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THYROID GLAND - Bailey and Love's Short Practice of Surgery (28th Ed.)

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1. EMBRYOLOGY

• The thyroglossal duct develops from the median bud of the pharynx
• The foramen caecum (junction of anterior 2/3 and posterior 1/3 of the tongue) is the vestigial remnant of this duct
• This initially hollow structure migrates caudally, passing in close continuity with - and sometimes through - the developing hyoid cartilage
• The parathyroid glands develop from the 3rd and 4th pharyngeal pouches
• The thymus also arises from the 3rd pouch - as it descends, it takes the inferior parathyroid with it. This is why the inferior parathyroid (from 3rd pouch) lies inferior to the superior gland - but can be found anywhere along this line of descent
• The developing thyroid lobes amalgamate with structures from the 4th pharyngeal pouch: the superior parathyroid and ultimobranchial body
• Parafollicular C cells from the neural crest reach the thyroid via the ultimobranchial body - they produce calcitonin

• Thyroglossal cysts (anywhere from foramen caecum to isthmus)
• Lingual thyroid
• Pyramidal lobe (most common embryological variant)
• Ectopic parathyroid positions

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2. SURGICAL ANATOMY

Gross Anatomy

• Normal weight: 20-25 g
• The functioning unit is the lobe supplied by a single arteriole, consisting of 24-40 follicles lined with cuboidal epithelium
• The follicle contains colloid in which thyroglobulin is stored
• Covered by a true capsule and surrounded by pretracheal fascia

Arterial Supply

Venous Drainage

Lymphatic Drainage

• Juxtathyroid "Delphian" nodes (pretracheal)
• Paratracheal nodes
• Nodes on superior and inferior thyroid veins

• Deep cervical nodes (Levels II, III, IV, V)
• Mediastinal nodes (Level VII)

Recurrent Laryngeal Nerve (RLN) - Of Supreme Surgical Importance

• Branch of the vagus nerve
• Left RLN: recurs around the arch of the aorta → runs in a more medial plane in the tracheo-oesophageal groove (longer course = more medial)
• Right RLN: recurs around the subclavian artery → runs more obliquely to reach the tracheo-oesophageal groove
• ~2% of nerves on the right are non-recurrent - these enter the larynx from above (associated with aberrant right subclavian artery)
• Enters larynx at the cricothyroid joint
• Located in the tracheo-oesophageal groove where it forms one side of Behr's triangle (sides: carotid artery, inferior thyroid artery, RLN)
• Found under the Tubercle of Zuckerkandl (posterolateral portion of the thyroid lobe) during mobilisation
• At greatest risk at Berry's ligament (condensation of pretracheal fascia binding thyroid to trachea)

External Branch of Superior Laryngeal Nerve (EBSLN)

• Runs with the superior thyroid artery close to the upper pole
• Injury causes loss of tension in the vocal cord → diminished power and range (particularly affects singers and professional voice users)

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3. PHYSIOLOGY (Brief)

• T3 and T4 are bound to thyroglobulin within colloid
• Synthesis steps: iodide trapping → oxidation → binding with tyrosine → coupling to form T3/T4
• T3 is the more important physiological hormone; produced in periphery by conversion from T4
• T3 is quick-acting (hours); T4 acts more slowly (4-14 days)
• Free T3: 3.5-7.5 μmol/L; Free T4: 10-30 nmol/L; TSH: 0.3-3.3 mU/L
• Negative feedback via hypothalamus-pituitary-thyroid (HPT) axis with TRH and TSH

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4. CLASSIFICATION OF THYROID CONDITIONS

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5. SIGNS AND SYMPTOMS

Features Common to All Thyroid Swellings

• Swelling in anterior neck that moves on swallowing (key sign)
• Thyroglossal cyst also moves on protrusion of tongue
• Pressure symptoms: dysphagia, dyspnoea, stridor, SVC obstruction (retrosternal)
• Hoarseness (RLN involvement - suggests malignancy)

Symptoms of Hypothyroidism

• Weight gain, cold intolerance, constipation
• Fatigue, lethargy, slowed mentation
• Dry skin, hair loss, bradycardia
• Menorrhagia, infertility
• Periorbital oedema, hoarse voice
• Hyporeflexia, myopathy

