Revisiting Low-Risk Thyroid Papillary Microcarcinomas Resected Without Observation: Was Immediate Surgery Necessary?

Low-risk thyroid papillary microcarcinomas (PMCs) without evidence of metastasis grow slowly if at all. However, we recommended surgery for tumors touching the trachea (TR) or located in the course of the recurrent laryngeal nerve (RN). Here we compared the cases of low-risk PMC patients who underwent immediate surgery to cases of TR- and RN-involved PMCs.

We enrolled 1143 low-risk PMC patients who underwent immediate surgery in the years 2006-2014. The PMCs of 437 patients touched the TR on imaging studies: 270, 104, and 63 were graded as low, intermediate, and high risk, respectively, for TR invasion based on the angles between the tumor and the TR surface. The tumor was in the course of the RN in 144 patients, with 35 graded low risk and 109 high risk for RN invasion based on the normal rim of the thyroid in the direction of the RN.

Invasion of the TR cartilage was observed only in high-risk patients. Peritracheal connective tissue was resected in 21, 15, and 6 of the high-, intermediate- and low-risk patients, respectively. Significant invasion of the RN requiring complete resection was observed in only nine patients at high risk for RN invasion. The incidence of TR invasion in high- and intermediate patients and the incidence of RN invasion in the high-risk patients were significantly higher than those of the low-risk patients. Tumors <7 mm did not show TR or RN invasion.

Among PMCs that touched the TR or were located in the course of the RN, observation could be the first choice for tumors < 7 mm and those ≥ 7 mm judged as low risk for TR or RN invasion. However, for PMCs with high-risk features, immediate surgery after cytological diagnosis by a needle aspiration biopsy is recommended.