Residency · Residency · Diagnostic Radiology
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.
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 |
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.
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
- 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.
- 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.
- 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.
- 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.