Symptoms of Hyperthyroidism (Thyrotoxicosis)

• Weight loss despite increased appetite
• Heat intolerance, sweating
• Palpitations, tachycardia, AF
• Tremor, anxiety, irritability
• Diarrhoea, oligomenorrhoea
• Proximal myopathy

Graves' Disease - Specific Signs

• Exophthalmos (proptosis) / ophthalmopathy (Figure 55.17)
• Lid lag, lid retraction
• Pretibial myxoedema
• Thyroid acropachy (clubbing)
• Diffuse vascular goitre with bruit

Features Suggesting Malignancy

• Age extremes (teenager or elderly)
• Male sex
• Hard, irregular texture
• Apparent fixity
• RLN palsy (hoarseness + non-occlusive cough, confirmed by laryngoscopy - "almost pathognomonic")
• Cervical lymphadenopathy along internal jugular vein (almost diagnostic of PTC)
• Rapid enlargement / painful nodule (usually haemorrhage but malignancy must be excluded)

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6. INVESTIGATIONS

Biochemical

• Serum TSH (immunochemiluminometric assay) - most sensitive initial test
• Free T3 and Free T4
• Thyroid autoantibodies: Anti-TPO (>25 units/mL significant) and antithyroglobulin (>1:100 significant) - for autoimmune disease
• TSH receptor antibodies (TRAb) - in Graves' disease
• Calcitonin - for suspected medullary thyroid carcinoma

Imaging

• Ultrasonography - gold standard for evaluation of thyroid nodules; performed by trained operator; identifies nodule characteristics, guides FNAC
• Nuclear scintigraphy (Technetium/Iodine scan) - identifies hot/cold nodules; used in suspected toxic adenoma
• CT/MRI - for retrosternal extension, tracheal compression assessment; CT if swallowing/breathing symptoms
• PET scan - reserved for specific oncological scenarios

Cytology

• FNAC (Fine-needle aspiration cytology) - performed under ultrasound guidance

Note: FNA cannot distinguish follicular adenoma from follicular carcinoma - this requires histological assessment of capsular/vascular invasion. All Thy3-5 require surgery.

Other

• Laryngoscopy - to assess vocal cord function preoperatively (especially if hoarse, or prior thyroid surgery)
• CT chest - for retrosternal goitre (assess extent, tracheal deviation/compression)

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7. INDICATIONS FOR SURGERY (Table 55.4)

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8. PREOPERATIVE PREPARATION

For Thyrotoxic Patients (Mandatory - prevent thyroid storm)

• Carbimazole or propylthiouracil - restore to euthyroid state over weeks
• Given to achieve euthyroid state before surgery

• Propranolol 40 mg three times daily (up to 80 mg TDS or nadolol 320 mg OD if needed)
• Also inhibits peripheral conversion of T4 to T3
• Rapid clinical response - patient euthyroid in days, not weeks
• Critical: Must continue for 7 days postoperatively (hormone levels remain high for some days after surgery)

• Given for 10 days before operation, with carbimazole or beta-blocker
• Produces transient remission, reduces vascularity of the gland
• Gives additional safety if morning beta-blocker dose missed on day of surgery
• Not universal in use

For All Thyroid Surgery

• Assessment of vocal cord function (laryngoscopy) pre-op
• Cross-sectional imaging for retrosternal goitre
• Calcium and PTH levels (baseline)
• Nerve monitor endotracheal tube (intraoperative neurophysiology monitoring)
• Patient positioning: supine, arms at side, head on ring, neck extended with shoulder roll, reverse Trendelenburg

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9. TYPES OF THYROID OPERATIONS

1. Total lobectomy
2. Isthmusectomy
3. Subtotal lobectomy

• Total thyroidectomy = 2 × total lobectomy + isthmusectomy
• Subtotal thyroidectomy = 2 × subtotal lobectomy + isthmusectomy
• Near-total thyroidectomy (Dunhill procedure) = total lobectomy + isthmusectomy + subtotal lobectomy
• Lobectomy = total lobectomy + isthmusectomy

