THYROID

Dr Lohith SDNB ResidentDepartment of General SurgeryBMJH,Bangalore

HISTORY

● Term 'thyroid' was coined by Thomas Warton in 17th century

● Emil Theoder Kocher is considered as the Father of Modern Thyroid surgery

● First thyroidectomy is considered to be done more than 1000 years ago by Abu-al-Qasim

● The earliest account of thyroidectomy was probably given by Roger Frugardi, 1170

The thyroid glandThe thyroid glandANATOMY AND EMBRYOLOGYLobesPositionBlood supplyDevelopmentParathyroid glands

The thyroid gland derives its name from the thyroid cartilage which resembles a shield

(G. thyreos = shield)

Function The thyroid gland

is an endocrine gland that is responsible for the secretion of thyroxin and thyrocalcitonin

Lobes The thyroid gland

consists of two lobes united in front of the second, third and fourth tracheal rings by an isthmus of gland tissue.

isthmusisthmus

Lobes Each lobe is pear-

shaped consisting of a narrow upper pole and a broader lower pole

upper poleupper pole

lower polelower pole

Thyroid scan This nuclear scan uses

an injectable radioactive compound. When injected into the bloodstream the compound will be concentrated in the thyroid gland resulting in an image of the gland

The test can be useful in diagnosis of thyroid tumor

Position

It lies under cover of sternothyroid and sternohyoid muscles on the side of the larynx and trachea

ster

noth

yroi

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ster

nohy

oid

Position

The upper pole of the thyroid cannot normally rise above the level of the oblique lineoblique line of the thyroid cartilage

Thyroid, upper pole

sternothyroidthyrohyoidcricothyroid

The thyroid gland is caught in the pocket of sternothyroid

thyroidcr

icoid

thyr

oid

carti

lage

sternothyroidsternothyroid

thyrohyoid

cricothyroid

Position

The lower pole of the thyroid gland extends along the side of the trachea as low as the sixth tracheal ring

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Position

Because of the proximity of the thyroid gland to the trachea and esophagus, goiter causes compression of the trachea and esophagus resulting in dyspnea and dysphagia respectively

esophagusesophagus

Retro-sternal goitre with tracheal deviationRetro-sternal goitre with tracheal deviation

Retro-sternal Retro-sternal goitre with goitre with esophageal esophageal deviationdeviation

Pyramidal lobe In about 40% of

people, there is a small upwards extension of the isthmus called the pyramidal lobe.

Levator glandulae thyroidae The pyramidal lobe

may be attached to the hyoid bone by fibrous or muscular tissue (levator glandulae thyroidae).

Variations Bifurcation of the

lower end of the pyramidal process, one part going to each lateral lobe

Variations Pyramidal process

attached to the left lobe of the gland, isthmus absent.

Variations Both pyramidal

process and isthmus are absent.

Pre-tracheal fascia The thyroid gland

is surrounded by a fibrous capsule and is enclosed in the pre-tracheal fascia

Pre-tracheal fascia The pre-tracheal

fascia attaches the thyroid gland to the trachea and larynx

thus the thyroid moves upwards on swallowing, an important diagnostic feature for lumps in the neck

thyroid

larynx

Blood supply The thyroid gland is very

vascular The vessels lie

between the capsule and the pre-tracheal fascia.

In some pathological conditions such as thyrotoxicosis, owing to its high vascularity, the blood flow can be heard with a stethoscope as a bruit

Thyroid arteries The main arteries

are the superior and inferior thyroid arteries.

superiorsuperiorthyroid a.thyroid a.

inferiorinferiorthyroid a.thyroid a.

Superior thyroid artery

Arises from the anterior surface of the external carotid immediately distal to the carotid bifurcation.

externalexternalcarotid a.carotid a.

carotidcarotidbifurcationbifurcation

Superior thyroid artery Arches downwards,

giving a sternomastoid branch and a superior laryngeal branch that enters the larynx with the nerve of the same name

superiorlaryngeala. & n.

Superior thyroid artery enters deep

to sternothyroid

ster

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Superior thyroid vessels

Superior thyroid artery before reaching

the upper pole of the gland, and within the pre-tracheal fascia, it divides into two main branches one for either surface of the gland

anterior posterior

Superior thyroid artery the posterior

branch anastomoses with the inferior thyroid artery

posterior br.of superiorthyroid a.

inferiorthyroid a.

