Clinical impact of microscopic extrathyroidal extension in patients with papillary thyroid microcarcinoma treated with hemithyroidectomy

Background: Pathologically confirmed microscopic extrathyroidal extension (ETE) is often identified after hemithyroidectomy in patients with papillary thyroid microcarcinoma (PTMC). Without the presence of microscopic ETE, these patients would be optimal candidates for hemithyroidectomy. Aim: The present study aimed at evaluating the clinical impact of microscopic ETE on the recurrence of PTMC treated with hemithyroidectomy. Subjects and methods: We compared the clinicopathological characteristics and 5-year outcomes for 262 PTMC patients without ETE and 86 with microscopic ETE who were treated with hemithyroidectomy between January 2004 and December 2010. Results: The mean tumour size was larger (0.67 vs. 0.54 cm, p < 0.001) and the proportion of tumours measuring ≥0.5 cm was higher (84.9 vs. 66.8%, p = 0.001) in patients with microscopic ETE as compared with patients without ETE. Occult multifocal disease was more frequent in patients with microscopic ETE than in those without ETE (14.0 vs. 6.5%, p = 0.030). However, the recurrence rate was not different between the two groups during the mean 55.8-month follow-up period. In addition, univariate and multivariate analyses revealed no meaningful association between recurrence and microscopic ETE in patients with PTMC treated with hemithyroidectomy. Conclusions: Although microscopic ETE was associated with large tumour size and multifocal disease, its clinical impact on disease recurrence was not significant in PTMC patients treated with hemithyroidectomy. Therefore, microscopic ETE identified after hemithyroidectomy would not be an absolute indication for completion thyroidectomy in patients with PTMC.