Which of the following is NOT an indication for thyroid nodule fine‑needle aspiration: a nodule increasing in size over time, nodules larger than 1 cm with suspicious ultrasound features, nodules associated with abnormal ipsilateral lymph nodes, a 0.4 cm nodule, or nodules larger than 1.5 cm with mixed cystic‑solid ultrasound features?

Answer: D) 0.4 cm nodule is NOT an indication for FNA

A 0.4 cm (4 mm) thyroid nodule should NOT undergo fine-needle aspiration, as nodules <5 mm should always be monitored with ultrasound rather than biopsied due to their low clinical risk. 111

Size-Based FNA Thresholds by Risk Category

The AACE/ACE 2016 guidelines provide clear size cutoffs based on ultrasound risk stratification:

Very Small Nodules (<5 mm)

• Never biopsy - monitor with ultrasound only
• The 0.4 cm nodule in option D falls into this category

Small Nodules (5-10 mm)

• FNA only if high-risk ultrasound features (marked hypoechogenicity, irregular margins, microcalcifications, taller-than-wide) AND pathologic lymph nodes or extrathyroidal extension
• Also appropriate with personal/family history of thyroid cancer

Intermediate-Sized Nodules (>10 mm)

• FNA indicated for nodules without definite benign appearance (intermediate US risk)
• This covers option B (>1 cm with suspicious features)

Larger Low-Risk Nodules (≥20 mm)

• FNA for spongiform, isohyperechoic, or predominantly cystic nodules (>50% cystic) even without suspicious features
• Also if progressively increasing in size
• This covers option E (>1.5 cm mixed cystic-solid)

Why the Other Options ARE Indications

Option A (Nodule increasing in size): Progressive enlargement is an explicit indication for FNA, even in low-risk appearing nodules ≥20 mm 11

Option B (>1 cm with suspicious features): Nodules >10 mm with suspicious ultrasound findings clearly warrant FNA 11

Option C (Abnormal ipsilateral lymph nodes): Nodules associated with pathologic lymph nodes should undergo FNA, even if 5-10 mm in size 11

Option E (>1.5 cm mixed cystic-solid): Mixed nodules ≥20 mm (which includes >1.5 cm) warrant FNA even without suspicious features 11

Clinical Pitfall

The key error would be biopsying very small nodules (<5 mm) based solely on patient anxiety or "just to be sure." These tiny nodules have extremely low clinical significance, and the procedure risks are not justified. Even with suspicious features, nodules this small require additional high-risk factors (pathologic nodes, extrathyroidal spread, or strong family history) before considering FNA in the 5-10 mm range.