Prediction of mediastinal lymph node metastasis in medullary thyroid carcinoma

Background: Mediastinal lymph node metastases can be life threatening owing to their proximity to vital organs. Reliable identification of mediastinal metastasis is of utmost importance for timely mediastinal lymph node dissection, although suitable clinicopathological variables for their detection in patients with thyroid cancer have yet to be identified. Methods: This was an analysis of 83 consecutive patients with radiological suspicion of mediastinal metastasis who underwent trans-sternal mediastinal lymph node dissection for node-positive medullary thyroid carcinoma between November 1994 and March 2003. Results: Univariate analysis revealed that extrathyroidal extension (P < 0.001), distant metastasis (P 0.001), the preoperative serum calcitonin level (P = 0.001), operation type (P = 0-004), contralateral cervicolateral metastasis (P = 0.016) and bilateral nodal metastasis (P = 0.031) were significantly associated with mediastinal involvement. Only extrathyroidal extension remained significant in a multivariate logistic regression analysis of mediastinal lymph node metastasis. Prediction of mediastinal metastasis by extrathyroidal extension was best at reoperation, with a specificity of 97 per cent and a positive predictive value of 88 per cent. Conclusion: Mediastinal lymph node dissection should be considered in patients undergoing reoperation for node-positive medullary thyroid carcinoma who have extrathyroidal extension and cervical lymph node metastases.