Diagnosis: Cystic nodal metastasis from papillary thyroid carcinoma (PTC)
Papillary carcinoma accounts for 60% of all malignant neoplasms of the thyroid gland. It is usually seen in women (female-male ratio, 3:1) in the third or fourth decade of life. Because it preferentially spreads via the lymphatics, 50% of the patients with PTC have nodal metastasis at presentation.1 The primary tumor in the thyroid gland may often be small or even occult, with 20% of the patients having nodal metastasis as the sole or initial manifestation.2 In such instances, awareness of the lymphatic drainage from the thyroid gland is essential to identify the “occult primary.” The lymphatics drain superiorly from the thyroid gland along the superior thyroid vessels to the precricoid and upper and middle jugular nodes, laterally along the middle thyroid vein to the middle and lower jugular nodes, and inferiorly along the inferior thyroid vessels to the pretracheal, paratracheal, and lower jugular nodes.3 Less frequently, nodes in the posterior triangle, supraclavicular fossa, mediastinum, and contralateral side of the neck may also be involved. Submandibular and submental lymph node involvement is extremely rare. Clinical and anatomical reviews consider the central lymphatics to be the primary pathway for lymphatic drainage of thyroid carcinoma and the lateral neck nodes to be the secondary levels of lymphatic spread. More unusual, but still well documented, are lymphatic pathways to the retropharyngeal region that may cause retropharyngeal metastatic lymphadenopathy, with no intervening involvement of the jugular nodes. This pathway of lymphatic spread of PTC may account for the occasional metastases to the skull base.