Thyroid gland: goitre, nodules, cancer and thyroidectomy

Overview

The thyroid is the commonest endocrine organ operated on. PGET questions centre on four things: surgical anatomy (the laryngeal nerves and parathyroids), the work-up of a thyroid swelling, the types of thyroid cancer, and the complications of thyroidectomy.

Breast and thyroid together carry about two of the six Breast and Endocrine MCQs, so this chapter is high yield.

Surgical anatomy and embryology

• The thyroid starts at the foramen caecum (junction of anterior two-thirds and posterior third of the tongue) and descends along the thyroglossal duct, passing close to (or through) the hyoid.
• Parathyroids: superior from the 4th pouch; inferior from the 3rd pouch (with the thymus), so the inferior gland can lie anywhere along the thymic path.
• C cells (parafollicular) come from the neural crest via the ultimobranchial body. They make calcitonin and give rise to medullary carcinoma.
• The isthmus lies over the 2nd to 3rd tracheal rings.
• Lymph drains first to the central compartment (level VI), then to the lateral deep cervical nodes (levels II to V) and the upper mediastinum (level VII).

The nerves

• The left RLN hooks under the aortic arch; the right hooks under the subclavian artery, so it runs more obliquely.
• About 2% of right RLNs are non-recurrent; they enter the larynx directly from the vagus. This goes with a retro-oesophageal right subclavian artery.
• Berry's ligament (a thickening of pretracheal fascia binding the gland to the trachea) is where the RLN is at greatest risk.
• The tubercle of Zuckerkandl (posterolateral bulge of the lobe) usually lies over the RLN, so it is a landmark for finding it.

Thyroglossal cyst

• Midline neck swelling, usually just below the hyoid, in a child or young adult.
• Moves up on swallowing and on protruding the tongue (it is tethered to the hyoid).
• May become infected and burst, leaving a thyroglossal sinus or fistula.
• Rarely it holds the patient's only working thyroid tissue, so check with ultrasound first.
• Treatment: Sistrunk's operation: remove the cyst, the whole tract, the central body of the hyoid and a core of tongue base up to the foramen caecum. Simple excision leads to recurrence.

Classification of thyroid swellings

Simple goitre

• Iodine deficiency is the main cause of endemic goitre worldwide, including the northern mountain areas of Pakistan (the Himalayan belt). Daily need is about 0.1-0.15 mg of iodine. Iodised salt is the preventive measure.
• Dyshormonogenesis (inherited enzyme defects) explains many sporadic goitres. Pendred syndrome = goitre plus sensorineural deafness.
• Goitrogens: brassica vegetables (cabbage, kale), PAS, antithyroid drugs. Very large amounts of iodide are themselves goitrogenic.
• Natural history: diffuse hyperplasia, then areas of activity and inactivity, haemorrhage and necrosis, then nodules. Commoner in women.
• Sudden painful enlargement of a nodule is usually bleeding into a nodule, though it raises suspicion of cancer.

Indications for surgery in multinodular goitre: pressure symptoms (breathing or swallowing), retrosternal extension with compression, suspicion of cancer, toxicity, and cosmesis. Most patients with no symptoms need no operation.

Retrosternal goitre

• Usually grows down from a neck goitre. May compress the trachea or oesophagus, or cause superior vena cava obstruction.
• CT of the neck and thoracic inlet is the best test for tracheal compression.
• Most can be removed through a neck (cervical) incision; a sternotomy is rarely needed.
• After removing a long-standing large goitre, stridor with normal cord movement suggests tracheomalacia.

Investigating a thyroid swelling

FNAC categories (UK Thy system)

The solitary nodule

• Palpable nodules are common, especially in women. About 15% of clinically isolated swellings prove malignant; 30-40% are follicular adenomas; most of the rest are colloid nodules or cysts.
• Features raising suspicion: male, extremes of age, history of neck irradiation in childhood, family history (MEN 2), rapid growth, hard fixed lump, hoarseness (RLN palsy), and lymph nodes.
• A pure cyst may be aspirated, but refilling is common; a cyst that recurs or leaves a lump is excised.