Selecting the Procedure

Surgical Technique of Thyroidectomy (Key Steps)

• Incision: Kocher's (collar) incision - 2 finger-breadths above clavicle, in skin crease
• Subplatysmal flaps raised; strap muscles divided in midline
• Superior pole vessels divided close to thyroid (to protect EBSLN)
• RLN identified and traced throughout its course
• Parathyroids identified and preserved with their blood supply
• Berry's ligament divided - highest risk point for RLN
• Haemostasis; drain optional (not shown to prevent haematoma)
• Strap muscles approximated (not watertight closure to allow haematoma escape)

New Technology

• Intraoperative nerve monitoring (IONM) - nerve monitor ETT/electrode wrap
• Harmonic scalpel / LigaSure for haemostasis
• Remote-access approaches (robotic, transoral endoscopic thyroidectomy vestibular approach - TOETVA)

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10. POSTOPERATIVE COMPLICATIONS

Early

• ~1 in 50 patients develop haematoma
• Almost all within first 24 hours
• Arterial bleed → rising tension → venous oedema of larynx → airway obstruction → death
• Management: Remove skin sutures immediately → secure airway (endotracheal intubation) → evacuate haematoma → control bleeding point

• Unilateral or bilateral; transient or permanent
• BAETS audit: RLN palsy rate 1.8% at 1 month, declining to 0.5% at 3 months for first operations
• Permanent paralysis is rare if nerve identified at operation
• If transected ends identified: reanastomose immediately
• If segment excised (malignancy): ansa cervicalis anastomosis (maintains muscle innervation, improves voice quality)
• Permanent: speech therapy; medialization procedures if unacceptable voice
• Bilateral injury: respiratory obstruction requiring tracheostomy

• Loss of tension in the vocal cord
• Diminished power and range - particularly problematic for professional voice users
• Often subtle on routine assessment

• Required after total thyroidectomy (100%)
• ~1 in 3 patients after lobectomy require supplementation
• Higher rates with positive thyroid autoantibodies
• Thyroxine replacement started day 1 postoperatively after total thyroidectomy

• Due to removal or ischaemia of parathyroid glands (vascular injury more important than inadvertent removal)
• Permanent hypoparathyroidism should be <1%
• Presents 2-5 days postoperatively (rarely delayed 2-3 weeks)
• Symptoms: paraesthesia of fingers, toes or around mouth; tetany; Chvostek's/Trousseau's signs
• Highest risk: total thyroidectomy + central neck dissection
• Management: calcium monitoring; oral/IV calcium; calcitriol

• Acute exacerbation of hyperthyroidism
• Occurs if thyrotoxic patient inadequately prepared for thyroidectomy - now extremely rare with proper preop
• Treatment:
  • Supportive: IV fluids, ice packs (cooling), O2, diuretics, digoxin (for AF), sedation, IV hydrocortisone
  • Specific: Carbimazole 10-20 mg 6-hourly; Lugol's iodine 10 drops 8-hourly or sodium iodide 1 g IV; Propranolol IV (1-2 mg) or oral (40 mg 6-hourly)

Late

• Cellulitis more common than appreciated
• Significant subcutaneous or deep infection possible

• With or without sinus formation
• Seen with non-absorbable (especially silk) sutures
• Prevention: use absorbable ligatures and sutures throughout

• Even after subtotal resection - up to 100% at 30 years in Graves' disease
• Risk of remnant regrowth requiring difficult revision surgery

• Young women particularly affected cosmetically

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11. POSTOPERATIVE CARE

• Recovery room, then overnight ward observation
• Vigilance for haematoma (first 24 hours critical)
• Post total thyroidectomy: serial calcium monitoring; patient educated about hypocalcaemia signs
• Thyroxine replacement started day 1 post total thyroidectomy
• Clinic review: histology, wound inspection, laryngoscopy for vocal cord function, TFTs and calcium if required

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QUICK SUMMARY TABLE

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THYROID - Bailey & Love (28th Ed.) Chapter 55

