Posterior and Anterior Triangles Flashcards
Boundaries of posterior triangle
roof: cervical investing fascia
anterior: posterior border of SCM
posterior: anterior border of trapezius
inferior: superior margin of clavicle
floor: prevertebral fascia covering neck musculature (posterior, middle and anterior scalene), levator scapulae, splenius capitis and sometimes the semispinalis capitis
NOTE: the passage of the inferior belly of the omohyoid diides the posterior triangle into a larger, more superior OCCIPITAL TRIANGLE and a smaller, more inferior OMOCLAVICULAR (SUPRACLAVICULAR, SUBCLAVIAN TRIANGLE)
General contents of posterior triangle
external jugular vein and tributaries
cutaneous nerves of the cervical plexus: lesser occipital, great auricular, transverse cervical, supraclavicular
spinal accessory nerve
brachial plexus
inferior belly of the omohyoid muscle
third portion of the subclavian artery, transverse cervical, suprascapular, descending or dorsal scapular and occipital arteries
deep cervical lymph nodes (a portion of)
Spinal accessory nerve (CN XI); GSE in the posterior triangle
Spinal accessory nerve (CN XI); GSE
After exiting the jugular foramen between the internal carotid artery and internal jugular vein, the spinal accessory nerve passes posterior and lateral to the vein to enter the medial superior aspect of the SCM. After providing innervation to the SCM, the nerve exits the muscle on its medial posterior surface. It then crosses the floor of the posterior triangle obliquely and inferiorly in a posterior direction where it will eventually pass deep to the trapezius to participate in forming the SUBTRAPEZIAL PLEXUS (with branches of ventral rami of spinal nerves C3 and C4)
Brachial plexus in the posterior triangle in the neck
Composed of ventral rami of spinal nerves C5-T1
Roots of the plexus pass between the anterior and middle scalene muscles (SCALENE TRIANGLE) in the anterior inferior portion of the posterior triangle
CLINICAL NOTE: hypertrophy of these muscles can place undue pressure upon the root of brachial plexus resulting in Thoracic Outlet Syndrome
Axillary sheath
An extension of the prevertebral layer of fascia which covers the scalene muscles invests the roots of the brachial plexus along with the subclavian artery.
This is present in the posterior triangle of the neck.
cervicoaxillary canal
the axillary sheath, complete with trunks and cords of the brachial plexus and axillary artery, passes through the cervicoaxillary canal to enter the axilla.
Branches of the brachial plexus in the posterior triangle of the neck
a. Dorsal scapular n. (C5)- passes through the middle scalene to gain the ventral surface of the levator scapulae upon which it descends continuing along the medial border of the scapula ventral to the rhomboid muscles
b. Accessory phrenic n. - usually arises as a branch of C5 which descends parallel to the phrenic n. on the lateral surface of the anterior scalene muscle.
c. Nerve to subclavius- arises from the upper trunk (C5-C6), cescends anterior to the brachial plexus and the subclavian vessels and posterior to the clavicle to enter the deep surface of the muscle.
d. Suprascapular n. (C5,6)- arises from teh junction of C5 and C6 (upper trunk), parallels the course of the suprascapular vessels to the area of the scapular notch to innervate the supra and infraspinatus muscles.
e. Long thoracic n. (C5,6,7)- formed by twigs of C5,6,7 which join dorsal to the brachial plexus to descend into the axilla on the lateral surface of serratus anterior muscle which it innervates.
f. Direct branches to the scalene muscles supplied collectively by C5-C8
Arteries of the posterior triangle of the neck
Occipital a. - 5th branch of the external carotid artery passes from behind the SCM at the apex of the posterior triangle and ascends to supply the posterior scalp (in company with the greater occipital n.)
Transverse cervical and suprascapular aa. - branches of the thyrocervical trunk (from the 1st portion of the subclavian artery in the root of the neck), cross the posterior triangle inferiorly, medial (deep) to the inferior belly of the omohyoid muscle.
