Incidental papillary thyroid microcarcinoma in consecutive patients undergoing thyroid surgery for benign disease. A single center experience.

BACKGROUND: There has recently been an increase in the incidental histological diagnosis of papillary thyroid microcarcinoma (I-PTMC), that varies from 3.5% in autopsies studies, to 5.2% in thyroid specimens from thyroid surgery, up to 9.4% in patients from areas of endemic goiter. AIM: To evaluate the incidence and the histological characteristics of I-PTMC in patients undergoing thyroidectomy for benign thyroid diseases, and to evaluate sex, age, toxic and non-toxic goiter, Hashimoto's thyroiditis as potential risk factors. MATERIALS AND METHODS: Prospective observational study on 124 patients, median age 56.3 +/- 13.25sd range 24-80 years, 93(75%)F, 31(25%)M, with surgical indications for toxic and non-toxic uni/multinodular goiters, in pharmacological euthyroidism. An accurate histological examination (HE) of entirely embedding thyroid samples was performed to identify microscopic foci of I-PTCM. Logistic regression analysis of the abovementioned parameters was performed to identify the risk factors. RESULTS: Total incidence of I-PTMC was 15.3%(19/124), with F/M ratio 2:1. All I-PTMCs were intraparenchymal with an intact thyroid capsule; 68.5% were bilateral-multifocal, 21% unilateral-unifocal, 10.5% unilateral-multifocal; maximum diameter was <5mm in 57.9% and >= 5mm in 42.1%; 63.1% were follicular variant, 36.9% classical variant; intra-thyroid lymphatic invasion and lymph node infiltration of the central compartment and para-tracheal was found in the only patient with "tall-cell" classical variant. No risk factors was found. CONCLUSIONS: The incidence higher than that reported in the literature, is probably due to the accurate HE of entirely embedding thyroid samples, which is the most important tool to identify microscopic foci of I-PTCM. The highest reported rate of bilateral multifocality of the neoplasm recommend the total thyroidectomy as surgical treatment of choice, also in patients undergoing thyroid surgery for "presumptive" benign diseases.