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1. EMBRYOLOGY

• The thyroid originates from the median bud of the pharynx (thyroglossal duct)
• The foramen caecum (junction of anterior 2/3 and posterior 1/3 of tongue) is the vestigial remnant
• The duct migrates caudally, passing through or adjacent to the developing hyoid cartilage
• Parathyroids develop from the 3rd and 4th pharyngeal pouches
• The thymus also arises from the 3rd pouch - as it descends it drags the inferior parathyroid with it, which is why the inferior parathyroid lies below the superior (but can be found anywhere along this line of descent)
• Parafollicular C cells (calcitonin-secreting) reach the thyroid from neural crest cells via the ultimobranchial body

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2. SURGICAL ANATOMY

Arterial Supply

Venous Drainage

Lymphatic Drainage

• Delphian nodes (juxtathyroid/pretracheal)
• Paratracheal nodes
• Nodes on superior and inferior thyroid veins

• Deep cervical nodes (Levels II, III, IV, V)
• Mediastinal nodes (Level VII)

Recurrent Laryngeal Nerve (RLN) - Surgically Critical

• Branch of the vagus nerve
• Left RLN: recurs around the arch of aorta → runs more medially in the tracheo-oesophageal groove
• Right RLN: recurs around the subclavian artery → runs more obliquely
• ~2% on the right are non-recurrent (enter larynx from above - associated with aberrant right subclavian artery)
• Located in the tracheo-oesophageal groove, forms one side of Behr's triangle (carotid artery + inferior thyroid artery + RLN)
• Found under the Tubercle of Zuckerkandl during lateral lobe mobilisation
• Greatest risk at Berry's ligament (pretracheal fascia binding thyroid to trachea at cricothyroid joint)

External Branch of Superior Laryngeal Nerve (EBSLN)

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3. CONDITIONS / CLASSIFICATION

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4. SIGNS AND SYMPTOMS

All Thyroid Swellings

• Anterior neck swelling moving on swallowing (hallmark)
• Pressure symptoms: dysphagia, dyspnoea, stridor (retrosternal extension)
• Superior vena cava obstruction (large retrosternal goitre)

Hypothyroidism

• Weight gain, cold intolerance, constipation, fatigue, bradycardia
• Dry skin, hair loss, periorbital oedema, hoarse voice
• Menorrhagia, hyporeflexia

Hyperthyroidism (Thyrotoxicosis)

• Weight loss with good appetite, heat intolerance, sweating
• Palpitations, tachycardia, atrial fibrillation
• Tremor, anxiety, diarrhoea, oligomenorrhoea
• Proximal myopathy

Graves' Disease (additional)

• Exophthalmos, lid lag, lid retraction, chemosis
• Pretibial myxoedema
• Thyroid acropachy (clubbing)
• Thyroid bruit (very vascular gland)

Features Suggesting Malignancy

• Extremes of age, male sex
• Hard, irregular, fixed swelling
• Hoarseness + non-occlusive cough = RLN palsy (almost pathognomonic)
• Cervical lymphadenopathy along internal jugular vein (almost diagnostic of PTC)
• Rapid growth or sudden pain (usually haemorrhage, but exclude malignancy)

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5. INVESTIGATIONS

Biochemical

• Serum TSH - most sensitive test (immunochemiluminometric assay; can detect very low values)
• Free T3 and Free T4 - interpreted with TSH
• Thyroid autoantibodies: Anti-TPO (>25 U/mL significant), antithyroglobulin (>1:100 significant)
• TRAb (TSH receptor antibodies) - for Graves' disease
• Calcitonin - for suspected medullary carcinoma

Imaging

• Ultrasound - gold standard for nodule evaluation; guides FNAC
• Scintigraphy (Tc99m or I123) - hot vs cold nodules; toxic adenoma
• CT/MRI - retrosternal extension, tracheal compression (arms-down position preferred)
• PET - selected oncology cases

Cytology - FNAC (Thy Classification)

Other

• Laryngoscopy - preop vocal cord assessment (especially if hoarse or previous neck surgery)

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6. PREOPERATIVE PREPARATION

For All Thyroid Patients

• Vocal cord assessment (laryngoscopy)
• Baseline TFTs and calcium/PTH
• Cross-sectional imaging if retrosternal/large goitre
• Intraoperative nerve monitoring (IONM) setup if planned

