I. Overview.
1, More than 90% of thyroid cancer is differentiated thyroid cancer (DTC). DTC originates from thyroid follicular epithelial cells and mainly includes papillary thyroid carcinoma (PTC) and follicular carcinoma (FTC), a few are Hurthle cell or eosinophilic tumors.
2. Most DTCs progress slowly and have a nearly benign course with a high 10-year survival rate. However, certain subtypes such as hypercellular type of PTC, columnar cell type, diffuse sclerosis type, solid subtype, and extensive infiltration type of FTC are prone to extrathyroidal invasion and distant metastasis, with high recurrence rate and relatively poor prognosis.
Hypofractionated thyroid cancer also belongs to the category of DTC, with high invasiveness, easy metastasis, poor prognosis and difficult treatment.
The treatment of DTC includes surgery, postoperative 131I, TSH suppression, etc. Surgery is very important and individualized comprehensive treatment is the development trend.
Second, thyroidectomy for DTC.
1.Factors to determine the extent of thyroidectomy: tumor size; whether there is invasion of surrounding tissues; whether there are lymph nodes and distant metastases; unifocal or multifocal; whether there is history of radiation exposure in childhood; whether there is family history of thyroid cancer or thyroid cancer syndrome; gender, pathological subtype and other risk factors.
2.According to TNM (cTNM) stage, risk of tumor death/recurrence, pros and cons of various surgical procedures and patients’ wishes, comprehensive consideration should not be made in general.
3.Total/near-total thyroidectomy.
(1) Scope of resection: total thyroidectomy is the removal of all thyroid tissue visible to the naked eye. Near-total thyroidectomy is the removal of almost all thyroid tissue visible to the naked eye, while retaining <1g of thyroid tissue, such as thyroid tissue at the laryngeal nerve entry and parathyroid glands.
(2) Advantages: one-time treatment of multifocal lesions; facilitates postoperative monitoring of recurrence and metastasis; facilitates postoperative 131I therapy; reduces the chance of tumor recurrence and reoperation; accurately assesses postoperative staging and risk stratification.
(3) Disadvantages: permanent hypothyroidism, increased probability of damage to parathyroid glands and laryngeal recurrent nerve, high skill requirements for surgeons.
(4) Indications: history of head and neck radiation exposure or radioactive dust exposure in childhood; primary foci >4 cm; multiple cancer foci, bilateral cancer foci; poor pathological subtypes (hypercellular, columnar cell, diffuse sclerosing, solid subtypes of PTC, extensive infiltrative, and hypofractionated types of FTC); existing distant metastases requiring postoperative 131I therapy; bilateral cervical lymph node metastases; extraglandular invasion.
(5) Relative indications: 1-4 cm straight transection with high risk factors for thyroid cancer or combined with contralateral thyroid nodules.
4.Lobar + isthmus resection.
(1) Advantages: It helps to protect the parathyroid glands, the recurrent laryngeal nerve and part of the thyroid function.
(2) Disadvantages: May miss small lesions; unfavorable for postoperative monitoring by Tg and 131I systemic imaging.
(3) Indications: single lesion of Q1 cm in one lobe, low risk of recurrence, no history of childhood head and neck radiation exposure, no nodules in the contralateral lobe.
(4) Relative indications: single lesion Q4cm in one lobe, the rest as above.
5.Lymph node dissection in the central region of the neck.
Cervical lymph node metastasis is a risk factor for increased recurrence rate and decreased survival rate of DTC. 20% to 90% of patients have cervical lymph node metastasis at the time of diagnosis, mostly in the lymph nodes of the central region of the neck (region VI). 28% to 33% of lymph node metastases are not detected by preoperative imaging and intraoperative exploration, but are diagnosed after prophylactic central region lymph node dissection. Lymph node dissection in the ipsilateral central region of the lesion is recommended with effective preservation of the parathyroid glands and the recurrent laryngeal nerve. The clearance includes: the thymus at the upper from the inferior border of the thyroid cartilage, and the medial border of the carotid sheath at the lateral border, including the pre-tracheal, paratracheal, and anterior laryngeal lymph nodes.
6. Non-central lymph node dissection of the neck.
Cervical lymph node metastasis can also involve lymph nodes in the lateral neck (zone II-V) and anterior mediastinum (zone VII), and resection of these lymph nodes can reduce the recurrence rate and mortality. Resection of lymph nodes by subdivision is preferable to resection of affected lymph nodes only. Lateral cervical zone lymph node dissection is recommended for DTC patients with non-central zone lymph node metastases.