Brachial Plexus

GROSS ANATOMY

Overview

• Brachial plexus is neural highway to upper limbs

Formed from C5-T1 roots combining to form 3 trunks, 6 divisions, 3 cords, and 5 terminal branches (classic description)

– 5 terminal branches are ulnar, median, musculocutaneous, axillary, and radial nerves

Many variations in this classic anatomy exist

– Cannot rely on having definite number of trunks, divisions, or cords at any particular location

US Anatomy

• 5 specific areas should be assessed to ensure complete evaluation

Extraforaminal, interscalene, supraclavicular, infraclavicular, and axillary areas
• Extraforaminal area (5 roots)

Single large anterior ramus emerging from spinal cord levels C5-T1

– Seen between anterior and posterior tubercles of C5 and C6 cervical vertebrae

– Anterior tubercle of C7 transverse process is small, so root is seen lying anterior to posterior tubercle

– C8 and T1 roots more difficult to see due to their deep location
• Interscalene area (5 roots → 3 trunks)

Between scalenus anterior muscle anteromedially and scalenus medius muscle posterolaterally

Roots unite to form trunks in most distal interscalene area

– Upper (C5-6), middle (C7), lower (C8, T1) trunks

– Average cross-sectional area of these trunks is 7 mm² (upper), 9 mm² (middle), and 9 mm² (lower)

– Upper (C5-6) trunk or part of it may run through or anterior to anterior scalene muscle

– Dorsal scapular artery may run posteriorly between upper and middle trunks

Suprascapular nerve arises from upper trunk

– Normal cross-sectional area of scapular nerve is 2.8 mm ± 0.8 mm

Interscalene triangle common site for nerve block
• Supraclavicular area (6 divisions)

Trunks divide into anterior and posterior divisions in supraclavicular fossa

– 3 trunks → 6 divisions

Lie posterior and superoposterior to subclavian artery (“bunch of grapes”)

Anterior divisions innervate anterior (flexor) muscles

Posterior divisions innervate posterior (extensor) muscles

Transverse cervical artery often loops over divisions of brachial plexus

Costoclavicular space is between clavicle and 1st rib

– Narrowest passageway for brachial plexus

– Can be compressed with fracture of clavicle or 1st rib

– Not possible to see costoclavicular space with US
• Infraclavicular area (3 cords)

Passageway between supraclavicular fossa and apex of axilla

Also called retropectoralis minor space or subcoracoid space

6 divisions → 3 cords, which position themselves lateral, medial, and posterior to axillary artery

– Lateral and medial cords innervate flexor muscles

– Posterior cord innervates extensor muscles

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Tags: Diagnostic Ultrasound Musculoskeletal

Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

GROSS ANATOMY

Overview

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Brachial Plexus

Brachial Plexus

US Anatomy

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Radiology Key

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Brachial Plexus

Brachial Plexus

GROSS ANATOMY

Overview

US Anatomy

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