Anatomy Flashcards
(33 cards)
The thyroid gland originates from the
median and lateral thyroid anlages
calcitonin-secreting parafollicular C cells arise from
Lateral thyroid anlage
thyroglossal duct Cyst
thyroglossal duct does not completely obliterate and the epithelial duct cells remain
a thyroglossal duct cyst may arise from a persistent connection between the thyroid gland and the foramen cecum.
This scenario typically presents as a painless midline neck mass at or near the level of the hyoid, although it can be found near the base of the tongue or at the thyroid gland proper
Sistrunk procedure
excision of the entirety of the cyst and surrounding thyroglossal duct tract, including the central portion of the hyoid bone
Ectopic Thyroid
from the foramen cecum down to the anterior mediastinum.
can lead to the formation of a lingual thyroid gland near the base of the foramen cecum.
This abnormal thyroid tissue is often associated with inadequate thyroid hormone production with subsequent goitrous enlargement»_space; Surgical excision is occasionally necessary for these cases.
other common locations for ectopic thyroid tissue
along the path of the thyrothymic tract
along the descending path of the thymus gland.
Foci of normal thyroid tissue along this tract are typically referred to as thyroid rests.
These rests can occur in up to 50% of people and are typically not thought to be pathologic findings in and of themselves
Tx for thyroid rest
Surgical treatment of thyroid rest tissue may occasionally be indicated if clinically relevant;
examples of this include thyroid cancer requiring resection of a thyroid rest as a part of thyroidectomy or local compressive symptoms
Thyroid Location
behind the sternohyoid and sternothyroid strap muscles and the superficial and middle layers of the deep cervical fascia.
Pyramidal lobe
In half to three-quarters of people, a pyramidal lobe extends superiorly from the isthmus and represents the caudal remnant of the thyroglossal duct
Landmark for Distal RLN
The tubercle of Zuckerkandl and Berry ligament are relatively constant anatomic landmarks for identification of the distal recurrent laryngeal nerve (RLN), which typically runs just posterior to these structures
Another Landmark
The direction of the inferior thyroid artery as it enters the thyroid gland is another important landmark used for the identification of the RLN, which typically crosses the artery perpendicularly
Artries in thyroid
The superior thyroid arteries originate from the external carotid arteries, and divide as they enter the superior poles of the thyroid lobes.
The inferior thyroid arteries are branches from the thyrocervical trunks of the subclavian arteries.
In about 2% of people, a third artery called the thyroid ima artery arises directly from the aorta or innominate artery
Supply to Parathyroid
Branches of the inferior and superior arteries also supply the parathyroid glands.
there can be significant anatomic variation around the arterial supply to the superior glands, which can be supplied by the inferior thyroid artery alone, the superior thyroid artery alone, or both
Venous Drianage
The superior thyroid veins typically run parallel to the superior thyroid arteries and drain into the internal jugular veins.
The inferior thyroid veins run in a caudal direction from the inferior poles of the thyroid lobes and drain into the innominate veins.
The middle thyroid veins are highly variable but typically arise from the lateral aspect of the mid thyroid lobes; they drain into the internal jugular veins.
LNs
The bulk of lymphatic drainage from the thyroid first goes to the perithyroidal lymph nodes in the central neck collectively grouped as level VI, which includes the lymph nodes between the two carotid arteries and bounded by the hyoid bone superiorly and the sternal notch inferiorly.
The lateral neck jugular lymph nodes (IIa, III and IV) as well as those in the posterior triangle of the neck (particularly level Vb) also drain lymphatics from the thyroid
Skip metastases
Skip metastases that avoid Level VI and extend directly from the primary tumor (typically in the superior pole of the thyroid) to the lateral neck are exceptional cases that occur in less than 15% of cases
RLN
The RLN innervates the motor function of all of the intrinsic laryngeal muscles except for the cricothyroid.
It carries sensory fibers from the lower larynx, as well as minor motor and sensory fibers from the trachea and esophagus.
Unilateral injury to the RLN leads to paralysis of the ipsilateral vocal fold, with typical symptoms ranging from voice complaints such as hoarseness and vocal fatigue to aspiration.
Bilateral RLN injury with subsequent bilateral vocal fold paralysis may require tracheostomy
EBSLN
The EBSLN innervates the cricothyroid muscles, and it contributes to vocal fold tone and tension.
EBSLN injury leads to difficulties with achieving high pitch and vocal projection and volume.
LNs Compartments
Level VI contains the thyroid gland and the adjacent nodes bordered superiorly by the hyoid bone, inferiorly by the innominate (brachiocephalic) artery, and laterally on each side by the carotid sheaths.
Level II, III, and IV nodes are arrayed along the jugular veins on each side, bordered anteromedially by level VI and laterally by the posterior border of the sternocleidomastoid muscle.
Level III nodes are bounded superiorly by the level of the hyoid bone and inferiorly by the inferior aspect of the cricoid cartilage
Cont
levels II and IV are above and below level III, respectively.
The level I node compartment includes the submental and submandibular nodes above the hyoid bone and anterior to the posterior edge of the submandibular gland.
Level V nodes are in the posterior triangle, lateral to the lateral edge of the sternocleidomastoid muscle.
The inferior extent of level VI is defined as the suprasternal notch.
Many authors also include the pretracheal and paratracheal superior mediastinal lymph nodes above the level of the innominate artery (sometimes referred to as level VII)
Both RLNs are derived from the
sixth branchial arches below the sixth aortic arches.
the two nerves then anchor to and follow the right and left fourth aortic arch structures, which develop into differing arteries—the right subclavian artery and the aortic arch
Loop ?
The left RLN loops under the ligamentum arteriosum at the aortic arch and travels in the tracheoesophageal groove until it reaches the thyroid.
The right RLN loops under the right carotid-subclavian artery junction and migrates to the cricothyroid joint at the insertion into the larynx.
Because of the lateral location of the right carotid-subclavian junction and the shorter length of the course of the right RLN, this nerve can be identified traveling in a slightly anterior plane and an oblique direction compared to the left RLN, which tends to stay relatively deep and straight in the tracheoesophageal groove.
anatomic landmarks for RLN
- The tubercle of Zuckerkandl typically lies just anterior and lateral to the nerve.
- the nerve crosses the artery (usually posteriorly) and typically curves anteriorly toward the ligament of berry before diving posteriorly again into the laryngeal insertion point at the cricothyroid joint.
preservation of all of the branches is important to preserve nerve function; this is particularly true for the anterior branches of RLN, which predominantly provide motor innervation.
NON Recurrent ?
RLN also may course in a nonrecurrent fashion
branching in a direct path from the cervical vagus
On the right side, this is associated with and likely secondary to an aberrant right subclavian artery arising directly from the aortic arch instead of the innominate artery (called the “lusoria artery”).
> > absence of a normal right subclavian-carotid junction to pull down the right RLN
A left-sided nonrecurrent nerve can occur in the extremely rare scenarios of a patient with situs inversus
