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