From the Guidelines
The best imaging test to diagnose thyroid cancer is ultrasound, as it is the primary imaging modality for evaluating thyroid nodules and detecting potential thyroid cancer due to its high sensitivity, lack of radiation exposure, and wide availability. Thyroid ultrasound can clearly visualize the thyroid gland's structure, identify nodules as small as 1-2 mm, and characterize suspicious features such as irregular margins, microcalcifications, hypoechogenicity, and increased vascularity that may indicate malignancy 1. According to the ESMO clinical practice guidelines for diagnosis, treatment, and follow-up of thyroid cancer, ultrasound features associated with malignancy include hypoechogenicity, microcalcifications, absence of peripheral halo, irregular borders, solid aspect, intranodular blood flow, and shape (taller than wide) 1.
When evaluating thyroid nodules, the following characteristics should be considered:
- Nodule size: Fine needle aspiration cytology (FNAC) 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
- Ultrasonographic features: Suspicious features at US, such as irregular margins, microcalcifications, and hypoechogenicity, should be submitted to FNAC 1
- Clinical suspicion: History of head and neck irradiation, family history of thyroid cancer, suspicious features at palpation, and presence of cervical adenopathy should be considered when evaluating thyroid nodules 1
In addition to ultrasound, fine-needle aspiration biopsy (FNAB) guided by ultrasound is typically the next step for nodules with suspicious ultrasound features to obtain cells for cytological examination 1. The American College of Radiology Appropriateness Criteria also support the use of ultrasound as the primary imaging modality for evaluating thyroid nodules and detecting potential thyroid cancer 1.
It is essential to note that while other imaging modalities, such as CT scan, MRI, or nuclear medicine studies like radioiodine scans, may be necessary in cases where ultrasound findings are inconclusive or when evaluating for metastatic disease, ultrasound remains the cornerstone of thyroid cancer detection due to its excellent visualization of thyroid tissue, safety profile, and cost-effectiveness 1.
From the Research
Imaging Tests for Thyroid Cancer Diagnosis
- The most commonly used imaging tests for diagnosing thyroid cancer include ultrasound, computerized tomography (CT), magnetic resonance imaging (MRI), and scintigraphic procedures 2.
- Ultrasound is a highly sensitive method for detecting thyroid nodules and characterizing them as benign or malignant, with a sensitivity of 92.53% and specificity of 33.88% 3.
- The Thyroid Imaging Reporting And Data System (TIRADS) guidelines are used to analyze the morphological features of thyroid nodules observed during ultrasound, helping to predict the likelihood of malignancy 3.
Comparison of Imaging Tests
- Ultrasound is preferred over fine-needle aspiration biopsy (FNAB) due to its faster and less invasive nature, although FNAB is still necessary for a definitive diagnosis 3, 4.
- CT and MRI are useful for identifying tumor extension to neighboring structures and detecting distant metastases, but are not as sensitive as ultrasound for detecting recurrent malignancy in regional cervical lymph nodes 2, 5.
- Scintigraphic procedures, such as radioiodine scan and positron emission tomography, are useful for detecting recurrent or metastatic disease, especially in cases of non-iodine avid dedifferentiated or poorly differentiated thyroid cancer 2.
Clinical Applications
- Ultrasound is used to guide fine-needle aspiration biopsy and to evaluate the neck for local recurrence and nodal metastatic disease after thyroidectomy 4, 6.
- Ultrasound is also used to stage thyroid cancer by identifying cervical lymph nodes suspicious for metastasis, allowing for targeted biopsy and treatment 6.
- The choice of imaging test depends on the specific clinical scenario and the suspected type of thyroid cancer, with ultrasound being a key component of thyroid cancer diagnosis and management 3, 2, 6.