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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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