What is the recommended follow-up for a thyroid nodule classified as Bethesda II (Benign) after fine-needle aspiration cytology (FNAC)?

Follow-Up Management for Bethesda II (Benign) Thyroid Nodules

For thyroid nodules classified as Bethesda II (Benign) after fine-needle aspiration cytology (FNAC), regular ultrasound monitoring at 6-12 month intervals initially, then annually if stable, is recommended. 1

Initial Follow-Up Protocol

• First follow-up ultrasound: 6-12 months after benign FNAC
• Subsequent follow-up: Annually if nodule remains stable
• Duration of follow-up: At least 3-5 years

Indications for Repeat FNAC

Repeat FNAC should be performed if any of the following occur during follow-up:

1. Significant growth in the previously benign nodule

   • Growth defined as >20% increase in at least two dimensions or >50% increase in volume

2. Development of suspicious sonographic features:

   • Hypoechogenicity
   • Microcalcifications
   • Irregular or microlobulated margins
   • Taller-than-wide shape
   • Extrathyroidal extension

3. Initial cytology was inadequate or non-diagnostic

Risk Stratification Based on Ultrasound Features

The ACR TI-RADS (Thyroid Imaging Reporting and Data System) can be used to further stratify follow-up recommendations:

• ACR TI-RADS 3 nodules (low suspicion):

  • Have excellent negative predictive value (94.6-100%) 2
  • Consider longer intervals between follow-up ultrasounds (12-18 months)

• ACR TI-RADS 4 and 5 nodules (moderate to high suspicion):

  • Despite benign cytology, have higher risk of malignancy (6.1% and 66.7% respectively) 2
  • Require more vigilant follow-up (every 6 months initially)

Evidence Supporting Follow-Up Recommendations

The malignancy rate for nodules with benign cytology (Bethesda II) is generally low. Studies show malignancy rates of:

• 3.2% in pre-Bethesda period
• 2.6% in post-Bethesda period 3

This low malignancy rate supports the safety of ultrasound follow-up rather than immediate intervention for Bethesda II nodules.

Special Considerations

• Small (<1.5 cm) nodules with high-suspicion features: Despite benign cytology, nodules with ACR TI-RADS 4 and 5 features that are <1.5 cm may still carry malignancy risk (5.7% and 25.0% respectively) 2

• Highly suspicious nodules: For nodules with highly suspicious features on ultrasound (ACR TI-RADS 5) but benign cytology, consider repeat FNAC sooner (within 3-6 months) rather than waiting for growth 3

• Patient risk factors: More vigilant follow-up may be warranted for patients with:

  • History of head and neck radiation
  • Family history of thyroid cancer
  • Suspicious clinical features

Common Pitfalls to Avoid

1. Relying solely on FNAC results when clinical or sonographic findings are worrisome

   • Clinical context must always be considered 1

2. Failure to have cytology reviewed by a pathologist with expertise in thyroid disorders

   • This can lead to inaccurate diagnoses 1

3. Discontinuing follow-up too early

   • Some malignancies may grow slowly and become apparent only after several years

4. Ignoring patient symptoms

   • Even with benign cytology, new symptoms like voice changes, dysphagia, or rapid growth should prompt re-evaluation

By following these evidence-based recommendations for the follow-up of Bethesda II thyroid nodules, clinicians can effectively monitor patients while minimizing unnecessary procedures and optimizing outcomes related to morbidity, mortality, and quality of life.