1. Symptoms
Most patients with thyroid nodules have no clinical symptoms. They are usually detected during physical examination by thyroid palpation and neck ultrasonography. Most thyroid nodules are benign, and malignant tumors account for about 5% to 10%. In combination with hyper- or hypothyroidism, the corresponding clinical manifestations may occur.
Benign thyroid nodules or malignant tumors may increase in size and may cause compression symptoms, often compressing the trachea and esophagus and displacing them. If malignant tumor locally invades the surrounding organ structures, symptoms such as hoarseness, dysphagia, hemoptysis and dyspnea may also appear. MTC tumor cells secrete active substances such as calcitonin and 5-hydroxytryptamine, which can cause symptoms such as diarrhea, palpitation and flushing.
2. Physical signs
The nodules are irregular in shape and fixed with surrounding tissues, and gradually increase in size, hard in texture and unclear in boundary. If the nodes are accompanied by lymph node metastasis in the neck, the lymph nodes in the neck may be enlarged by palpation. Compression or invasion of sympathetic nerve may cause Horner syndrome.
3. Invasion and metastasis
(1) Local invasion: Thyroid cancer can locally invade the recurrent laryngeal nerve, trachea, esophagus, cricoid cartilage and larynx, and even invade the prevertebral tissues, and laterally invade the internal jugular vein, vagus nerve or common carotid artery in the cervical sheath.
(2) Regional lymph node metastasis: PTC is prone to early regional lymphatic metastasis, and most of the patients with PTC already have cervical lymphatic metastasis at the time of diagnosis. lymph node metastasis of PTC is usually ipsilateral to the primary foci and follows the lymphatic drainage pathway station by station, and its lymphatic drainage is usually first to the paratracheal lymph nodes, then to the internal jugular vein lymph node chain (zone II-IV) and posterior jugular lymph nodes (zone V), or down the paratracheal to the superior mediastinum. The most common site of metastasis is zone VI, followed by zones III, IV, II and V. When lymph node metastasis occurs in the lateral cervical zone of PTC, it is mainly multi-zone metastasis, but only single-zone metastasis is rare. Lymphatic metastasis in zone I is rare (<3%). Rare lymph node metastasis sites include retropharyngeal/parapharyngeal, intraparotid, and axillary fossa.
(3) Distant metastasis: lung is the common distant metastasis organ of thyroid cancer, and metastasis to bone, liver and intracranial area can also occur. Follicular thyroid cancer, poorly differentiated thyroid cancer and undifferentiated cancer have a higher risk of distant metastasis.
4. Common complications
Most of the thyroid cancers are differentiated thyroid cancers with relatively slow growth and serious complications are rare. ATC may cause hoarseness, dyspnea and hemoptysis due to invasion of the laryngeal nerve, trachea and other peripheral organs, and may cause electrolyte disorders due to intractable diarrhea in MTC patients, or severe respiratory distress due to rapid progression of ATC.