ACR Thyroid Imaging Reporting and Data System (ACR TI-RADS)

TI-RADS is a reporting system for thyroid lesions on ultrasound proposed by the American College of Radiology (ACR)¹. AThe previous gradingACR system from 2015 ² which was reliant on descriptive reports from 2015 was supersededupdated by a 2017 white paper, with a structuredfocus on risk stratification.

There is now a standardised scoring system, and with recommendations for fine needle aspiration (FNA) or ultrasound follow-up of clinically significant malignancies, while reducing biopsies for benign lesions.

Ultrasound features

Scoring is determined from five categories of ultrasound findings. The higher the score, the higher the TR level and likelihood of malignancy.

If multiple nodules are present, only the four highest scoring nodules should be included in the report for clarity and reproducibility.

One score is assigned from each of the following categories:

• composition:
  • cystic or completely cystic: 0 points
  • spongiform: 0 points
  • mixed cystic and solid: 1 point
  • solid or almost completely solid: 2 points
• echogenicity:
  • anechoic: 0 points
  • hyper- or isoechoic: 1 point
  • hypoechoic: 2 points
  • very hypoechoic: 3 points
• shape:
  • wider than tall: 0 points
  • taller than wide: 3 points
• margin:
  • smooth: 0 points
  • ill-defined: 0 points
  • lobulated/irregular: 2 points
  • extra-thyroidal extension: 3 points

Any and all findings in the final category are also added to the other four scores.

• echogenic foci:
  • none: 0 points
  • large comet tail artefact: 0 points
  • macrocalcifications: 1 point
  • peripheral/rim calcifications: 2 points
  • punctate echogenic foci: 3 points

Scoring and classification

• TR1: 0 points
  • benign
• TR2: 2 points
  • not suspicious
• TR3: 3 points
  • mildly suspicious
• TR4: 4-6 points
  • moderately suspicious
• TR5: ≥ 7 points
  • highly suspicious

Recommendations

• TR1: no FNA/follow-up required
• TR2: no FNA required
• TR3: ≥ 1.5 cm follow up, ≥ 2.5 cm FNA
  • follow up: 1, 3 and 5 years
• TR4: ≥ 1.0 cm follow up, ≥ 1.5 cm FNA
  • follow up: 1, 2, 3 and 5 years
• TR5: ≥ 0.5 cm follow up, ≥ 1.0 cm FNA
  • annual follow up for up to 5 years

Biopsy is recommended for suspicious lesions (TR3 - TR5) with the above size criteria. If there are multiple nodules, the two with the highest TI-RADS grades should be sampled rather than the two largest.

Interval enlargement on follow up is felt to be significant if there is a increase of 20% and 2 mm in two nodules, or a 50% increase in volume. If the TI-RADS level increases between scans, an interval scan the following year is again recommended.

Changes to 2017 system

The previous TR1 grade for "normal thyroid gland" can now include simple cysts, meeting 0 points on the above criteria. Purely anechoic/cystic lesions are assigned 0 points, whereas before if included as "very hypoechoic" they would have been assigned 3 points and a likely fruitless FNA.

Margins (and haloes) should be included in the measurement of lesions. If margins are ill-defined, for example in a heterogenous or multi-nodular gland, 0 points should be assigned.

Frank invasion of surrounding structures is a unfavourable prognostic sign and is assigned 3 points. If minimal extra-thyroidal extension is suspected without frank invasion, especially with otherwise benign features, caution should be used when reporting.

Please note: This article (Spring 2017) is based on a proposed classification system, which should be known to radiologists, and may help them in characterising thyroid lesions. It may be used for risk stratification on sole discretion of personnel or institution, and should be complemented by FNA as required.