Infrahyoid Anterior Neck Triangles, Levels of Cervical Lymph Nodes and Root of Neck Flashcards
Don't overburden yourself with the levels of cervical lymph nodes.
Outline the boundaries of the anterior triangle of the neck. (anterior, posterior, base, apex, roof)
Anterior: anterior midline of the neck
Posterior: anterior border of sternocleidomastoid
Base: lower border of body of the mandible and a line extending from the angle of mandible to the mastoid process
Apex: suprasternal notch at the meeting point between the anterior border of the sternocleidomastoid and anterior median line
Roof: investing layer of deep cervical fascia
[Diagram 1] [Diagram 2]
Further notes:
The superficial fascia over the fascial roof contains platysma in the upper and anterior parts. The cervical branch of facial nerve and ascending and descending branches of transverse cervical cutaneous nerve traverse the plane between the platysma and the fascial roof of the triangle.
digastric muscle
(a) origin
(b) insertion
(c) action
(d) innervation
(a) origin
✔ It has two bellies: anterior and posterior.
✔ Origin of posterior belly: mastoid notch on medial surface of mastoid process of temporal bone.
✔ Origin of anterior belly: digastric fossa of lower border of mandible, close to symphysis menti
(b) insertion
Attachment of intermediate tendon between two bellies to body of hyoid bone.
[Diagram]
(c) action
Anterior belly: opens mouth by lowering mandible, raises hyoid bone
Posterior belly: pulls hyoid bone upward and back
[Alternatively, the actions of digastric can be stated as: (1) depression of the mandible when the hyoid bone is fixed, (2) elevation of the hyoid bone and larynx when the mandible is fixed.]
(d) innervation
✔ anterior belly is innervated by the nerve to mylohyoid muscle [a branch of the inferior alveolar nerve that arises from the mandibular nerve. The anterior belly is a derivative of the 1st pharyngeal arch.]
✔ the posterior belly is innervated by the digastric branch of the facial nerve [The posterior belly is a derivative of the second pharyngeal arch.]
omohyoid muscle
(a) origin
(b) insertion
(c) action
(d) innervation
(a) origin, (b) insertion
✔ It has two bellies: inferior and superior.
✔ The inferior belly originates from the inferior border of the scapula, medial to the suprascapular notch.
✔ From there, the muscle inclines anteriorly and superiorly towards the lower part of the neck, inserting into the omohyoid’s intermediate tendon.
✔ The superior belly begins at the intermediate tendon and runs superiorly to be attached to the lower border of the hyoid bone.
✔ [The intermediate tendon lies at the level of arch of cricoid cartilage and is anchored to the clavicle by fascial sling derived from investing layer of deep cervical fascia.]
(c) action
✔ it depresses the hyoid bone following its elevation during the act of swallowing [This action reopens the laryngeal inlet, which is normally closed of during swallowing to prevent inhalation of the food bolus. Thus, the act of opening the laryngeal inlet reestablishes breathing after swallowing. All the infrahyoid muscles share this function.]
(d) innervation
✔ superior belly is innervated by the superior root of ansa cervicalis (C1)
✔ inferior belly receives fibers from spinal nerves C1, C2 and C3 (via ansa cervicalis)
Click on Answer to view important landmarks in the neck.
- Hyoid bone between the floor and the superior end of the neck.
- Thyroid cartilage
- Cricoid cartilage
- Cricothyroid membrane
- Tracheal rings [particularly the 1st, 2nd and 3rd rings]
- Thyrohyoid membrane
The infrahyoid muscles of the neck/strap muscles of the neck are ribbon-like and comprise 4 paired muscles. List these muscles.
(a) Sternohyoid
(b) Sternothyroid
(c) Thyrohyoid
(d) Omohyoid
Omohyoid and sternohyoid are superficial to thyrohyoid and sternothyroid.
