Elucidating mechanisms of recurrent laryngeal nerve injury during thyroidectomy and parathyroidectomy

BACKGROUND: Intraoperative nerve monitoring during thyroidectomy, parathyroidectomy, or related central neck procedures can elucidate actual or potential mechanisms of recurrent laryngeal nerve (RLN) injury, especially visually intact nerves, which were previously unknown to the endocrine surgeon. STUDY DESIGN: In this prospective evaluation study, 373 patients underwent 380 consecutive thyroidectomy- or parathyroidectomy-related operations using intraoperative nerve monitoring, with 666 RLNs at risk. The success of visual and functional identification of the RLN, persistent loss of RLN function to nerve stimulation, the mechanism and location of RLN injury, and anatomy of the RLN or technical difficulties that appeared potentially risky for RLN injury were recorded. RESULTS: RLN was identified visually or functionally in 98.2% of nerves at risk. Initial intraoperative injury to the RLN occurred in 25 nerves at risk (3.75%). It was significantly more likely to be a visually intact RLN (n = 22; 3.3%) than a transected RLN (n = 3; 0.45%), p < 0.001. Paralysis persisted in 2 RLNs (0.3%). Visual misidentification accounted for only 1 RLN injury; the most common cause of injury resulted from traction to the anterior motor branch of a bifurcated RLN near the ligament of Berry (n = 7; 28%), then paratracheal lymph node dissection (n = 6; 24%), incorporating ligature (n = 4; 16%), and adherent cancer (n = 4; 16%). Fifty nerves at risk (7.5%) were identified as particularly at risk for injury, most notably those with anatomic variants (n = 26; 52%) and large or vascular thyroid lobes (n = 19; 38%). CONCLUSIONS: RLN injury during thyroidectomy or parathyroidectomy occurs intraoperatively significantly more often to a visually intact RLN than to a transected nerve. The anterior motor branch of an RLN bifurcating near the ligament of Berry is particularly at risk of traction injury.