External laryngeal nerve in thyroid surgery: is the nerve stimulator necessary?

OBJECTIVE: To find out the incidence and type of external laryngeal nerves during operations on the thyroid, and to assess the role of a nerve stimulator in detecting them.
DESIGN: Prospective, non-randomised study.
SETTING: Teaching hospital, Malaysia.
SUBJECTS: 317 patients who had 447 dissections between early January 1998 and late November 1999.
MAIN OUTCOME MEASURES:
Number and type of nerves crossing the cricothyroid space, and the usefulness of the nerve stimulator in finding them.
RESULTS: The nerve stimulator was used in 206/447 dissections (46%). 392 external laryngeal nerves were seen (88%), of which 196/206 (95%) were detected with the stimulator. However, without the stimulator 196 nerves were detected out of 241 dissections (81%). The stimulator detected 47 (23%) Type I nerves (nerve > 1 cm from the upper edge of superior pole); 86 (42%) Type IIa nerves (nerve < 1 cm from the upper edge of superior pole); and 63 (31%) Type IIb nerves (nerve below upper edge of superior pole). 10 nerves were not detected. When the stimulator was not used the corresponding figures were 32 (13%), 113 (47%), and 51 (21%), and 45 nerves were not seen. If the nerve cannot be found we recommend dissection of capsule close to the medial border of the upper pole of the thyroid to avoid injury to the nerve.
CONCLUSION: Although the use of the nerve stimulator seems desirable, it confers no added advantage in finding the nerve. In the event of uncertainty about whether a structure is the nerve, the stimulator may help to confirm it. However, exposure of the cricothyroid space is most important for good exposure in searching for the external laryngeal nerve.