Thyroid Gland & Thyroglossal Cyst😍

Thyroid Gland

Development

Develops from thyroglossal duct

First endocrine gland to develop

Thyroglossal cyst: along the course of the duct

Lingual thyroid: most common site for ectopic thyroid

Location

Anterior neck, deep to sternothyroid and sternohyoid

Extends from C5 to T1 vertebral level

A- C5
B- C6
C- C7
D- T1

Capsule

Prostate

True capsule:

condensation of fibrous stroma

False capsule:

from pre-tracheal fascia

Removed with true capsule during surgery

Sternothyroid muscle support

Prevent upward extension of thyroid swelling.

Strap-like muscle

originates from sternum → manubrium
inserts onto the thyroid cartilage

Structure

Butterfly shaped

Two lobes connected by isthmus

Isthmus: at 2nd to 4th tracheal rings

Pyramidal lobe:

may arise from isthmus (remnant of thyroglossal duct)

Relations

Sternohyoid and sternothyroid muscles

Medial

2 tubes:

Trachea
Oesophagus

2 muscles:

Inferior constrictor
Cricothyroid

2 nerves:

RLN
ELN

Posterior

Near esophagus and parathyroid glands

Artery Supply

Superior Thyroid Artery

Branch of External Carotid Artery

Ligated close to gland during surgery to preserve External Laryngeal Nerve (ELN)

Inferior Thyroid Artery

Branch of Thyrocervical trunk

Supplies Parathyroid glands, esophagus, and thymus.

Capsular branches

ligated close to gland
to avoid parathyroid devascularisation

But ITA is ligated away from gland

Mnemonic: Inferior () people are common (CCA), boring (Beahr), comes repeatedly (RLN), keep them away (Ligate away from gland)

Thyroid Ima artery

Direct branch of aortic arch.

Mnemonic: keep superior people close and inferior people away

Nerves

ELN (External Laryngeal Nerve)

M/c nerve injured during thyroidectomy

Supplies Cricothyroid muscle

Controls vocal cord tensor.

Function: Tensor, adductor (intrinsic muscle)

Injury → Hoarseness (due to inability to tense cords) → Low pitch

Mnemonic: Ele (ELN) monu CT (cricothyrodi) edukkan poyapo tension (Tensor) ayi

Preserved by ligating STA close to gland

m/c goes unnoticed

U/L or B/L: Hoarseness/inability to speak at high pitch.
Not life threatening.

RLN (Recurrent Laryngeal Nerve)

Runs near Inferior Thyroid Artery

Important for voice preservation

Injured: Left > Right

Left RLN

Longer course than right
It turns under the remnant of left 6th arch artery.

Ligamentum arteriosum (fibrous remnant).

Right RLN

winds around the Right subclavian artery.

RLN Identified via Beahr's triangle boundaries

Boundaries:

Common carotid artery (lateral).
Inferior thyroid artery (superior).
Recurrent laryngeal nerve (RLN) (medial).

Applied Aspect:

Identified to prevent RLN injury during surgeries like thyroidectomy.

Triangle of concern

Berry ligament-RLN-Trachea

Nerve Injury

Commonest RLN injured:

Left RLN (longer course)

Commonest cause bilateral RLN palsy:

Surgical trauma (esp. Total thyroidectomy)

B/L RLN Palsy

⛔ Posterior Cricoarytenoid → Safety muscle of VC → Abductor
Stridor, aphonia, breathlessness (Life threatening)
Inability to extubate

ㅤ	U/L RLN injury	SLN Injury
Presentation	• Unilateral vocal cord paralysis • Hoarseness • Post-op dysphonia • Dyspnea • Difficulty in deglutition	• ILN → Aspiration → Absent cough reflex • ELN → Low pitch
Vocal cord appearance	• RLN injury = Paramedian	• RLN + SLN injury = Cadaveric/intermediate

Types of Vocal Cord Palsy

Complete/adductor palsy

SLN + RLN palsy
VC in cadaveric/intermediate position (3.5 mm from midline)

Incomplete/abductor palsy

RLN palsy
Cricothyroid intact
VC in median/paramedian position (1.5 mm from midline)

Clinical Features

Lateralisation of VC

Kashima → Type 2 thyroplasty
Woodmans → cordectomy + Arytenoidectomy

Surgical Trauma

Site of injury	Nerve injured
Base of skull	Complete vagus / SLN
Carotid triangle	ILN / ELN / SLN
Upper pole of thyroid	ELN ↳ most common injured in thyroid surgery
Lower pole of thyroid	RLN ↳ 2nd most common injured in thyroid surgery ↳ Rt > Lt
Mediastinal	Left RLN ↳ also in Ortner’s / cardiovocal syndrome

Normal VC position	during
Lateral	Deep inspiration
Paramedian	Rest
Median	Phonation

During total thyroidectomy for papillary carcinoma thyroid in a thirty-six-year-old lady, the
recurrent laryngeal nerve of right side was sacrificed for oncological safety. The next day, the patient complained of breathy voice. A fiberoptic laryngoscopy on the second post-operative day showed vocal cord paralysis of the right side. What would be the positions of the right and left vocal cords in this patient, on phonation?
(A) Right cadaveric, left intermediate
(B) Right intermediate, left intermediate
(C) Right paramedian, left median
(D) Right paramedian, left paramedian

