Thyroid cancer is the most common malignancy in the endocrine system, and papillary thyroid cancer accounts for more than 80% of these tumors. Although highly differentiated thyroid cancer has a long natural course and low malignancy, and has a high 10-year survival rate of about 93% like benign diseases, its 10-year recurrence rate is reported to be 20%. The majority of these are metastases found in the original cancer bed or in the central region, or in the ipsilateral lymph nodes. Common factors for postoperative recurrence include young age at presentation, large primary tumor, extravascular infiltration, or existing distant metastases. Patients who undergo total thyroidectomy and cervical lymph node dissection if local metastasis is suspected at the time of initial presentation have a higher propensity for local lymph node metastasis, with a recurrence rate of 33.9% according to some studies. If a recurrence is seen in the residual thyroid, the morbidity and mortality rate will be even higher. With the change of medical technology, the management of postoperative local metastasis of thyroid cancer is also in the process of innovation. In addition to classical surgical treatment and radioiodine treatment, minimally invasive treatment under ultrasound guidance has emerged, as described below. Surgery is the best choice for invasive thyroid cancer, but the extent of debridement has been controversial. The main reasons for this controversy are the natural properties of thyroid cancer: slow growth and relative sensitivity to postoperative adjuvant therapy. The controversy is divided into two main schools of thought: one is to remove the entire mass and the invading tissue, including the defined margins of the operative area, when often many margins are unnecessary; the other school of thought is to remove the tumor by separating it from the laryngeal recurrent nerve, trachea and blood vessels and apply adjuvant therapy postoperatively. Although the first approach is more consistent with oncologic resection principles, the latter procedure will allow the patient to retain more neck function. Ultrasound-guided percutaneous anhydrous alcohol injection therapy Percutaneous anhydrous alcohol injection therapy has been used for many cancer treatments. In the case of the thyroid, for example, it is used for toxic goiters and thyroid cysts. In 2007, the Yonsei Medical Research Institute in Korea reported 16 patients with postoperative lymph node metastases from thyroid cancer who received ultrasound-guided transdermal anhydrous alcohol injection and were followed up for two years after surgery. All 16 patients underwent total thyroidectomy and lymph node dissection in the central region at the time of the first surgery, and postoperative I131 therapy and levothyroxine tablet suppression and replacement therapy were administered. These 16 patients presented with 24 metastases (8 in the thyroid and 16 in the lymph nodes), which were confirmed by fine needle penetration biopsy. An average of 1.1 ml of 99% alcohol was slowly injected into the masses under ultrasound localization until the echogenicity of the masses disappeared. We determined that treatment was effective if the swelling disappeared and no cancer cells could be detected by fine-needle puncture biopsy or if cancer cells could be detected but the swelling decreased in volume by >50% during subsequent follow-up. If the first injection was unsuccessful, the anhydrous alcohol injection could be repeated after a three-month interval, and multiple operations were performed in most of these 24 metastases (two treatments in 18 lesions, three treatments in two lesions, and four treatments in one lesion). During the 2-year follow-up, one patient developed a new metastasis, and after treatment with simple anhydrous alcohol injection, the size of the mass decreased from 16 mm to 2 mm, and the patient requested reoperation. After treatment with percutaneous anhydrous alcohol injection, all 16 patients developed temporary pain in the operative area, which disappeared 24 hours after surgery. Hoarseness was present in only 1 patient, but the voice returned to normal after 5 days. Ultrasound-guided percutaneous radiofrequency ablation Ablation has been successfully used for many years to treat metastatic liver cancer. Similar techniques include radiofrequency, cryopreservation, laser, microwave, and focused ultrasound, all of which are currently being used exploratively as minimally invasive clinical strategies for the treatment of postoperative metastatic lymph nodes in papillary thyroid cancer. Percutaneous radiofrequency ablation under local anesthesia has been used as an alternative option to surgery for patients with localized metastases after surgery for highly differentiated thyroid cancer. The treatment procedure involves ultrasound-guided three-dimensional localization of the tumor followed by percutaneous insertion of an ablation probe. Ablation therapy can be performed in the operating room or with mobile surgical equipment. The history of radiofrequency ablation techniques uses heat to destroy tissue. Radiofrequency energy is generated by varying the electrical current causing intercellular ion movement. An insulated 15-gauge probe is inserted into the tissue, which is composed of several forks that disperse once the probe reaches the proper location. The star-like distribution of the forks ensures a uniform distribution of heat. The current between the implanted electrode and the dorsal pad of the patient’s skin in vitro causes the movement of extracellular ions, which generates frictional heat. The hyperthermia leads to disruption of cell membrane fluids, cell electrophysiology, cytoskeletal protein structures and deoxyribonucleic acid, which in turn causes cell death. Although most tumors require 45-50°C for cell death, if the expected ablation field increases, temperatures higher than 50°C are required, and some literature reports the application of 