1. Ultrasonography
(1) Identification of benign and malignant nodules: Ultrasonography is simple and non-invasive, with high specificity and sensitivity for thyroid nodule examination, and can clearly display information on the boundary, morphology, size and internal structure of nodules. Neck ultrasonography should determine the size, number, location, cystic solidity, shape, borders, calcification, blood supply and relationship to surrounding tissues of thyroid nodules, as well as assess the presence of abnormal lymph nodes in the neck and their location, size, morphology, blood flow and structural features.
Other signs of malignancy include solid hypoechoic nodules, halo absence, extrathyroidal invasion, and abnormal ultrasound signs in the cervical lymph nodes. Other signs of abnormal cervical lymph nodes include microcalcifications, cystic changes, hyperechogenicity, and peripheral blood flow within the lymph nodes, in addition to rounded lymph nodes, irregular or blurred borders, uneven internal echogenicity, disappearance of lymphatic portals, or poorly demarcated dermal medulla.
The ability to identify thyroid nodules and lymph nodes correlates with the clinical experience of the sonographer. The thyroid imaging reporting and data system (TI-RADS), which assesses the malignancy of thyroid nodules, helps standardize thyroid ultrasound reporting and is recommended for use when available. However, the TI-RADS classification is not unified at present, and the criteria in Table 1 can be referred to. Ultrasonography and ultrasound elastography can be used as complementary tools, but are not recommended for routine application.
Table 1 TI-RADS classification for ultrasound assessment of thyroid nodules(2) Ultrasound-guided fine-needle aspiration biopsy (FNAB): Fine-needle aspiration biopsy (FNAB) uses a fine needle to puncture the thyroid nodule, obtain the cellular components, and diagnose the nature of the lesion by cytology. Ultrasound guidance can improve the success rate of extraction and diagnostic accuracy, as well as facilitate the protection of important tissue structures during puncture and determine the presence of hematoma after puncture, and is recommended as a further diagnostic method to determine the benignity and malignancy of thyroid nodules.
FNAB can be divided into negative pressure and non-negative pressure FNA, which can be selected or used in combination as appropriate in clinical work. To improve the accuracy of FNAB, the following methods can be used: repeated puncture sampling at multiple sites of the same nodule; sampling at parts of the nodule where ultrasound suggests suspicious signs; sampling at solid sites of cystic nodules, while cytology of cystic fluid can be performed.
Indications for ultrasound-guided FNAB (US-FNAB) of thyroid nodules: US-FNAB is recommended for thyroid nodules >1 cm in diameter with ultrasound assessment of malignant signs; for thyroid nodules ≤1 cm in diameter, puncture biopsy is not routinely recommended, but US-FNAB may be considered if one of the following conditions exists FNAB: ultrasound suggestive of a malignant thyroid nodule; abnormal cervical lymph nodes on ultrasound; history of radiation exposure to the neck or radiation contamination during childhood; family history of thyroid cancer or thyroid cancer syndrome; positive 18F-fluorodeoxyglucose (18F-FDG); abnormal serum calcitonin level elevated.
(ii) Indications for exclusion of US-FNAB: thyroid nodules with autonomic uptake confirmed by thyroid nuclide imaging; nodules with purely cystic nature suggested by ultrasonography.
(iii) Contraindications for US-FNAB of thyroid nodules: bleeding tendency, significantly prolonged bleeding and clotting times, significantly reduced prothrombin activity; possible damage to adjacent vital organs by the puncture needle route; long-term use of anticoagulants; difficulty in cooperation with frequent coughing and swallowing; refusal of invasive examination; infection at the puncture site, which must be treated before puncture. Menstruation in women is a relative contraindication.
(3) Ultrasound examination during follow-up: For patients who have not undergone surgical treatment, attention should be paid to whether the original nodule volume increases or the aforementioned malignant signs appear during ultrasound follow-up. An increase in nodule volume is defined as an increase in nodule volume of more than 50% or an increase in at least 2 diameter lines of more than 20% (and more than 2 mm), which is an indication for FNAB; for cystic nodules, the decision to perform FNAB should be based on the growth of the solid portion.
In postoperative thyroid patients, attention should be paid to the presence of solid occupancies in the operative bed area and the presence of malignant cervical lymph nodes during follow-up. Ultrasound is difficult to identify benign lesions and recurrent lesions in the operative bed, and the evaluation of cervical lymph nodes is the same as preoperatively. The indications for postoperative puncture of suspicious cervical lymph nodes: for lymph nodes with the smallest diameter greater than 8mm and ultrasound suggesting abnormalities, cytological examination of fine needle puncture material + eluate detection of Tg level can be considered; for lymph nodes smaller than 8 mm, follow-up observation can be performed if they do not grow or threaten the surrounding important structures.
2. CT
CT scan is valuable to evaluate the extent of thyroid tumor, its relationship with surrounding important structures such as trachea, esophagus, carotid artery and the presence of lymph node metastasis. CT has the advantage of observing the central group of lymph nodes, the upper mediastinal group of lymph nodes and the posterior pharyngeal group of lymph nodes, and can observe the posterior sternal thyroid lesions, larger lesions and their relationship with the surrounding structures, and can clearly show calcified foci of various shapes and sizes, but for nodules with a maximum diameter of ≤5 mm and However, it is not good for patients with diffuse lesions combined with nodules. For recurrent thyroid cancer, CT can provide information about the residual thyroid gland, assess the location of the lesion and its relationship with the surrounding tissues, evaluate the size and location of metastatic lymph nodes, and assess the presence of pulmonary metastases. If there is no contraindication to the use of iodine contrast, enhancement scans should be routinely performed for thyroid lesions. Thin layer images can show smaller lesions and clearly show the relationship between the lesion and the surrounding tissues and organs.
3. MRI
MRI has high tissue resolution and can be used for multi-directional and multi-parametric imaging to evaluate the extent of the lesion and its relationship to the surrounding important structures. Dynamic enhancement scanning, diffusion-weighted imaging and other functional imaging can evaluate the benignity and malignancy of nodules. The shortcomings of MRI are its insensitivity to calcification, long examination time, and susceptibility to breathing and swallowing movements.
4. Positron emission tomography
Positron emission tomography-computed tomography (PET-CT) is not recommended as a routine test for thyroid cancer diagnosis, but can be considered in the following cases: ①Patients with DTC have elevated Tg (>10ng/ml) during follow-up, and iodine 131 (131I) diagnostic whole body scan (Dx-WBS) is negative to detect metastases; ② pre-treatment staging of MTC and post-operative calcitonin elevation to detect metastases; ③ pre-treatment staging and post-operative follow-up of undifferentiated thyroid cancer; ④ pre-treatment evaluation of 131I in patients with invasive or metastatic DTC (manifested as poor uptake of iodine in lesions with increased PET-CT metabolism, making it difficult to benefit from 131I therapy)