What is the recommended workup for a thyroid nodule?

Thyroid Nodule Workup

The recommended workup for a thyroid nodule should begin with thyroid ultrasound as the essential first-line diagnostic procedure, followed by fine-needle aspiration cytology (FNAC) for nodules >1 cm or smaller nodules with suspicious features, and serum calcitonin measurement to rule out medullary thyroid cancer. 1

Initial Diagnostic Evaluation

Step 1: Thyroid Ultrasound

• Essential first-line diagnostic procedure for all thyroid nodules 1
• Evaluates for suspicious sonographic features:
  • Hypoechogenicity
  • Microcalcifications
  • Absence of peripheral halo
  • Irregular borders
  • Solid composition
  • Intranodular blood flow
  • Shape (taller than wide) 2, 1

Step 2: Laboratory Testing

• Thyroid function tests:
  • Serum TSH measurement is the best initial laboratory test 1, 3
  • If TSH is low, measure free T4 and obtain a thyroid scan with 99Tc to identify "hot" nodules 1, 4
  • If TSH is high, measure thyroid peroxidase antibody 1, 3
• Serum calcitonin measurement:
  • Recommended as part of initial evaluation 1
  • Higher sensitivity than FNAC for detecting medullary thyroid cancer (5-7% of thyroid cancers) 2, 1

Step 3: Fine-Needle Aspiration Cytology (FNAC)

• Indicated for:
  • Any thyroid nodule >1 cm 2, 1
  • Nodules <1 cm with suspicious clinical or ultrasonographic features 2, 1
• Clinical risk factors warranting FNAC for smaller nodules:
  • History of head and neck irradiation
  • Family history of thyroid cancer
  • Suspicious features on palpation
  • Presence of cervical adenopathy 2, 1
• Ultrasound-guided FNAC is preferred to improve diagnostic accuracy 1
• Results should be reported according to the Bethesda Classification System 1, 4

Management Based on Diagnostic Results

For Benign Nodules:

• Regular ultrasound monitoring:
  • 6-12 month intervals initially
  • Annually if stable 1
• Repeat FNAC if significant growth or development of suspicious sonographic features 1

For Malignant or Suspicious Cytology:

• Surgical management with total or near-total thyroidectomy is recommended for:
  • Nodules ≥1 cm with diagnosis of differentiated thyroid carcinoma (DTC)
  • Metastatic, multifocal, or familial DTC regardless of size 2, 1
• Less extensive procedures may be considered for small, intrathyroidal tumors with favorable histology 1

For Indeterminate Cytology:

• Consider molecular testing to better discriminate benign from malignant nodules 1, 4
• With normal TSH and "cold" appearance on thyroid scan, surgery should be considered 2

Common Pitfalls to Avoid

1. Omitting calcitonin measurement could miss medullary thyroid cancer 1
2. Relying solely on reassuring FNA results when clinical findings are worrisome - clinical context must always be considered 1
3. Failure to have cytology reviewed by a thyroid pathology expert can lead to inaccurate diagnoses 1
4. Using thyroid ultrasound as a screening test in asymptomatic individuals without palpable nodules 3
5. Overlooking the need for follow-up of benign nodules, which should undergo regular ultrasound monitoring 1

Remember that while thyroid nodules are common (4-50% of the population depending on diagnostic procedures and patient age), thyroid cancer is relatively rare (approximately 5% of all thyroid nodules) 2, 5. A systematic, risk-based approach using ultrasound and, when indicated, FNAC facilitates appropriate management while minimizing unnecessary testing and interventions.