• Clinical science

Thyroid nodules

Abstract

Thyroid nodules are abnormal growths within the thyroid gland. They are present in approx. 50% of the general population but only palpable in 5–10% of the population. They are more common in women, especially in iodine-deficient regions, and their incidence increases with age. Thyroid nodules are the clinical manifestation of various underlying thyroid diseases. The majority of them are benign (∼ 95%), with colloid cysts, follicular adenomas, and Hashimoto's thyroiditis being the most common causes. Approx. 5% of thyroid nodules are malignant, with papillary carcinoma being the most common. Thyroid hormone assay is the best initial test in the evaluation of thyroid nodules. Thyroid ultrasonography can detect features suspicious of malignancy in a nodule and the diagnosis can be confirmed on ultrasound-guided fine needle aspiration cytology. Radioiodine uptake scan (thyroid scintigraphy) is used to evaluate nodules in patients with hyperthyroidism, to localize the autonomously functioning tissue. Based on their iodine uptake on radioiodine scans, thyroid nodules may be autonomous/hot (increased uptake) or non-functional/cold (decreased uptake). The most common hot nodules are toxic adenomas and dominant nodules of toxic multinodular goiters. With a 5–15% risk of malignancy, cold nodules are clinically significant. Treatment depends on the underlying etiology and includes, e.g., surgery (thyroidectomy) for malignant and autonomous nodules, fine needle aspiration for thyroid cysts, and observation for small, benign nodules.

Epidemiology

  • Sex: > (4:1)
  • Incidence: increases with age 50% of the population has thyroid nodules by the age of 50. Most nodules, however, are not palpable.
  • Geographic distribution: most common in inland regions without iodine fortification programs, where iodine content in food and water is low

References:[1][2]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

Benign thyroid nodules (∼ 95% of cases)

Malignant thyroid nodules (∼ 5% of cases)

Thyroid nodules in pregnancy

  • Thyroid nodules detected during pregnancy are managed in the same way as in nonpregnant patients.
  • Thyroid scintigraphy is, however, contraindicated.
  • Surgery, when indicated, can be deferred until after the pregnancy in most cases but is relatively safe during the second trimester.

References:[1][3]

Diagnostic steps for a solitary thyroid nodule

  • Nodule revealed during physical examination or incidentally on imaging
  • Initial tests: thyroid ultrasound and TSH levels
    • ↑ or normal TSHconsider FNA based on sonographic criteria or follow-up if criteria are not met
    • TSHthyroid scintigraphy
      • Hot nodulecheck T3 and FT4 to assess cause of hyperthyroidism
      • Cold nodule → consider either FNA (based on sonographic criteria) or monitoring (with repeat ultrasounds) if criteria are not met
  • Sonographic criteria for fine-needle aspiration (FNA)
    • Solid nodule with suspicious appearance (e.g., oval shape, irregular border, calcifications) that are ≥ 1 cm in diameter
    • Nodules ≤ 1 cm in patients with risk factors for malignancy (see “Etiology” above)
    • Large thyroid nodules (≥ 1.5–2 cm), even if they appear benign

References:[1][3]

Follicular adenoma

References:[4]

Toxic adenoma

References:[5][6]

Toxic multinodular goiter

References:[7][8][9][10][11]

Thyroid cysts

  • Classification
    • Simple cysts are exclusively fluid-filled nodules lined by benign epithelial cells.
    • Complex cysts are partly solid and partly cystic and carry a 5–10% risk of malignancy.
  • Etiology
  • Clinical features
    • Hemorrhage into a cyst → pain and rapid enlargement of the nodule
    • A large cyst or extensive hemorrhage can cause compression symptoms (e.g., hoarseness, dysphagia)
  • Diagnostics
    • Ultrasound to assess size and appearance
      • If low suspicion of malignancy but size > 2 cmFNA
      • If high suspicion of malignancy and size > 1 cmFNA :
  • Treatment

References:[12][13][14]