Understanding the ACR TI-RADS System: A Patient's Guide to Thyroid Nodule Evaluation

Table of Contents

• Introduction: Why Thyroid Nodule Evaluation Matters
• Overview of the ACR TI-RADS System
• How the System Was Developed
• Key Feature Categories Explained
• The Scoring and Risk Level System
• Biopsy and Follow-Up Recommendations
• Special Considerations
• Reporting and Measurement Details
• What This Means for Patients
• System Limitations
• Source Information

Introduction: Why Thyroid Nodule Evaluation Matters

Thyroid nodules are extremely common findings during neck ultrasound examinations. Research shows that up to 68% of adults have thyroid nodules detectable on high-resolution ultrasound. The vast majority of these nodules are benign (non-cancerous), which presents a significant challenge for healthcare providers: how to identify the small number that are malignant (cancerous) or require surgery without subjecting countless patients with benign nodules to unnecessary procedures.

Currently, fine-needle aspiration (FNA) biopsy is the most effective practical test to determine whether a nodule is malignant. However, since most nodules are benign, and even many malignant nodules (particularly those smaller than 1 cm) often show indolent or nonaggressive behavior, not all detected nodules require biopsy or surgery.

This balancing act has become increasingly important as studies reveal concerning trends in thyroid cancer diagnosis. In South Korea, widespread screening thyroid ultrasound in asymptomatic patients led to a rapid increase in reported papillary thyroid cancer incidence, yet mortality remained extremely low. In the United States between 2003-2007, overdiagnosis of thyroid cancer (defined as diagnosis of tumors that wouldn't cause symptoms or death if left alone) accounted for 70-80% of cases in women and 45% of cases in men.

The ACR TI-RADS system was developed to address this challenge by providing a reliable, noninvasive method to identify which nodules warrant biopsy based on a reasonable likelihood of biologically significant malignancy, ultimately helping to reduce unnecessary procedures while still detecting clinically important cancers.

Overview of the ACR TI-RADS System

The ACR Thyroid Imaging, Reporting and Data System (TI-RADS) is a standardized approach for radiologists to evaluate and report thyroid nodules found on ultrasound. The system categorizes ultrasound features into five main categories that help determine how suspicious a nodule appears for malignancy.

In this system, ultrasound features are classified as benign, minimally suspicious, moderately suspicious, or highly suspicious for malignancy. Each feature is assigned points, with more suspicious features receiving higher points. When assessing a nodule, the radiologist selects applicable features from each category and sums the points to determine the nodule's overall ACR TI-RADS level, which ranges from TR1 (benign) to TR5 (high suspicion of malignancy).

The system then provides specific recommendations for biopsy or ultrasound follow-up based on both the TR level and the nodule's maximum diameter. For higher suspicion levels (TR3 through TR5), the guidelines provide size thresholds at or above which biopsy should be recommended. The system also establishes lower size limits for recommending follow-up ultrasound for TR3, TR4, and TR5 nodules to limit unnecessary repeat scans for nodules likely to be benign or not clinically significant.

How the System Was Developed

The ACR TI-RADS was developed by a committee of expert radiologists convened by the American College of Radiology in 2012. The committee had three main goals: provide recommendations for reporting incidental thyroid nodules, develop a set of standard terms for ultrasound reporting, and create a TI-RADS based on this standardized language.

The committee's recommendations represent consensus opinions developed through conference calls, email discussions, and online surveys. These recommendations are based on thorough literature review, analysis of data from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) Program, evaluation of existing risk classification systems, and expert opinion.

The committee established several key attributes for the risk classification algorithm. They determined it should be founded on ultrasound features defined in their previously published lexicon, easy to apply across different ultrasound practices, able to classify all thyroid nodules, and evidence-based to the greatest extent possible.

It's important to understand that these recommendations serve as guidance for practitioners who incorporate ultrasound in managing adult patients with thyroid nodules, not as absolute standards. interpreting and referring physicians must apply their professional judgment to each case, and decisions about biopsy should also account for the referring physician's preference and the patient's individual risk factors, anxiety levels, other health conditions, life expectancy, and other relevant considerations.

