A practical description of the lymphatic drainage of the thyroid gland for the thyroid surgeon has been proposed by Taylor (12). The results of his studies, which are clinically very relevant to the lymphatic spread of thyroid carcinoma, are summarized in the following:
The most constant site to which dye goes when injected into the thyroid is the trachea, the wall of which contains a rich network of lymphatics. This fact probably accounts for the frequency with which the trachea is involved by thyroid carcinoma, especially when it is anaplastic. This involvement is sometimes the limiting factor in surgical excision.
A chain of lymph nodes lies in the groove between the trachea and the esophagus.
Lymph can always be shown to drain toward the mediastinum and to the nodes intimately associated with the thymus.
One or more nodes lying above the isthmus, and therefore in front of the larynx, are sometimes involved. These nodes have been called the Delphian nodes (named for the oracle of Delphi) because it has been said that, if palpable, they are diagnostic of carcinoma. However, this clinical sign is often misleading.
Central lymph node dissection clears out all these lymph nodes from one carotid artery to the other carotid artery and down into the superior mediastinum as far as possible.
A constant group of nodes lies along the jugular vein on each side of the neck. The lymph glands found in the supraclavicular fossae may also be involved in more distant spread of malignant disease from the thyroid gland. Finally, it should not be forgotten that the thoracic duct on the left side of the neck, a lymph vessel of considerable size, arches up out of the mediastinum and passes forward and laterally to drain into the left subclavian vein, usually just lateral to its junction with the internal jugular vein. If the thoracic duct is damaged, the wound is likely to fill with lymph; in such cases, the duct should always be sought and tied. A wound that discharges lymph postoperatively should always raise suspicion of damage to the thoracic duct or a major tributary. A lateral lymph node dissection encompasses removal of these lateral lymph nodes. Rarely, the submental nodes are involved by metastatic thyroid cancer as well.