2.3: Axilla

 

Axilla (400)

Floor (399)

Axillary fascia from serratus ant ® deep fascia of arm & over axillary folds.

-           broad  suspensory ligament runs from pec minor to the fascial floor

Anterior wall

Pec major and minor, subclavius, clavipectoral fascia.

Posterior wall (397)

Subscapularis, teres major, lat dorsi tendon

- anterior and post walls converge on intertubercular groove with long head of biceps between.

Medial wall

Serratus anterior (inf border = 4th rib)

Apical boundaries

Clavicle, scapula and 1st rib; the posterior triangle communicates through here.

Axillary Contents

Axilla transmits neurovascular bundle from neck ® upper limb. 

Axillary Artery (398, 400)

Continuation of 3rd part of subclavian.  Emerges behind serratus ant at the border of first rib (Pl 25).

-           becomes the brachial artery at the lower border of teres major

Cords of BP approach and embrace axillary artery in its 2nd part; axillary vein lies anteromedial.

In axillary operations arm is laterally rotated and abducted to straighten the arterial course

® surface markings: line from middle of clavicle to groove behind coracobrachialis.

Pec minor forms landmarks for 1st, 2nd and 3rd parts

1st part: medial cord posterior; lateral and posterior cords superolateral; used for axillofemoral bypass. 

-           enclosed with BP in axillary sheath, projection of prevertebral fascia.

2nd part: cords of BP clasp artery accordant with their names

3rd part: branches of cords clasp artery in same relationship.

-           except the median root of median nerve crosses laterally to join lateral root

Surgical Approach

First part: split clavicular head of pec major; incise clavipect fascia

Rest: approach via axilla, b/n coracobrachialis and long head triceps.

Branches 1:2:3 (mnemonic: Subclavian Travels Laterally Surfacing at Arm Pit)

First part

1) Superior thoracic artery ® both pectoral muscles

Second Part

1) Thoracoacromial artery ® pierces clavipect fascia (see 400)

-           four branches: clavicular, deltoid, acromial, pectoral, radiate away at R angles to each other

2) Lat Thoracic artery ® follows lower border of pec minor ® pec major/minor and breast

Third Part

1) Subscapular artery ® (largest) gives circumflex scapular artery then becomes thoracodorsal.

-           circumflex scapular passes through posterior axilla b/n subscapularis and teres major, then curves back around lateral scapular border.

2) Anterior circumflex humoral – deep to coracobrachialis, runs up intertubercular groove to enter capsule, then passes around surgical neck to anastomose with:

3) post circumflex humeral – larger, through quadrangular space with axillary nerve

-           supplies deltoid, triceps, shoulder and anastomoses with profunda brachii.

Axillary Vein (400)

Basilic vein joins venae comitantes of brachial a above lower border of axilla to form axillary v.

-           hence apical landmark in axillary dissection

Becomes subclavian v at upper border of 1st rib ant to scalenus anterior.

Tributaries as for artery except cephalic v which drains into first part above pec minor.  No sheath.

-           subscapular veins are multiple, lie on posterior axilla, encountered in axillary clearance

-           remember lateral thoracic connects to thoracoepigastric to superficial epigastric to GSV

Axillary Nodes (399)

20-30 of them.

(1) Anterior (pectoral) group:  along anterior medial wall, drain most of breast and anterior trunk.

(2) Posterior scapular group: posteromedial wall, drain axillary tail and posterior trunk

(3) Lateral group: lie medial to axillary vein; drain upper limb

All drain into ® (4) central group (deep in axillary fat) ® (5) apical group (apex of axilla)

® subclavian lymph trunk ® thoracic duct (or right lymphatic duct.)

-           few afferents make way into inferior deep cervical nodes.

Level I: lateral to lower pec minor

Level II: behind pec minor

Level III: medial to pec minor’s upper border (ie named as for axillary artery divisions)

Sentinal Node
Variable anatomical site, usually in level I or II, occasionally inIII.
In melanoma of back, may be in quadralateral space bounded by spacularis, teres major, long head triceps and humerus.

Nerves Associated with Axillary Dissection

1. Lateral pectoral nerve
From divisions of brachial plexus or lateral cord
Crosses over axllary artery and vein around medial border of pec major --> then pierces clavipectoral fascia
Gives off a communciating branch to the medial pectoral nerve; this loop lies over the axillary artery

2. Medial pectoral nerve
From medial cord, more distally than lateral pectoral nerve.
Posterior to axillay artery, emerges between artery and vein
- receives communicating loop from lateral nerve
Then penetrates pec minor and supplies it.
These nrves start close to axillary artery, so dividing pec major at or above the artery should spare the nerves.

3. Intercostobrachial n.
Cutaneous branch from 2nd intercostal nerve.  Exits b/n first and second ribs
Traverses axilla to supply skin on medial upper arm.
Exits chest 2cm or so anterior to lineo flong thoracic.  Is often divided during block dissection of axilla.
(Frequently another lower one arising from the 3rd nerve.)

