Predictive Factors for Incidental Contralateral Carcinoma in Patients with Unilateral Micropapillary Thyroid Carcinoma

Background: Whether thyroid lobectomy alone is a sufficient treatment for papillary thyroid microcarcinoma (PTMC) remains controversial. The aim of this study is to evaluate the predictive factors for incidental contralateral carcinoma in patients confirmed of unilateral PTMC preoperatively. Methods: Between January 2007 and December 2009, 393 patients underwent thyroid surgery for unifocal and unilateral PTMC preoperatively at Pusan National University Hospital. A total thyroidectomy with central neck dissection was routinely performed for these patients during this study period. Results: Among the 393 cases in the cohort, 77 patients (19.6%) had incidental PTMC in the contralateral lobe. In patients with incidental contralateral carcinoma, there was higher prevalence in extrathyroid extension, occult ipsilateral carcinoma, pathologic Hashimoto's thyroiditis, and central lymph node metastasis compared to those without contralateral carcinoma. The mean tumor size also increased in patients with contralateral carcinoma. Multivariate logistic regression showed that extrathyroid extension (P = 0.049), occult ipsilateral carcinoma (P < 0.001), pathologic Hashimoto's thyroiditis (P = 0.038), and central lymph node metastasis (P = 0.002) were predictive factors for incidental contralateral carcinoma. Conclusion: In conclusion, multifocality in the ipsilateral lobe, central lymph node metastasis, extrathyroid extension, and Hashimoto's thyroiditis is associated with the presence of contralateral carcinoma. Thus, if these factors are found by preoperative and/or postoperative evaluation, total thyroidectomy or completion thyroidectomy is necessary for the treatment of PTMC.