Clinicopathological features of papillary thyroid microcarcinoma with a diameter less than or equal to 5 mm

This retrospective study was conducted to assess the epidemiological, clinical and histologic characteristics of incidentally identified and presurgically diagnosed papillary thyroid microcarcinomas less than or equal to 5 mm in size (small PTMC).

Cases from October 2003 to February 2018 were retrieved from pathology databases, and their clinicopathological features were reviewed.

There were a total of 182 cases of small PTMCs, 141 women and 41 men. The mean age at diagnosis was 53.5. Most of the small PTMCs were not detected on clinical examination and workup and were diagnosed incidentally during pathologic examination. 21.4% of small PTMCs showed multifocality, with 21 cases of unilateral multifocal lesions and 18 cases with bilateral multifocal tumors. Small PTMCs were most often follicular variant (51.9%) followed by classic type (47.5%). The average size of follicular variants appeared to be larger than that of the classic type PTMCs (2.84 ± 1.43 mm vs 2.26 ± 1.51 mm, P = 0.01). A total of 66 cases (36.3%) had regional lymph node sampling or selective neck dissection and 15 of these cases identified lymph node metastasis (22.7%). 46.7% of patients with node positive microcarcinomas were male compared with 16% male in group with negative lymph nodes (P = 0.03).

Small PTMCs (≤5 mm) are often multifocal and bilateral and histology is commonly both the classical and follicular variant of PTC. While often diagnosed incidentally small PTMC can lead to regional lymph node involvement in a significant portion of cases and evaluation of the regional lymph nodes should be considered in the clinical management of these patients.