Key Feature Categories Explained

The ACR TI-RADS evaluates five key characteristic categories of thyroid nodules, with each category containing specific features that contribute points to the overall suspicion score:

Composition

This category describes what the nodule is made of:

• Cystic or almost completely cystic (0 points): Filled with fluid, almost universally benign
• Spongiform (0 points): Composed predominantly (>50%) of small cystic spaces, highly correlated with benign cytology
• Mixed cystic and solid (1 point): Combination of fluid-filled and solid components
• Solid or almost completely solid (2 points): Mostly solid tissue

Echogenicity

This refers to how the nodule appears compared to normal thyroid tissue:

• Anechoic (0 points): Applies to cystic or almost completely cystic nodules
• Hyperechoic or isoechoic (1 point): Brighter than or similar to normal thyroid tissue
• Hypoechoic (2 points): Darker than normal thyroid tissue
• Very hypoechoic (3 points): Darker than the strap muscles in the neck

Shape

This category evaluates the nodule's orientation:

• Wider-than-tall (0 points): The nodule is wider than it is tall
• Taller-than-wide (3 points): The nodule is taller than it is wide, a specific indicator of malignancy

Margin

This describes the border or edge of the nodule:

• Smooth (0 points): Well-defined, regular border
• Ill-defined (0 points): Unclear borders
• Lobulated or irregular (2 points): Jagged, spiculated, or sharp angles
• Extra-thyroidal extension (3 points): Extension beyond the thyroid border, obvious invasion = malignancy

Echogenic Foci

These are bright spots within the nodule that may represent different features:

• None or large comet-tail artifacts (0 points): V-shaped echoes >1 mm deep, associated with colloid, strongly indicative of benignity
• Macrocalcifications (1 point): Coarse bright spots with acoustic shadowing
• Peripheral (rim) calcifications (2 points): Calcifications along the nodule's margin
• Punctate echogenic foci (3 points): Small bright spots that may correspond to psammomatous calcifications associated with papillary cancers

The Scoring and Risk Level System

The ACR TI-RADS uses a points-based system where radiologists assess nodules across all five categories and sum the points to determine a risk level:

TR1 - Benign (0 points): These nodules have characteristics strongly associated with benign conditions. No biopsy is recommended regardless of size.

TR2 - Not Suspicious (2 points): These nodules show minimal concerning features. No biopsy is recommended regardless of size.

TR3 - Mildly Suspicious (3 points): These nodules have some features that warrant attention but are likely benign. Biopsy is recommended if ≥ 2.5 cm, with follow-up ultrasound if ≥ 1.5 cm.

TR4 - Moderately Suspicious (4-6 points): These nodules have several concerning features. Biopsy is recommended if ≥ 1.5 cm, with follow-up ultrasound if ≥ 1 cm.

TR5 - Highly Suspicious (7 points or more): These nodules have multiple highly concerning features. Biopsy is recommended if ≥ 1 cm, with follow-up ultrasound if ≥ 0.5 cm.

It's worth noting that although a nodule could theoretically receive zero points and be classified as TR1, most nodules receive at least two points because a nodule with mixed cystic and solid composition (1 point) will also receive at least one more point for the echogenicity of its solid component.

Biopsy and Follow-Up Recommendations

The ACR TI-RADS provides specific size thresholds for biopsy recommendations based on the suspicion level:

For TR3 (mildly suspicious) nodules, biopsy is recommended at ≥ 2.5 cm, with follow-up ultrasound suggested for nodules ≥ 1.5 cm. This higher threshold reflects the committee's analysis showing cancer risk levels of no more than 5% for TR3 nodules.

For TR4 (moderately suspicious) nodules, biopsy is recommended at ≥ 1.5 cm, with follow-up ultrasound suggested for nodules ≥ 1 cm. These nodules carry a 5-20% risk of malignancy.

For TR5 (highly suspicious) nodules, biopsy is recommended at ≥ 1 cm, with follow-up ultrasound suggested for nodules ≥ 0.5 cm. These nodules have at least a 20% risk of malignancy.

The committee established these specific size thresholds after considering several factors: analysis of a database of more than 3,000 proven thyroid nodules, published and newly performed SEER data analyses that showed a slight increase in distant metastases at 2.5 cm, and slight increments in 10-year relative and thyroid cancer-specific mortality at 3 cm.

The system also accounts for the known discrepancy between ultrasound measurements and actual pathologic sizes, with ultrasound typically resulting in larger measurements than found during surgery. For example, in a study of 205 papillary carcinomas ≤1.5 cm, the mean diameter on ultrasound was 2.65 ± 1.07 cm compared with 1.97 ± 1.17 cm on pathology.

Special Considerations

Papillary Thyroid Microcarcinomas

The ACR TI-RADS aligns with other guidelines in recommending against routine biopsy of nodules smaller than 1 cm, even highly suspicious ones. However, the system acknowledges that some thyroid specialists advocate active surveillance ("watchful waiting"), ablation, or lobectomy for papillary microcarcinomas (very small thyroid cancers).

