Incidental and non-incidental thyroid microcarcinoma.

There is no clear therapeutic approach for thyroid microcarcinoma (TMC). This may be as a consequence of recent observations that have reported biologically different types of TMC, which should be treated differently. The objective of the present study was to compare incidental TMC (ITMC) and non-incidental TMC (NITMC) in order to assess the differences in the incidence, diagnostic results, clinicopathological characteristics and surgical treatment. The study consisted of a retrospective chart review of 3,218 patients consecutively admitted and surgically treated in a single institution due to thyroid pathology. A total of 246 (7.64%) patients presented with a thyroid malignancy, and 97 (39.43%) of these individuals were diagnosed with TMC; 37 (38.14%) patients exhibited ITMC and 60 (61.86%) exhibited NITMC. All 37 (100.00%) patients with ITMC exhibited a papillary type of cancer. In the NITMC group, 1 (1.67%) patient presented with follicular microcarcinoma, 1 (1.67%) individual with papillary- and follicular-type microcarcinoma, 1 (1.67%) individual with medullary microcarcinoma, and the remaining 57 (95.00%) patients presented with papillary microcarcinoma. The number of younger patients (<45 years old) was higher in the NITMC group, but this difference was not significant (P=0.205). In all patients with ITMC, ultrasound-guided fine-needle aspiration biopsy did not reveal malignant processes. In the NITMC group, the number of larger tumors (>5 mm) was significantly higher compared with that in the ITMC group (P<0.001). ITMC was significantly associated with multinodular goiter (MNG) (P<0.001). Amongst the NITMC group, 18.33% of patients presented with cervical lymph node involvement (P<0.001). Overall, the incidence of TMC is high, and consists of ITMC and NITMC, although the prevalence of NITMC is higher than that of ITMC. The majority of ITMCs and NITMCs are composed of a papillary type of cancer. The majority of ITMCs have dimensions ≤5 mm in diameter and are significantly associated with MNG. In comparison with ITMC, NITMC more often presents with aggressive features such as cervical lymph node metastases, so the surgical approach to this tumor should be more radical.