Download MBBS (Bachelor of Medicine, Bachelor of Surgery) General Surgery PPT 15 Thyroid Lecture Notes
THYROID
Today 's learning.......
Embryology
Anatomy
Physiology
Thyroid function test
Imaging
Cytology
Embryology of thyroid
Embryology of thyroid............
. 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.
. Week 5:
Formation of thyroglossal duct.
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.
Important facts related to thyroid
. Thyroid tissue migrates inferiorly
. The duct portion begins to involute
. Site of connection thyroglossal duct with pharynx-
"Foramen Caecum"
Important facts related to thyroid........
. Distal part of the thyroglossal duct may
develop "Pyramidal Lobe".
. Thyroid gland may develop in any part at the
midline of the thyroglossal duct.
lingual, suprahyoid, retrohyoid or infrahyoid
positions.
. Thyroid gland is relatively large in newborn
babies.
Anatomy of thyroid
. Normal thyroid gland weighs about 15-25 g in
adults.
."Butterfly" in shape.
. Two lobes:
Consists of right and left lobes
Anterolateral to the larynx and trachea
. Thin isthmus unites the lobes over the trachea.
Anatomy of thyroid.........
. Anteriorly in the neck at the level of the C5 -T1
vertebrae.
. Deep to the sternothyroid and sternohyoid
muscles
. Superior pole-
Lateral to inferior constrictor muscle and
cricothyroid muscle.
At the level of 1st tracheal ring.
. Inferior pole-
Extends up to the level of 5th or 6th tracheal rings
Anatomy of thyroid.........
Surgical importance:
Thyroid swel ing never
moves upward
Anatomy of thyroid.........
. Pyramidal lobe:
~50% of thyroid glands.
Extends superiorly from the isthmus.
. "Levator glandulae thyroideae":
Fibrous tissue connecting pyramidal lobe with hyoid bone.
. Accessory thyroid tissue
A band of connective tissue, often containing accessory
thyroid tissue, may continue from the apex of the pyramidal
lobe.
Surgical importance.
Anatomy of thyroid.........
. Thyroid Gland Capsule:
True capsule:
A thin fibrous capsule, which sends septa deeply into the
gland.
Divides the thyroid tissue into microscopic lobules.
False/ Surgical capsule:
External to the true capsule.
A loose sheath formed by the visceral portion of the pre-
tracheal layer of deep cervical fascia.
Investing layer of deep cervical fascia
Pretracheal fascia
Prevertebral
layer of deep
cervical fascia
Anatomy of thyroid.........
.Ligament of berry:
. Surgical importance:
Formed from thickened pre-tracheal fascia
RLN often passes through this ligament.
On the inner surface of the gland
Also contains the terminal branches of inferior thyroid
artery.
Connect gland to cricoid cartilage
Anatomy of thyroid.........
. Arteries of the Thyroid Gland:
Highly vascular.
Supplied by:
o Superior thyroid arteries.
o Inferior thyroid artery.
Vessels lie between the fibrous capsule
and loose fascial sheath.
Anatomy of thyroid.........
. Superior thyroid artery (STA):
Descend to the superior poles of the gland.
Pierce the pre-tracheal layer of deep
cervical fascia.
Divide into anterior and posterior branches.
Anatomy of thyroid.........
. Inferior thyroid arteries (ITA):
Branches of the thyrocervical trunks.
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
gland.
. Right and left S TA and ITA arteries form anastomoses
within the gland.
Anatomy of thyroid.........
. Thyroid Ima Artery:
Approx. 10% of people have small unpaired thyroid ima
artery
Possible sources of Ima artery:
o Branch of brachiocephalic trunk
o Arch of the aorta
o Right common carotid/subclavian/internal thoracic arteries
Ascends on the anterior surface of the trachea and
continues to the thyroid isthmus.
Presence of this artery must be considered before
tracheotomy (as a potential source of bleeding!)
Anatomy of thyroid.........
. Veins of the Thyroid Gland:
Form thyroid plexus of veins on the anterior surface
of the thyroid gland- Three pairs of thyroid veins
(superior, middle, inferior)
1. Superior thyroid veins- accompany the STA.
2. Middle thyroid veins- do not accompany but run
essentially parallel courses with the ITA.
3. Inferior thyroid veins- accompany the thyroid ima
artery (if artery is present)
Anatomy of thyroid.........
. Important nerves:
Superior Laryngeal Nerve (SLN)
o Two branches- internal and external
Recurrent Laryngeal Nerve (RLN)
Anatomy of thyroid.........
. Superior laryngeal nerve:
Originates at the inferior ganglion of vagus nerve.
Average length of SLN is about 1.5 to 2 cm.
Courses:
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:
o Large- Internal laryngeal branch.
o Smaller- External laryngeal branch.
Anatomy of thyroid.........
. Internal Laryngeal Nerve:
Passes between thyrohyoid muscle and the thyrohyoid
membrane.
Pierces the thyrohyoid membrane along with superior
laryngeal artery and vein.
After entering into the larynx this nerve divides into three
branches i.e. superior, middle and inferior.
Supply sensation to:
Interior of larynx.
Supraglottis and pyriform sinus.
Anatomy of thyroid.........
