Background: When surgeons decide to perform lobectomy as the treatment of papillary thyroid carcinomas (PTCs), they must consider the possibility of contralateral cancer. We wanted to determine the incidence of bilateral PTCs (bPTCs) and analyze their characteristics. We also wanted to determine how many patients with bPTC were missed preoperatively.
Methods: From January 2007 to May 2011, a total of 466 patients with PTC who were treated by total thyroidectomy at a single institution were enrolled. Patients were divided into two groups based on bilaterality. The patients with bPTCs were further investigated regarding the preoperative presence of the contralateral tumor.
Results: Bilaterality was seen in 29.8 % of PTC patients. In all, 36.8 % of PTCs ≥ 1 cm, and 25.7 % were papillary thyroid microcarcinomas (PTMCs). The presence of PTC in the contralateral lobe was missed in 15.8 % of bPTCs and in 21.3 % of bPTMCs. The rates of preoperatively nondetected contralateral cancer were 4.7 and 5.5 % for PTCs and PTMCs, respectively. Tumor size and multifocality were factors associated with bilaterality (p = 0.014 and p < 0.001, respectively).
Conclusions: Bilaterality is found more frequently when the tumor is large. Multifocality also can help predict the possibility of bilaterality. Therefore, total thyroidectomy may be necessary for patients with a multifocal or large tumor. It should be noted that the presence of a contralateral cancer is missed in 4.7 and 5.5 % of patients with preoperatively diagnosed unilateral PTC and PTMC, respectively.