Surgery Surgery · Anatomy

Thyroid Surgery Anatomy

Thyroid surgery is the most common endocrine operation. Four structures are at risk during every thyroid resection — knowing their anatomy, relations, and identification techniques is essential for safe surgery.

✦ The Mnemonic

"Really Elegant Protective Surgery"

RLN · EBSLN · Parathyroids · blood Supply — four structures at risk during thyroid surgery

R Recurrent Laryngeal Nerve (RLN) Loops under aorta (left) and subclavian (right); ascends in tracheo-oesophageal groove; enters larynx behind cricothyroid joint; supplies all intrinsic laryngeal muscles except cricothyroid

E External Branch of Superior Laryngeal Nerve (EBSLN) Runs with superior thyroid artery; supplies cricothyroid muscle; injury → loss of high-pitched voice (not hoarse)

P Parathyroid Glands 4 glands (2 superior, 2 inferior); superior more constant; inferior from 3rd pharyngeal pouch (more variable); at risk in total thyroidectomy → hypoparathyroidism

S Superior Thyroid Artery (blood Supply) First ECA branch; ligated during thyroid surgery; EBSLN runs with it — ligate close to the gland

📚 Clinical Breakdown

The RLN is the most critical structure in thyroid surgery. On the left, it loops under the aortic arch; on the right, it loops under the right subclavian artery. Both ascend in the tracheo-oesophageal groove and enter the larynx posterior to the cricothyroid joint. Intraoperative nerve monitoring (IONM) is now standard practice.

RLN injury: unilateral = hoarseness (voice change) + risk of aspiration. Bilateral = bilateral vocal cord adduction in the midline → stridor, respiratory distress, and potentially fatal airway obstruction requiring emergency tracheostomy.

Hypoparathyroidism post-thyroidectomy: transient (most cases — resolves within weeks as devascularised glands recover) or permanent (<2% in experienced hands). Presents with hypocalcaemia: perioral numbness, carpal-pedal spasm (Trousseau's sign), Chvostek's sign (facial twitching on percussion of facial nerve). Supplement with calcium + alfacalcidol (active vitamin D).

RLN left loop Under aortic arch

RLN right loop Under right subclavian artery

EBSLN injury Loss of high notes; cricothyroid muscle palsy; not complete hoarseness

Trousseau's sign Carpal spasm on BP cuff inflation → hypocalcaemia

⭐ Clinical Pearl

Inferior parathyroids are the most surgically challenging — they arise from the 3rd pharyngeal pouch alongside the thymus, and their migration is highly variable (they can be anywhere from the jaw to the mediastinum). The superior parathyroids (4th pouch) are more constant — typically 1 cm above the inferior thyroid artery and posterior to the RLN.

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