The clinical impact of minimal extrathyroidal extension (ETE) in patients with conventional papillary thyroid microcarcinoma (PTMC) is still controversial. The clinicopathologic characteristics of patients with or without minimal ETE or recurrence and the clinical impact of minimal ETE were investigated.

This study included 288 patients with conventional PTMC (mean age, 46.6 years; 262 female and 26 male subjects) and more than 5 years of follow-up. Patients were divided into two groups according to ETE and recurrence, and clinicopathologic characteristics between two groups were investigated. Disease-free survival was calculated to compare the clinical impact of minimal ETE between patients with and without ETE.

Mean size (6.9 mm) of PTMCs in patients with minimal ETE (n = 89) was significantly larger than that in those (5.8 mm) without (n = 199) (P < 0.001). Tumor size [odds ratio (OR) = 1.185; 95% confidence interval (CI) 1.052–1.334], central lymph node (LN) metastasis at diagnosis (OR 2.105; 95% CI 1.182–3.750), and not well-defined margin on ultrasound (OR 3.808; 95% CI 1.055–13.736) were significantly associated with minimal ETE. Twelve patients (4.2%) had recurrence. No clinicopathologic factor was associated with recurrence. Disease-free survival was not significantly different between patients with and without minimal ETE (P = 0.671).

Minimal ETE was statistically significantly associated with tumor size, central LN metastasis, and not well-defined margin on ultrasound. Minimal ETE had no impact on recurrence in patients with conventional PTMC.