– Transverse cervical a.- eventually exits the posterior triangle by passing deep to the trapezius muscle which it supplies.
– Suprascapular a. - paralleled by its accompanying vein, it is joined by teh suprascapular n. as it passes out of the posterior triangle laterally to enter the scapular region.
Subclavian artery (3rd portion)- portion lateral to the anterior scalene located in the extreme anterior inferior extent of the posterio triangle. It passes from between the anterior and middle scalene muscles and accompanied by the trunks of the brachial plexus, is invested with prevertebral fascia (axillary sheath).
- possible branches: (inconsistent)
- —— transverse cervical a. can arise from this portion anomalously
- ——- suprascapular a. - can arise from this portion anomalously
- ——– dorsal scapular a. - passes dorsalward through the brachial plexus in the vicinity of the middle trunk to gain the ventral surface of the levator scapulae and descends parallel to the dorsal scapular n. ventral to the rhomboids along the medial border of the scapula.
Lymphatics of the posterior triangle
located DEEP to investing fascia
- composed of nodes of the deep cervical system which accompany the:
- spinal accessory n. (accessory nodes)
- transverse cervical a.- (transverse cervical nodes)
Accessory nodes
located along the path of CN XI, receive lymph from superficial lymph nodes of hte head (located SUPERFICIAL to the investing fascia) including:
- occipital nodes which drain the occipital area
- retroauricular nodes, which drain the posterior parietal area
Transverse cervical nodes
which receive lymph from the posterior thorax under the trapexius, the accessory chain of nodes, lateral areas of the neck, upper anterior thoracic wall including the mammary gland and sometimes drainage from the apical nodes of hte axillary system, drain to the INFERIOR DEEP CERVICAL NODES (along the internal jugular vein) to the jugular lymph trunk or directly into the internal jugular or subclavian vein.
Boundaries of the anterior triangle
roof: investing cervical fascia
anterior: line from symphysis menti to sternal notch
posterior: anterior border of SCM
superior: inferior margin of mandible
floor: structural components of the visceral compartment of the neck
Muscles of the anterior triangle
Digastric Sylohyoid Mylohyoid Sternoyoid Sternthyroid Thyrohyoid Omohyoid
Suprahyoid muscles
digastric, stylohyoid, mylohyoid
infrahyoid (strap) muscles
sternohyoid
sternothyroid
thyrohyoid
omohyoid
Digastric muscle
a two-bellied muscle with an intermediate tendon which passes through the attachment of the stylohyoid muscle and is tethered to the hyoid bone via a fascial sling
O: Anterior belly- digastric fossa of mandible
- - Posterior belly- mastoid notch of temporal bone
I: Hyoid bone via fascial sling from intermediate tnedon
A: elevates hyoid and base of tongue; with hyoid fixed via infrahyoid musculature, assists in opening the mouth
N: Anterior belly: mylohoid n (CN V3)
- - posterior belly: digastric branch of facial n. (CN VII)
Stylohyoid
O: Posterior base of styloid process
I: body of hyoid bone near lesser horn
A: elevates and retracts the hyoid and base of the tongue
N: digastric branch of facial n. (CN VII)
Mylohyoid
O: Mylohyoid line of both sides of mandible
I: Midline raphe from symphysis menti to body of hyoid bone
A: elevates hyoid and floor of mouth; when hyoid is fixed depresses mandible
N: Mylohyoid branch of trigeminal (CN V3)
Sternohyoid
O: Posterior surface of manubrium at sternoclavicular joint, clavicle and posterior sternoclavicular ligament
I: inferior margin body of hyoid
A: depresses hyoid and larynx
N: Ansa cervicalis of cervical plexus
Sternothyroid
O: Posterior surface of manubrium inferior to sternohyoid
I: oblique line of thyroid cartilage
A: depresses larynx
N: Ansa cervicalis of cervical plexus
Thyrohyoid
O: oblique line of thyroid cartilage
I: inferior margin of body and greater horn of hyoid
A: Depresses hyoid and tongue when larynx is fixed from below; elevates larynx when hyoid is fixed from above
N: C1 via hypoglossal N.
