Incidental Thyroid Nodule (CT / MR / PET)
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ACR Incidental Thyroid 2015·reviewed 2026-07-01
- •This is a triage tool deciding who needs a dedicated thyroid ultrasound. Once ultrasound is obtained, categorize and decide on FNA using ACR TI-RADS — not this algorithm.
- •Suspicious features on the cross-sectional study (local invasion of adjacent structures, or abnormal/pathologic cervical lymph nodes) warrant ultrasound and clinical referral regardless of nodule size or patient age.
- •Focal (not diffuse) FDG-PET uptake in the thyroid carries a meaningful malignancy risk (~one-third in reported series) and warrants ultrasound regardless of size. Diffuse uptake is usually thyroiditis and does not require ultrasound.
- •For nodules without suspicious features, the size threshold for ultrasound depends on age: ≥1 cm in patients younger than 35, and ≥1.5 cm in patients 35 or older. This two-tier threshold limits workup of clinically insignificant nodules while catching the higher-consequence cancers in younger patients.
- •Measure the nodule on the axial image where it is largest. When multiple nodules are present, apply the threshold to the largest.
How was the incidental thyroid finding detected?
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Sources
- Hoang JK, et al. Managing Incidental Thyroid Nodules Detected on Imaging: White Paper of the ACR Incidental Thyroid Findings Committee. J Am Coll Radiol. 2015;12(2):143-150.
- Tessler FN, et al. ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee. J Am Coll Radiol. 2017;14(5):587-595.
Educational reference for clinicians — not medical advice. Verify against the primary source before acting on it; guidelines change. Final decisions rest with the interpreting physician and your institution's protocols.