Thyroid Adenoma

Content of This Page

1- Introduction

2- Causes

3- Symptoms

4- Investigations & Lab Results

5- Prognosis

6- Treatment

Introduction

Thyroid Adenoma is a benign (non-cancerous), solitary tumor arising from the follicular cells of the thyroid gland. It is usually well-encapsulated and does not invade surrounding tissues. Most thyroid adenomas are non-functional and asymptomatic, but some can become toxic adenomas, meaning they produce thyroid hormones independently of TSH regulation, leading to hyperthyroidism.

These adenomas are often discovered incidentally during a neck examination or imaging for another reason. Though benign, they must be evaluated carefully to differentiate them from follicular thyroid carcinoma, as they can appear similar on imaging and cytology.

© image from Wikimedia Commons

Causes

  • Somatic mutations in thyroid follicular cells (especially in the TSH receptor or GNAS gene)

  • Chronic stimulation by thyroid-stimulating hormone (TSH) — can promote cell proliferation

  • Iodine deficiency — leads to increased TSH stimulation and follicular cell growth

  • Radiation exposure to the head or neck during childhood

  • Genetic predisposition — family history of thyroid nodules or tumors

  • Female gender and advancing age — thyroid nodules, including adenomas, are more common in women and older adults

© image from Wikimedia Commons

Symptoms

-If non-toxic (non-functioning) adenoma:

  • Painless, solitary thyroid nodule

  • Noticeable lump or swelling in the neck

  • Cosmetic concerns

  • Occasional discomfort or tightness in the neck (if large)

  • Rarely, difficulty swallowing or breathing (from compression of nearby structures)

-If toxic (functioning) adenoma:

  • Signs of hyperthyroidism, such as:

    • Weight loss despite normal or increased appetite

    • Heat intolerance

    • Palpitations

    • Tremors

    • Anxiety or nervousness

    • Menstrual irregularities

    • Fatigue

    • Increased sweating

Investigations & Lab Results

  • Thyroid Function Tests:
    TSH:
    ↓ in toxic (functioning) adenoma
    → Normal in non-functioning adenoma
  • Free T4 / T3:
    ↑ in toxic adenoma
    → Normal in non-functioning adenoma
  • Thyroid Antibodies:
    → Negative (helps exclude autoimmune thyroid diseases)
  • Thyroid Ultrasound:
    → Solitary, well-defined, encapsulated nodule
    → May show solid or cystic areas, internal vascularity
  • Radioactive Iodine Uptake Scan (RAIU):
    ↑ uptake (“hot” nodule) in toxic adenoma
    ↓ uptake (“cold” nodule) in non-functioning adenoma
  • Fine Needle Aspiration (FNA):
    → Suggests follicular neoplasm but cannot definitively distinguish adenoma from carcinoma (requires histopathology)
 

Prognosis

  • Generally excellent, as most thyroid adenomas are benign and slow-growing.

  • No invasion or metastasis occurs in true adenomas, which remain well-encapsulated.

  • Toxic adenomas causing hyperthyroidism can be effectively treated with radioactive iodine, surgery, or medications.

  • Rarely, a follicular adenoma may be misdiagnosed if it is actually a minimally invasive carcinoma—histopathology after surgery is definitive.

  • With appropriate monitoring or treatment, recurrence is rare and quality of life is unaffected in most cases.

Treatment

1. Observation

  • For small, non-functioning, asymptomatic adenomas

  • Regular monitoring with:

    • Physical exams

    • Thyroid function tests

    • Ultrasound

  • Fine-needle aspiration (FNA) if nodule changes or grows

2. Surgery (Lobectomy or Thyroidectomy)

  • Indicated for:

    • Large nodules causing pressure symptoms

    • Suspicion of cancer (especially follicular neoplasm on FNA)

    • Patient preference or cosmetic concern

    • Toxic adenomas not responsive to medical or RAI treatment

3. Radioactive Iodine Therapy (RAI)

  • Used for toxic (functioning) adenomas

  • Destroys hyperfunctioning thyroid tissue and controls hyperthyroidism

  • Less invasive than surgery

4. Antithyroid Medications

  • Methimazole or propylthiouracil (PTU) used short-term for toxic adenomas

  • Helps control symptoms before definitive treatment (RAI or surgery)

  • Not a long-term solution in most cases

5. Beta-Blockers

  • For symptomatic relief in hyperthyroid patients (e.g., palpitations, tremors)

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