Thyrotoxicosis and surgery

• Antithyroid drugs (carbimazole, propylthiouracil): given for about 6 months to 2 years; relapse occurs in at least half.
• Surgery is preferred in a large goitre, progressive eye disease, refusal of radiation, or pregnancy where drugs fail. Radioiodine can worsen eye disease and is forbidden in pregnancy.
• Propylthiouracil is preferred in the first trimester; carbimazole is linked to aplasia cutis of the scalp.

Preparing a toxic patient for thyroidectomy

1. Make the patient euthyroid with carbimazole 30-40 mg daily (usually 8-12 weeks).
2. Beta-blocker (propranolol 40 mg three times daily) controls symptoms; propranolol also reduces peripheral T4 to T3 conversion. If used, continue it for 7 days after surgery because hormone levels stay high.
3. Iodide (Lugol's iodine) for 10 days before surgery makes the gland less vascular and firmer. Never use iodide alone.

Thyroid cancer

• Women are affected about three times as often as men.
• Papillary microcarcinoma is a papillary cancer under 10 mm; many never progress and can be watched.
• Age is the main prognostic factor in differentiated cancer. The AJCC 8th edition uses an age cut-off of 55 years.

Treatment of differentiated (papillary and follicular) cancer

• Low risk, single focus confined to the thyroid: lobectomy is acceptable and spares the other RLN and parathyroids.
• High risk (large tumour, extrathyroid spread, nodal or distant metastases): total thyroidectomy, plus a therapeutic neck dissection for involved nodes.
• Radioiodine (I-131) after total thyroidectomy for high-risk disease; uptake needs a high TSH (stop thyroxine or give recombinant TSH).
• TSH suppression with thyroxine in high-risk patients.
• Follow-up marker: thyroglobulin, which should become undetectable after total thyroidectomy and ablation.

Medullary carcinoma

• Total thyroidectomy plus central neck dissection (C cells are throughout both lobes; no iodine uptake, so radioiodine and TSH suppression do not help).
• Screen for RET mutation and exclude phaeochromocytoma before surgery.
• MEN 2A: medullary carcinoma, phaeochromocytoma, hyperparathyroidism. MEN 2B: medullary carcinoma, phaeochromocytoma, mucosal neuromas, Marfanoid habitus.
• Carriers of a RET mutation are offered prophylactic thyroidectomy in childhood.

Thyroiditis

Thyroidectomy

• Types: lobectomy (hemithyroidectomy), total thyroidectomy (two lobectomies plus isthmus), near-total (Dunhill), and subtotal. Subtotal has largely been abandoned because of recurrence.
• Consent covers scar, bleeding, RLN injury, hypocalcaemia and hypothyroidism.
• Prophylactic antibiotics are not routinely needed for clean thyroid surgery.

Complications

Quick revision

• Nodule work-up: TSH, ultrasound, ultrasound-guided FNAC (Thy1-Thy5).
• Thy3f follicular lesion: diagnostic lobectomy; capsular or vascular invasion = carcinoma.
• Papillary 80%, lymphatic; follicular 10%, blood; medullary from C cells; anaplastic fatal in months.
• RLN with inferior thyroid artery, at risk at Berry's ligament; external laryngeal nerve with superior thyroid artery.
• Haematoma: open the wound at the bedside first.
• Hypocalcaemia day 2-5 after total thyroidectomy: IV calcium gluconate if symptomatic.
• Graves preparation: carbimazole to euthyroid, beta-blocker, Lugol's iodine 10 days.
• Thyroglossal cyst moves with tongue protrusion; Sistrunk's operation removes the hyoid body.

Written by The House Job from standard references (Bailey & Love).

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