The guidelines for cytopathological diagnosis of thyroid cancer consist of the sampling, production and diagnostic report of thyroid FNA.
(1) FNA sampling: There are two methods of sampling thyroid FNA: palpation-guided FNA and ultrasound-guided FNA. The outer diameter of the needle is 22-27 G. A thicker needle can be used for lesions with significant fibrosis, while a thinner needle can be used for lesions with an abundant blood supply. A small amount of negative pressure or no negative pressure should be given to the needle, and the needle should be performed in multiple angles and quickly. The number of needle insertions per nodule is 1 to 3, depending on the amount of needle aspirate. For cystic nodules, the solid area should be taken in a targeted manner.
(2) Production of FNA: The production techniques of cell specimens include conventional smear, liquid-based production and cell block sectioning. Conventional smear is the most commonly used filming method, in which the cells obtained from FNA are directly coated on a slide, dried and fixed in alcohol. If the explanted material is cystic fluid, liquid-based filming will enrich the cells in the cystic fluid, resulting in a more abundant smear than the conventional smear. For rare types of thyroid tumors that are clinically suspected, such as medullary carcinoma, undifferentiated carcinoma, and metastatic carcinoma, it is best to add a cell block to facilitate immunocytochemical testing. The combination of conventional smear and liquid-based filming can improve the accuracy of diagnosis, and on-site evaluation of cellular specimens can be carried out in units with conditions to improve the satisfaction rate of sampling.
(3) Diagnostic cytopathology report: The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) is used for diagnostic cytopathology reports. Grade II, benign; Grade III, atypical cells of unknown significance/follicular lesions of unknown significance; Grade IV, follicular neoplasm/suspicious follicular neoplasm; Grade V, suspicious malignancy; and Grade VI, malignant (Table 2). Patients with different cytologic diagnostic grades have different risks of malignancy and different clinical management measures (Table 3)
Table 2 Diagnostic grading criteria for TBSRTCTable 3 Risk of malignancy and clinical management for each diagnostic grade of TBSRTC