Thyroid Disorders & Surgery

Surgical thyroid disease spans the spectrum from benign multinodular goitre to aggressive anaplastic carcinoma. For NEET PG, the perennial yield lies in nodule workup (FNAC + Bethesda), the four cancers, total thyroidectomy and its two feared complications — recurrent laryngeal nerve injury and hypocalcaemia.

Surgical anatomy you must own

The thyroid is enclosed in the pretracheal fascia (false capsule) over its own true capsule; this is why it moves with deglutition — a key clinical sign distinguishing it from other neck swellings. It does not move with tongue protrusion (that is a thyroglossal cyst). Blood supply:

Artery	Origin	Companion nerve at risk
Superior thyroid artery	External carotid	External branch of superior laryngeal nerve (EBSLN) — supplies cricothyroid
Inferior thyroid artery	Thyrocervical trunk (subclavian)	Recurrent laryngeal nerve (RLN) — close relation at ligament of Berry
Thyroidea ima (10%)	Brachiocephalic/arch	—

Venous drainage: superior and middle thyroid veins → internal jugular; inferior thyroid vein → brachiocephalic.

High-yield: Ligate the superior thyroid artery close to the gland to spare the EBSLN; ligate the inferior thyroid artery away from the gland (laterally) to spare the RLN and preserve the parathyroid blood supply (parathyroids are chiefly supplied by the inferior thyroid artery).

The RLN is most vulnerable at the ligament of Berry and where it crosses the inferior thyroid artery. A non-recurrent laryngeal nerve occurs on the right (~0.5–1%) with an aberrant right subclavian artery (arteria lusoria) and is a classic trap question.

Goitre — classification

"Goitre" = any enlargement of the thyroid.

1. Simple (non-toxic) goitre — diffuse hyperplastic → multinodular (commonest worldwide; iodine deficiency is leading global cause).
2. Toxic goitre — Graves' (diffuse), toxic multinodular (Plummer's), toxic adenoma (solitary).
3. Neoplastic — benign (follicular adenoma) and malignant.
4. Inflammatory — Hashimoto's, de Quervain's (subacute granulomatous), Riedel's thyroiditis.
5. Rare — amyloid.

Retrosternal goitre: extension below the thoracic inlet. Suspect with positive Pemberton's sign (facial congestion, stridor, raised JVP on arm elevation — thoracic inlet obstruction). CT neck/thorax is investigation of choice for extent; most are removed via the cervical (collar) approach, sternotomy rarely needed.

Solitary thyroid nodule — the central workup

A clinically solitary nodule is malignant in ~10–15%. The first investigation is serum TSH, which directs the pathway.

TSH low (suppressed) → radioisotope (Tc-99m / I-123) scan → hot nodule (autonomous, almost never malignant) → treat hyperthyroidism.

TSH normal or high → ultrasound + FNAC (FNAC is the single most useful diagnostic test for a thyroid nodule).

High-yield: A cold nodule on scintigraphy has ~15–20% malignancy risk; a hot nodule is almost always benign. But remember the modern flow starts with TSH, then USG/FNAC — scan only if TSH is low.

Ultrasound features suggesting malignancy (TI-RADS): solid hypoechoic, taller-than-wide shape, irregular/spiculated margins, microcalcifications, extrathyroidal extension.

Bethesda system for reporting thyroid FNAC

Category	Diagnosis	Malignancy risk	Management
I	Non-diagnostic / unsatisfactory	5–10%	Repeat FNAC under USG
II	Benign	0–3%	Follow-up
III	AUS / FLUS (atypia/follicular lesion of undetermined significance)	10–30%	Repeat FNAC / molecular testing
IV	Follicular neoplasm / suspicious for follicular neoplasm	25–40%	Diagnostic hemithyroidectomy (lobectomy)
V	Suspicious for malignancy	50–75%	Lobectomy or total thyroidectomy
VI	Malignant	97–99%	Total thyroidectomy

High-yield: FNAC cannot distinguish follicular adenoma from follicular carcinoma — the diagnosis of malignancy needs capsular and/or vascular invasion on histology. Hence Bethesda IV → diagnostic hemithyroidectomy for definitive histology.

Thyroid carcinomas

Papillary carcinoma (PTC) — commonest (~80%)

• Arises from follicular cells; associated with radiation exposure and RET/PTC, BRAF mutations.
• Spreads via lymphatics → cervical nodes (lateral aberrant thyroid = nodal metastasis from occult PTC).
• Best prognosis (10-yr survival >90%); multifocal/bilateral common.
• Histology: Orphan Annie eye nuclei (optically clear), nuclear grooves, intranuclear pseudoinclusions, psammoma bodies (laminated calcified).