Omohyoid
a two-bellied muscle with an intermediate tendon which is tethered to the posterior surface of the clavicle and first rib via a fascial sling
O: Superior belly- inferior margin greater horn of hyoid
- - inferior belly- superior margin of scapula near notch and suprascapular ligament.
I: Via fascial sling of infrahyoid fascia to clavicle and first rib and sheath to subclavian vein
A: stabilizes, retracts and depresses hyoid and larynx
N: ansa cervicalis of cervical plexus
Thyroid gland
endocrine gland; follicular cells secrete thyroxin which controls metabolic rate; parafollicular C cells secrete calcitonin which decreases circulating Ca++ levels
located posterior to the sternohyoid and sternothyroid muscles
limited above by the attachment of the sternothyroid to the oblique line of the thyroid cartilage; extends below approximately to the level of the sixth tracheal ring
Composed of two laterally displaced lobes (rounded inferiorly and tapered superiorly) attached via an isthmus and surrounded by a thin connective tissue capsule; the isthmus typically crosses the 2nd, 3rd and 4th tracheal rings
Pretracheal fascia forms a capsule-like envelope surrounding the entirety of gland; attached to the cricoid via a medial fascial extension of this fascia
Medially, contacts the trachea, recurrent laryngeal nn. and esophagus
limited laterally by the carotid sheath and its contents.
Clinical note re: thyroid
a pyramidal lobe may exist at the junction of the isthmus with the left lobe extending superiorly toward the hyoid. This lobe marks the descent of the thyroid primordium through the thyroglossal duct. Also, in the absence of a pyramidal lobe, ectopic glandular tissue may remain active along this route of descent thereby forming thyroglossal duct cysts.
Blood supply to the thyroid gland
Superior thyroid artery
Inferior thyroid artery
thyroid ima artery (10%)
Superior thyroid artery
first branch of the external carotid artery
courses along the superior medial margin of the thyroid gland
Major branches:
- superior laryngeal a. - pierces the thyrohyoid membrane with the internal laryngeal n. (vagus) to provide branches to the interior of the larynx
- anterior branch- branches to the anterior portion of the thyroid gland; anastomoses with opposite counterpart
- posterio branch- branches to the posterior portion of gland; anastomoses with branches ofthe inferior thyroid artery.
Minor branches include muscular branches to the strap muscles, SCM, inferior constrictor and esophagus.
Inferior thyroid artery
branch of the thyrocervical trunk (1st part of subclavian artery)
ascends along the medial border of the anterior scalene muscle
passes BEHIND the carotid sheath and sympathetic trunk at the level of the thyroid cartilage; the middle cervical ganglion rests on the inferior thyroid artery
porvides branches to the pharynx, larynx, trachea and esophagus before providing glandular branches to the posterior inferior portion of the thyroid gland
anastomoses with posterior branches of the superior thyroid artery
Thyroid ima artery (10%)
Variable, unpaired branch of the brachiocephalic or directly from the aortic arch
ascends the ventral surface of trachea to gain the thyroid isthmus
anastomoses with branches of inferior thyroid arteries
Clinical note- tracheostomy
care must be observed as a midline incision may interrupt the course of the thyroid ima a. if present. The origin of this artery from the brachiocephalic a. or aorta makes this especially problematic.
Venous drainage of thyroid
Composed of 3 pairs of thyroid veins which spring from venous plexuses on the surface of the gland
- Superior thyroid veins- drain the area supplied by the superior thyroid artery; follow the course of the superior thyroid artery, cross the common carotid to drain into the internal jugular veins
- Middle thyroid eins- drain the lateral surface of the gland directly to the internal jugular veins
- Inferior thyroid veins- drain the inferior portion of the thyroid gland, esophagus, larynx and trachea; descend on the surface of the trachea and drain to right and left brachiocephalic veins; may fuse to form a single THYROID IMA VEIN which characteristically drains to the LEFT brachiocephalic vein.
