TIRADS 1 Lesion Definition
A TIRADS 1 (TR1) lesion is a benign thyroid nodule that scores zero points on the ACR TI-RADS ultrasound classification system, indicating no risk of malignancy and requiring no biopsy or follow-up. 1
Classification Criteria
According to the ACR TI-RADS system, a nodule achieves TR1 status by scoring 0 points across all ultrasound feature categories 1:
Ultrasound Features for TR1 (0 points total):
- Composition: Cystic or almost completely cystic (0 points) OR spongiform (0 points)
- Echogenicity: Anechoic (0 points)
- Shape: Wider-than-tall (0 points)
- Margin: Smooth (0 points)
- Echogenic foci: None or large comet-tail artifacts (0 points)
Clinical Significance
TR1 nodules carry 0% malignancy risk and require no intervention 2. This is the only TIRADS category where both biopsy and surveillance imaging are unnecessary, regardless of nodule size.
Key Clinical Points:
- No FNA required at any size threshold
- No follow-up ultrasound needed
- These are definitively benign lesions that can be left alone
- Examples include simple cysts and spongiform nodules (>50% cystic composition with multiple small cystic spaces)
Practical Application
The TR1 designation is relatively uncommon because most thyroid nodules contain at least some solid component. Once a nodule has any solid elements (mixed cystic-solid composition = 1 point), it automatically scores at least 2 total points (1 for composition + minimum 1 for echogenicity of the solid component), moving it to TR2 or higher 1.
The TR1 category effectively identifies the small subset of thyroid nodules that are unequivocally benign and can be dismissed from further evaluation, reducing unnecessary procedures and patient anxiety.