What is the best confirmative diagnostic tool for a midline firm solid neck nodule larger than 1 cm that moves with swallowing?

Diagnostic Approach to Midline Firm Solid Neck Nodule Moving with Swallowing

For a midline firm solid neck nodule larger than 1 cm that moves with swallowing, Fine-Needle Aspiration Cytology (FNAC) is the best confirmative diagnostic tool. 1

Initial Diagnostic Approach

• Ultrasound (US) should be used as the first-line imaging modality for initial evaluation of a suspected thyroid nodule or midline neck mass 1
• US provides high-resolution imaging to confirm the nodule is within the thyroid and characterizes it for risk of malignancy 1
• US features associated with malignancy include hypoechogenicity, microcalcifications, absence of peripheral halo, irregular borders, solid aspect, intranodular blood flow, and shape (taller than wide) 1

Diagnostic Algorithm

1. Initial Imaging: Ultrasound

   • Confirms location of the nodule (thyroid vs. non-thyroid origin) 1
   • Characterizes nodule features (solid vs. cystic, size, suspicious features) 1
   • Evaluates for cervical lymphadenopathy 1

2. Laboratory Testing: TSH

   • Should be performed to assess thyroid function 1
   • Helps determine if the patient is euthyroid, hypothyroid, or hyperthyroid 1
   • Subnormal TSH may indicate a toxic nodule requiring different management 1

3. Confirmative Testing: FNAC

   • For nodules >1 cm, FNAC is the best confirmative test 1
   • Should be ultrasound-guided for better accuracy 1, 2
   • Provides cytological diagnosis with high sensitivity for malignancy 1

4. Cross-sectional Imaging (CECT)

   • Not routinely needed for initial evaluation of thyroid nodules 1
   • Indicated when there is suspicion of:
     • Substernal extension 1
     • Invasive disease 1
     • Compression of surrounding structures 1

Evidence-Based Rationale

• FNAC has higher sensitivity compared to other methods for diagnosing thyroid malignancy in nodules >1 cm 1
• According to ESMO Clinical Practice Guidelines, FNAC should be performed in any thyroid nodule >1 cm and in those <1 cm if there are suspicious clinical or ultrasonographic features 1
• FNAC is a very sensitive tool for differential diagnosis of benign and malignant nodules, though it has limitations with inadequate samples and follicular neoplasia 1, 2

Important Considerations

• The malignancy rate in thyroid nodules is approximately 5% of all thyroid nodules 1
• For nodules >3 cm, FNAC has a positive predictive value of 71%, specificity of 97%, and sensitivity of 56% 2
• False-negative rates of approximately 4.7% have been reported for large nodules 2
• If FNAC is inadequate, it should be repeated 1
• In case of follicular neoplasia on FNAC with normal TSH and "cold" appearance on thyroid scan, surgery should be considered 1

Special Situations

• For cystic or partially cystic nodules, the risk of malignancy is lower (2.2% when solid portion <50%, 7.4% when solid portion >50%) 3
• Microcalcifications and eccentric solid components in partially cystic nodules are associated with increased risk of malignancy 3
• In patients over 40 years of age, especially with smoking history, vigilance for malignancy is warranted 1

While ultrasound is essential for initial evaluation and TSH helps assess thyroid function, FNAC remains the gold standard confirmative test for thyroid nodules >1 cm that move with swallowing.