TIRADS Classification

  • The ultrasound features in the ACR TI-RADS are categorized as:
    • Benign
    • Minimally suspicious for malignancy
    • Moderately suspicious for malignancy
    • Highly suspicious for malignancy
  • Points are given for all the ultrasound features in a nodule, with more suspicious features being awarded additional points:
    • The figure presents these features arranged per the five lexicon categories
  • When assessing a nodule, the reader selects one feature from each of the first four categories and all the features that apply from the final category and sums the points:
    • The point total determines the nodule’s ACR TI-RADS level:
      • Which ranges from TR1 (benign) to TR5 (high suspicion of malignancy)
    • Note that although it is possible for a nodule to be awarded zero points and hence be characterized as TR1, all other nodules merit at least two points because a nodule that has a mixed cystic and solid composition (one point) will also gain at least one more point for the echogenicity of its solid component
    • Finally, although sonoelastography is a promising technique, it is probably not available in many ultrasound laboratories and is not incorporated into the ACR TI-RADS

ACR TI-RADS Feature Categories

  • In this section, we elaborate on the five groups of ultrasound findings, ACR TI-RADS levels, and size thresholds. Readers are encouraged to refer to the lexicon white paper for detailed descriptions of all the categories and features:
    • As well, any history of prior FNA or ethanol ablation should be sought, as these procedures may lead to a suspicious appearance at follow-up ultrasound

 Composition

  • Nodules that are cystic or almost completely cystic merit no points because they are almost universally benign
  • Similarly, a spongiform architecture is highly correlated with benign cytology, regardless of its relative echogenicity or other features:
    • However, a spongiform nodule must be composed predominantly (>50%) of small cystic spaces
  • Nodules should not be characterized as spongiform solely on the basis of the presence of a few, scattered cystic components in an otherwise solid nodule
  • “Mixed cystic and solid” combines two features from the lexicon, predominately solid and predominately cystic
  • The appearance of the solid component is more important than the overall size of the nodule or the proportion of solid versus cystic components in determining whether biopsy is warranted
  • Solid material that is eccentric and has an acute angle with the nodule’s wall is suspicious, as is solid material with moderately or highly suspicious characteristics, such as decreased echogenicity, lobulation, and punctate echogenic foci
  • As well, although color Doppler ultrasound has not been shown to reliably discriminate between benign and malignant nodules, the presence of flow in solid components distinguishes tissue from echogenic debris or hemorrhage. Inconsequential debris may be identified by layering or motion elicited by changes in patient position

 Echogenicity

  • This feature refers to a nodule’s reflectivity relative to adjacent thyroid tissue, except for very hypoechoic nodules, in which the strap muscles are used as the basis for comparison. This category also includes “anechoic,” a zero-point feature that was absent from the lexicon
  • It applies to cystic or almost completely cystic nodules that would otherwise be given three points because of their very hypoechoic appearance

 Shape

  • A taller-than-wide shape is an insensitive but highly specific indicator of malignancy
  • This feature is evaluated in the axial plane by comparing the height (“tallness”) and width of a nodule measured parallel and perpendicular to the ultrasound beam, respectively:
    • A taller-than-wide configuration is usually evident on visual inspection and rarely requires formal measurements

 Margin

  • The presence of a halo is neither discriminatory nor mutually exclusive with other margin types; therefore, we elected to omit it
  • They included “ill defined” in this group so that any reporting template that incorporates a field for margin will not be left empty if a nodule is not well defined
  • “Lobulated or irregular margin” refers to a spiculated or jagged edge, with or without protrusions into the surrounding parenchyma
  • It may be difficult to recognize this finding if the nodule is ill defined, is embedded in a heterogeneous gland, or abuts multiple other nodules
  • If the margin cannot be determined for any reason, zero points should be assigned.Extension beyond the thyroid border is classified as extensive or minimal
  • Extensive extrathyroidal extension (ETE) that is characterized by frank invasion of adjacent soft tissue and/or vascular structures is a highly reliable sign of malignancy and is an unfavorable prognostic sign
  • Minimal ETE may be suspected sonographically in the presence of border abutment, contour bulging, or loss of the echogenic thyroid border
  • However, agreement among pathologists for identification of minimal ETE is poor, and its clinical significance is controversial
  • Therefore, practitioners should exercise caution when reporting minimal ETE, particularly for otherwise benign-appearing nodules

 Echogenic Foci

  • “Large comet-tail artifacts” are echogenic foci with V-shaped echoes >1 mm deep to them. They are associated with colloid and are strongly indicative of benignity when found within the cystic components of thyroid nodules
  • “Macrocalcifications” are coarse echogenic foci accompanied by acoustic shadowing. Evidence in the literature regarding their association with increased malignancy risk is mixed, especially in nodules lacking other malignant features
  • Given published data that show a weakly positive relationship with malignancy, macrocalcifications are assigned one point, recognizing that the risk is increased if the nodule also contains moderately or highly suspicious features that warrant additional points.Peripheral calcifications lie along all or part of a nodule’s margin. Their correlation with malignancy in the literature is variable
  • However, because some publications suggest that they are more strongly associated with malignancy than macrocalcifications, they are awarded two points
  • Some authors have called attention to interrupted peripheral calcifications with protruding soft tissue as suspicious for malignancy, but with low specificity
  • In the ACR TI-RADS, this appearance qualifies as a lobulated margin, which adds another two points to the nodule’s total assignment
  • In nodules with calcifications that cause strong acoustic shadowing that precludes or limits assessment of internal characteristics, particularly echogenicity and composition, it is best to assume that the nodule is solid and assign two points for composition and one point for echogenicity
  • Punctate echogenic foci are smaller than macrocalcifications and are nonshadowing
  • In the solid components of thyroid nodules, they may correspond to the psammomatous calcifications associated with papillary cancers and are therefore considered highly suspicious, particularly in combination with other suspicious features
  • This category includes echogenic foci that are associated with small comet-tail artifacts in solid components, as distinguished from the large comet-tail artifacts described earlier
  • Notably, small echogenic foci may be seen in spongiform nodules, where they probably represent the back walls of minute cysts
  • They are not suspicious in this circumstance and should not add to the point total of spongiform nodules

 Additional Benign Appearances

  • Several ultrasound findings have been described as characteristic of benign nodules with a high degree of reliability
  • These include a uniformly hyperechoic (“white knight”) appearance, as well as a variegated pattern of hyperechoic areas separated by hypoechoic bands reminiscent of giraffe hide, both in the setting of Hashimoto’s thyroiditis
  • Because of their scarcity, the committee chose not to formally incorporate these patterns in the ACR TI-RADS chart
ACR Thyroid Imaging Reporting and Data System Ti-rads White Paper of the ACR Ti-rads CommitteeDownload