Invasion of a Recurrent Laryngeal Nerve from Small, Well-Differentiated Papillary Thyroid Cancers: Patient Selection Implications for Active Surveillance.

Background: The success of an active surveillance management approach to low-risk papillary thyroid cancer (PTC) is heavily dependent on proper patient selection. For example, primary tumors located in a subcapsular position immediately adjacent to the trachea or a recurrent laryngeal nerve (RLN) are considered to be inappropriate for active surveillance. Since pre-operative imaging cannot reliably rule out extrathyroidal extension or reveal the full course of the RLN relative to the thyroid gland, it is important for clinicians to understand subcapsular tumor locations and minimum tumor sizes that are most likely to be associated with gross invasion of the RLNs. Methods: We assessed the medical records of 123 patients treated at Memorial Sloan Kettering Cancer Center (MSK) between 1986 and 2015 who had a primary PTC tumor demonstrating gross extrathyroidal extension to either the right or left RLN. Thirty patients with a primary tumor ≤2 cm in diameter demonstrating extrathyroidal extension into an RLN were included in the analysis. Results: Gross invasion of an RLN by tumors ≤2 cm is a rare event that was seen in only 0.8% (35/4,334) of patients with PTC who underwent initial thyroid surgery at MSK between 1986 and 2015. Gross RLN invasion was associated with subcapsular PTC tumors located in either the right paratracheal area (60%), left paratracheal area (36.7%), or right lateral posterior lobe area not adjacent to the trachea (3.3%). Only a quarter of the patients had imaging findings suggestive of extrathyroidal extension and only 30% had clinically apparent vocal paresis/paralysis on pre-operative examination. Invasion of the RLN was not observed for primary tumors <0.9 cm in diameter, regardless of tumor location. Conclusions: Well-differentiated PTC tumors ≥0.9 cm in maximal diameter which are located in the right paratracheal, left paratracheal, and right lateral posterior lobe subcapsular positions are usually not appropriate for active surveillance even in the absence of definitive evidence for nerve invasion on pre-operative imaging or vocal cord examination. Patient selection for active surveillance management should take into account not only the size and growth rate of a tumor but also its location in relation to the expected course of RLNs.