Follicular carcinoma (FTC) — ~10%

• Older patients, iodine-deficient areas; spreads by haematogenous route → bone, lung.
• Diagnosed by capsular/vascular invasion; Hürthle cell variant is more aggressive and iodine-resistant.

Medullary carcinoma (MTC) — ~5%

• Arises from parafollicular C cells (neural crest) → secretes calcitonin (tumour marker) and CEA.
• Amyloid stroma on histology.
• ~25% familial: MEN 2A (MTC + phaeochromocytoma + parathyroid hyperplasia), MEN 2B (MTC + phaeo + mucosal neuromas + marfanoid habitus), or familial MTC — all from RET proto-oncogene mutations.

High-yield: In any MTC, exclude phaeochromocytoma first (plasma/urinary metanephrines) and operate on the phaeo before the thyroid to avoid intra-operative hypertensive crisis. Prophylactic thyroidectomy is offered to RET mutation carriers.

Anaplastic carcinoma — ~1–2%

• Elderly, rapidly enlarging hard mass, stridor/dysphagia; worst prognosis (survival in months).
• Largely inoperable; management is palliative (isthmusectomy/tracheostomy for airway, chemoradiation).

Primary thyroid lymphoma

• Non-Hodgkin B-cell, on a background of Hashimoto's thyroiditis; treated with chemo/radiotherapy, not surgery.

Feature	Papillary	Follicular	Medullary	Anaplastic
Cell of origin	Follicular	Follicular	C cells	Follicular
Spread	Lymphatic	Haematogenous	Both	Local + both
Marker	Thyroglobulin	Thyroglobulin	Calcitonin/CEA	—
Iodine uptake (for RAI)	Yes	Yes	No	No
Prognosis	Best	Good	Intermediate	Worst

Management of differentiated thyroid cancer (DTC = papillary + follicular)

Flow: confirm cytology (Bethesda) → assess risk (size, extension, nodes, age) → surgery (lobectomy vs total thyroidectomy) → radioactive iodine (RAI) ablation in intermediate/high risk → TSH-suppressive levothyroxine → surveillance with serum thyroglobulin + neck USG.

• Lobectomy (hemithyroidectomy): low-risk PTC <1–4 cm, unifocal, no extrathyroidal extension, no nodes.
• Total thyroidectomy: tumour >4 cm, bilateral/multifocal, extrathyroidal extension, nodal/distant metastasis, prior radiation, MTC, anaplastic.
• Central compartment (level VI) neck dissection: therapeutic for clinically involved nodes; lateral neck dissection for proven lateral disease.
• RAI (I-131): only DTC takes up iodine; given after total thyroidectomy in selected cases to ablate remnant/micrometastases. MTC and anaplastic do not respond.
• Thyroglobulin is the tumour marker for DTC follow-up (it should be undetectable after total thyroidectomy + ablation); calcitonin for MTC.

High-yield: Levothyroxine after thyroidectomy serves two purposes — physiological replacement and TSH suppression (to remove the growth stimulus on any residual DTC).

Toxic goitre — surgical angle

Indications for surgery in hyperthyroidism: large goitre with compressive/cosmetic symptoms, coexisting suspicious nodule, failed/intolerant to drugs, pregnancy with severe disease, ophthalmopathy (avoid RAI). Render euthyroid pre-op with antithyroid drugs (carbimazole/propylthiouracil) + beta-blocker (propranolol); Lugol's iodine for 10 days pre-op reduces vascularity (Plummer's effect). Surgery of choice today is total thyroidectomy for Graves'.

Complications of thyroidectomy

1. Haemorrhage / tension haematoma

Most feared early complication — expanding neck haematoma compresses the airway (largely via venous congestion and laryngeal oedema). It is an emergency: open the wound at the bedside, evacuate the clot, then return to theatre. Keep a clip/suture-remover at the bedside.

2. Recurrent laryngeal nerve injury

• Unilateral injury → ipsilateral cord paralysis in paramedian position → hoarse, weak voice; often compensated by the other cord.
• Bilateral injury → both cords paramedian/adducted → stridor and airway obstruction → may need emergency re-intubation/tracheostomy. This is the dreaded outcome.
• The external laryngeal nerve (EBSLN) injury → loss of high-pitched voice (cricothyroid) — relevant for singers.

High-yield: Routine pre- and post-operative laryngoscopy to document cord function is standard. Intra-operative nerve monitoring helps but identification and preservation of the nerve is the gold standard.

3. Hypocalcaemia / hypoparathyroidism

From parathyroid devascularisation or inadvertent removal.