For this reason, biopsy of 5- to 9-mm TR5 nodules may be appropriate under certain circumstances through shared decision making between the referring physician and patient. The ultrasound report should indicate whether the nodule can be measured reproducibly on follow-up studies and whether it's located in critical areas near the trachea or tracheoesophageal groove (where the recurrent laryngeal nerve is located), as these locations may complicate future surgery.

Additional Benign Appearances

Several ultrasound findings have been described as characteristic of benign nodules with high reliability, including a uniformly hyperechoic appearance ("white knight") and a variegated pattern of hyperechoic areas separated by hypoechoic bands resembling giraffe hide (particularly in Hashimoto's thyroiditis). However, due to their relative scarcity, the committee chose not to formally incorporate these patterns into the ACR TI-RADS chart.

Reporting and Measurement Details

Accurate sizing of thyroid nodules is critical because the maximum dimension determines whether a lesion should be biopsied or followed. The ACR TI-RADS provides specific guidance on how nodules should be measured and documented:

Nodules should be measured in three dimensions: (1) maximum dimension on an axial image, (2) maximum dimension perpendicular to the previous measurement on the same image, and (3) maximum longitudinal dimension on a sagittal image. For obliquely oriented nodules, these measurements may differ from those used to determine taller-than-wide shape, but this rarely presents practical problems.

Measurements should include any halo around the nodule if present. Practices may use linear dimensions to calculate volume, a feature available on many ultrasound machines. Whatever method is used, consistency within each practice is important for tracking nodule changes over time.

The definition of significant nodule growth is important for follow-up recommendations. In the ACR TI-RADS, significant enlargement is defined as a 20% increase in at least two nodule dimensions with a minimal increase of 2 mm, or a 50% or greater increase in volume. These criteria align with those adopted by other professional societies.

What This Means for Patients

The development of the ACR TI-RADS reflects an important shift in how healthcare providers approach thyroid nodules and thyroid cancer. The committee specifically aimed to address the discrepancy between the sharp rise in thyroid cancer diagnosis and treatment (resulting from increased detection and biopsy) and the lack of commensurate improvement in long-term outcomes.

This system acknowledges that diagnosing every thyroid malignancy should not be the goal. Like other professional societies, the ACR recommends biopsy of high-suspicion nodules only if they are 1 cm or larger, and biopsy of low-risk nodules only when they measure 2.5 cm or more.

The recommendations for follow-up ultrasound significantly reduce the possibility that important malignancies will remain undetected over time and are consistent with an increasing trend toward active surveillance ("watchful waiting") for low-risk thyroid cancer.

For patients, this means:

• More consistent evaluation and reporting of thyroid nodules across different providers
• Reduced unnecessary biopsies for clearly benign nodules
• Appropriate monitoring of intermediate-risk nodules
• Timely identification of nodules that truly warrant biopsy
• Better shared decision-making between patients and providers

System Limitations

While the ACR TI-RADS provides valuable guidance, patients should understand several limitations:

The system does not include a TR0 category to indicate a normal thyroid gland, nor does it include subcategories within each TR level. The committee decided against a pattern-based approach used by some other organizations because research showed that approach was unable to classify 3.4% of nodules, of which 18.2% were malignant.

The system does not incorporate sonoelastography, a promising technique that assesses tissue stiffness, because it's not widely available in many ultrasound laboratories.

Additionally, any history of prior fine-needle aspiration or ethanol ablation should be communicated to your radiologist, as these procedures may lead to a suspicious appearance on follow-up ultrasound that doesn't represent actual cancer.

Most importantly, these recommendations should not be construed as absolute standards. Your interpreting and referring physicians must apply their professional judgment to your specific case, considering your individual risk factors, anxiety levels, other health conditions, and preferences.

Source Information

Original Article Title: ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee

Authors: Franklin N. Tessler, MD, CM; William D. Middleton, MD; Edward G. Grant, MD; Jenny K. Hoang, MBBS; Lincoln L. Berland, MD; Sharlene A. Teefey, MD; John J. Cronan, MD; Michael D. Beland, MD; Terry S. Desser, MD; Mary C. Frates, MD; Lynwood W. Hammers, DO; Ulrike M. Hamper, MD; Jill E. Langer, MD; Carl C. Reading, MD; Leslie M. Scoutt, MD; A. Thomas Stavros, MD

Publication: Journal of the American College of Radiology, 2017;14:587-595

Note: This patient-friendly article is based on peer-reviewed research and aims to accurately represent the original scientific content while making it accessible to educated patients.