Sternohyoid muscle
1. Origin
2. Insertion
3. Innervation
4. Action
- Origin: Posterior aspect of sternoclavicular joint and adjacent manubrium of sternum
- Insertion: Body of hyoid bone medial to attachment of omohyoid muscle
- Innervation: Anterior rami of C1 to C3 through the ansa cervicalis
- Action: Depresses hyoid bone after swallowing. Note that omohyoid does this during swallowing.
- [Diagram]
Sternothyroid muscle
a) Origin
b) Insertion
c) Innervation
d) Action
a) Origin: Posterior surface of manubrium of sternum
b) Insertion: Oblique line on lamina of thyroid cartilage
c) Innervation: Anterior rami of C1 to C3 through the ansa cervicalis
d) Action: draws larynx (thyroid cartilage) downward
Thyrohyoid muscle
a) Origin:
b) Insertion:
c) Innervation:
d) Action:
a) Origin: Oblique line of thyroid cartilage
b) Insertion: Greater horn and adjacent aspect of body of hyoid bone
c) Innervation: Fibers from anterior ramus of C1 carried along hypoglossal nerve [XII]
d) Action: Depresses hyoid bone, but when hyoid bone is fixed raises larynx
[Diagram]
For convenience of description, the anterior triangle has been subdivided, by the digastric muscle and superior belly of omohyoid muscle, into the following 31⁄2 triangles. List those triangles.
- Submental triangle (half only)
- Digastric (submandibular) triangle
- Carotid triangle
- Muscular triangle
- [Diagram]
State the boundaries and contents of the muscular triangle.
Boundaries:
Anterior: Anterior median line of the neck, extending from hyoid bone to the suprasternal notch.
Anterosuperior: Superior belly of the omohyoid.
Posteroinferior: Anterior border of sternocleidomastoid.
Roof: It is formed by investing layer of deep cervical fascia. The superficial fascia over the roof contains anterior jugular vein and associated lymph nodes. [Anterior jugular vein was covered in posterior neck triangles flashcards.]
Contents:
✔ Infrahyoid muscles, viz. sternothyroid, sternohyoid, and thyrohyoid. (One would argue that they form the floor of the muscular triangle.)
✔ The important deeper structures in the region of muscular triangle are thyroid gland, trachea, and esophagus.
State the clinical relevance of the muscular triangle.
boundaries of this triangle are used as landmarks during surgeries
State the location and gross morphology of the thyroid gland.
Location:
- anterior lower neck, in front of the trachea and below the thyroid cartilage
- enclosed by pretracheal layer of deep cervical fascia
Gross morphology:
- has two lobes-right and left lateral lobes, which are somewhat conical
- the two lobes are connected together by a narrow, median isthmus
- a pyramidal lobe may be present, attached to the isthmus and projecting towards the hyoid bone
Describe the extents of the thyroid gland.
✔ The lobes extend from the level of C5-T1 vertebrae
✔ Upper extent: oblique line of thyroid cartilage
✔ Lower extent: 4th or 5th tracheal ring
✔ The isthmus lies at the level of the 2nd to 3rd or 4th tracheal ring, and measures less than 1.5 cm in thickness
Relations of the lobes of the thyroid gland are best described with its surfaces. State the relations of the anterolateral (superficial) surface of the thyroid lobe. [Hint: 4 muscular, 1 vascular]
- Sternothyroid
- Sternohyoid
- Superior belly of omohyoid
- Sternocleidomastoid muscle (more of the anterior border)
- Anterior jugular vein
[Diagram 1: Relational Anatomy of the Thyroid Gland]
[Diagram 2: Relational Anatomy of the Thyroid Gland]
[Diagram 3: Relational Anatomy of the Thyroid Gland]
[Diagram 4: Relational Anatomy of the Thyroid Gland]
State the relations of the medial surface of the thyroid lobe.
