L6: Anterior triangle Flashcards
Clinical applications of anterior triangle
- Thyroid (goitre)
- Central vein catheterization (between 2 heads of SMC)
- Penetrating trauma
- Cricothyroidotomy/tracheostomy
Anterior triangle borders and triangles within
Borders: midline of neck, inferior border of mandible and anterior border of SMC
Contains: submandibular triangle, submental triangle, muscular triangle and carotid triangle
Infrahyoid muscles (strap muscles)
- sternohyoid muscle (most superficial)
- sternothyroid muscle - thyroid cartilage (oblique line) to sternum
- thyrohyoid muscle - thyroid cartilage to hyoid bone
- omohyoid muscle - hyoid bone to shoulder (lat. to SMC)
Cervical plexus - sensory
Direct branches from anterior rami: lesser occipital n, great auricular n, supraclavicular n, transverse cervical n
Cervical plexus - motor
= Ansa cervicalis (loop)
Thyrohyoid m supplied by C1 (sup. root)
Sternothryoid, sternohyoid, omohyoid suppplied by C2/C3 (inf. root)
Thyroid anatomy/location
After removing strap muscle, thyroid is deep to pretracheal fascia
Lateral lobes either side of trachea, isthmus in middle
Isthmus on top of 2nd/3rd tracheal cartilage rings
Lobes can come up as far as upper border of thyroid cartilage
(Cricoid cartilage under thyroid cartilage)
Thyroid arterial and venous
Arterial:
- Superior thyroid a (from external carotid a) - runs
downward to upper pole of lat. lobe, divides into ant. and
post. glandular branches
- Inferior thyroid a (from subclavian a) - runs upward behind
carotid sheath to lower pole of lat. lobe, divides into inf.
and ascending branch
- May have ima artery direct from arch of aorta supplying
isthmus (variant)
Venous:
Superior and middle thyroid veins drain back to internal jugular vein
Inferior thyroid vein drains to brachiocephalic vein
(impt in metastases of cancer)
Thyroid lymphatics and innervation
Lymphatics:
Drains back to paratracheal and deep cervical lymph nodes (posteroinferior group)
Innervation:
Sympathetic - middle cervical ganglion (runs w arteries)
(sympathetic chain has 3 branches: inf, middle, sup)
Parasympathetic - vagus (recurrent laryngeal n)
Clinical relevance of thyroid gland (surgery)
On either side of thyroid lobes (laterally) is common carotid sheath containing internal jugular v, common carotid a, vagus n)
Between trachea and oesphagus is recurrent laryngeal n
When removing thyroid - take care not to damage carotid a and recurrent laryngeal n
Thyroid embryology
Originates at foramen cecum and descends to final position below thyroid cartilage via tract of thyroglossal duct
- Lingual thyroid - when tissue stays within tongue
- Accessory thyroid tissue - between tongue and hyoid
bone
- Cervical thyroid - below hyoid bone
- Outpouching of thyroid lobe - pyramidal thyroid
- If thyroglossal duct does not close - food can enter (bad
breath)
Suprahyoid muscles
- Anterior belly of digastric (most superficial)
- Mylohyoid m (deep to anterior belly)
- Stylohyoid m (attached to styloid process)
- Posterior belly of digastric (attached to mastoid process)
(stylohyoid and post. belly in same plane as mylohyoid
but lateral) - Geniohyoid m (deep to ant. belly and mylohyoid)
Innervation of suprahyoid muscles
- Facial n (VII): post. belly and stylohyoid (as it exits
stylomastoid foramen) - V3 (mandibular branch of V): ant. belly of digastric and
mylohyoid - C1 (from cervical plexus): geniohyoid (was originally 1
muscle with thyrohyoid so both C1 supply)
Carotid artery - internal and external
Bifurcation @ C3/C4
Internal carotid: has no branches in the neck (supplies the head)
- Lies in carotid sheath initially medial to int. jugular v and
anterior to vagus n
- Origin is dilated forming carotid sinus which contains
baroreceptors
- Carotid body w its chemoreceptors usually behind
bifurcation of common carotid a
External carotid: gives branches immediately after bifurcation of common carotid
- Superior thyroid a
- Ascending pharyngeal a
- Lingual a
- Facial a
- Occipital a
- Posterior auricular a
- Maxillary a
- Superior temporal a
Venous drainage
External jugular v = formed by posterior auricular v and retromandibular v
Internal jugular v = formed by sigmoid sinus, exits skull via jugular foramen and joins subclavian to form brachiocephalic v
Vagus nerve [X]
Exits skull: through jugular foramen (w IX and XI)
Travels through: carotid sheath (between int. carotid and int,. jugular v)
At root of neck: stays close to midline (compared to phrenic n), passes in front of subclavian a and behind subclavian v to enter mediastinum
Branches: pharyngeal branch, int. and ext. branches of superior laryngeal, cardiac branch, recurrent laryngeal
