What is the recommended workup for incidentally found asymptomatic thyroid nodules?

Workup for Incidentally Found Asymptomatic Thyroid Nodules

Fine-needle aspiration (FNA) is the preferred initial diagnostic procedure for evaluating suspicious thyroid nodules, with the decision to perform FNA guided by nodule size and ultrasound characteristics. 1

Initial Evaluation

1. Thyroid Ultrasound

   • Essential first-line imaging for all thyroid nodules
   • Evaluates nodule characteristics:
     • Size (in three dimensions)
     • Composition (solid, cystic, or mixed)
     • Echogenicity
     • Margins
     • Presence of calcifications
     • Vascularity

2. TSH Measurement

   • Should be obtained before FNA when possible
   • Higher TSH levels are associated with increased risk of differentiated thyroid cancer 1

3. Risk Stratification Based on Size and Ultrasound Features

   Nodule Size	Management
   <1.0 cm	Monitor with ultrasound if no suspicious characteristics
   1.0-1.4 cm	Consider FNA if suspicious characteristics present
   ≥1.5 cm	FNA recommended 1, 2

Suspicious Ultrasound Features

Nodules with the following characteristics have higher risk of malignancy:

• Central hypervascularity
• Microcalcifications
• Irregular borders
• Solid composition
• Hypoechogenicity
• Absence of peripheral halo 1, 3

FNA Decision-Making

FNA should be performed for:

1. Nodules ≥1.5 cm in diameter
2. Nodules 1.0-1.4 cm with suspicious ultrasound features
3. Any size nodule with highly suspicious features and:
   • History of head and neck irradiation
   • Family history of thyroid cancer
   • Suspicious cervical lymphadenopathy
   • Focal FDG uptake on PET scan 1

Interpretation of FNA Results

FNA results are typically categorized as:

1. Carcinoma or suspicious for malignancy
2. Follicular or Hürthle cell neoplasm
3. Follicular lesion of undetermined significance
4. Thyroid lymphoma
5. Benign (nodular goiter, colloid goiter, hyperplastic nodule, Hashimoto's thyroiditis)
6. Insufficient/non-diagnostic 1

Additional Testing

• Calcitonin measurement: While recommended by some clinicians (especially in Europe), there is controversy regarding cost-effectiveness in the United States 1
• Molecular testing: Consider for nodules with indeterminate cytology to reduce unnecessary surgical procedures 4

Follow-up of Benign or Non-biopsied Nodules

• Small nodules (<1 cm) without suspicious features: Follow-up as clinically indicated
• Nodules with benign cytology: Periodic ultrasound surveillance
• For nodules under active surveillance: Initial follow-up at 6-12 months, then annually if stable 3

Management Pitfalls to Avoid

1. Overdiagnosis: Not all incidentally discovered nodules require FNA; consider size and ultrasound features
2. Inadequate sampling: Ultrasound-guided FNA improves diagnostic yield compared to palpation-guided FNA
3. Failure to recognize high-risk features: Age <15 years or >65 years, male gender, history of radiation exposure, and family history of thyroid cancer increase malignancy risk 1
4. Unnecessary surgery: Most thyroid nodules (85-95%) are benign and can be safely monitored 3

Remember that incidentally discovered thyroid nodules have a lower risk of malignancy (approximately 5%) compared to clinically apparent nodules, particularly when discovered on CT, MRI, or ultrasound performed for other reasons 5.