- Esophagus and trachea
- Pharynx and larynx
- Inferior pharyngeal constrictor and cricothyroid muscle
- The external laryngeal and recurrent laryngeal nerves
[Diagram 1: Relational Anatomy of the Thyroid Gland]
[Diagram 2: Relational Anatomy of the Thyroid Gland]
[Diagram 3: Relational Anatomy of the Thyroid Gland]
[Diagram 4: Relational Anatomy of the Thyroid Gland]
State the extents of the carotid sheath.
It extends from the arch of the aorta to the skull base.
State the relations of the posterolateral surface of the thyroid lobe.
Related to carotid sheath and its contents i.e.
1. Common carotid artery
2. Internal jugular vein
3. Vagus nerve
Further notes:
The ansa-cervicalis is embedded in the anterior wall of the sheath while cervical sympathetic chain lies posterior to sheath in front of prevertebral fascia.
[Diagram 1]: Relational Anatomy of the Thyroid Gland
[Diagram 2]: Relational Anatomy of the Thyroid Gland
[Diagram 3]: Relational Anatomy of the Thyroid Gland
[Diagram 4]: Relational Anatomy of the Thyroid Gland
relations of the posterior border of the thyroid gland
- parathyroid glands
- inferior thyroid artery
[Diagram 1: Posterior Surface of the Thyroid Gland]; The anterior surface is shown also shown.
[Diagram 2: Posterior Surface of the Thyroid Gland]; Here it clearly captures the two relations of the posterior border of the gland. The anterior surface is also shown.
State the relations of the thyroid isthmus.
Anteriorly: anterior jugular veins, sternothyroid, sternohyoid
Posteriorly: cervical trachea, with its intervening 2-4 rings
Superiorly: anastomosis between the anterior branches of two superior thyroid arteries.
Inferiorly: Along this border inferior thyroid vein emerge and thyroidea ima artery (when present) enters
Describe the arterial supply to the thyroid gland. Here, describe superior thyroid artery.
Superior thyroid artery
✓ the 1st anterior branch of the external carotid artery [Diagram]
✓ runs downwards and forwards in company with the external laryngeal nerve, which it leaves near the upper pole of the thyroid lobe
✓ divides into the anterior and posterior glandular branches at the apex of the lobe
✓ anterior branch eventually anastomoses with its fellow on the contralateral side at the upper superior border of the thyroid
✓ posterior branch descends along the posterior border of the lobe to anastomose with the ascending branch of the inferior thyroid artery ipsilaterally
Area of supply of superior thyroid artery: upper one-third of the lobe and upper half of the isthmus.
[Diagram: Arterial supply to the thyroid gland] [Cadaveric image]
Further notes:
The external laryngeal nerve is a branch of the superior laryngeal nerve, which is a branch of the vagus nerve. [Diagram]
Describe the arterial supply to the thyroid gland. Here, describe inferior thyroid artery, and thyroidea ima artery.
-
Inferior thyroid artery
✓ terminal branch of thyrocervical trunk
✓ runs with recurrent laryngeal nerve
✓ the artery gives 4 or 5 branches. One ascending branch anastomoses with the posterior branch of the superior thyroid artery.
✓ Area of supply of inferior thyroid artery: lower two-third of the lobe and lower half of the isthmus. -
Thyroidea ima artery
✓ in 30% cases
✓ a branch of the brachiocephalic trunk or may arise directly from the arch of aorta. It enters the isthmus from below.
[Diagram]: Arterial supply to the thyroid gland
[Diagram]: Variable relationship of recurrent laryngeal nerve with the inferior thyroid artery
Further notes:
The recurrent laryngeal nerve presents a variable relationship with the inferior thyroid artery. It may pass behind or in front of the loop of the artery or between the branches of the artery.
The superior thyroid artery is a branch of ____(a)____, whereas the inferior thyroid artery is a branch of ____(b)____.
(a) the external carotid artery
(b) the thyrocervical trunk
Describe the venous drainage of the thyroid gland.
