Download MBBS General Surgery PPT 15 Thyroid Lecture Notes

THYROID

Today 's learning.......

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Embryology

Anatomy

Physiology

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Thyroid function test

Imaging

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Cytology
Embryology of thyroid

Embryology of thyroid............

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. Arises as an endodermal diverticulum from the floor of the pharynx.

. Week 3: Thickening in the floor between the 1st and 2nd pharyngeal pouches.

. Week 4: Endoderm evaginates ventral y (into the mesoderm) to form the thyroid diverticulum.

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. Week 5:

Formation of thyroglossal duct.

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Bifurcation on the tip of Thyroglossal duct forms isthmus and the lateral lobes of the gland.

. Weeks 5-6: Growth of duct down to the neck, migration down to the neck.

. Week 7: Final position in relation to the larynx and the trachea.

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Important facts related to thyroid

. Thyroid tissue migrates inferiorly

. The duct portion begins to involute

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. Site of connection thyroglossal duct with pharynx-

"Foramen Caecum"

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Important facts related to thyroid........

. Distal part of the thyroglossal duct may

develop "Pyramidal Lobe".

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. Thyroid gland may develop in any part at the

midline of the thyroglossal duct.

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lingual, suprahyoid, retrohyoid or infrahyoid

positions.

. Thyroid gland is relatively large in newborn

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babies.
Anatomy of thyroid

. Normal thyroid gland weighs about 15-25 g in

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adults.

."Butterfly" in shape.

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. Two lobes:

Consists of right and left lobes

Anterolateral to the larynx and trachea

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. Thin isthmus unites the lobes over the trachea.

Anatomy of thyroid.........
. Anteriorly in the neck at the level of the C5 -T1

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vertebrae.

. Deep to the sternothyroid and sternohyoid

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muscles

. Superior pole-

Lateral to inferior constrictor muscle and

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cricothyroid muscle.

At the level of 1st tracheal ring.

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. Inferior pole-

Extends up to the level of 5th or 6th tracheal rings
Anatomy of thyroid.........

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Surgical importance:

Thyroid swel ing never

moves upward

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Anatomy of thyroid.........

. Pyramidal lobe:

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~50% of thyroid glands.

Extends superiorly from the isthmus.

. "Levator glandulae thyroideae":

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Fibrous tissue connecting pyramidal lobe with hyoid bone.

. Accessory thyroid tissue

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A band of connective tissue, often containing accessory

thyroid tissue, may continue from the apex of the pyramidal
lobe.

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Surgical importance.
Anatomy of thyroid.........

. Thyroid Gland Capsule:

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True capsule:

A thin fibrous capsule, which sends septa deeply into the

gland.

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Divides the thyroid tissue into microscopic lobules.

False/ Surgical capsule:

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External to the true capsule.

A loose sheath formed by the visceral portion of the pre-

tracheal layer of deep cervical fascia.

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Investing layer of deep cervical fascia

Pretracheal fascia

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Prevertebral

layer of deep

cervical fascia

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Anatomy of thyroid.........

.Ligament of berry:

. Surgical importance:

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Formed from thickened pre-tracheal fascia

RLN often passes through this ligament.

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On the inner surface of the gland

Also contains the terminal branches of inferior thyroid

artery.

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Connect gland to cricoid cartilage

Anatomy of thyroid.........

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. Arteries of the Thyroid Gland:

Highly vascular.

Supplied by:

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o Superior thyroid arteries.
o Inferior thyroid artery.

Vessels lie between the fibrous capsule

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and loose fascial sheath.
Anatomy of thyroid.........

. Superior thyroid artery (STA):

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Descend to the superior poles of the gland.

Pierce the pre-tracheal layer of deep

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cervical fascia.

Divide into anterior and posterior branches.

Anatomy of thyroid.........

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. Inferior thyroid arteries (ITA):

Branches of the thyrocervical trunks.

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Run supero-medial y posterior to the carotid sheaths to

reach the posterior aspect of the gland.

Supply postero-inferior aspect with inferior poles of the

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gland.

. Right and left S TA and ITA arteries form anastomoses

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within the gland.
Anatomy of thyroid.........

. Thyroid Ima Artery:

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Approx. 10% of people have small unpaired thyroid ima

artery

Possible sources of Ima artery:

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o Branch of brachiocephalic trunk
o Arch of the aorta
o Right common carotid/subclavian/internal thoracic arteries

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Ascends on the anterior surface of the trachea and

continues to the thyroid isthmus.

Presence of this artery must be considered before

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tracheotomy (as a potential source of bleeding!)

Anatomy of thyroid.........

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. Veins of the Thyroid Gland:

Form thyroid plexus of veins on the anterior surface

of the thyroid gland- Three pairs of thyroid veins

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(superior, middle, inferior)

1. Superior thyroid veins- accompany the STA.

2. Middle thyroid veins- do not accompany but run

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essentially parallel courses with the ITA.

3. Inferior thyroid veins- accompany the thyroid ima

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artery (if artery is present)
Anatomy of thyroid.........

. Important nerves:

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Superior Laryngeal Nerve (SLN)

o Two branches- internal and external

Recurrent Laryngeal Nerve (RLN)

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Anatomy of thyroid.........

. Superior laryngeal nerve:

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Originates at the inferior ganglion of vagus nerve.

Average length of SLN is about 1.5 to 2 cm.

Courses:

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o Posterior and medial to the internal carotid artery.
o Descends antero-inferiorly to reach the larynx.

At the level of Greater Cornu of hyoid bone it divides:

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o Large- Internal laryngeal branch.
o Smaller- External laryngeal branch.
Anatomy of thyroid.........

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. Internal Laryngeal Nerve:

Passes between thyrohyoid muscle and the thyrohyoid

membrane.

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Pierces the thyrohyoid membrane along with superior

laryngeal artery and vein.

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After entering into the larynx this nerve divides into three

branches i.e. superior, middle and inferior.

Supply sensation to:

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Interior of larynx.

Supraglottis and pyriform sinus.

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Anatomy of thyroid.........

. Internal Laryngeal Nerve:

Superior division divides into 2-3 branches supplying sensations to

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o Lingual surface of epiglottis, lateral aspect of glosso-epiglotic fold.

Middle division innervates

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o Aryepiglotic fold, vocal folds, vestibular folds and the posterior aspect of arytenoid.

Inferior division

o The largest of the branches of superior laryngeal nerve.

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o It lies along the medial aspect of pyriform fossa.
Anatomy of thyroid.........

. External laryngeal nerve

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Course:

o At the level of superior horn of thyroid cartilage turns medial y.
o And runs posterior and parallel to the oblique line.
o Lies deep to the STA.

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o Relationship with the superior pole of thyroid gland is highly

variable.

Anatomy of thyroid.........

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.

. Anatomical

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Relationships

between STA and External Branch
of SLN:

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Closely related to external laryngeal

nerve at its origin.

Nerve moves away from the artery

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as artery approaches the upper pole
of the gland.
Anatomy of thyroid.........

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. In order to avoid injury of External Laryngeal Nerve:

STA need to be ligated just near the superior pole.

. Complication:

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Superior laryngeal nerve injury:

o Paralysis of the cricothyroid muscle.
o Changes in the pitch of the voice.

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o Inability to make explosive sounds.
o Bilateral injury presents as a tiring and hoarse voice.

Anatomy of thyroid.........

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. Relationship of the EB-SLN and STA:

Original y described by Cernea And Colleagues.

Type 1 anatomy- nerve crosses the artery 1 cm above the

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superior aspect of the thyroid lobe.

Type 2 anatomy-

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? 2a- nerve crosses the artery <1 cm above the thyroid pole

? 2b- nerve crosses the artery <1 cm below the thyroid pole
Anatomy of thyroid.........

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. RLN- Always asymmetric.

Anatomy of thyroid.........

. Right recurrent laryngeal nerve:

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Arises from vagus in the chest.

Reaches neck by crossing anterior to right subclavian

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artery.

Loops around Right subclavian artery to reach the

trachea-oesophageal groove.

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Ascends posterior to thyroid gland.

