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Incidental Thyroid Nodule (ACR)

Guided recommendation from the ACR Incidental Thyroid Findings white paper (Hoang et al., JACR 2015) — the 3-tiered approach (suspicious features → age + size). Answer the questions below.

Note: this encodes the ACR 2015 Incidental Thyroid Findings white paper (Figs 1–3), which is the right reference for a nodule found incidentally on CT, MRI, PET, or extrathyroidal ultrasound. It is not ACR TI-RADS (Tessler 2017), which is a separate risk-stratification system for dedicated thyroid ultrasound. Does not apply to patients with clinical risk factors / symptoms for thyroid cancer. Apply to the largest nodule when multiple.

General guidance, not standard of care. Final management of a worked-up nodule rests on the dedicated thyroid ultrasound.

Parses patient age and nodule size to pre-select below — always review.

ACR Incidental Thyroid algorithm — definitions

Suspicious features (modality-specific)

CT / MRI (Fig 1): abnormal lymph nodes (calcification, cystic components, increased enhancement; nodal enlargement >1.5 cm short axis for jugulodigastric nodes or >1 cm for other nodes — size alone has low specificity) and/or local invasion of adjacent tissues.

Extrathyroidal ultrasound (Fig 3): microcalcifications, marked hypoechogenicity, lobulated or irregular margins, taller-than-wide shape on transverse view.

FDG-PET (Fig 2): focal uptake is itself the high-risk feature (malignancy rate 33%–35%); diffuse uptake without a corresponding mass is not focal and is not worked up by this algorithm.

3-tiered logic (no suspicious features, normal life expectancy)

Tier driven by patient age and axial nodule size: age <35 y → further evaluation if nodule ≥1 cm; age ≥35 y → further evaluation if nodule ≥1.5 cm. Below the size cutoff → no further workup.

Comorbidities / limited life expectancy

If serious comorbidities or limited life expectancy (where thyroid cancer is unlikely to affect quality of life or survival), no further evaluation is recommended — unless clinically warranted or specifically requested by the patient or referring physician.

PET-avid / other nuclear medicine

Focal FDG-PET uptake (normal life expectancy) → dedicated thyroid ultrasound AND FNA of the PET-avid lesion regardless of sonographic findings. MIBI / octreotide-avid nodule → dedicated thyroid ultrasound, with FNA decided by sonographic criteria.

Hoang JK, Langer JE, Middleton WD, et al. Managing Incidental Thyroid Nodules Detected on Imaging: White Paper of the ACR Incidental Thyroid Findings Committee. J Am Coll Radiol 2015;12:143–150.