Characteristics of lymph node metastasis in thyroid cancer

Thyroid cancer is a relatively common tumor, which poses a great threat to the patient's health. If thyroid cancer metastasizes, it may be through the lymph nodes. After surgery, pathological examination of the lymph nodes can reveal that 50% of metastases may occur. At this time, the primary disease must be actively treated to avoid causing greater harm to the patient's health and to avoid causing greater impact on the patient's life safety.

Papillary thyroid carcinoma is the most common type of thyroid cancer. Its main metastatic route is cervical lymph node metastasis, and hematogenous metastasis is rare. Follicular carcinoma rarely metastasizes to lymph nodes, but relatively more often metastasizes to blood. Both types of thyroid cancer generally have a long course of disease and good recovery after surgical treatment, and are well-differentiated thyroid cancers. Medullary carcinoma is rare, but cervical lymph node metastasis is more common. Poorly differentiated carcinoma is rare, highly malignant, and often metastasizes to lymph nodes and blood. The main cause of death is due to local lesions, accounting for 80%-86% of all thyroid deaths.

Characteristics of thyroid cancer lymph node metastasis: Thyroid cancer is often accompanied by ipsilateral cervical lymph node metastasis, and all areas of the neck except the chin area may be involved. The metastatic lymph nodes are mostly around the internal jugular vein. They can also metastasize to the posterior cervical triangle or to the mediastinal lymph nodes via the lymphatic vessels, and rarely to the submandibular area. Even for patients with negative cervical lymph nodes in clinical examination, 50% of the cervical lymph node specimens were still found to be metastatic after postoperative pathological examination. For those with palpable swollen lymph nodes clinically, postoperative pathological confirmation of cancer metastasis is basically 100%. Under normal circumstances, superficial cervical lymph nodes will not swell. Once they swell, especially the lymph nodes between the anterior cervical strap muscles and the sternocleidomastoid muscles, it means that there is retrograde metastasis of the lymphatic vessels. The cervical lymph node metastases can penetrate the lymph node capsule, fuse into masses, or invade adjacent blood vessels, nerves, and surrounding soft tissues. Contralateral lymph node metastasis occurs in approximately 4% of cases.

The relationship between the primary lesion and the cervical lymph node metastasis rate (1) generally occurs on the same side of the primary lesion. The more severe the thyroid cancer invasion, the greater the chance of metastasis. (2) The rates of cervical lymph node metastasis vary among different types of thyroid cancer (see figure). Papillary adenocarcinoma is prone to cervical lymph node metastasis, and follicular thyroid cancer is prone to hematogenous metastasis. (3) The lymph node metastasis rate is significantly increased when the tumor invades the capsule. (4) Patients whose tumor originates from the periphery of the thyroid gland have a higher rate of cervical lymph node metastasis. (5) Thyroid cancer of any size may metastasize. According to statistics from Ye Zhen et al., the metastasis rate is 85.7% when the diameter of cancer tissue is less than 1.0 cm, and 37% when the diameter is greater than 2.0 cm. However, there was no statistically significant difference between tumor size and cervical lymph node metastasis.

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