Is Fine Needle Aspiration Biopsy (FNAB) still required for Thyroid Imaging Reporting and Data System (TI-RADS) 5 thyroid nodules with a high suspicion of malignancy?

FNAB Recommendation for TI-RADS 5 Thyroid Nodules

FNAB is NOT automatically required for all TI-RADS 5 nodules—the decision depends critically on nodule size, with current guidelines creating a paradoxical gap for nodules ≤10 mm where FNA may not be recommended despite high suspicion, yet active surveillance remains a safe alternative. 1, 2

Size-Based Algorithm for TI-RADS 5 Nodules

For Nodules >10 mm (1 cm)

• Perform ultrasound-guided FNAB immediately for any TI-RADS 5 nodule exceeding 1 cm, as this represents high suspicion warranting tissue diagnosis before treatment decisions 2, 3
• FNA should target solid components under real-time ultrasound visualization to maximize diagnostic yield 3, 4
• The combination of multiple high-risk features (marked hypoechogenicity, microcalcifications, irregular margins, solid composition) in nodules >1 cm mandates cytological confirmation 2, 5

For Nodules ≤10 mm

• Active surveillance is a safe alternative to immediate FNAB for EU-TIRADS 5 nodules ≤10 mm in selected patients without suspicious lymphadenopathy 6
• European and American guidelines explicitly do NOT recommend routine FNA for highly suspicious nodules ≤10 mm to avoid overdiagnosis of clinically insignificant papillary microcarcinomas 1, 2, 6
• In a prospective study of 80 patients with EU-TIRADS 5 nodules ≤10 mm managed with active surveillance (median follow-up 36 months), only 20% required conversion to surgery, with all confirmed malignancies achieving remission postoperatively 6

The Guideline Paradox for Small TI-RADS 5 Nodules

Current guidelines create an impossible clinical dilemma: TI-RADS systems do not recommend FNA for nodules <1 cm, yet alternative treatments like thermal ablation require confirmed malignancy before intervention 1. This leaves clinicians unable to:

• Stage the lesion without surgery 1
• Apply risk stratification systems that require postoperative histology 1, 2
• Determine cancer subtype preoperatively with reliability 1

Patients appropriately question why a nodule should be treated despite lack of indication for FNA, and how nonsurgical options can be considered before malignancy is confirmed 1.

When to Perform FNAB Despite Size <10 mm

Override the size threshold and perform FNAB for nodules <1 cm if ANY of these high-risk clinical factors are present:

• History of head and neck irradiation (increases malignancy risk 7-fold) 2
• Family history of thyroid cancer, particularly medullary carcinoma or familial syndromes 2
• Suspicious cervical lymphadenopathy on ultrasound 2, 6
• Age <15 years or rapid nodule growth 2
• Subcapsular location with concern for extrathyroidal extension 2

Active Surveillance Protocol for TI-RADS 5 Nodules ≤10 mm

If FNAB is deferred in favor of surveillance:

• Perform repeat ultrasound at 12-month intervals to assess for volumetric increase ≥50% or development of suspicious lymph nodes 6
• Trigger FNAB if volumetric increase ≥50% occurs (occurred in 35% of patients at median 36-month follow-up) 6
• Trigger FNAB if suspicious lymph node develops (occurred in 3.8% of patients) 6
• When FNAB is eventually performed after surveillance, 45.8% yield malignant cytology, confirming the appropriateness of delayed biopsy 6

Evidence Quality and Nuances

The recommendation against routine FNA for TI-RADS 5 nodules ≤10 mm represents a major shift from traditional practice and reflects growing recognition that:

• Overdiagnosis of papillary microcarcinomas leads to unnecessary thyroidectomies without improving mortality or quality of life 1, 2
• Active surveillance of small papillary carcinomas is safe, with progression rates manageable through monitoring 6
• ACR TI-RADS implementation reduces FNAB volume by 70% (from 1,044 to 314 nodules) while missing only 0.9% of malignancies, most of which are microcarcinomas amenable to delayed treatment 7

Critical Pitfall to Avoid

Do not assume that high TI-RADS score automatically equals immediate FNAB indication—this outdated approach drives overtreatment 1, 7. The 2021 European study demonstrated that 47% of confirmed papillary carcinomas in TI-RADS 5 nodules ≤10 mm remained safely in follow-up without surgery 6, validating the surveillance approach for appropriately selected patients.

Technical Requirements When FNAB Is Performed

• Ultrasound guidance is mandatory—palpation-guided aspiration is obsolete 3, 4
• Target the solid portion of any mixed cystic-solid nodules, as this carries highest malignancy risk 2
• Request on-site cytopathology evaluation if available to reduce inadequacy rates 4
• Repeat FNA under ultrasound guidance if initial sample is nondiagnostic (occurs in 5-20% of cases) 2