Thyroid nodule

Discovery of a thyroid nodule, a nodule in the thyroid gland, either by the patient or incidentally during physical examination, is a common presentation of thyroid neoplasms or cysts. 95% of thyroid nodules are benign.

Some thyroid tumours produce thyroid hormones, causing hyperthyroidism, in which case they’re called “toxic”.

Etiology

These are the most common causes of thyroid nodule:

• Benign thyroid nodule
  • Follicular adenoma
  • Toxic adenoma
  • Thyroid cyst
• Malignant thyroid nodule
  • Thyroid carcinoma

The most common thyroid nodule is the follicular adenoma. Follicular adenomas are derived from the follicular epithelium. They’re solitary, well-circumscribed masses that may give rise to painless uninodular goiter.

Toxic adenomas are follicular adenomas which produce thyroid hormones. These toxic adenomas have acquired a gain-of-function mutation in the TSH receptor complex, allowing the follicular cells to be stimulated even in the absence of TSH. They’re common in iodine deficient regions, but very rare in iodine sufficient regions.

Multinodular goitre (MNG) is a complication of long-standing nodular goitre which occurs when multiple nodules develop. These nodules may be toxic (toxic multinodular goitre) or non-toxic (non-toxic multinodular goitre).

Diagnosis and evaluation

The following modalities are used in the evaluation of thyroid nodules:

• Ultrasound
• Thyroid scintigraphy – shows the distribution of thyroid function
• FNAB
• CT

When a new thyroid nodule is found, TSH should be measured, and the nodule should be examined with ultrasound. If the ultrasound shows features suspicious for malignancy, a fine needle aspiration biopsy (FNAB) is usually performed to determine the dignity, if the nodule is over a certain size. If the nodule is too small for FNAB, it’s monitored regularly.

If TSH is low, thyroid scintigraphy is performed to look for whether the nodule is hot (produces hormones) or cold (doesn’t). A single hot nodule is likely a toxic adenoma, while multiple hot nodules usually refers to a toxic multinodular goitre. Hot nodules are rarely malignant.

Treatment

Toxic adenoma and toxic multinodular goitre are treated with radioiodine therapy or surgical removal. Compensated toxic adenoma is managed with observation only.

Malignant cold nodules are treated with surgery. Benign cold nodules are treated with observation if < 3 cm, and surgery if > 3 cm.