When To Recommend Ultrasound

Red flags override size

• Focal FDG-avid thyroid nodule on PET/CT.
• Local invasion or extrathyroidal extension on CT/MRI.
• Suspicious cervical lymph nodes.
• Consider clinical context: limited life expectancy or severe comorbidity may make work-up inappropriate.

If no high-risk feature

• Age under 35 years: consider thyroid ultrasound when the nodule is greater than 1.0 cm.
• Age 35 years or older: consider thyroid ultrasound when the nodule is greater than 1.5 cm.
• Below threshold: no thyroid ultrasound or FNA recommendation if there are no suspicious features.

Report / assess

• Maximum nodule size, patient age, PET avidity, extrathyroidal invasion, suspicious cervical nodes, and clinical context.
• Smaller incidental nodules without PET avidity, invasion, or suspicious nodes can be described in the body of the report but usually should not be emphasized in the impression.

Workflow / Red Flags

Stepwise approach

• Detect on CT, MRI, or PET/CT; measure the nodule and note modality.
• Look for red flags: FDG uptake, invasion, or suspicious cervical nodes.
• If no red flag is present, apply the age and size threshold.
• If referred to ultrasound, use TI-RADS / ATA / ETA to choose FNA, surveillance, or no further action.

Suspicious features

• Extrathyroidal extension into trachea, esophagus, strap muscles, mediastinum, or adjacent soft tissues.
• Cystic cervical nodes, microcalcifications, irregular margins, or clearly abnormal nodal morphology.
• Suspicious nodes or invasion should move the patient into an urgent specialty pathway with tissue diagnosis as clinically appropriate.

After ultrasound

• Benign ultrasound pattern: no FNA; often no further action.
• Low or intermediate suspicion: follow-up or FNA only if size threshold is met.
• High suspicion: FNA if threshold is met; close follow-up for smaller nodules.

Report Language

No work-up threshold met

• Incidental [x] cm thyroid nodule. No suspicious invasion or cervical lymphadenopathy. Based on age and size criteria, no thyroid ultrasound or biopsy is recommended.

Ultrasound recommended by size

• Incidental [x] cm thyroid nodule. No suspicious invasion or cervical lymphadenopathy. Based on patient age and nodule size, recommend nonemergent thyroid ultrasound for characterization.

PET-avid or suspicious

• Focal FDG uptake in a thyroid nodule. Recommend thyroid ultrasound for characterization, with FNA depending on ultrasound risk category.
• Thyroid lesion with [extrathyroidal extension / suspicious cervical lymphadenopathy]. Recommend thyroid ultrasound and endocrine/ENT evaluation with tissue sampling as clinically appropriate.

Practical note

• CT/MRI should not assign TI-RADS; TI-RADS is assigned on dedicated thyroid ultrasound.
• Open the thyroid ultrasound TI-RADS page.