Goitre

Sub-section: Thyroid Section: Endocrine

Definition

• Abnormal growth of the thyroid gland
• Diffuse or nodular
• Associated with normal, decreased, or increased thyroid hormone production
• Causes of goitre vary with geography
  • Worldwide the most common cause is Iodine deficiency.
  • In Iodine-replete countries such as New Zealand, the most common causes of goitre are multi nodular goitre, Graves’ disease, and Hashimoto’s disease.

Incidence

• Female:male 5:1
• Usually middle-aged

Classification

• Diffuse (colloid) goitre or simple hyperplastic goitre
  • Iodine deficiency (most common worldwide)
    • Hyperplasia of the gland, due to increased circulating TSH, in order to increase production of thyroid hormone
  • Secondary iodine deficiency
    • Drugs or dietary substances that interfere with iodine trapping or thyroxine synthesis
  • Other
    • Graves’ disease (hyperthyroidism)
    • Hashimoto’s thyroiditis (hypothyroidism)
    • Subacute thyroiditis
    • Rarer causes include medication induced goitre, tumours, infiltrative diseases, and thyroiditis.
• Multinodular goitre
  • Multinodular goiter
  • Thyroid adenoma
  • Thyroid cancer

Multinodular goitre

Pathology

• Nodular goitre may develop as a result of disorganised thyroid follicular cell growth in response to stimulation (TSH) and the presence of a risk factor which can be either iodine deficiency or a goitrogen (foods)
• Thyroid contains areas of hyperplasia and hypoplasia side by side
• Causes
  • Hyperplasia - some areas response more than others
  • Other ares undergo Involution, degeneration, haemorrhage, and fibrosis
  • Repeated cycles → MNG
• Often a family history so a genetic component
• Some nodules eventually become autonomous due to activating mutations in the TSH receptor or G proteins within the thyroid follicular cells
• The following observations support this sequence of events
  • Thyroid volume is larger in older patients
  • The longer the patient has a gοiter, the larger the size of the gοiter
  • The larger the size of the goitеr, the lower the serum TSH concentration
• If there is a solid nodule in MNG - 1-6% chance of malignancy
• MNG autopsy studies found 2-17% incidental cancer

Clinical features

• Painless enlarging lump or neck swelling
• Pemberton’s sign
• Obstructive goiter:
  • Dysphagia
  • Compression of a recurrent laryngeal nerve may cause transient or permanent vocal cord palsy, resulting in hoarseness
  • Phrenic nerve paralysis
  • Horner’s syndrome due to compression of the cervical sympathetic chain
  • Rarely, jugular vein compression or thrombosis, cerebrovascular steal syndromes, or even the superior vena cava syndrome

Diagnosis

• TFTs
  • If normal - MNG or diffuse goitre
  • If TSH high - Hashimotos thyroiditis
  • If TSH low - thyrotoxicosis
• USS
  • If a single node then needs to be investigated as per Thyroid nodule work up
  • If single node + TSH suppressed then possible toxic MNG - need radio-iodine scan + work up to exclude malignancy
  • Suspicious USS characteristics
    • Hypoechogenicity
    • Micocalcifications
    • Intranodular vascularity
    • Taller than wide dimensions
    • Blurred margins
• CT
  • Can assess for tracheal compression or intrathoracic extension of the goitre

Substernal/Intrathoracic Goitre

• Intrathoracic extension of an enlarged thyroid
  • Generally occurs as a result of MNG
• Usually secondary
  • Inferior extensions of multinodular goitres
    • Based on the inferior thyroid vasculature
  • Expand downward into the anterior mediastinum
• Primary substernal goitre rare (1%)
  • Arises as aberrant thyroid tissue within the anterior or posterior mediastinum
    • Based on the intrathoracic vasculature
    • Not supplied by the inferior thyroid artery

Management

• If asymptomatic do not need to treat
• I-131
  • 90% will have a 50-60% reduction in goitre volume after 12-18mo with reduction in compression symptoms
  • Dose response

Surgical management

• Thyroidectomy or surgical decompression causes rapid symptom relief
• Indications
  • Large goitre with compressive symptoms
    • Symptoms
      • Dyspnea, dysphagia, cough
    • Signs
      • Tracheal narrowing on CT
      • Extrinisic compression on barrium swallow
      • Abnormal flow volume loop (air way obstruction)
  • Intrathoracic extension
  • Thyrotoxicosis
  • Suspicious for malignancy or cannot exclude on FNA
• Total thyroidectomy
  • Surgery of choice in symptomatic patients because subtotal will have a high chance of recurrence of symptoms

Prognosis

• Goitre
• Histology
  • Multinodular goitre 90%
  • Follicular adenoma 7.5%
  • Malignancy 2.5%