What is ACR TI-RADS?
The American College of Radiology Thyroid Imaging Reporting and Data System (ACR TI-RADS) is a standardized risk stratification system for thyroid nodules detected on ultrasound. Published in 2017, it provides a structured approach to categorizing thyroid nodules based on their ultrasound features and recommending whether fine-needle aspiration (FNA) biopsy or follow-up imaging is needed.
ACR TI-RADS uses a point-based system across five ultrasound feature categories: composition, echogenicity, shape, margin, and echogenic foci. Points are summed to determine the TI-RADS level (TR1 through TR5), which then guides management recommendations based on nodule size.
The system was designed to reduce unnecessary biopsies of benign nodules while ensuring that suspicious nodules are appropriately evaluated. Thyroid nodules are extremely common (found in up to 68% of the population on ultrasound), but only about 5–15% are malignant.
Ultrasound Categories
Composition
| Finding | Points | Description |
|---|---|---|
| Cystic or almost completely cystic | 0 | >95% fluid-filled; very low malignancy risk |
| Spongiform | 0 | Aggregation of multiple microcystic components ≥50% of volume |
| Mixed cystic and solid | 1 | Both solid and fluid components present |
| Solid or almost completely solid | 2 | >95% solid composition |
Echogenicity
| Finding | Points | Description |
|---|---|---|
| Anechoic | 0 | No internal echoes (purely cystic) |
| Hyperechoic or isoechoic | 1 | Same as or brighter than surrounding thyroid tissue |
| Hypoechoic | 2 | Darker than surrounding thyroid tissue |
| Very hypoechoic | 3 | Darker than adjacent strap muscles; more suspicious |
Shape
| Finding | Points | Description |
|---|---|---|
| Wider-than-tall | 0 | Horizontal orientation; typical of benign nodules |
| Taller-than-wide | 3 | Vertical orientation; highly suspicious for malignancy |
Margin
| Finding | Points | Description |
|---|---|---|
| Smooth | 0 | Well-defined, even margin |
| Ill-defined | 0 | Margin cannot be clearly delineated |
| Lobulated or irregular | 2 | Uneven, angular, or spiculated margin |
| Extra-thyroidal extension | 3 | Nodule extends beyond thyroid capsule; very suspicious |
Echogenic Foci
| Finding | Points | Description |
|---|---|---|
| None or large comet-tail artifacts | 0 | No calcifications; comet-tail = benign colloid |
| Macrocalcifications | 1 | Coarse calcifications with posterior shadowing |
| Peripheral (rim) calcifications | 2 | Calcification around nodule perimeter |
| Punctate echogenic foci | 3 | Tiny bright dots without shadowing; suggest psammoma bodies (papillary carcinoma) |
TI-RADS Levels
| Level | Points | Suspicion | FNA Threshold | Follow-up Threshold |
|---|---|---|---|---|
| TR1 | 0 | Benign | No FNA | No follow-up |
| TR2 | 2 | Not suspicious | No FNA | No follow-up |
| TR3 | 3 | Mildly suspicious | ≥ 2.5 cm | ≥ 1.5 cm |
| TR4 | 4–6 | Moderately suspicious | ≥ 1.5 cm | ≥ 1.0 cm |
| TR5 | ≥ 7 | Highly suspicious | ≥ 1.0 cm | ≥ 0.5 cm |
TI-RADS Decision Diagram
FNA Biopsy Guidelines
Fine-needle aspiration (FNA) biopsy is the gold standard for evaluating thyroid nodules. The ACR TI-RADS provides size-based thresholds for recommending FNA based on the suspicion level:
- TR1 & TR2: No FNA recommended regardless of size. These nodules are considered benign or not suspicious.
- TR3 (mildly suspicious): FNA if ≥ 2.5 cm; follow-up ultrasound if ≥ 1.5 cm. The high size threshold reflects the low malignancy probability.
- TR4 (moderately suspicious): FNA if ≥ 1.5 cm; follow-up if ≥ 1.0 cm. These nodules have intermediate malignancy risk.
- TR5 (highly suspicious): FNA if ≥ 1.0 cm; follow-up if ≥ 0.5 cm. Low size threshold due to high suspicion.
For nodules below the FNA threshold but at or above the follow-up threshold, repeat ultrasound in 1, 2, 3, or 5 years depending on TI-RADS level is recommended. Nodules below both thresholds generally do not require follow-up.
Bethesda System
When FNA is performed, the cytology results are reported using the Bethesda System for Reporting Thyroid Cytopathology, which categorizes results into six diagnostic categories:
| Category | Diagnosis | Malignancy Risk | Usual Management |
|---|---|---|---|
| I | Non-diagnostic/Unsatisfactory | 5–10% | Repeat FNA |
| II | Benign | 0–3% | Clinical follow-up |
| III | Atypia of undetermined significance (AUS) | 6–18% | Repeat FNA or molecular testing |
| IV | Follicular neoplasm/suspicious for FN | 10–40% | Diagnostic lobectomy |
| V | Suspicious for malignancy | 45–60% | Lobectomy or total thyroidectomy |
| VI | Malignant | 94–96% | Total thyroidectomy |
Thyroid Nodule Evaluation
Thyroid nodules are extremely common, detected in 19–68% of the general population by high-resolution ultrasound. The vast majority are benign (85–95%). The goal of evaluation is to identify the small percentage that are malignant while avoiding unnecessary invasive procedures.
The standard evaluation pathway includes:
- History and physical exam: Risk factors for malignancy include radiation exposure, family history of thyroid cancer, rapid growth, hoarseness, and fixed nodule.
- TSH level: If low (hyperthyroidism), a radionuclide thyroid scan is recommended. "Hot" (functioning) nodules are almost never malignant.
- Thyroid ultrasound: Characterize the nodule using TI-RADS features and measure its dimensions.
- FNA biopsy: Based on TI-RADS level and size thresholds.
- Molecular testing: For indeterminate cytology (Bethesda III/IV), molecular markers (Afirma, ThyroSeq) can help reclassify nodules.
Frequently Asked Questions
What are punctate echogenic foci?
Punctate echogenic foci (PEF) are tiny bright dots (<1 mm) seen within the nodule without posterior acoustic shadowing. They are believed to represent psammoma bodies (concentric calcific laminations) and are strongly associated with papillary thyroid carcinoma. PEF carry the highest point value (3 points) in the echogenic foci category.
What does "taller-than-wide" mean?
A taller-than-wide nodule has a greater anteroposterior dimension than its transverse dimension when measured on transverse view. This shape suggests growth perpendicular to the tissue plane, which is characteristic of infiltrative malignant behavior. It carries 3 points in the TI-RADS system.
Should all thyroid nodules be biopsied?
No. The ACR TI-RADS was specifically designed to reduce unnecessary biopsies. Only nodules that meet both the suspicion threshold (based on US features) and the size threshold warrant FNA. Many small, benign-appearing nodules can be safely monitored or ignored entirely.
How often should follow-up ultrasound be performed?
ACR recommends follow-up intervals based on TI-RADS level: TR3 nodules every 1–3 years, TR4 every 1–2 years, and TR5 annually. If a nodule grows significantly (≥20% in two dimensions or ≥50% volume increase), FNA should be reconsidered regardless of the initial recommendation.
Is TI-RADS applicable to pediatric patients?
ACR TI-RADS was developed and validated primarily in adult populations. While it can be used as a guide in pediatric patients, thyroid nodules in children and adolescents have a higher malignancy rate (approximately 20–25%), so lower thresholds for biopsy may be appropriate. Pediatric-specific guidelines should also be consulted.