What is the first investigation tool in the assessment of thyroid nodules in a patient presenting with midline neck swelling?

First-Line Investigation for Thyroid Nodules

Ultrasound (US) is the first-line diagnostic procedure for detecting and characterizing thyroid nodules in a patient presenting with midline neck swelling. 1

Rationale for Ultrasound as First Investigation

• Ultrasound is recommended by the American College of Radiology as the first-line imaging modality for evaluating the thyroid and anterior neck due to its:

  • High sensitivity for nodule detection
  • Non-invasive nature
  • Cost-effectiveness
  • Absence of radiation exposure 2

• Ultrasound provides critical information about:

  • Nodule characteristics (size, composition, echogenicity)
  • Suspicious features that may indicate malignancy
  • Status of surrounding lymph nodes 1, 2

Diagnostic Algorithm for Thyroid Nodules

1. Ultrasound examination - First step to characterize the nodule(s)

   • Assess for suspicious features: hypoechogenicity, microcalcifications, absence of peripheral halo, irregular borders, solid aspect, intranodular blood flow, and shape (taller than wide) 1
   • Multiple suspicious features increase specificity for malignancy 1

2. TSH measurement - After ultrasound characterization

   • If TSH is suppressed: Radionuclide thyroid scan to determine if nodule is functioning 3, 4
   • If TSH is normal or elevated: Proceed with fine needle aspiration cytology (FNAC) based on ultrasound findings 3

3. Fine needle aspiration cytology (FNAC) - Guided by ultrasound findings

   • Indicated for nodules >1 cm or <1 cm with suspicious clinical or ultrasound features 1
   • FNAC should be performed on suspicious nodules identified by ultrasound 1

Why Other Options Are Not First-Line

• Free T3 and Free T4 (Options A and B): These are thyroid function tests that help evaluate thyroid function but do not provide information about nodule characteristics. They are not recommended as first-line investigations for thyroid nodules 1, 3

• TSH (Option D): While TSH is an important part of thyroid nodule evaluation, it is typically measured after ultrasound has characterized the nodule 3, 4. TSH alone cannot characterize a nodule or determine malignancy risk.

Important Considerations

• Ultrasound features associated with increased malignancy risk include hypoechogenicity, microcalcifications, irregular borders, solid composition, and absence of peripheral halo 1, 2

• FNAC is a very sensitive tool for differentiating between benign and malignant nodules but should be performed after ultrasound characterization 1

• Thyroid function tests (T3, T4, TSH) and thyroglobulin measurement are of limited help in diagnosing thyroid cancer but are useful for evaluating thyroid function 1

• In a 35-year-old patient, thorough evaluation is particularly important as thyroid cancer can be more aggressive in younger patients 1

By following this evidence-based approach with ultrasound as the first investigation, clinicians can effectively evaluate thyroid nodules and determine appropriate next steps for management, ultimately improving patient outcomes related to morbidity and mortality.