Anterior Triangle of Neck-Fri, Sept 29
Terms
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- Boundaries:
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*superiorly, inferior border of mandible
*medially, by midline
*laterally, anterior border of SCM - fascia and layers of neck:
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1. superficially, layer of fat; platysma lies in this plane
2. deep investing layer of fascia-surrounds whole neck
3. pretracheal fascia-surrounds trachea and thyroid gland
4. prevertebral deep investing fascia-posterior of neck; surrounds muscles associated with vertebral column
5. buccopharyngeal fascia-posterior to esophagus, anterior to prevertebral fascia
6. retropharyngeal space- anterior to prevertebral fascia and posterior to buccopharyngeal fascia; bounded laterally by carotid sheaths
**infections in this space can drain inferiorly toward heart - subdivisions of anterior triangle:
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1. submental triangle-inferior to mandible anteriorly
a)bound on either side by anterior belly of digastric muscle
b)hyoid bone forms the base of triangle
2. submandibular triangle-bound superiorly by mandible and on either side by anterior and posterior bellies of digastrics
3. carotid triangle-
a)bound superiorly by posterior belly of digastric
b)inferolaterally by anterior border of SCM
c)inferomedially by superior belly of omohyoid muscle
4. muscular triangle-
a)dorsolaterally, superior belly of omohyoid
b)inferolaterally, by SCM - Platysma
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*allows grimace
*innervated by cervical branch of facial nerve (CN VII) - Contents of triangle: muscles
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1. hyoid bone: superior to thyroid cartilage, which is superior to cricoid cartilage; between hyoid and thyroid cartilage is thyrohyoid membrane
2. strat or infrahyoid muscles-depress the hyoid bone
a)superior belly of omohyoid-arises from fascial sling on clavicle and inserts on hyoid
b)sternohyoid-passes from sternum and clavicle up to hyoid
c)sternothyroid-sternum and clavicle up to thyroid cartilage; depresses larynx
d)thyrohyoid-runs from thryoid cartilage up to hyoid; elevates larynx; C1
e)digastric muscles-anterior belly inserts on digastric fossa of mandible
f)deep to digastric, mylohyoid-arises from mylohyoid line on inferior border of mandible and inserts on hyoid bone and median raphe; elevate hyoid - Ansa Cervicalis and Cervical Plexus
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*part of cervical plexus
*associated with ECA and its tributaries
*lies lateral to carotid sheath
*cutaneous innervation of anterior triangle is by transverse cervical nerves from C2 and C3 - Ansa Cervicalis
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1. Hypoglossal nerve (CNXII)
*associated posteriorly with a muscular branch of occipital artery (lies anterior)
*CNXII runs anterior to ECA
*A branch of C1 travels with hypoglossal and branches off to innervate thyrohyoid and geniohyoid
*superior root of ansa cervicalis extends anteriorly in front of the CCA to give branches to sternohyoid, inferior belly of omohyoid, and sternothyroid
*posteriorly and laterally, anterior rami of C2 and C3 run posterior to IJV to loop around and join the C1 to form the ansa cervicalis - Carotid Triangle
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*hypoglossal nerve passes inferior to posterior belly of digastric; enters submandibular triangle
*good landmark to find this nerve with occipital artery branch
*superior thyroid artery runs inferiorly and gives off the superior laryngeal artery, which pierces the thyrohyoid membrane
*external laryngeal nerve, branch of superior laryngeal nerve (CNX), passes with superior thyroid artery
*IL nerve gives sensory (GVA) to larynx and pharynx superior to vocal chords
*recurrent laryngeal nerve (CNX) innervates inferior to vocal chords
*external laryngeal nerve-also branch of superior laryngeal, moves lower to innervate the cricothyroid muscle (SVE)
*Branches of ECA - Branches of ECA:
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1. ascending pharyngeal
2. superior thyroid
3. lingual
4. facial-gives rise to ascending tonsilar branch
5. occipital
6. posterior auricular
Terminal branches:
7. superficial temporal
8. maxillary-gives off several branches - Thyroid Gland:
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*rests anteriorly in neck
*surrounded by 2 layers of investing fascia
*carotid sheath is on either side
*superior thyroid artery from ECA
*inferior thyroid artery from thyrocervical trunk
*may also be a persistent thyroglossal duct passing up to foramen cecum on posterior aspect of tongue
*venous drainage by superior, middle, and inferior thyroid veins; inferior drains into brachiocephalic trunk; other 2 drains into IJV - Parathyroid glands
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**regulate calcium and calcitonin in the body
**tetany-if glands removed during thyroidectomy, seizures due to sudden plunge in serum calcium - Submandibular Triangle
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1. hypoglossal nerve-passes posterior to posterior belly of digastric
2. stylohyoid muscle-runs from styloid pocess on skull down to hyoid, running anterior to posterior belly of digastric, but inserting just posterior to fibrous sling
3. facial artery-deep to mandible and lateral to mylohyoid
4. anterior belly of digastric-inserts on digastric fossa of mandible; innervated by nerve to mylohyoid, a branch of inferior alveolar nerve
5. posterior belly of digastric-arises from mastoid notch at base of skull; innervated by CNVII
6. lingual artery-passes deep to mylohyoid, while hypoglossal nerve passes laterally
7. submandibular gland and duct
8. lingual nerve-crosses duct twice
9. submandibular ganglion-found posterolaterally to lingual nerve, receiving presynaptic parasympathetic fibers from chorda tympani nerve, a branch of facial nerve
10. facial nerve-passes postganglionic fibers to sublingual gland
11. hyoglossus-major extrinsic muscle of tongue; deep to mylohyoid muscle
12. geniohyoid muscles-superior to mylohyoid at midline; arise from inferior mental spin and run to hyoid bone; innervated by C1 by way of hypoglossal nerve - Bifurcation of CCA:
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1. carotid body: located on posterior aspect of bifurcation; sensitive to oxygen and CO2 saturation; glossopharyngeal nerve
2. carotid sinus: thickened area anteriorly; glossopharyngeal nerve by way of nerve to carotid sinus; regulates blood pressure