Thyroid pathology

Key points

The thyroid gland is a small butterfly-shaped endocrine organ situated at the base of the neck below the larynx

It functions as the metabolic control centre of the body, regulating growth, development and energy balance through thyroid hormone production

It is highly vascular and clinically significant in both endocrine and surgical pathology

“A tiny butterfly-shaped gland at the base of your neck, like a DJ at a concert, controlling your vibe, energy, mood, weight, temperature, and heartbeat”

Embryology

The thyroid originates from endoderm in the floor of the primitive pharynx around the 3rd to 4th week of gestation

It descends anteriorly along the thyroglossal duct to reach its final position anterior to the trachea below the cricoid cartilage

Remnants of this tract can persist as a thyroglossal duct cyst which moves with swallowing and tongue protrusion

Ectopic thyroid tissue may occur anywhere along this descent, most commonly at the tongue base (lingual thyroid)

Absence or hypoplasia of the thyroid gland can result in congenital hypothyroidism

Parafollicular or C cells originate from ultimobranchial bodies derived from the fourth pharyngeal pouch

Anatomy

The thyroid consists of two lateral lobes joined by an isthmus and sometimes a pyramidal lobe

It lies over the 2nd to 4th tracheal rings and is enclosed by a true capsule and a false capsule (pretracheal fascia)

Berry’s ligament anchors the gland to the trachea and closely relates to the recurrent laryngeal nerve

The gland is highly vascular with rich arterial and venous networks

Vascular Supply

Arterial supply includes the superior thyroid artery from the external carotid and the inferior thyroid artery from the thyrocervical trunk

A thyroid ima artery may arise from the brachiocephalic trunk in some individuals

Venous drainage occurs via superior and middle veins to the internal jugular and inferior veins to the brachiocephalic vein

Awareness of these variations is essential to avoid surgical haemorrhage

Innervation

Sympathetic fibres from cervical sympathetic ganglia provide vasomotor control

Parasympathetic fibres arise from the vagus nerve indirectly

Hormone release is regulated by thyroid-stimulating hormone (TSH) from the anterior pituitary

Histology and Cell Types

Follicular cells form spherical follicles and produce thyroid hormones (T3 and T4) from iodinated thyroglobulin under TSH influence

Parafollicular cells or C cells secrete calcitonin which lowers serum calcium by inhibiting osteoclastic activity

Physiology

Triiodothyronine (T3) is the active hormone and thyroxine (T4) is the prohormone converted to T3 in peripheral tissues

Thyroid hormones increase basal metabolic rate, oxygen consumption and heat production

They enhance carbohydrate metabolism by stimulating gluconeogenesis and glycogenolysis and increase gastrointestinal glucose absorption

In lipid metabolism they promote lipolysis and reduce serum cholesterol levels

Protein synthesis is stimulated at normal hormone levels but catabolism occurs in excess

Cardiovascular effects include increased heart rate, systolic pressure and catecholamine sensitivity

They are essential for normal brain development, cognition and linear growth, working synergistically with growth hormone

In reproductive health they maintain normal menstrual cycles, fertility and spermatogenesis

Recurrent Laryngeal Nerve

A branch of the vagus nerve looping differently on each side

The right nerve loops under the subclavian artery and the left under the aortic arch

Both ascend in the tracheoesophageal groove and enter the larynx near the cricothyroid joint

They supply motor fibres to all intrinsic laryngeal muscles except the cricothyroid and sensory fibres below the cords

Unilateral injury causes hoarseness and aspiration risk

Bilateral injury leads to airway obstruction requiring tracheostomy

“Surgical Pearl: The recurrent laryngeal nerve is embedded in Berry’s ligament in up to 70% of cases – a common site of nerve injury”

Thyroid Physiology and Investigation

T3 and T4 are produced in thyroid follicles from iodide under the influence of TSH and attached to thyroglobulin

Ectopic thyroid tissue is usually poorly functioning and may enlarge or become cystic under TSH stimulation

Thyroid function is assessed with serum TSH, free T3 and T4 levels and autoantibodies where indicated

Imaging may include ultrasound and thyroid uptake scans for nodules or goitre

Thyroglossal Cysts

Result from failure of thyroglossal duct atrophy between weeks 5–10 of gestation

The cysts are lined by columnar or stratified squamous epithelium and may contain ectopic thyroid tissue in 8%

Risk of infection and inflammation is common and around 1% of adult thyroid cancers arise within these cysts

Treatment is by Sistrunk’s procedure which removes the cyst, central hyoid bone and the tract to the foramen caecum

Careful dissection prevents rupture and recurrence which occurs in 10–20% of cases

If carcinoma is identified, further management depends on completeness of excision and presence of residual tissue

Thyroiditis

Acute suppurative thyroiditis is an infective process, sometimes secondary to a pyriform sinus fistula, and presents with neck pain, fever and tenderness

Treatment includes antibiotics and drainage if abscess forms

Autoimmune Hypothyroidism (Hashimoto’s Thyroiditis)