Inferior thyroid artery Is a branch

of the thyrocervical trunk from the subclavian artery. subclavian a.subclavian a.

thyrocervicalthyrocervicaltrunktrunk

inferiorinferiorthyroid a.thyroid a.

Inferior thyroid artery Ascends and

turns medially at the level of the cricoid cartilage to enter the back of the gland some distance above the lower pole.

Inferior thyroid artery The tortuous course of

the inferior thyroid artery is due to the fact that in every swallow the thyroid gland ascends a few centimeters and must naturally drag its blood supply with it.

If this artery has no capability to elongate, it would be traumatized

Inferior thyroid artery Divides outside

the pre-tracheal fascia into four or five branches that pierce the fascia separately to reach the lower pole of the gland.

Remember that the superior Remember that the superior thyroid artery divides within the thyroid artery divides within the pretracheal fasciapretracheal fascia

The recurrent laryngeal nerve lies normally behind the branches of the inferior thyroid artery

The recurrent laryngeal nerve lies normally behind the branches of the inferior thyroid artery

but it is common for the nerve to pass between the artery branches before they pass through the fascia.

The recurrent laryngeal nerve always lies behind the pre-tracheal fascia and if this structure remains intact during thyroidectomy the nerve will not have been divided

recurrent laryngeal n.

inferior thyroid a.

Both thyroid arteries are related to nerves which must be avoided when tying the arteries.

A little distance behind the superior thyroid artery is the external laryngeal nerve. superior thyroid a.

external laryngeal n.

external laryngeal n.

internal laryngeal n.

superior laryngeal n.

Superior laryngeal nerve variationsvagusvagus

internalinternal

externalexternal

To avoid injury to the external laryngeal nerve, the superior thyroid artery is ligated and sectioned near the superior pole of the thyroid gland where it is notnot so closely related to the nerve as it is at its origin.

Section of the external laryngeal nerve produces weakness of voice, since the vocal fold cannot be tensed.

The cricothyroid muscle is paralyzed Cricothyroid tenses the vocal cordCricothyroid tenses the vocal cord

The recurrent laryngeal nerve has a variable relationship to the inferior thyroid artery

because of its proximity to the inferior thyroid artery and the pre-tracheal fascia it may be injured while ligating the artery during thyroidectomy

hence the advisability of ligating the inferior thyroid artery well lateral to the gland before it begins to divide into its terminal branches.

the inferior thyroid artery gives off esophageal and inferior laryngeal branches before its terminal distribution into the thyroid gland

site ofinferiorthyroid a.ligation

site ofsuperiorthyroid a.ligation

The variable relationship of the inferior thyroid artery to the recurrent laryngeal nerve makes thyroid surgery a potential risk to normal speech

The recurrent laryngeal nerve supplies all the intrinsic muscles of the larynx

it is advisable that a surgeon about to perform a thyroidectomy examines the vocal cords prior to operation, so that if there is any problem postoperatively one knows at least the origin of the lesion.

Recurrent laryngeal nerve damage

Is a complication of thyroid surgery that causes paralysis of the vocal cords

When bilateral the voice is almost absent as the two vocal folds cannot be adducted.

Recurrent laryngeal nerve damage

A unilateral recurrent laryngeal nerve injury may not be noticed in normal speech but would be very detrimental to a singers career.

The thyroid arteries anastomose freely with each other and with tracheal and esophageal arteries.

In operations of partial or sub-total thyroidectomy, all four arteries are tied

In operations of partial or sub-total thyroidectomy, all but the posterior part of the gland excised

remainingthyroidtissue

the dangerous anatomy lies in the posterior lateral lobes (recurrent laryngeal nerve and the parathyroid glands) Recurrent

laryngeal n.

parathyroidgland

The remains of the gland are located alongside the trachea and contain the parathyroid glands, the whole being supplied with blood by the anastomosis

Thyroidae ima artery In about 10% of

individuals, an unpaired artery, the thyroidae ima (L. ima = lowest) is a small occasional artery from the brachiocephalic trunk, or left common carotid artery, or direct from the arch of the aorta

Thyroidae ima artery Ascends anterior to

trachea and supplies the isthmus of the thyroid gland.

Thyroidae ima artery The possible presence

of the thyroid ima artery must be remembered when incising the trachea inferior to the isthmus.

