# Thyroid Ultrasound and TI-RADS

## Introduction

Thyroid nodules are exceedingly common, detected in up to 68% of the general population by high-resolution ultrasound. The vast majority are benign; the clinical challenge lies in identifying the 5-15% that harbor malignancy. The **Thyroid Imaging Reporting and Data System (TI-RADS)**, developed by the American College of Radiology (ACR), provides a standardized, point-based framework for risk stratification and biopsy recommendation.

## Normal Thyroid Anatomy on Ultrasound

The thyroid gland is a bilobed structure connected by the **isthmus**, located anterior to the trachea at the level of C5-T1. Normal parenchyma is **homogeneously hyperechoic** relative to the adjacent strap muscles. Each lobe measures approximately 4-6 cm (length) x 1.3-1.8 cm (AP) x 1.5-2.0 cm (transverse). The **recurrent laryngeal nerve** runs in the tracheoesophageal groove posteriorly, and the **carotid artery** and **internal jugular vein** lie laterally.

![Annotated transverse ultrasound of normal thyroid gland demonstrating homogeneous echotexture and surrounding landmarks](thyroid-normal-anatomy-us.png)

## Ultrasound Technique

### Patient Positioning

The patient is positioned supine with the neck hyperextended using a shoulder roll. A high-frequency **linear transducer (10-15 MHz)** is standard. Systematic scanning is performed in transverse and longitudinal planes for each lobe and the isthmus.

### Key Imaging Parameters

**Gray-scale imaging** evaluates nodule composition, echogenicity, shape, margin, and echogenic foci. **Color Doppler** assesses the vascularity pattern (peripheral vs. intranodular). **Elastography** is an optional adjunct for stiffness assessment.

## ACR TI-RADS Point System

The ACR TI-RADS assigns points across five categories, and the total determines the TI-RADS level and management recommendation.

### Composition (Choose one)

Cystic or almost completely cystic nodules receive **0 points**. Spongiform nodules also receive **0 points**. Mixed cystic and solid nodules receive **1 point**. Solid or almost completely solid nodules receive **2 points**.

### Echogenicity (Choose one)

Anechoic nodules receive **0 points**. Hyperechoic or isoechoic nodules receive **1 point**. Hypoechoic nodules receive **2 points**. Very hypoechoic nodules receive **3 points**.

### Shape (Choose one)

Wider-than-tall nodules receive **0 points**. **Taller-than-wide** nodules receive **3 points** and carry high specificity for malignancy.

### Margin (Choose one)

Smooth margins receive **0 points**. Ill-defined margins receive **0 points**. Lobulated or irregular margins receive **2 points**. **Extrathyroidal extension** receives **3 points**.

### Echogenic Foci (Choose all that apply)

None or large comet-tail artifacts receive **0 points**. Macrocalcifications receive **1 point**. Peripheral (rim) calcifications receive **2 points**. **Punctate echogenic foci** (suspicious for psammoma bodies) receive **3 points**.

## TI-RADS Categories and Management

| TI-RADS Level | Points | Risk | FNA Threshold | Follow-up Threshold |
|---|---|---|---|---|
| TR1 (Benign) | 0 | < 2% | No FNA | No follow-up |
| TR2 (Not Suspicious) | 2 | < 2% | No FNA | No follow-up |
| TR3 (Mildly Suspicious) | 3 | ~5% | >= 2.5 cm | >= 1.5 cm |
| TR4 (Moderately Suspicious) | 4-6 | 5-20% | >= 1.5 cm | >= 1.0 cm |
| TR5 (Highly Suspicious) | >= 7 | > 20% | >= 1.0 cm | >= 0.5 cm |

![Comparison panel of TI-RADS categories showing representative nodule ultrasound images from TR1 through TR5](ti-rads-categories-panel.png)

## Suspicious Features and Differential Diagnosis

**Papillary thyroid carcinoma** typically appears solid, hypoechoic, taller-than-wide, with punctate echogenic foci and irregular margins. **Follicular neoplasm** is solid, isoechoic, and well-circumscribed with a halo, though ultrasound alone cannot reliably distinguish adenoma from carcinoma. **Medullary carcinoma** is solid and hypoechoic and may contain coarse calcifications. A **benign colloid nodule** is typically cystic or spongiform with comet-tail artifacts from colloid crystals.

## Lymph Node Assessment

The cervical lymph nodes at **levels II-VI** should always be evaluated. Suspicious features include **round morphology**, loss of fatty hilum, **microcalcifications**, cystic change, and peripheral vascularity. Metastatic papillary carcinoma nodes may appear cystic and hyperechoic.

![Abnormal cervical lymph node with loss of fatty hilum, microcalcifications, and cystic change suspicious for metastatic thyroid carcinoma](suspicious-cervical-lymph-node-us.png)

## Key Clinical Pearls

A **purely cystic** nodule is virtually never malignant and should not be biopsied. **Spongiform** morphology (aggregation of multiple microcystic components comprising more than 50% of the nodule) has a greater than 99.7% negative predictive value for malignancy. Punctate echogenic foci in a cystic nodule are likely **colloid crystals** (comet-tail artifact), not microcalcifications. TI-RADS size thresholds apply to the **largest dimension** of the nodule. Always document and measure up to **four dominant nodules** and any nodule with suspicious features.

## References

1. Tessler FN, Middleton WD, Grant EG, et al. ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee. *J Am Coll Radiol*. 2017;14(5):587-595.
2. Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer. *Thyroid*. 2016;26(1):1-133.
3. Middleton WD, Teefey SA, Reading CC, et al. Multiinstitutional Analysis of Thyroid Nodule Risk Stratification Using the American College of Radiology Thyroid Imaging Reporting and Data System. *AJR Am J Roentgenol*. 2017;208(6):1331-1341.
4. Grant EG, Tessler FN, Hoang JK, et al. Thyroid Ultrasound Reporting Lexicon: White Paper of the ACR Thyroid Imaging, Reporting and Data System (TIRADS) Committee. *J Am Coll Radiol*. 2015;12(12 Pt A):1272-1279.