To compare the clinical and sonographic characteristics of aggressive and nonaggressive papillary thyroid microcarcinomas (PTMC) in order to improve the preoperative predictive value of aggressive PTMC.

A total of 309 patients with PTMC from January 2014 to December 2016 were included in this study. Patients with lymphatic metastasis, extrathyroidal invasion, reccurence, distant metastasis and death were classified into aggressive PTMC group, and patients without above characteristics were classified into nonaggressive group. Clinical and sonographic features were reviewed and compared between the two groups.

Among the 309 patients, 76 cases (24.6%) were aggressive PTMC, and 233 cases (75.4%) were nonaggressive. Patients were younger and larger cancerous nodules, microcalcification, capsular inconnection and multifocality were seen more frequently in aggressive PTMC group compared with nonaggressive group. The best cut-off value of age and diameter were 44.5 years and 0.66 cm respectively. Advanced age was the protective factor and larger tumor size and multifocality were independent risk factors for PTMC aggressiveness. The capsular invasion was related with the lateral cervical lymph node metastasis while other features were not.

Extra attention should be paid to patients with age<44.5 years, tumor size>0.66 cm and multifocal cancerous nodules because their PTMCs are more likely to be aggressive. Thyroid capsule adjacent to the cancerous nodule should be observed carefully. If there is interruption in the capsule, lateral cervical lymph nodes should be carefully examed.

Ultrasonography; Papillary thyroid microcarcinomas; Aggressiveness; Clinical characteristics