Lymphatic drainage of the thyroid
interlobular lymphtics coalesce to form a subcapsular plexus
From this plexus of lymphatic channels ascend and descend to nodes located in the immediate region
Nodes involved include:
a. pre-laryngeal (juxtavisceral)
b. pre-tracheal and para-tracheal (juxtavisceral)
c. superior and inferior deep cervical
In general, lymph from the superior one-half of the gland drains to superior deep cervical nodes, the inferior one-half drains to inferior deep cervical nodes. However, all lymph from the thyroid gland ultimately drains to the deep cervical nodes.
Innervation of the thyroid gland
preganglionic sympatheti fibers arise from spinal cord levels T1-T4 to ascend in the sympathetic chain where they will synapse in ganglia of the parathyroid glands
postganglionic sympathetic fibers travel from the superior, middle and cervicothoracic ganglia (fused inferior cervical and 1st thoracic ganglia) VIA the sympathetic cardiac nerves, superior and inferior laryngeal nerves and on the surfaces of arteries supplying the gland.
Some of these fibers are vasomotor while others are thought to end in the vicinity of follicular epithelial cells.
Parathyroid glands
2-6 small flattened ovoid bodies located beneath the capsule of the thyroid gland on its dorsal surface
Occur superiorly (at the levels of the cricoid cartilage) and inferiorly (at the inferior pole of the thyroid gland)
Secrete parathormone which is important in achieving a balance between serum and skeletal calcium levels by increasing serum calcium levels through mobilization of stored calcium (skeletal) and increased calcium uptake from the gut.
SHares blood supply, venous and lymphatic drainage and nerve supply of the thyroid gland.
inadvertent removal of the parathyroid leads to
tetany and death
Trachea (cervical portion)
continuation of airway below cricoid cartilage of larynx
cervical portion accounts for about 1/2 the length
Composed of incomplete cartilaginous rings united by membranous tissue; rings are approx 2.5 cm in diameter and are closed posteriorly by the TRACHEALIS muscle, an autonomically innervated (smooth) muscle which regulates tracheal diameter.
Relations of trachea
anterior: isthmus of the thyroid gland (rings 2-4), sternothyroid, sternohyoid, inferior thyroid veins, jugulovenous arch
lateral: superiorly: lobes of hte thyroid gland. inferiorly: carotid sheath
posterior: esophagus, recurrent laryngeal nerves.
blood supply of trachea
inferior thyroid arteries
venous drainage of trachea
inferior thyroid veins
lymphatic drainage of trachea
juxtavisceral nodes (pre-tracheal, para-tracheal, inferior deep cervical nodes)
innervation of trachea
sympathetics directly from sympathetic trunk
parasympathetics from vagus and recurrent laryngeal nerves.
Esophagus (cervical portion)
Extends inferiorly from the inferior border of the cricoid cartilage opposite the 6th cervical vertebra.
located in the midline it inlines to the left as it descends through the neck
muscle of cervical portion is striated
Relations of the esophagus
anterior: trachea, recurrent laryngeal nerves
lateral: thyroid gland, carotid sheath, thoracic duct on the left
posterior: buccopharyngeal, alar, and pre-vertebral fascia over pre-vertebral muscles and vertebral column
blood supply of esophagus
inferior thyroid arteries
venous drainage of esophagus
inferior thyroid veins
lymphatic drainage of esophagus
paratracheal and inferior deep cervical lymph nodes
innervation of esophagus
sympathetics: sympathetic trunk (vasomotor and glandular)
parasympathetics: recurrent laryngeal nerves (muscular tone and glandular)