Mandatory for Thyrotoxic Patients (to prevent thyroid storm)

• Carbimazole or propylthiouracil
• Restore to euthyroid state; takes weeks

• Propranolol 40 mg TDS (up to 80 mg TDS; or Nadolol 320 mg OD)
• Also blocks peripheral T4 → T3 conversion
• Patient euthyroid in days
• Must continue for 7 days postoperatively (thyroid hormone levels remain elevated for days after surgery)

• Given with carbimazole or beta-blocker
• Reduces gland vascularity
• Adds safety if beta-blocker dose is missed on the day of operation
• Not universally used

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7. TYPES OF THYROID OPERATIONS

1. Total lobectomy
2. Isthmusectomy
3. Subtotal lobectomy

Procedure Selection by Indication

Bailey's dictum on Graves': "Thyroid failure should not be regarded as a failure of treatment, but recurrent toxicity is."

Surgical Technique (Key Steps)

• Patient position: Supine, neck extended, shoulder roll, reverse Trendelenburg
• Incision: Kocher's collar incision 2 finger-breadths above clavicle in skin crease
• Subplatysmal flaps, strap muscles divided in midline
• Superior pole: vessels ligated close to thyroid (protect EBSLN)
• RLN identified and traced throughout its course throughout the case
• Parathyroids identified and preserved with vascular pedicles
• Berry's ligament divided carefully
• Haemostasis; strap muscles not closed watertight (allows haematoma to escape subcutaneously)
• Drain: not proven to prevent haematoma

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8. POSTOPERATIVE COMPLICATIONS

A. Early, Life-Threatening

• Most frequent life-threatening complication (~1 in 50 patients)
• Almost all develop within first 24 hours
• Mechanism: arterial bleed → rising central compartment pressure → exceeds venous pressure → laryngeal venous oedema → airway obstruction → death
• Management: Immediately remove skin sutures (releases pressure), call senior, secure airway with ETT, evacuate haematoma, control bleeding point
• Wound drains do NOT have a protective effect

• Immediate respiratory obstruction
• Requires emergency tracheostomy

B. Early, Non-Life-Threatening

• BAETS audit: 1.8% at 1 month, declining to 0.5% at 3 months for first operations
• Transient more common than permanent
• Permanent paralysis rare if nerve identified intraoperatively
• If transected → reanastomose immediately; if segment excised → ansa cervicalis anastomosis
• Long-term: speech therapy, medialization procedures

• Loss of vocal tension → diminished power and pitch range
• Often subtle; critical for professional voice users

• Ischaemia of parathyroids (vascular injury) more important than inadvertent removal
• Permanent hypoparathyroidism < 1%
• Onset: typically 2-5 days postop (rarely 2-3 weeks)
• Symptoms: paraesthesia of fingers, toes, perioral; tetany; Chvostek's sign; Trousseau's sign
• Highest risk: total thyroidectomy + central neck dissection
• Management: serial calcium monitoring, oral/IV calcium, calcitriol

• Occurs in inadequately prepared thyrotoxic patient - now very rare with proper preop
• Supportive: IV fluids, ice packs, O2, diuretics, digoxin (for AF), sedation, IV hydrocortisone
• Specific: Carbimazole 10-20 mg 6-hourly, Lugol's iodine 10 drops 8-hourly (or sodium iodide 1 g IV), Propranolol IV 1-2 mg or oral 40 mg 6-hourly

• 100% after total thyroidectomy
• ~1 in 3 patients after lobectomy
• Higher with positive thyroid autoantibodies
• Thyroxine started day 1 postoperatively after total thyroidectomy

C. Late

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9. POSTOPERATIVE CARE (Summary)

• Overnight inpatient observation (UK standard - haematoma risk)
• Hourly wound observations for haematoma in first 24 hours; staff must know to remove sutures if swelling develops
• Serial calcium levels after total thyroidectomy; educate patient on symptoms of hypocalcaemia
• Start thyroxine day 1 (total thyroidectomy)
• 4-week follow-up: histology review, wound check, laryngoscopy, TFTs, calcium

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