Characterised by low T3 and T4 with raised TSH and positive thyroid peroxidase or thyroglobulin antibodies

Common in patients with Trisomy 21 or Turner syndrome

Associated with increased risk of thyroid papillary carcinoma and thyroid lymphoma

Autoimmune Hyperthyroidism (Graves’ Disease)

Caused by TSH receptor-stimulating antibodies leading to diffuse gland enlargement and excess hormone secretion

Most common cause of hyperthyroidism in children and adolescents with a female to male ratio of about 5:1

Features include goitre, hyperthyroidism and eye signs such as exophthalmos

Neonatal thyrotoxicosis occurs in about 1% of infants born to mothers with active Graves’ disease due to antibody transfer

Treatment includes beta-blockade, antithyroid drugs (carbimazole, propylthiouracil) and surgery if medical therapy fails or compression occurs

Lugol’s iodine may be given preoperatively to reduce gland vascularity and minimise risk of thyroid storm

Goitre

Simple goitre results from iodine deficiency leading to TSH-driven thyroid hyperplasia

Usually euthyroid and often managed conservatively unless compressive or cosmetically significant

Toxic multinodular goitre develops after long-standing stimulation with low iodine intake

Treatment involves antithyroid drugs followed by surgery for failure of medical control or compressive symptoms

‘Hot nodules’ on scan are usually resected due to functional autonomy

Thyroid Neoplasms

Benign lesions include colloid nodules, follicular adenomas and multinodular goitre

Malignant tumours include papillary, follicular, medullary and anaplastic carcinoma

Paediatric thyroid malignancies often present as painless neck masses or lymphadenopathy

Red flag features include hypoechoic solid nodules, irregular margins, family history and prior radiation exposure

Investigation includes ultrasound, thyroid function tests, fine needle aspiration cytology and calcitonin or RET testing if medullary carcinoma suspected

Treatment is total thyroidectomy with or without neck dissection followed by lifelong thyroxine therapy

Complications include recurrent laryngeal nerve injury and postoperative hypocalcaemia

“Multidisciplinary approach: Involves endocrinologist, geneticist and oncologist"

Thyroidectomy

Performed for malignancy, large goitre causing compression or uncontrolled Graves’ disease

Types include lobectomy, hemithyroidectomy, subtotal and total thyroidectomy

Anaesthesia is general with nerve monitoring

• Patient is placed supine with neck extended

• A transverse Kocher collar incision is made and subplatysmal flaps are elevated

• Strap muscles are retracted and the pretracheal fascia is opened

• Veins are ligated and the gland is mobilised by dividing its ligaments

• Recurrent laryngeal and superior laryngeal nerves and parathyroid glands are preserved

• Posterior capsule is left intact where possible in subtotal procedures

• Meticulous haemostasis is ensured and a drain may be inserted

• Postoperative care includes monitoring of airway, calcium, and voice

Recurrent Laryngeal Nerve Injury Management

If bruised or stretched intraoperatively avoid further handling and allow recovery

If transected attempt microsurgical repair or nerve grafting

Postoperatively diagnosis is made by nasoendoscopy or laryngeal EMG

Unilateral injury is managed with voice therapy, injection laryngoplasty or medialisation procedures

Bilateral injury may require airway surgery or tracheostomy to maintain patency

“Surgeon’s Pledge: I shall not cut what I have not seen. I shall not burn what lies beneath”

Postoperative Considerations

Calcium should be checked 4 hours after thyroidectomy to detect hypocalcaemia from parathyroid injury

If calcium remains normal supplements are unnecessary

Thyroxine replacement is required after total thyroidectomy

Page edited by Prof. Ashok Daya Ram MBBS, FRCS, FRCPS, FEBPS, FRCS (Paed Surgery), Consultant Paediatric and Neonatal Surgeon, Norfolk and Norwich University Hospital, Norwich, UK. October 2025

References

Hirschl, Ron, et al., editors. "Thyroid Disease." Pediatric Surgery NaT, American Pediatric Surgical Association, 2020. Pediatric Surgery Library, www.pedsurglibrary.com/apsa/view/Pediatric-Surgery-NaT/829132/all/Thyroid_Disease.

Mincer DL, Jialal I. Hashimoto Thyroiditis. [Updated 2023 Jul 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459262/

Pokhrel B, Bhusal K. Graves Disease. [Updated 2023 Jun 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK448195/

Hirschl, Ron, et al., editors. "Thyroglossal Duct Cyst." Pediatric Surgery NaT, American Pediatric Surgical Association, 2020. Pediatric Surgery Library, www.pedsurglibrary.com/apsa/view/Pediatric-Surgery-NaT/829081/all/Thyroglossal_Duct_Cyst.

Balalaa N, Megahed M, Ashari MA, Branicki F. Thyroglossal duct cyst papillary carcinoma. Case Rep Oncol. 2011 Jan 29;4(1):39-43. doi: 10.1159/000324405. PMID: 21526005; PMCID: PMC3082488.