As the thyroidae ima runs anterior to the trachea, it is a potential source of serious bleeding

Thyroid veins The veins are three in

number on each side the superior thyroid

vein from the upper pole follows the artery and enters the internal jugular vein or the common facial vein

Superior thyroid v.

Internal jugular v.

The middle thyroid vein is short and wide, it enters the internal jugular vein

Thyroid veins

middle thyroid v.

Internal jugular v.

From the isthmus and lower pole of the gland the inferior thyroid veins form a plexus within the pre-tracheal fascia that descends in front of the trachea to reach the left brachiocephalic vein

Thyroid veins

inferior thyroid vv.

brachiocephalic v.

As the inferior thyroid veins cover the anterior surface of the trachea inferior to isthmus, they are potential sources of bleeding during tracheotomy (also remember the situation of the thyroidae ima artery).

Inferior thyroid veins

Development of the thyroid gland

The gland begins as a diverticulum from the floor of the embryonic pharynx

Development of the thyroid gland

The diverticulum grows caudally superficial to the hyoid before dividing into two lobes

The stem of the diverticulum, the thyroglossal duct, normally disappears

hyoid

Thyroglossal duct

Development of the thyroid gland

After the tongue has developed, it can be seen that the point of outgrowth of the thyroglossal duct is the foramen cecum (of Morgagni) [Morgagni, Giovanni Battista, 1682-1771, a Padua anatomist and pathologist, also known for hydatid of Morgagni (appendix testis) and anal columns (of Morgagni)].

Thyroglossal cyst cysts derived from

the duct may also appear anywhere between the foramen cecum and the normal position in the midline of the neck1. Beneath foramen cecum2. Floor of the mouth3. Suprahyoid4. Subhyoid5. On thyroid cartilage6. At level of cricoid cartilage

Thyroglossal cyst Can be

diagnosed because characteristically it moves upwards as the patient puts his tongue out.

Infection of a thyroglossal cyst may spread to a persistent thyroglossal duct which must be then excised

Although the duct lies ventral to the hyoid bone, it passes up for a short distance behind the body, which therefore has to be excised with the duct

Accessory thyroid gland Aberrant thyroid

tissue may appear between the foramen cecum and the normal position

Lingual thyroid

Rarely the thyroid fails to descend during development resulting in the development of a lingual thyroid

Ectopic thyroid

Failure of descent mar result in a superior cervical thyroid in the region of the hyoid bone

the thyroid may sometimes descended too far and be found in the superior mediastinum

Parathyroid glands Two on each side They are yellow-brown

endocrine glands, about the size of a small pea (about 0.5x0.8 cm ovoids)

They are important because of their role in calcium metabolism. They secrete parathormone that mobilizes bone calcium and increases gut and kidney calcium absorption

Parathyroid glands Are located

posterior to the thyroid gland between its capsule and fascial sheath

Superior parathyroid glands more constant in

position embedded in the

posterior surface of the thyroid gland, a short distance above the entry of inferior thyroid artery (and the level of the cricoid cartilage).

Inferior parathyroid glands variable in position usually embedded

behind the lower pole but is often found elsewhere (they may even present in the superior mediastinum).

Para

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The parathyroids develop from the endoderm of the third (inferior gland) and fourth (superior gland) pharyngeal pouches

The thymusthymus also develops from the third pouch and may therefore carry the inferior parathyroidparathyroid with it when it descends into the thorax.

Para

thyr

oid

deve

lopm

ent

Parathyroid glands, blood supply

The glands are usually supplied by the inferior thyroid arteries but may also be supplied by both superior and inferior thyroid arteries

posterior br.of superiorthyroid a.

inferiorinferiorthyroid a.thyroid a.

Parathyroid glands Awareness of the

close relationship between the parathyroid glands and the thyroid gland is essential to prevent removal or damage of the parathyroid glands during thyroidectomy.

The parathyroid glands are usually safe during subtotal thyroidectomy because the posterior part of the thyroid gland is preserved

The variability in position of the parathyroid glands may create a problem during total thyroidectomy; in this case the parathyroid glands are saved by following their small vessels which are kept intact before the thyroid is removed.

LYMPHATICS● Lymphatic drainage of thyroid gland has been proposed by

Taylor. His studies shows clinically relevant lymphatic spread in thyroid malignancy

● Central compartment of neck -

– Tracheal LN

– Chain of LN which lie in tracheo-oesophageal groove

– One or more LN lying above isthmus – 'delphian nodes'● B/L central LN dissection (level 6 dissection)

– Clears all LN from carotid artery to other and down into superior mediastinum.

● Lateral compartment of neck● A constant group of LN lies along IJV on each side (level 2,3,4).

LN in supraclavicular fossa or more laterally level 5 LN may also be involved in thyroid malignancy

● Thoracic duct on left side of neck arches up out of mediastinum and passes forwards and laterally to drain into left subclavian vein / IJV

● Lateral LN dissection –● removal of level 2, 3, 4 and 5 LN. Vagus N, symphatheticc

ganglia, phrenic N, brachial plexus and spinal accessory N are preserved

Investigations

USG in Thyroid-gland enlarged or not-nodular/diffuse-single/multiple-lymphnode assessment-guide to FNAC-benign or malignant depending on vascularityPeripheral-benignCentral -malignant

Disadvntage of USG in ThyroidNo information about retrosternal thyroid staging.

Radioisotope Usually was preferred earlier But now avoid as much as possible 3 indications:- Toxicity associated with nodularity- To locate ectopic thyroid- To locate metastatic I123 should be avoided because of long t1/2.Tc99 should be used.

Important points Most common cause of nodularity in

Thyroid –colloid>follicular adenoma 80% of thyroid nodule are benign, 20%

are malignant. Chance of malignancy-Euthyroid > hypothyroid > hyperthyroid(<1%)-Cold > warm> hot So to summarize cold euthyroid is a deadly

combination.

Important points IOC for systemic spread of

carcinoma Thyroid –PET scan FNNAC(Fine Needle Non Aspiration

Cytology) in this morphology is better accepted then FNAC.

Therefore in thyroid gland FNNAC is preferred more than FNAC.

Thyroidectomy● INDICATIONS

● As therapy for patients with thyrotoxicosis● To treat benign and malignant thyroid tumours● To alleviate pressure symptoms (respiratory distress, dysphagia) with

benign/ malignant process● Cosmetic purpose● To establish a definitive diasgnosis of a mass within thyroid gland,

especialy when cytological analysis is either non diagnostic or indeterminate

● Suspicion of malignancy in benign nodule like, hard nodule, sudden increase in size, involvement of adjacent structures, enlarged lymphnode and recurrent cyst.

TYPES

● Thyroid lobectomy / Hemithyroidectomy

● Subtotal thyroidectomy● Near total thyroidectomy● Total thyroidectomy● Completion thyroidectomy

Types: Sub-total: about 8gms , or a tissue,

size of pulp of finger is retained on lower pole on both sides and rest is removed. Commonly done in toxic thyroid, MNG.

Total: entire gland is removed. Done in malignancy.

Near-total: both lobes except the lower pole which is very close to recurrent laryngeal nerve and parathyroid is removed. Here <2gm of tissue is left behind.

Hemi: along with removal of one lobe, entire isthmus is removed. Done in benign disease of only one lobe, thyroid cyst, solitary nodule.

PRE OPERATIVE EVALUATION● Ultrasonography● Fine needle aspiration cytology – FNAC● Thyroid function tests – TFT● CT scan● Thyroid uptake scan● Laryngoscopy● Serum Calcium, Parathormone (PTH)

PRE OPERATIVE PREPARATION Thyrotoxic patient are rendered euthyroid;

Carbimazole 10-15mg 8hourly, when patient become euthyroid(in about 4weeks) they are maintained on 5-10mg

Propranolol 80mg 6hourly 4-7days before operation. Symptoms and signs are usually controlled within 24hours. Continued 8-10days post op

Lugol’s iodine; 2weks pre-operatively to reduce the vascularity of the gland

PRE OPERATIVE CONSENT● Scar● Airway obstruction● Voice changes● Hypoparathyroidism● Hypothyroidism

ANAESTHESIA Anaesthesia is general with cuffed

endotracheal tube POSITION

patient is placed in a supine position initially with the neck extended by placing a ring beneath the head and a sandbag roll beneath the shoulder.

The table is tilted 20–30 degrees “head up” to aid in emptying the neck veins.

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The skin is prepped from the chin to the upper thorax

Drapes are applied; head scarf, sides of the neck, chest-abd, large covering the legs. The are secured with clips

Surgeon and assistant scrub and gown, the stands on the opposite side to be operated upon(usually the larger gland first)

Incision Site of incision is indented with suture A transverse skin crease incision is placed 2-

3cm above the sternal notch about 8cm long extending to the lateral borders of sternocleidomastoid.