90°C for 2 minutes for lymph nodes with postoperative metastases from thyroid cancer. In 2006, the Brown Institute of Medical Research reported 16 patients with postoperative local metastases of thyroid cancer treated with percutaneous radiofrequency ablation under local anesthesia. Twelve women and four men (age distribution 28-84 years, mean age 53 years) were included, and the mean diameter of all tumors was 17 mm (distribution was 8-40 mm). All 16 patients underwent fine needle biopsy to confirm that 15 of them were papillary carcinomas and 1 was a medullary carcinoma. The follow-up period after treatment ranged from 10 to 68 months, with a mean of 40.7 months. All patients were followed up with color Doppler and serum thyroglobulin testing, with additional serum calcium testing in patients with medullary carcinoma. Thirteen of these 16 patients had only 1 metastasis and all received 1 radioablation. Only 1 patient had a new metastasis behind the original metastasis after 10 months, and the patient refused reoperation, and the patient received anhydrous alcohol injection because of the location of the mass near the internal carotid artery. The other 3 patients received multiple radiofrequency ablation treatments because they were multiple metastases, and none of them developed new metastases during the follow-up. One patient developed hoarseness after radiofrequency ablation of metastatic lymph nodes in the central region, and although the hoarseness improved after 2 months, laryngoscopy showed paralysis of the right vocal cord. one patient developed a skin burn of approximately 5 mm at the entrance of the probe, which improved after 2 weeks. All 16 patients presented with self-limiting bleeding and regional discomfort in the operating area, but all resolved after 1 to 2 weeks. Particle implantation therapy Radioactive particle inter-tissue implantation internal irradiation is an emerging treatment for malignant tumors, which mainly applies computerized stereotactic planning system to implant radioactive particles according to the size and shape of the tumor into the tumor or into the tissues invaded by tumor infiltration under the guidance of modern imaging equipment, and emits continuous, short-distance radiation through a miniature radioactive source, so that the tumor tissues suffer the maximum degree of killing while The tumor tissues are killed to the maximum extent, while the normal tissues are not damaged or only slightly damaged. Based on the natural properties of highly differentiated thyroid cancer, which is less malignant and slower growing, I125 particle implantation is a promising treatment option. The study of Kunming Medical College reported that particles could also be implanted in the lymph node metastasis pathway during intraoperative resection of thyroid cancer to prevent postoperative recurrence, or when the surgical field adhesions were too severe to be resected, the implantation of particles was a remedial treatment, and no serious complications such as laryngeal nerve injury and avascular necrosis occurred after surgery. The experimental study of radiation damage to the common carotid artery in rabbits by I125 particle implantation by Guozhen Wei et al. suggested that three 0.5mCiI125 particles arranged continuously at 10mm intervals caused little radiation damage to the large blood vessels of rabbits and were safe for clinical use. as a very important therapeutic measure. The study pointed out that when solid tumor response rate was used as the evaluation standard, it appeared that the tumor was not absorbed after particle radiotherapy although necrosis occurred, or was accompanied by fibrosis, and the volume did not shrink or shrink significantly, which could not accurately reflect the therapeutic effect, and most scholars believe that it is more accurate to use PET-CT to evaluate the therapeutic effect. For metastatic thyroid cancer, we can also apply serum thyroglobulin to detect the therapeutic effect. Discussion Surgery is still the gold standard for the treatment of postoperative local metastases of thyroid cancer, but the difficulty and risk of surgery are greatly increased because the surgical area is reoperated and the tissue adhesions and scars are disturbed because of the first surgery. Traditionally, ultrasound is used to detect tumor recurrence. High-frequency ultrasound can detect lymph nodes with a maximum diameter of less than 10 mm, even though they are often located within the scar tissue of the original surgical area. These scar adhesions often lead to disorganization of the normal structures around the neck, which will make it difficult to completely remove the mass even when reoperation is performed. Therefore, reoperation often leads to a significant increase in the rate of surgical complications, and ultrasound-guided minimally invasive treatment has promising beginnings. Percutaneous radiofrequency ablation and percutaneous anhydrous alcohol injection also have their own advantages and disadvantages in the treatment of postoperative local metastasis of thyroid cancer. Radiofrequency ablation has greater killing efficacy than anhydrous alcohol injection and can cause more extensive damage to the swelling, and the energy of radiofrequency ablation can be regulated. This allows RF ablation to treat larger swellings than anhydrous alcohol injection. However, as the treatment energy increases, it can also lead to irreversible damage to the peripheral nerves in the operative area. Therefore, some scholars believe that radiofrequency ablation is more suitable for swellings larger than 10 mm in diameter and slightly distant from the nerve, while anhydrous alcohol injection treatment is suitable for swellings relatively close to the nerve and less than 10 mm in diameter. Therefore, the size and anatomical location of the mass are decisive factors in deciding whether to apply radiofrequency ablation or anhydrous alcohol injection as the first-line treatment.