• Transient (common) vs permanent (<2% in expert hands).
• Symptoms: circumoral/peripheral paraesthesia, carpopedal spasm, Chvostek's sign (facial twitch on tapping facial nerve), Trousseau's sign (carpal spasm on inflating BP cuff above systolic — more specific), tetany, prolonged QT, laryngospasm.
• Onset typically 24–72 h post-op.
• Treat: oral calcium + active vitamin D (calcitriol); severe symptomatic tetany → IV calcium gluconate slowly.

High-yield: Trousseau's sign is more specific than Chvostek's for hypocalcaemic tetany. Always check magnesium — refractory hypocalcaemia may be due to hypomagnesaemia.

4. Thyroid storm

Peri-operative crisis in inadequately prepared thyrotoxic patient: hyperpyrexia, tachyarrhythmia, agitation, delirium. Manage with propranolol, propylthiouracil, Lugol's iodine (given ≥1 h after PTU), hydrocortisone, cooling.

5. Others

Wound infection, hypertrophic scar/keloid, tracheomalacia (long-standing large goitre → softened tracheal rings → collapse on extubation), hypothyroidism (after total thyroidectomy — expected, needs lifelong levothyroxine).

Mnemonic for thyroidectomy complications — "Bleeding Nerves Cause Tetany & Storms": Bleeding/haematoma, Nerve (RLN/EBSLN), Calcium (hypoparathyroidism → Tetany), thyroid Storm, hypothyroidism, tracheomalacia.

Thyroiditis comparison (rapid)

Type	Key feature	Pain	Antibody / cause
Hashimoto's	Commonest hypothyroidism (non-iodine areas), risk of lymphoma	Painless	Anti-TPO, anti-thyroglobulin
de Quervain's (subacute)	Post-viral, raised ESR, painful, self-limiting	Painful	Viral
Riedel's	Woody-hard fixed gland, IgG4-related, mimics cancer	Painless	Fibrosis
Postpartum	Transient hyper → hypo	Painless	Anti-TPO

Key differentials of a neck swelling

• Thyroglossal cyst — midline, moves with tongue protrusion and deglutition (Sistrunk's operation for excision).
• Branchial cyst — anterior border of sternocleidomastoid, upper third.
• Lymph node / lymphoma — does not move with swallowing.
• Carotid body tumour (chemodactoma) — pulsatile, mobile side-to-side only (not vertically), splaying of carotid bifurcation (lyre sign).

Recently asked / exam angle

• First investigation of a thyroid nodule = serum TSH (then USG/FNAC; scan only if TSH low). Repeatedly tested as a sequence MCQ.
• Bethesda category IV → diagnostic hemithyroidectomy because FNAC cannot separate follicular adenoma from carcinoma.
• Orphan Annie eye nuclei + psammoma bodies = papillary; amyloid stroma + calcitonin = medullary.
• MTC + MEN 2 + RET gene; rule out and treat phaeochromocytoma before thyroid surgery.
• Non-recurrent laryngeal nerve on the right with aberrant right subclavian (arteria lusoria).
• Ligate superior thyroid artery close to gland (EBSLN), inferior thyroid artery away from gland (RLN + parathyroids).
• Bilateral RLN palsy → stridor (airway emergency); Trousseau more specific than Chvostek for hypocalcaemia.
• Pemberton's sign for retrosternal goitre; Lugol's iodine reduces gland vascularity pre-op.
• Anaplastic carcinoma in the elderly with rapidly enlarging hard mass — worst prognosis.
• Thyroglobulin = DTC marker; calcitonin = MTC marker.

Rapid revision

1. Thyroid swelling moves with deglutition; thyroglossal cyst additionally moves with tongue protrusion.
2. TSH is the first test for a thyroid nodule; FNAC is the most useful diagnostic test.
3. Hot nodule = almost always benign; cold nodule = ~15–20% malignant.
4. Bethesda VI = malignant → total thyroidectomy; IV = follicular neoplasm → lobectomy.
5. Papillary = lymphatic spread, best prognosis, Orphan Annie nuclei & psammoma bodies, radiation-linked.
6. Follicular = haematogenous spread (bone/lung); diagnosed by capsular/vascular invasion.
7. Medullary = C cells, calcitonin, amyloid, RET/MEN 2; check metanephrines first.
8. Anaplastic = elderly, hard rapidly growing mass, worst prognosis, palliative.
9. Ligate superior thyroid artery near gland, inferior thyroid artery away from gland.
10. Bilateral RLN injury → stridor/airway obstruction; non-recurrent nerve on the right.
11. Post-op hypocalcaemia at 24–72 h: paraesthesia, Chvostek & Trousseau (more specific), treat with calcium + calcitriol.
12. Tension haematoma = open the wound at bedside immediately; thyroglobulin (DTC) and calcitonin (MTC) are the follow-up markers.