Occult Contralateral Lateral Lymph Node Metastases in Unilateral N1b Papillary Thyroid Carcinoma.

Therapeutic lateral neck dissection (ND) is recommended for N1b papillary thyroid carcinoma (PTC), while prophylactic contralateral lateral ND is not. Given the paucity of data, we investigated the frequency of and risk factors for occult lymph node metastases (LNM) in the contralateral lateral neck for N1b patients. This is a retrospective study conducted at a cancer center. Inclusion criteria were: unilateral PTC and ipsilateral lateral LNM confirmed by fine-needle aspiration biopsy. Patients with contralateral lateral LNM or bilateral tumor on ultrasound were excluded. All patients were treated with total thyroidectomy, bilateral central ND, ipsilateral therapeutic lateral ND and prophylactic contralateral ND of levels III-IV, followed by radioactive iodine. Sixty-three patients met the inclusion criteria. Occult contralateral lateral LNM were found in 23/63 patients (36.5%) who had more LNM in ispilateral (p = .01) and contralateral level VI (p < .0001), more frequent microscopic tumor in the contralateral lobe (p = .017) and a trend toward being at high risk (p = .06). Using receiver operating characteristic analysis, a cutoff of >4 LNM in ipsilateral level VI optimized sensitivity and specificity for predicting contralateral lateral LNM, with a sensitivity of 74%, specificity of 65%, positive predictive value of 55% and negative predictive value of 81%. Neck recurrence occurred in 14%, with only 1 patient recurring only in the contralateral lateral neck (1.5%). Occult LNM in the contralateral lateral neck was found in 36.5% of patients. Five or more ipsilateral central LNM may aid in predicting contralateral lateral LNM, and high-risk patients may be more at risk. The clinical benefit of prophylactic contralateral lateral ND remains doubtful, however.