What is the best next step in managing a patient with a 2 cm solid thyroid nodule found on ultrasound?

Fine Needle Aspiration (FNA) is the Best Next Step

For a 2 cm solid thyroid nodule, ultrasound-guided fine needle aspiration (FNA) biopsy should be performed immediately, as this represents the definitive diagnostic test to determine malignancy risk and guide surgical decision-making. 1, 2

Rationale for Immediate FNA

• All thyroid nodules ≥1 cm require FNA evaluation, and your patient's 2 cm nodule clearly exceeds this threshold regardless of other ultrasound features 1, 2, 3, 4

• Solid composition carries inherently higher malignancy risk compared to cystic nodules, making tissue diagnosis essential even without other suspicious features 1

• The American College of Surgeons and National Comprehensive Cancer Network specifically recommend evaluation of nodules larger than 2 cm, even without suspicious features, due to increased malignancy risk 1

• FNA achieves approximately 95% diagnostic accuracy and has fundamentally transformed thyroid nodule management by more than doubling the surgical yield of malignancy 2

Why Other Options Are Incorrect

Option A (Repeat ultrasound in 6 months):

• Surveillance without tissue diagnosis is inappropriate for a 2 cm solid nodule 1, 2
• Observation is only appropriate for nodules <2 cm with confirmed benign cytology on prior FNA 2
• Delaying diagnosis risks progression of potentially malignant disease

Option B (Thyroid scan with Iodine):

• Radionuclide scanning is only indicated when TSH is suppressed, suggesting a hyperfunctioning nodule 2, 3, 4
• In euthyroid patients, thyroid scanning does not help determine malignancy risk 1
• Hyperfunctioning ("hot") nodules are rarely malignant and represent <5% of all nodules 2, 5
• The question does not indicate suppressed TSH, making this test premature

Option D (CT neck):

• Ultrasound is the only appropriate initial imaging modality for thyroid nodule characterization 1
• CT provides no additional diagnostic value for determining malignancy in thyroid nodules 1
• CT is reserved for assessing extrathyroidal extension in confirmed malignancy, not initial diagnosis

Technical Approach to FNA

• Ultrasound guidance is mandatory rather than palpation-guided approach, as it allows real-time needle visualization, confirms accurate sampling, and is superior in terms of accuracy, patient comfort, and cost-effectiveness 1, 2

• Results should be reported using the Bethesda Classification System (Categories I-VI), which stratifies malignancy risk from 1-3% (benign) to 96-98% (malignant) 1, 2, 3, 4

• If FNA shows follicular neoplasia (Bethesda IV) with normal TSH, proceed to thyroid scan to determine if the nodule is "cold," which would warrant surgical excision 1, 2

Critical Additional Workup

• Measure serum TSH before FNA to determine if radionuclide scanning is needed and because higher TSH levels are associated with increased risk for differentiated thyroid cancer 1, 2

• Consider serum calcitonin measurement as part of the diagnostic workup to screen for medullary thyroid cancer, which has higher sensitivity than FNA alone 1, 2, 5

• Perform complete cervical lymph node ultrasound evaluation when thyroid nodules are discovered, as lymph node metastases alter surgical planning 2

Important Pitfalls to Avoid

• Do not rely on thyroid function tests alone for malignancy assessment, as most thyroid cancers present with normal thyroid function 1

• False-negative FNA results occur in up to 11-33% of cases, so a reassuring FNA should not override concerns when worrisome clinical findings persist 1

• For inadequate FNA samples, repeat FNA under ultrasound guidance is recommended 1

• Nodules 3-6 cm have the highest false-negative rates (6-8%), mostly due to encapsulated follicular variant of papillary carcinoma 6