What is the incidence of lymph node metastases in differentiated thyroid cancer (DTC), and when is a neck dissection indicated?
DTC (predominantly papillary) involves cervical lymph nodes in 30% to 80% of cases. In the majority of cases, the metastatic nodes are not clinically evident; therefore, all patients should undergo preoperative full-neck ultrasonography to assess for abnormal nodes. Unlike many other malignancies, the presence of occult lymph node metastases does not worsen the outcome for most patients with differentiated thyroid cancer, and routine neck dissection does not clearly improve outcomes except for patients in the high-risk group. Moreover, neck dissection may increase the risk of complications. For these reasons, the decision to perform a prophylactic neck dissection for differentiated thyroid cancer is somewhat controversial. The following are some general guidelines:
• All patients with clinically palpable nodes require a compartment (central and/or lateral) dissection at the same time as thyroidectomy.
• Any suspicious nodes on preoperative ultrasonography should be subjected to FNA and, if positive, should be removed via formal neck dissection as above.
• Physical examination, ultrasonography, and intraoperative assessment are not sensitive in detecting nodal metastases in the central neck. It has been debated whether a prophylactic central neck dissection at the time of thyroidectomy is indicated for papillary carcinoma. The current American Thyroid Association (ATA) Guidelines Task Force state that prophylactic central neck dissection may be indicated in patients with advanced tumors (> 4 cm and/or grossly invasive) or if there are known lateral nodal or distant metastases. Thyroidectomy alone may be appropriate for noninvasive tumors < 4 cm.