O. Brown1, J. Miller1, N. Al-Attar1, G. Shaughness1, N. Rosculet1, A. Avram1, D. Hughes1 1University Of Michigan,Ann Arbor, MI, USA
Introduction: Differentiated thyroid cancer (DTC) is treated with thyroidectomy and removal of malignant lymph nodes identified preoperatively. Despite attempts to resect regional metastatic disease, residual malignant lymph nodes are often found on diagnostic and/or post-therapy radioiodine scans at the time of radioactive iodine treatment. The objective of this study is to identify the most common locations of and reasons for residual lymph node metastases following initial surgical treatment of DTC.
Methods: In this retrospective study, we reviewed the charts of 352 patients with high-risk DTC treated at the University of Michigan from 2007 to 2014. Postoperatively, all patients underwent pre-ablation 131-Iodine scans with SPECT/CT. The laterality of the primary tumor and the presence and location of nodal metastases were noted. We compared the location of the nodal metastases with cervical lymph node levels that were dissected to determine the reason for residual nodal metastases (incomplete node dissection vs. omission of node dissection in that compartment due to failure to identify nodal involvement preoperatively).
Results: A total of 146/352 (41.48%) patients with high-risk DTC were found to have residual lymph node metastases on diagnostic 131-I SPECT/CT following initial surgical treatment. These 146 patients had a combined total of 218 nodal metastases. Relative to the primary tumor, 71.56% (n=156) were ipsilateral, 22.02% (n=48) were contralateral, and 6.42% (n=14) were undefined, meaning they were classified as central neck (level VI/VII) without a designation of laterality. Cervical lymph node levels VI, III, and II were found to have the greatest frequencies of residual metastases, with 33.94% (n=74), 22.94% (n=50), 18.81% (n=41), respectively. Levels I and V had the lowest frequencies of metastases, with 0.46% (n=1) and 0.00% (n=0), respectively. Residual metastases occurred because of an incomplete lymph node dissection in 72 patients (49.32%), a missed diagnosis in 55 patients (37.67%), or a combination of the two in 19 patients (13.01%).
Conclusion: The surgical management of high-risk DTC should include complete nodal dissection in all involved compartments. Particular attention should be given to complete dissection in levels VI, III, and II, especially ipsilateral to the primary tumor, as these are prevalent areas of residual nodal metastasis. Efforts to improve pre-operative diagnostic techniques and to refine lymph node dissection practices may reduce the incidence of residual nodal metastasis.
