From the Guidelines
The shape of a thyroid nodule, specifically its height-to-width ratio, is a critical factor in determining the risk of malignancy, with taller-than-wide nodules being more suspicious for cancer. When evaluating thyroid nodules, the height-to-width ratio is a key characteristic that helps predict the risk of malignancy. According to the most recent and highest quality study 1, thyroid nodules that are taller than wide (height-to-width ratio >1) are more likely to be malignant, while nodules that are wider than tall (height-to-width ratio <1) are more likely to be benign. This shape characteristic is included in ultrasound risk stratification systems and is used to determine whether a nodule requires biopsy. The biological explanation for this phenomenon relates to how thyroid cancers grow, with malignant nodules tend to grow across normal tissue planes in a perpendicular direction to the thyroid surface, creating a taller-than-wide appearance 1. In contrast, benign nodules typically expand along the path of least resistance parallel to the thyroid surface, resulting in a wider-than-tall configuration. Some key points to consider when evaluating thyroid nodules include:
- The height-to-width ratio is one of the more reliable indicators of malignancy, with a taller-than-wide shape carrying a positive predictive value of approximately 70-90% for malignancy.
- Other suspicious characteristics, such as irregular margins, microcalcifications, and hypoechogenicity, should always be considered alongside the height-to-width ratio when evaluating thyroid nodules 1.
- Fine-needle aspiration cytology (FNAC) is an important technique used along with ultrasound for the diagnosis of thyroid nodules, and should be performed in any thyroid nodule >1 cm and in those <1 cm if there is any clinical or ultrasonographic suspicion of malignancy 1. It is essential to consider the height-to-width ratio of a thyroid nodule as part of a comprehensive evaluation, including clinical history, ultrasound characteristics, and FNAC results, to determine the risk of malignancy and guide management decisions.
From the Research
Clinical Significance of Thyroid Lesion Shape
The shape of a thyroid lesion is a significant factor in determining its potential malignancy. Radiologists report thyroid lesions as either wider than taller or taller than wider due to the clinical importance of this shape characteristic.
Height to Width Ratio
- The height to width ratio of a thyroid lesion is a crucial factor in assessing its risk of malignancy 2.
- A study found that a lower long to short ratio, indicating a more spherical shape, was associated with a higher risk of malignancy in thyroid nodules 2.
- The risk of malignancy increased as the long to short ratio approached 1.0, with a ratio of 1.00-1.50 having a 25.5% cancer risk, and a ratio of 1.51-2.00 having a 19.7% cancer risk 2.
Sonographic Features
- Sonographic features of thyroid lesions, including shape, can help differentiate between benign and malignant lesions 3.
- A taller-than-wide shape is considered a malignant finding, while an oval shape is more commonly associated with benign lesions 3.
- However, the follicular variant of papillary thyroid carcinoma can have relatively benign sonographic features, including a wider-than-taller shape, emphasizing the importance of fine-needle aspiration biopsy (FNAB) in diagnosis 3.
Diagnostic Evaluation
- Fine-needle aspiration biopsy (FNAB) is a crucial diagnostic tool for evaluating thyroid lesions, with a sensitivity of 77.8% in one study 3.
- The combination of sonographic features, including shape, and FNAB results can help improve the accuracy of diagnosis and risk stratification of thyroid lesions 3, 2.
- Other diagnostic factors, such as patient demographics, nodule size, and composition, should also be considered in the evaluation of thyroid lesions 4, 5.