Enters the larynx behind the cricothyroid articulation

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and inferior cornua of thyroid.
Anatomy of thyroid.........

. Left recurrent laryngeal nerve:

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Arises from vagus in the chest.

Crosses the arch of aorta to reach the

neck.

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Ascends posterior to gland to reach the

trachea-oesophageal groove.

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Anatomy of thyroid.........

. Major difference in course between Right and Left RLN:

Loops around- subclavian and aortic arch respectively

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In lower part- left RLN is more closely related to the trachea than right side.

In middle part of the course- RLN is found within the trachea-oesophageal groove commonly.

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At the lower pole of thyroid gland- right nerve is slightly more anterior than the left.
Anatomy of thyroid.........

. Motor supply of RLN:

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Anatomy of thyroid.........

. Relationship of RLN to the ITA
Anatomy of thyroid.........

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. Intraoperative localization of nerves:

EB-SLN:

o Jol 's Triangle

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o Space of Reeve

RLN:

o Boehar's Triangle

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o Simon Triangle

Anatomy of thyroid.........

. Non-recurrent laryngeal nerve:

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An anomaly of the RLN.

Origin is cervical.

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Direct course from the vagus nerve

to the larynx without looping
around.
Anatomy of thyroid.........

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. Types of NRLN:

Type 1- arises directly from the vagus and travels

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with the Superior Thyroid Pedicle vessels.

Type 2A- travels transversely, paral el and

superficial to the trunk of the Inferior Thyroid

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Artery .

Type 2B- travels in a transverse path paral el, but

deep to or between the branches of the Inferior

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Thyroid Artery.

Anatomy of thyroid.........

. Surgical importance of RLN:

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Unilateral RLN injury-

Paralysis of I/L intrinsic muscles of larynx i.e. loss of abduction

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Unopposed action of cricothyroid muscle i.e. adduction

Paramedian position of I/L vocal card

Voice will be breathy but compensation occurs i.e. near to

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normal

Airway will be patent but can be compromised during exertion
Anatomy of thyroid.........

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. Surgical importance of RLN:

Bilateral RLN injury-

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Paralysis of B/L intrinsic muscles of larynx i.e. loss of

abduction.

Unopposed action of cricothyroid muscle i.e.

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adduction.

Paramedian or median position of vocal card.

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Stridor during breathing because compromised

airway.

Anatomy of thyroid.........

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Anatomy of thyroid.........

. Zuckerkandl's tubercle (ZT)

Posterior extension of the lateral lobes.

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Composing of thyroid tissue only.

Anatomy of thyroid.........

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. Surgical importance of ZT:

Dissection and excision of ZT for total

thyroidectomy.

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Close relationship between ZT and recurrent

laryngeal nerve (RLN).

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Needs careful, fine, and very close dissection

around the nerve.

Safe identification of the nerve and resection of

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the tubercle.
Anatomy of thyroid.........

. Lymphatic Drainage of the Thyroid Gland

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Thyroid lymphatic vessels communicates with:

1st level: Pre-laryngeal, Pre-tracheal, and Para-tracheal lymph nodes

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2nd level:

? Superior deep cervical nodes (from the prelaryngeal nodes)

? and Inferior deep cervical nodes (from the pretracheal and paratracheal nodes).

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Some lymphatic vessels may drain into the brachiocephalic lymphatic nodes.

Presence of metastases in lymphatic nodes of neck can be first

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sign of thyroid carcinoma!!!

Anatomy of thyroid.........

. Innervation of Thyroid Gland:

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Derived from- (Superior, Middle, and Inferior) Cervical

Sympathetic Ganglia

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Nerves reach the thyroid through-

Cardiac periarterial plexus

Superior and inferior thyroid plexus

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Only vasomotor fibers- constriction of blood vessels
No secretomotor supply

Endocrine secretion from the thyroid gland is hormonal y

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regulated by the pituitary gland through TSH!
Histology of thyroid

. Each lobule of contains:

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20 to 40 follicles.

Composed of follicle cel s and colloid.

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Colloid fil s the follicle cavities

. Follicle cells produce thyroglobulin.

. Between follicles are Para-follicular cells, which

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produce Calcitonin.