4. Thoracodorsal nerve
From upper and lower subscapulars from posterior cord, passes down behind axillary a+v to lie on subscapularisthen enters lat dorsi.
Runs with subscapular arrtery in upper part of corse then thoracodorsal artery.
Lies on posterior wall of axilla; should be spared.

5. Long thoracic n.
From C5-7 roots, passes behind axillary a+v --> down on serratus anterior; exposed during axillary dissection.
To enter axillar anteriorly, the clavipectoral fascia is divided at lateral pec minor.
Takes surgeon into plane which may elevate this nerve from chest wall with axillary contents.
--> divide the fascia longitudinally in front of the nerve to allow it to drop back against the chest.

Brachial Plexus (400-1)

Ant. rami of C5-8 and T1 give off segmental branches to prevertebral muscles

10% prefixed (C4-8) and 10% postfixed (C6-T2)

-           preganglionic sympathetics mainly T2-6, grey rami c. carry postganglionics to roots of brachial plexus, hitch-hike through branches until near area for supply

® five roots lying behind scalenus ant

® three trunks  crossing lower part of post. triangle of neck

-           C5&6 root: upper trunk, C7 = middle trunk, C8&T1 = lower trunk

® trunks divide behind clavicle ant and post divisions (®flexors / extensors respectively)

® divisions unite at outer border of 1st rib to form 3 cords

-           C5-T1 (all) posteriors: posterior cord; C5-7 (upper & middle) anteriors: lateral cord; C8-T1 (lower) anteriors: medial cord

® cords enter axilla above first part, embrace 2nd part and ® branches at third part.

 

Roots

Between scalene muscles

Trunks

Lower posterior triangle

Divisions

Behind clavicle

Cords

In axilla

Supraclavicular Part

3 Branches from Roots

Dorsal scapular

C5

® rhomboids & lev scapulae

Enters scalenus medius, runs on serratus post, forms nv bundle with scap a’s at vert border.

N to subclavius

C5,6

® subclavius

Runs ant to trunks & subclav v to underbelly

May give accessary phrenic from C5 fibres.

Long thoracic

C5,6,7

® serratus ant

Through scalenus medius, down serratus ant then C7 fibres meet (run ant to scalenus m)

 

1 Branch from Trunks

Suprascapular n

Upper trunk

C5,6

® supra/infraspinatus, shoulder, AC jt.

Passes deep to trapezius and under transverse scapular lig.

 

0 Branches from Divisions (under clavicle)

Infraclavicular Part

3 Branches from lateral Cord (C5,6,7)

Lateral pectoral n

C5,6,7

Pec Major (upper fibres) and Minor

Pierces clavipectoral fascia (meets medial pectoral across axillary artery)

Musculocutaneous n

C5,6,7

Enters coracobrachialis, ® biceps, brachialis

continues as lat cutaneous n of forearm (see innervation notes)

Lateral Head of Median n

C5,6,7

= continuation of lat cord (see 2.10)

Embraces medial head of median n (C8, T1) over front of axillary artery.

 

5 Branches from Medial Cord (C8,T1)

Medial Pectoral n

C8, T1

Pierces pec minor then pec major (meets lat as above)

Medial Head of Median n

C8, T1

Crosses axillary artery to join lat head of median n (2.10)

Medial Cutaneous n of arm

C8, T1

(Smallest, most medial) ® runs down with axially vein ® skin of anteromed upper arm

Medial Cutaneous n of forearm (442)

C8, T1

(Large); runs b/n axillary a & v in front of ulnar nerve ® pierces fascia at elbow ® skin of lower arm & forearm via ant & post branches (sym with lat cut nerve of forearm)

Ulnar nerve

C8, T1

(Largest) Most posterior structure of medial arm.  May receive C7 fibres as branches from lat cord.  See 2.10.

 

5 Branches from Posterior Cord (C5,6,7,8,T1)

Upper Subscapular

C5,C6

® subscapularis (enters upper part of muscles)

Thoracodorsal n

C6,7,8

® lat dorsi (runs down post axillary wall, down teres major to lat dorsi’s deep surface). starts above subscapular art, later in front of it.

Lower subscapular

C5,6

® subscapularis, teres major

Axillary n

C5,6

via quadrangular space ®  just below capsule (with post circumflex humeral a); gives shoulder jt branch; then ® Ant br ® deltoid (and terminal twig reaches the skin from here)

Post br ® teres minor & deltoid & continues as upper lat cutaneous n of arm to upper part of posterior arm.

Radial n

C5,6,7,

8,T1

(Largest branch of whole plexus) via triangular space ® b/n long head of triceps & humerus (supplies long and medial heads)       (See 2.10)

®posterior cutaneous n of arm branch, then continues down extensor compartment of forearm