How is a Fine Needle Aspiration (FNA) biopsy of the thyroid ordered or referred to a radiologist or cytopathologist?

How to Order or Refer for Thyroid Fine Needle Aspiration (FNA)

Direct Answer: Who Performs Thyroid FNA

Thyroid FNA should be ordered as an ultrasound-guided procedure performed by a trained operator—typically a radiologist, endocrinologist, or surgeon with expertise in ultrasound-guided needle procedures—and the specimens must be interpreted by a cytopathologist with specific expertise in thyroid cytology. 1

Ordering Process and Provider Selection

Primary Ordering Options

• Refer to Interventional Radiology or Diagnostic Radiology: This is the most common pathway, as radiologists routinely perform ultrasound-guided thyroid FNA with high technical proficiency and have immediate access to cytopathology services. 1

• Refer to Endocrinology: Many endocrinologists perform thyroid FNA in their offices if they have ultrasound training and equipment, which can streamline the diagnostic process. 2

• Refer to Endocrine Surgery: Surgeons with ultrasound training may perform thyroid FNA as part of preoperative evaluation, particularly useful when surgical intervention is already being considered. 1

Critical Technical Requirements

• Ultrasound guidance is mandatory—palpation-guided FNA does not meet current guideline standards and has inferior accuracy compared to ultrasound-guided techniques. 1, 3

• The procedure should use a 25- or 27-gauge needle with proper technique to ensure adequate sampling. 4

• An experienced cytopathologist must be available to interpret the specimens, as thyroid FNA interpretation requires specific expertise. 1

When to Order Thyroid FNA

Size-Based Indications

• Any thyroid nodule >1 cm in clinically euthyroid patients warrants FNA as the first diagnostic test. 2

• Nodules <1 cm should undergo FNA only if suspicious ultrasound features are present PLUS high-risk clinical factors (history of head/neck irradiation, family history of thyroid cancer, suspicious cervical lymphadenopathy, age <15 years). 5

Ultrasound Features That Trigger FNA

• Microcalcifications (highly specific for papillary thyroid carcinoma) 2
• Marked hypoechogenicity (solid nodules darker than surrounding thyroid) 5
• Irregular or microlobulated margins 5
• Absence of peripheral halo 5
• Central hypervascularity (chaotic internal vascular pattern) 5
• Solid composition 5

High-Risk Clinical Factors

• History of head and neck irradiation (increases malignancy risk approximately 7-fold) 5
• Family history of thyroid cancer, particularly medullary carcinoma or familial syndromes 2, 5
• Rapidly growing nodule 5
• Firm, fixed nodule on palpation 5
• Vocal cord paralysis or compressive symptoms 5
• Suspicious cervical lymphadenopathy 5

Practical Ordering Algorithm

Step 1: Initial Workup Before FNA Referral

• Obtain TSH level ideally before FNA, though this is often impractical and FNA may be performed during the initial visit. 2

• Order thyroid ultrasound to characterize nodule features and assess cervical lymph nodes if not already performed. 2

Step 2: Determine FNA Indication

• Proceed with FNA if:
  • Any nodule >1 cm with ≥2 suspicious ultrasound features 5
  • Any nodule <1 cm with suspicious features PLUS high-risk clinical factors 5
  • Any nodule >4 cm regardless of ultrasound appearance (due to increased false-negative rate) 5
  • Suspicious cervical lymphadenopathy present 5

Step 3: Place the Referral

• Order as: "Ultrasound-guided fine needle aspiration biopsy of thyroid nodule"

• Include in referral:

  • Nodule size and location (right vs. left lobe, upper/mid/lower pole)
  • Specific ultrasound features (microcalcifications, hypoechogenicity, irregular margins, etc.)
  • Relevant clinical history (radiation exposure, family history, symptoms)
  • TSH level if available
  • Request that cytopathology slides be reviewed by a pathologist with expertise in thyroid disorders 2

Important Clinical Caveats

False-Negative Results

• A reassuring FNA should not override worrisome clinical findings, as false-negative results occur in up to 11-33% of cases. 6

• FNA is very sensitive for papillary thyroid carcinoma but less reliable for follicular carcinoma and medullary carcinoma (diagnosed or suspected in only 50% of cases based on cytology alone). 2

• Repeat FNA under ultrasound guidance is warranted for patients with longstanding thyroid nodules, particularly if at increased risk for cancer or if the nodule has changed morphologically over time. 7

Nondiagnostic Results

• Nondiagnostic/inadequate samples occur in 5-20% of cases and require repeat FNA under ultrasound guidance. 5

• If repeat FNA remains nondiagnostic, consider core needle biopsy or surgical biopsy to establish diagnosis. 2

Indeterminate Results

• Follicular neoplasm (Bethesda IV) cannot distinguish follicular adenoma from carcinoma on cytology alone and typically requires surgical excision for definitive diagnosis. 2, 1

• For Bethesda III (AUS/FLUS) or IV categories, molecular testing for BRAF, RAS, RET/PTC, and PAX8/PPARγ mutations may assist in management decisions, as 97% of mutation-positive nodules are malignant. 5

Pathology Review Requirements

• Pathology and cytopathology slides should be reviewed at the treating institution by a pathologist with expertise in thyroid disorders, not just by the performing institution's pathologist. 2

• Additional immunohistochemical studies (e.g., calcitonin staining) may be required to confirm medullary carcinoma diagnosis, as it can be missed on routine cytology. 2, 6

Common Pitfalls to Avoid

• Do not refer to providers without ultrasound capability—palpation-guided FNA does not meet current standards. 1

• Do not skip FNA and proceed directly to surgery without cytological confirmation, as this may result in inappropriate surgical extent. 5

• Do not rely on thyroid function tests (TSH, T3, T4) for malignancy assessment, as most thyroid cancers present with normal thyroid function. 5

• Do not perform FNA on nodules <1 cm without high-risk features, as this leads to overdiagnosis and overtreatment of clinically insignificant cancers. 5