Thyroid Nodule: Is it Cancer?

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What is a Thyroid Nodule?

A thyroid nodule is a discrete lesion within the thyroid gland that is radiologically distinct from the surrounding tissue. Nodules are common and found in 10 percent of the adult population. Luckily, most of them are benign. The clinical importance of thyroid nodules is the need to rule out thyroid cancer, which occurs in 7-15 percent of cases depending on age, sex, radiation exposure, family history and other factors. For the U.S. population, the lifetime risk of developing thyroid cancer is 1.1 percent. When a thyroid nodule is suspicious – meaning that it has characteristics that suggest thyroid cancer – the next step is usually a fine needle aspiration biopsy (FNAB).

Signs of Thyroid Cancer

Most thyroid nodules are asymptomatic, non-palpable and only detected on ultrasound or other anatomic imaging studies. The following characteristics increase the suspicion of cancer:

  • Swelling in the neck
  • A rapidly growing nodule
  • Firm, irregular and fixed nodule
  • Pain in the front of the neck, sometimes going up to the ears
  • Hoarseness or other voice changes that do not go away
  • Trouble swallowing
  • Trouble breathing
  • A constant cough that is not due to a cold

An FNAB helps determine if a nodule is malignant or benign. But about 30 percent of the time, the results are inconclusive or indeterminate – unable to determine if cancer is present. In this case, the recommended follow-up is a repeat FNAB, a core needle biopsy or a lobectomy/thyroidectomy – surgery to remove part or all of the thyroid gland. Once removed, the thyroid nodule is thoroughly evaluated by a pathologist to diagnose or dismiss thyroid cancer.

In large thyroid nodules, 4 cm or bigger, the FNAB results are highly inaccurate, misclassifying half of all patients with reportedly benign lesions. Additionally, Inconclusive FNAB results display a high-risk of differentiated thyroid carcinoma. Diagnostic lobectomy is strongly considered in patients with a significant thyroid nodule regardless of FNAB results.

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Understanding the Results

To address a significant variability in FNAB results, Bethesda System for Reporting Thyroid Cytopathology was devised in 2007. The system recognizes six diagnostic categories and provides an estimation of cancer risk within each category based on literature review and expert opinion.

Bethesda Diagnostic Category Risk of Malignancy Usual Management
I Non-diagnostic or unsatisfactory
  • Cyst fluid only
  • Virtually acellular specimen
  • Other (obscuring blood, dotting artifact, etc.)
1% to 4% Repeat FNA with ultrasound guidance
II Benign
  • Consistent with a benign follicular nodule (includes adenomatoid nodule, colloid nodule, etc.)
  • Consistent with lymphocytic (Hashimoto's) thyroiditis in the proper clinical context
  • Consistent with granulomatous (subacute) thyroiditis
  • Other
0% to 3% Clinical follow-up
III Atypia of undetermined significance or follicular lesion of undetermined significance   5% to 15% Repeat FNA
IV Follicular neoplasm or suspicious for a follicular neoplasm Specify if Hurthle cell (oncocytic) type 15% to 30% Surgical lobectomy
V Suspicious for malignancy
  • Suspicious for papillary carcinoma
  • Suspicious for medullary carcinoma
  • Suspicious for metastatic carcinoma
  • Syspicious for lymphoma
  • Other
60% to 75% Near-total thyroidectomy or surgical lobectomy
VI Malignant
  • Papillary thyroid carcinoma
  • Poorly differentiated carcinoma
  • Medullary thyroid carcinoma
  • Undifferentiated (anaplastic) carcinoma
  • Squamous cell carcinoma
  • Carcinoma with mixed features
  • Metastatic carcinoma
  • Non-Hodgkin's lymphoma
  • Other
97% to 99% Near-total thyroidectomy