The authors analyzed the characteristics of papillary thyroid microcarcinomas less than 0.5 cm in diameter to investigate an optimal extent of surgical resection.

Between October 1994 and October 2003, out of 635 cases of papillary thyroid microcarcinomas, 229 cases less than 0.5 cm in diameter were reviewed retrospectively to analyze their clinical and pathological characteristics.

Mean diameter of the carcinomas was 3.9±1.2 mm for carcinomas less than 0.5 cm in diameter (group 1) and 7.7±1.4 mm for carcinomas between 0.5 and 1.0 cm in diameter (group 2). Total thyroidectomy, subtotal thyroidectomy, lobectomy & isthmectomy in group 2 were carried out in 308 (75.9%), 72 (17.7%) and 26 (6.4%) cases. Follow by group 1 were carried out in 109 (47.6%), 84 (36.7%) and 36 (16.7%)cases respectively. Between the two groups, perithyroidal invasion was 29.3% and 49.0%, multifocality was 24.9% and 32.8%, bilaterality was 13.1% and 21.4%, lymph node metastasis was 10.1% and 18.3% respectively with each data showing statistical significance (P<0.05). Completion thyroidectomy was carried out in 14 cases, of which 8 cases revealed carcinomas in the residual thyroid lobe. The group 1 required completion thyroidectomy more than the group 2 (P=0.026). There were less cases of lymph node metastasis among the group 1. Nine out of the 36 cases (25%) of the group 1 which underwent lobectomy & isthmectomy needed completion thyroidectomy, among them 6 cases (66.7%) revealed papillary carcinoma in the residual thyroid lobe.

Micropapillary cancer was discovered more frequently by increasing the use of ultrasonography. Multifocality, bilateraluty and perithyroidal invasion were observed higher in group 2 rather than group 1. However, the relation between these facts and prognosis will need long term follow up.