Ultrasound is the preferred modality for thyroid screening and has advantages that are unmatched by other tests. First, the thyroid gland is superficial and can show a clearer ultrasound image. Secondly, ultrasound is flexible and easy to operate, and it can display the functional state of the thyroid and blood flow dynamically in real time, and the test results can be obtained immediately and can be repeatedly observed. Finally, ultrasound does not cause trauma or radiological damage.
In addition to observing lesions, ultrasound can also guide fine-needle aspiration biopsies of thyroid nodules or cervical lymph nodes.
Today, high-resolution ultrasound can detect thyroid nodules as small as 1 mm.
So what can an ultrasound tell us?
Can ultrasound determine the benignity or malignancy of a nodule?
According to the ultrasound features, an experienced doctor can diagnose whether a thyroid nodule “tends” to be benign or malignant. It is important to remember that there is no absolute relationship between the number and size of thyroid nodules and their benignity. In other words, more nodules and larger nodules do not indicate a greater likelihood of malignancy. Conversely, fewer and smaller nodules do not indicate less likelihood of malignancy.
So when you get the ultrasound report, don’t be overly concerned because of the number or size of the nodules, you need to have the report interpreted by a professional clinician before determining the benignity or malignancy of the nodules.
In fact, there are specific signs that doctors use to infer the benignity or malignancy of a nodule. For example, signs that are highly suggestive of a malignant nodule include:
- Pinpoint-like diffuse distribution or clusters of tiny calcified foci. However, not all calcifications are signs of thyroid cancer, and only tiny foci of calcification are cause for alarm.
- Substantial hypoechoic nodules.
- Irregular nodule margins.
- Nodule with irregular margins.
- Nodule encroaches on the thyroid envelope.
- The ratio of the longitudinal diameter of the nodule to the transverse diameter is greater than 1.
Signs that are highly suggestive of a benign nodule include:
- Purely cystic nodules.
- Nodules with more than 50% of their volume occupied by multiple vesicles.
- Nodules with spongy changes.
Can ultrasound detect lymph node metastases?
Ultrasound can also check for metastases in the lymph nodes of the neck in thyroid cancer.
Ultrasound can show lymph nodes in the central area of the neck and on both sides. In normal people, there are many lymph nodes in the neck, and in most people, ultrasound can reveal enlarged or more numerous lymph nodes in the neck due to factors such as inflammation, but this is not a reliable sign of metastatic thyroid cancer lymph nodes. The most important thing to remember is that the size and number of lymph nodes in the neck is not a reliable indicator of thyroid cancer.
Cancer may be suspected of invading a lymph node if your doctor sees the following features on an ultrasound: microcalcifications, cystic changes, loss of normal structure, abundant surrounding blood vessels, and full lymph node shape in the neck lymph node.
The lymph node condition can also assist the physician in inferring the benignity or malignancy of the thyroid nodule. If suspicious thyroid nodules are found along with suspicious metastatic lymph nodes, it suggests that the thyroid nodules are more likely to be malignant.
What are the limitations of ultrasound?
While ultrasound can provide a lot of important information, there is no denying that the accuracy of this test is closely related to the experience, technique, and ultrasound instrumentation of the physician performing it, and is influenced by a number of subjective factors. Diagnostic results may vary between hospitals and physicians.
For example, your ultrasound may show a “suspicious malignant nodule” in your thyroid during a physical exam, but after a follow-up exam in the hospital, your doctor may confirm that it is only a benign thyroid cyst.
Therefore, after a physical examination reveals a thyroid nodule, further review at a regular, specialized, experienced hospital is recommended, neither to overtreat nor delay treatment.
Summary
B ultrasound is highly valuable for diagnosing thyroid nodules, and the correct diagnosis depends on the experience of the ultrasonographer. Therefore, there is no need to be overly alarmed if a thyroid nodule is found incidentally during a physical examination. In fact, for most people, thyroid nodules do not require treatment and only require regular follow-up once a year.
Co-written by Dr. Naisi Huang, Cancer Hospital of Fudan University