The scapel (with size 15 blade) is slanted to divide the skin and platysma at different level to give a neater scar

Hemostasis is controlled with electrocautary or prior infiltration with lidocaine and adrenaline

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PROCEDURE Elevate the flap of skin with the platysma (the

assistant lifts the skin and the platysma upward with double skin hooks to allow for the creation of a subplatysmal flap).

Superiorly to the thyroid cartilage Inferiorly to the suprasternal notche Place Joll’s retractor to retract the skin flaps This procedure should be blood free, because the

superficial veins lie beneath the cervical fascia. Divide the deep cervical fascia longitudinally in the

midline, between the anterior jugular veins. At the lower part there is usually a transverse

cervical vein that needs to be clamped, divided, and ligated with 3-0 silk sutures

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The strap muscles (sternohyoid, and deeper sternothyroid) are carefully separated to allow their retraction laterally.

Assess goiter; The loose areolar tissue(capsule) overlying the thyroid gland is divided

with electrocautery. After the anterior surface of the thyroid has been thoroughly exposed,

the entire gland is carefully explored and palpated. The strap muscles are firmly retracted with a small loop retractor while the

thyroid gland is drawn medially Ligate and divide in continuity

Middle thyroid vein Superior thyroid vessels close to the gland(to avoid injury to the

external laryngeal nerve) between two proximal and one distal ligature.

The recurrent laryngeal nerve and the parathyroids are identified and preserved then the terminal branches inferior thyroid artery are ligated and divided close to the capsule. Or the inferior thyroid artery is identified far away from the gland ligated in continuity to avoid injury to the recurrent laryngeal nerve.

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The thyroid is then mobilized and removed; Divide isthmus and place hemostats around

margin of resection (run with interlocking 3-0 absorbable suture) leaving about 4g of thyroid from each lobe for subtotal

If a total thyroidectomy is being performed, the remaining lobe is removed in a similar fashion, with division of the middle thyroid vein, identification of the recurrent laryngeal nerve and parathyroid glands, and ligation and division of the superior pole and branches of the inferior thyroid vessels.

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CLOSURE Absolute haemostasis Suction drain to thyroid bed(beneath

the strap muscles) Close loosely in layers with

absorbable sutures Close the skin with sutures or clips Check vocal cords on extubation by

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OPERATIVE STEPS● Anaesthesia, Positioning & Draping

● Skin incision and creation of flaps

Exposure of thyroid gland

Mobilization and dissection of upper pole

Identification of RLN

Identification of parathyroid glands

Dissection of ITA and removal of gland

Closure

POST OPERATIVE MGT Half-hourly observation until conscious At the bed side

Michel clip remover in case of respiratory distress due to hematoma

10ml of 10% calcium gluconate in case of acute hypocalcamia

Keep semi-recumbent Review indirect laryngoscopy(especially if there is cord

impairment on extubation) Serum calcium regularly in the postoperative period Thyroid function tests at 6weeks postoperatively Remove

Drain when dry, 24-48hours postoperatively Sutures/clips, 2-3days postoperatively

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COMPLICATIONS EARLY

Haemorrhage Tetany

In first 3 days from corrected thyrotoxicosis After 1 week with hypoparathyroidism

Recurrent laryngeal nerve palsy 95% neurapraxia and resolves If bilateral, cord adduct to midline so needs immediate reintubation Thyroid crisis, if throtoxic patient is inadequately prepared rare with

modern technique Wound infection

LATE Keloid Hypothroidism- 20% Recurrent thyrotoxicosis- <5% of patients undergoing

thyroidectomy for grave disease

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RECENT ADVANCES● Minimally invasive thyroidectomy● Robotic transaxillary thyroid

surgery● Transoral thyroidectomy

QUESTIONS 1. What is the blood supply to the thyroid gland2. What are the preoperative measures prior to

thyroidectomy for thyrotoxicosis3. What are the types of thyroidectomy4. Outline the steps of thyroidectomy5. What are the complications of thyroidectomy6. What does the recurrent laryngeal nerve

supply and what is the consequence of it division

7. What does external laryngeal nerve supplies and what is the consequences of it division

8. What is the Simon’s triangle

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