Prediction of lateral lymph node metastases in medullary thyroid cancer.

Background: In medullary thyroid cancer (MTC), there is a concordance between central and lateral neck involvement, but this relationship has not been assessed quantitatively.

Methods: After compartment-oriented lymphadenectomy for untreated MTC, the numbers of central lymph node metastases with ipsilateral (195 patients) and contralateral (185 of 195 patients) lateral lymph node metastases were analysed retrospectively.

Results: With one to three positive central lymph nodes, involvement of the ipsilateral lateral neck increased from 10.1 per cent (with no central node involvement) to 77 per cent, and from a mean of 0.6 to 3.7 nodal metastases (P < 0.001). With four or more central nodes, the rate was 98 per cent, with 10.7 nodal metastases (P = 0.001). A weaker increase was observed in the contralateral lateral neck: with one to nine positive central nodes, contralateral lateral neck involvement increased from 4.9 to 38 per cent, and from a mean of 0.6 to 2.3 nodal metastases (P = 0.011). With ten or more positive central nodes, the rate rose to 77 per cent, with 6.2 nodal metastases (P = 0.009). With one exception, contralateral lateral nodal metastases coexisted with metastases in the central and ipsilateral lateral neck.

Conclusions: These data may lay the groundwork for more informed decision-making regarding dissection of the lateral neck compartments.