(a) Superior thyroid vein: emerges at the upper pole of the thyroid lobe, travels alongside the superior thyroid artery; terminates in the internal jugular vein.
(b) Middle thyroid vein: emerges from the lateral part of the gland; also drains into the internal jugular vein.
(c) Inferior thyroid vein/veins: emerge at the lower border of the isthmus, form plexus in front of the trachea and then run downwards to drain into the brachiocephalic veins. These veins receive other veins e.g. esophageal, tracheal and inferior laryngeal veins
[Diagram: venous drainage of the thyroid gland]
Further notes:
Sometimes a fourth vein, the thyroid vein (of Kocher) emerges between the middle and inferior thyroid veins to drain into the internal jugular vein.
The brachiocephalic veins drain into the superior vena cava.
State the nerve supply to the thyroid gland.
The thyroid gland is supplied by both sympathetic and parasympathetic nerve fibres:
1. The parasympathetic supply is derived from the vagus and recurrent laryngeal nerves. [recurrent laryngeal nerve is a branch of the vagus nerve]
2. The sympathetic supply is derived from the superior, middle, and inferior cervical sympathetic ganglia, but mainly from the middle one.
Describe the location and gross morphology of the parathyroid glands.
- small, ovoid or lentiform glands that lie in the posterior borders of the thyroid lobes
- usually 4 in number, each measuring 6mm by 3-4 mm by 1-2 mm
- the superior glands are more constant in their location than the inferior ones
Mention 2 ectopic sites of parathyroid glands.
- Inferior parathyroid glands may be found within the thymus.
- Superior parathyroid glands may be found within the tracheoesophageal groove and retroesophageal region.
State the origin, course, and distribution of the recurrent laryngeal nerve.
The recurrent laryngeal nerve (RLN), a branch of the vagus nerve (cranial nerve X), plays a crucial role in innervating the larynx.
Origin:
✔ The RLN emerges from the vagus nerve.
✔ There are two recurrent laryngeal nerves: one on the right and another on the left.
✔ These nerves are not symmetrical: [Diagram]
The left RLN loops under the aortic arch.
The right RLN loops under the right subclavian artery before ascending.
✔ Both nerves travel alongside the trachea.
Course:
✔ The right RLN has a shorter course, passing under the subclavian artery.
✔ The left RLN takes a more circuitous route:
It passes under the aortic arch and the ligamentum arteriosum.
✔ After branching, it ascends in a groove at the junction of the trachea and esophagus. [tracheoesophageal groove]
It then passes behind the posterior, middle part of the outer lobes of the thyroid gland.
✔ Finally, it enters the larynx underneath the inferior constrictor muscle, just posterior to the cricothyroid joint.
Distribution:
✔ The RLN supplies all the intrinsic muscles of the larynx, except for the cricothyroid muscles.
It provides sensation to the larynx below the vocal cords.
✔ Additionally, the RLN gives cardiac branches to the deep cardiac plexus and branches to the trachea, esophagus, and the inferior constrictor muscles.
✔ Notably, the posterior cricoarytenoid muscles, responsible for opening the vocal folds, are innervated by this nerve.
What is thyroidectomy?
A thyroidectomy is a common surgical procedure. In most cases it involves excision of part or most of the thyroid gland. This surgical procedure is usually carried out for benign diseases, such as multinodular goiter and thyroid cancer.
Further notes:
~ Given the location of the thyroid gland, there is a possibility of damaging other structures when carrying out a thyroidectomy, namely the parathyroid glands and the recurrent laryngeal nerve. Assessment of the vocal folds is necessary before and after thyroid surgery because the recurrent laryngeal nerves are closely related to ligaments that bind the gland to the larynx and can be easily traumatized during surgical procedures.
~ Since colossal sizes of goitre may damage the recurrent laryngeal nerve, it is good habit to do laryngoscopy before thyroidectomy, so that pre-operative damage can be distinguished from post-operative damage.
