From the Guidelines
Malignant thyroid nodules on ultrasound (US) are characterized by features such as hypoechogenicity, microcalcifications, absence of peripheral halo, irregular borders, solid aspect, intranodular blood flow, and a shape that is taller than wide, as outlined in the 2012 Annals of Oncology guidelines 1. When evaluating thyroid nodules, it is essential to consider multiple ultrasound characteristics, as the presence of a single suspicious feature is not definitive for malignancy. The combination of several concerning features, however, increases the specificity of US for detecting malignant nodules, although this comes at the cost of reduced sensitivity 1. Some key characteristics of malignant thyroid nodules on US include:
- Hypoechogenicity, or a darker appearance compared to surrounding thyroid tissue
- Microcalcifications, which are tiny, punctate, bright echoes within the nodule
- Absence of a peripheral halo, a characteristic often seen in benign nodules
- Irregular borders or poorly defined margins
- Solid composition rather than cystic
- Intranodular blood flow, indicating increased vascularity within the nodule
- A shape that is taller than wide, particularly in the transverse plane These features are integral to risk stratification systems like the Thyroid Imaging Reporting and Data System (TIRADS), which helps guide the selection of nodules for fine needle aspiration biopsy and definitive diagnosis. It is crucial to note that while no single feature is pathognomonic for malignancy, the presence of multiple suspicious characteristics significantly increases the likelihood of cancer, with solid hypoechoic nodules with microcalcifications carrying one of the highest risks 1.
From the Research
Imaging Characteristics of Malignant Thyroid Nodules on Ultrasound
The following are the imaging characteristics of malignant thyroid nodules on ultrasound (US):
- Solid or almost completely solid composition 2, 3, 4
- Microcalcifications 2, 5, 4
- Hypoechoic or very hypoechoic echogenicity 2, 5, 3, 4
- Irregular shape or lobulated margins 2, 5, 3
- Ill-defined borders 2
- Presence of punctate echogenic foci 3
- Wider-than-tall shape 3
- Rich in blood flow 4
- Lower internal echogenicity 4
- Higher serum Tg/nodule volume ratio 4
Ultrasound Features and Risk of Malignancy
The ultrasound features that are associated with a higher risk of malignancy include:
- Solid composition 3
- Lobulated or irregular margins 3
- Punctate echogenic foci 3
- Very hypoechoic echogenicity 3
- Microcalcifications 2, 5, 4
- Hypoechoic echogenicity 2, 5, 4
- Irregular shape 2, 5
Classification Systems
There are various classification systems used to evaluate thyroid nodules on ultrasound, including: