alongside the subclavian artery 1, 2.

Trunks

• The roots converge to form three trunks:
  • Superior trunk (C5-C6)
  • Middle trunk (C7)
  • Inferior trunk (C8-T1) 3, 5

Divisions

• Each trunk divides into anterior and posterior divisions 2, 3.
• This creates six divisions total (three anterior, three posterior) 3.

Cords

• The divisions reorganize into three cords, named for their relationship to the axillary artery:
  • Lateral cord (from anterior divisions of superior and middle trunks)
  • Posterior cord (from all three posterior divisions)
  • Medial cord (from anterior division of inferior trunk) 2, 3, 5
• The cords travel with the subclavian artery and vein in the infraclavicular region 2.

Terminal Branches

• The lateral cord divides into the musculocutaneous nerve and lateral branch of the median nerve 3.
• The medial cord divides into the medial branch of the median nerve and ulnar nerve 3.
• The posterior cord divides into the axillary and radial nerves 3, 5.

Clinical Relevance

Precise knowledge of brachial plexus anatomy is fundamental for diagnosing and treating plexopathies 2.

• MRI of the brachial plexus is the imaging modality of choice due to superior soft-tissue contrast and spatial resolution 1, 6.
• Distinguishing preganglionic (root avulsion) from postganglionic (plexus) injuries is critical because treatment approaches differ significantly 1, 2.
• The plexus can be affected by traumatic, neoplastic, inflammatory, infectious, or radiation-induced pathology 1, 2.

Anatomical Variations

Anatomical variations are common due to the complex neural architecture 4, 7.

• Prefixed plexus occurs when C4 contributes significantly (shifts the plexus superiorly) 7, 5.
• Postfixed plexus occurs when T2 contributes significantly (shifts the plexus inferiorly) 5.
• Awareness of these variations is essential for nerve blocks, surgical procedures, and imaging interpretation 7, 6.