. Internal Laryngeal Nerve:
Superior division divides into 2-3 branches supplying sensations to
o Lingual surface of epiglottis, lateral aspect of glosso-epiglotic fold.
Middle division innervates
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.
o It lies along the medial aspect of pyriform fossa.
Anatomy of thyroid.........
. External laryngeal nerve
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.
o Relationship with the superior pole of thyroid gland is highly
variable.
Anatomy of thyroid.........
.
. Anatomical
Relationships
between STA and External Branch
of SLN:
Closely related to external laryngeal
nerve at its origin.
Nerve moves away from the artery
as artery approaches the upper pole
of the gland.
Anatomy of thyroid.........
. In order to avoid injury of External Laryngeal Nerve:
STA need to be ligated just near the superior pole.
. Complication:
Superior laryngeal nerve injury:
o Paralysis of the cricothyroid muscle.
o Changes in the pitch of the voice.
o Inability to make explosive sounds.
o Bilateral injury presents as a tiring and hoarse voice.
Anatomy of thyroid.........
. 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
superior aspect of the thyroid lobe.
Type 2 anatomy-
? 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.........
. RLN- Always asymmetric.
Anatomy of thyroid.........
. Right recurrent laryngeal nerve:
Arises from vagus in the chest.
Reaches neck by crossing anterior to right subclavian
artery.
Loops around Right subclavian artery to reach the
trachea-oesophageal groove.
Ascends posterior to thyroid gland.
Enters the larynx behind the cricothyroid articulation
and inferior cornua of thyroid.
Anatomy of thyroid.........
. Left recurrent laryngeal nerve:
Arises from vagus in the chest.
Crosses the arch of aorta to reach the
neck.
Ascends posterior to gland to reach the
trachea-oesophageal groove.
Anatomy of thyroid.........
. Major difference in course between Right and Left RLN:
Loops around- subclavian and aortic arch respectively
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.
At the lower pole of thyroid gland- right nerve is slightly more anterior than the left.
Anatomy of thyroid.........
. Motor supply of RLN:
Anatomy of thyroid.........
. Relationship of RLN to the ITA
Anatomy of thyroid.........
. Intraoperative localization of nerves:
EB-SLN:
o Jol 's Triangle
o Space of Reeve
RLN:
o Boehar's Triangle
o Simon Triangle
Anatomy of thyroid.........
. Non-recurrent laryngeal nerve:
An anomaly of the RLN.
Origin is cervical.
Direct course from the vagus nerve
to the larynx without looping
around.
Anatomy of thyroid.........
. Types of NRLN:
Type 1- arises directly from the vagus and travels
with the Superior Thyroid Pedicle vessels.
Type 2A- travels transversely, paral el and
superficial to the trunk of the Inferior Thyroid
Artery .
Type 2B- travels in a transverse path paral el, but
deep to or between the branches of the Inferior
Thyroid Artery.
Anatomy of thyroid.........
. Surgical importance of RLN:
Unilateral RLN injury-
Paralysis of I/L intrinsic muscles of larynx i.e. loss of abduction
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
normal
Airway will be patent but can be compromised during exertion
Anatomy of thyroid.........
. Surgical importance of RLN:
Bilateral RLN injury-
Paralysis of B/L intrinsic muscles of larynx i.e. loss of
abduction.
Unopposed action of cricothyroid muscle i.e.
adduction.
Paramedian or median position of vocal card.
Stridor during breathing because compromised
airway.
Anatomy of thyroid.........
Anatomy of thyroid.........
. Zuckerkandl's tubercle (ZT)
Posterior extension of the lateral lobes.
Composing of thyroid tissue only.
Anatomy of thyroid.........
. Surgical importance of ZT:
Dissection and excision of ZT for total
thyroidectomy.
Close relationship between ZT and recurrent
laryngeal nerve (RLN).
Needs careful, fine, and very close dissection
around the nerve.
Safe identification of the nerve and resection of
the tubercle.
Anatomy of thyroid.........
. Lymphatic Drainage of the Thyroid Gland
Thyroid lymphatic vessels communicates with:
1st level: Pre-laryngeal, Pre-tracheal, and Para-tracheal lymph nodes
2nd level:
? Superior deep cervical nodes (from the prelaryngeal nodes)
? and Inferior deep cervical nodes (from the pretracheal and paratracheal nodes).
Some lymphatic vessels may drain into the brachiocephalic lymphatic nodes.
Presence of metastases in lymphatic nodes of neck can be first
sign of thyroid carcinoma!!!
Anatomy of thyroid.........
. Innervation of Thyroid Gland:
Derived from- (Superior, Middle, and Inferior) Cervical
Sympathetic Ganglia
Nerves reach the thyroid through-
Cardiac periarterial plexus
Superior and inferior thyroid plexus
Only vasomotor fibers- constriction of blood vessels
No secretomotor supply
Endocrine secretion from the thyroid gland is hormonal y
regulated by the pituitary gland through TSH!
Histology of thyroid
. Each lobule of contains:
20 to 40 follicles.
Composed of follicle cel s and colloid.
Colloid fil s the follicle cavities
. Follicle cells produce thyroglobulin.
. Between follicles are Para-follicular cells, which
produce Calcitonin.
This post was last modified on 07 April 2022