Contribution of intraoperative neural monitoring to preservation
of the external branch of the superior laryngeal nerve:
a randomized prospective clinical trial
Received: 17 June 2016 /Accepted: 16 December 2016 /Published online: 29 December 2016
Springer-Verlag Berlin Heidelberg 2016
Purpose The purpose of this study was to evaluate the effect
of intraoperative neuromonitoring (IONM) on the injury rate
of the external branch of the superior laryngeal nerve
(EBSLN) during thyroidectomy.
Methods A total of 133 consenting patients (98 female, 35
male; mean age, 45.6 ± 11.7 years) undergoing thyroidectomy
were randomly assigned to 2 groups. In group 1 (n =65pa-
tients, 105 nerves), superior thyroid pole dissection was per-
formed with no attempt to identify the EBSLN; in group 2
(n = 68 patients, 106 nerves), IONM was used to identify the
EBSLN during surgery. EBSLN function was evaluated by
intraoperative electromyography of the cricothyroid muscle.
The EBSLN Voice Impairment Index-5 (VII-5) was conduct-
ed preoperatively and at 1, 3, and 6 months postoperatively.
The primary outcome was the prevalence of EBSLN injury.
The secondary outcomes were the identification rate of the
EBSLN using IONM and changes in postoperative voice
Results EBSLN injury was detected in eight (12.3%) patients
and nine (8.6%) nerves in group 1 and in one (1.5%) patient
and one (0.9%) nerve in group 2 (patients, p =0.015;nerves,
p = 0.010). IONM contributed significantly to visual
(p < 0.001) and functional (p < 0.001) nerve identification in
group 2. The VII-5 indicated more voice changes in group 1
than 2 at 1, 3, and 6 months postoperatively (p = 0.012,
p =0.015,andp = 0.02, respectively).
Conclusion IONM contributes to visual and functional iden-
tification of the EBSLN and decreases the rate of EBSLN
injury during superior pole dissection. Routine use of IONM
to identify the EBSLN will minimize the risk of injury during
Keywords External branch of the superior laryngeal nerve
Vo ice c h a ng e
During thyroid surgery, the main structures that must be pre-
served to prevent postoperative voice deterioration are the
recurrent laryngeal nerve (RLN) and external branch of the
superior laryngeal nerve (EBSLN). The EBSLN innervates
the cricothyroid muscle (CTM), the primary function of which
is to increase the tension of the adducted ipsilateral vocal folds
during pitch elevation .
The EBSLN is prone to injury during thyroidectomy.
Damage to the EBSLN leaves the vocal cord abducted and
increases the risk of aspiration . EBSLN injury is related to
CTM motility impairment, altered voice frequency, modified
timbre, deterioration in producing high-pitched sounds, and
reduced voice quality projection; these changes are especially
noticeable in professional speakers and singers .
Injury to the EBSLN can occur during dissection and
clamping of the superior thyroid vessels because of the close
relationship between the nerve and vessels [4, 5]. Several tech-
niques have been described for preserving the EBSLN, including
* Mehmet Uludag
General Surgery, Sisli Hamidiye Etfal Training and Research
Hospital, Istanbul, Turkey
General Surgery, Bahcesehir University Medical Faculty,
Langenbecks Arch Surg (2017) 402:965–976