the frequency of multifocal involvement of the thyroid gland in patients with ptc varies widely between 18% and 87% . multifocal disease is also common in papillary thyroid microcarcinoma being identified in 38% of the cases . multifocal involvement of the thyroid gland in patients with ptc is associated with poorer prognosis and increased risk of lymph node metastasis and distant metastasis [ 4 , 5 ] . there are several factors that increase the risk of contralateral disease in patients with ptc including large tumors , being above 45 years of age , and involvement of lymph node(s ) . thus , considering the tumor multifocality and especially bilaterality of papillary thyroid carcinoma ( ptc ) is important while selecting the most appropriate surgical procedure . the aim of this study was to assess the bilaterality rate in ptc and the relationship between the tumor size and bilaterality . thyroidectomy specimens with a diagnosis of ptc were retrospectively reviewed in the pathology department of a tertiary care medical center . bilateral involvement was defined as at least 1 tumor focus in the contralateral lobe of the primary tumor . total and completion thyroidectomy specimens were included in the study ; unilateral lobectomy , subtotal thyroidectomy , and near - total thyroidectomy specimens were excluded . specimens were divided into three groups according to the size of the primary and contralateral tumor foci . tumors less than or equal to 1  cm ( microcarcinoma ) in each lobe were included in group 1 . group 2 consisted of tumors greater than 1  cm in one lobe and less than 1  cm in the other lobe . we identified 868 total thyroidectomy specimens with a diagnosis of ptc between 2001 and 2011 . of these cases , both thyroid lobes were involved in 262 cases ( 32% ) . there were 109 ( 42% ) , 121 ( 46% ) , and 32 cases ( 12% ) in group 1 , group 2 , and group 3 , respectively . in group 1 , 46 cases had a tumor size less than or equal to 0.5  cm . .   found bilateral disease in 32% of the cases and reported the incidence of multicentric disease as 50% . evaluated tumor bilaterality in patients initially treated with partial thyroidectomy for ptc and found one or more foci of ptc at histology of completion thyroidectomy in 44% of the patients . the rate of bilateral tumor was not different when patients were analyzed according to the classification of low or high risk . grigsby et al .   investigated the rate of contralateral ptc and found that 41% of the patients had ptc in the contralateral lobe . there was no difference in the rate of contralateral disease in low - risk patients and there were no significant differences between patients with or without contralateral disease with respect to primary tumor size . pitt et al .   performed either completion or total thyroidectomy in 228 patients with ptc and evaluated contralateral tumor rates . they observed no differences in the rate of contralateral disease in patients with primary ptc with tumor size 1  cm compared with those having disease with tumor size < 1  cm . they found multifocality as the only factor predictive of contralateral ptc in patients with microcarcinoma . investigated the risk factors associated with papillary thyroid microcarcinoma ( ptmc ) involving the thyroid lobes bilaterally at the time of diagnosis and 20% of the patients had bilateral involvement . although the bilaterality was frequent in case of multifocality , tumor size was not a predictive factor . zhou et al .   performed total thyroidectomy in 211 ptmc patients and reported multifocality and tumor size 7  mm as independent predictive factors for bilaterality . according to the american thyroid association guideline , thyroid lobectomy is recommended for patients with thyroid cancer with tumor size < 1  cm . the guideline also recommends bilateral or a unilateral procedure for patients with thyroid cancer with tumor sizes > 1  cm and < 4  cm without extrathyroidal extension and without clinical evidence of any lymph node metastases . however , we demonstrated that approximately one - third of the ptcs involve both thyroid lobes . among cases with bilateral involvement , 42% had tumor size less than or equal to 1  cm in each lobe . only 12% of the bilateral cases had a tumor size greater than 1  cm . these findings suggest that bilateral involvement is not associated with tumor size and even ptcs with tumor size less than 0.5 cm may show bilaterality .
background . tumor multifocality and bilaterality of papillary thyroid carcinoma ( ptc ) are important factors when selecting the most appropriate surgical procedure . 
 the aim of this study was to assess the bilaterality rate in ptc and the relationship between the tumor size and bilaterality . 
 materials and methods . 
 thyroidectomy specimens with a diagnosis of ptc were retrospectively reviewed in the pathology department of a tertiary care medical center . 
 specimens were divided into three groups according to the size of the primary and contralateral tumor foci . 
 tumors less than or equal to 1  cm in each lobe were included in group 1 . 
 group 2 consisted of tumors greater than 1  cm in one lobe and less than 1  cm in the other lobe . 
 tumors greater than 1  cm in each lobe were included in group 3 . results . 
 we identified 868 total thyroidectomy specimens with a diagnosis of ptc between 2001 and 2011 . 
 of these cases , both thyroid lobes were involved in 262 cases ( 32% ) . 
 there were 109 ( 42% ) , 121 ( 46% ) , and 32 cases ( 12% ) in group 1 , group 2 , and group 3 , respectively . 
 conclusion . 
 bilaterality is frequent in ptc and is not related to tumor size . 
 accordingly , the high frequency of bilateral disease in ptc should be kept in mind when determining the extent of the surgical procedure .