ANS

Treatment of Vocal Cord Palsy

Isshiki’s thyroplasty types

**TPM → “Ur voice will change after ur height increases”**

Type I (Medialisation/Proximalisation)

Thyroid cartilage pushed medially
Indication: U/L complete (adductor palsy)

Type II (Lateralisation)

Thyroid cartilage pulled laterally
Indication: B/L RLN palsy

Type III (Shortening)

Part of thyroid cartilage cut
Vocal cord shortened → pitch ↓
Indication: Puberphonia
Shorten the long man (shortening) who has guts (Gutzmann manoevre) but female sound (Puberphonia)

Type IV (Tightening/Tensing)

Indication: Androphonia
Lengthen () the short female with male voice (androphonia)

Note

Laryngeal inlet = epiglottis + arytenoid

ILN injury → loss of cough reflex

Galen’s anastomosis:

Between:

Internal laryngeal nerve (from SLN)
Recurrent laryngeal nerve (from RLN)

Clinical Testing

Hypoglossus (CN 12)

Test: ask patient to protrude tongue
If lesion present: tongue deviates towards the affected side (ipsilateral deviation)

Glossopharyngeal N (CN 9)

Test: pressure on soft palate/uvula
Also supply Glossopharyngeus

Circumvallate papillae

Present in the anterior 2/3rd part of the tongue
But special sensation carried by glossopharyngeal

Jugular canal

Carries the glossopharyngeal nerve (IX)
Fracture of the jugular canal

Loss of taste sensation in the posterior 1/3rd of the tongue

Venous Drainage

Superior thyroid vein → Internal jugular vein

Middle thyroid vein → Internal jugular vein

Present in 30% cases

1st vessel ligated during thyroid surgery

Inferior thyroid vein → from Left Brachiocephalic vein

Permanent tracheostomy

Indications of Tracheostomy

Mnemonic: Occupy Most Seats in Medical Association

O → Obstruction: Above T₂–T₄

M → prolonged Mechanical ventilation:

Most common indication for elective tracheostomy

S → Secretion removal / pulmonary toilet (coma, chest injury)

M → Maxillofacial, head & neck surgeries

A → Aspiration prevention (bilateral complete vocal cord palsy)

Tracheostomy Tube :

High volume, low pressure.

For air tight seal.

Position :

Rose’s position :

Extension at cervico-thoracic and atlanto-occipital joint.
Rose has extension everywhere

Tracheal incision :

2, 3, 4 tracheal rings.

Emergency

Vertical incision :

From lower border of cricoid to suprasternal notch

Elective

Horizontal incision/Skin crease incision :

2.5 cm above suprasternal notch

High tracheostomy :

Incision at T1
Indication : Ca larynx.
Complication : Laryngeal stenosis

Low tracheostomy :

Infections like Papillamatosis

Tube block :

C/f of complete block : Stridor.

Prevention : Saline/sodium bicarbonate suction.

Management : Change tracheostomy tube.

Structures Injured During Tracheostomy

Isthumus and below vessels

Isthmus of thyroid gland
Arteria thyroidea (Thyroid Ima artery)
Inferior thyroid vein

Surgical emphysema

D/t tight sutures → injure nearby structures

Berry’s ligament:

Pre-tracheal fascia condensation.

Attaches thyroid gland to trachea.

Moves with swallowing (deglutition)

Applied

Most common site of RLN injury during surgery
Prevents downward extension of swelling

Histology

Thyroid Follicles:

Lined by simple cuboidal epithelium.

Filled with colloid.
Colloid contains Thyroglobulin (PAS +ve).

Lining activates → columnar epithelium.

Parafollicular Cells (C-cells):

Secrete calcitonin.
Associated with medullary Ca. thyroid.
Derived from Neural Crest Cells which migrate to ultimo-brachial body

Parathyroid Gland

Superior parathyroid gland:

From 4th pharyngeal pouch
Superior “PARA” → 4 letter

Inferior parathyroid gland:

From 3rd pharyngeal pouch
Migrates with thymus
Inferior “PARA” → 4 - 1 = 3 letter

Supplied by Inferior Thyroid Artery

Risk of devascularisation if capsular branches ITA ligated far from gland

Parathyroid Supply:

ITA Branch of thyrocervical trunk

Capsular branches (ITA):

Ligated close to gland
Avoids parathyroid devascularisation

Superior Thyroid Artery:

Ligated close to gland during surgery
Saves ELN

Thyroglossal Cyst

Persistent thyroglossal tract.

M/C location: Subhyoid.

Long standing cyst → Papillary Thyroid Carcinoma.

C/F:

Midline swelling moves on deglutition.
Tongue protrusion.

IOC: FNAC.

Mx: Sistrunk Surgery.

Removes cyst + part of hyoid bone + tract till base of tongue.

C/I:

I and D
Can cause thyroglossal fistula.