Ann Surg Treat Res.  2022 Oct;103(4):205-216. 10.4174/astr.2022.103.4.205.

Is craniocaudal dissection of recurrent laryngeal nerve safer than lateral approach: a prospective randomized study comparing both techniques by using continuous intraoperative nerve monitoring

• Iscan Y
• Aygun N
• Sormaz IC
• Tunca F
• Uludag M
• Senyurek YG

• KMID: 2534123
• DOI: http://doi.org/10.4174/astr.2022.103.4.205

Abstract

Purpose
This study was performed to compare the real-time electromyographic (EMG) changes and the rate of recurrent laryngeal nerve (RLN) injury in craniocaudal and lateral approaches for RLN during thyroidectomy.
Methods
One hundred twelve and 86 patients were prospectively randomized to receive lateral (group 1) or craniocaudal (group 2) approach to RLN, respectively, under continuous intraoperative nerve monitoring.
Results
Loss of signal (LOS) occurred in 7 (2.0%) of 356 nerves at risk (NAR). LOS was significantly associated with repeated adverse EMG changes and presence of RLN entrapment at the ligament of Berry (LOB), which was accompanied by other clinicopathological or anatomical features, such as tubercle of Zuckerkandl (TZ), extralaryngeal branching, hyperthyroidism, autoimmune thyroid disease (ATD), or thyroid lobe volume of >29 cm ³ (P = 0.001 and P = 0.030, respectively). The rate of repeated adverse EMG changes and LOS in the NARs with LOB entrapment accompanied by other clinicopathological and anatomical features was higher in group 1 vs. group 2 (11.1% vs. 2.2%, respectively and 9.7% vs. 0%, respectively; P = 0.070). The total rate of vocal cord palsy (VCP) was significantly higher in group 1 than in group 2 (P = 0.005). The rate of permanent VCP showed no significant difference between the 2 groups.
Conclusion
The craniocaudal approach to the RLN is safer than the lateral approach in the RLNs with entrapment at the LOB accompanied by other features, such as TZ, extralaryngeal branching, hyperthyroidism, ATD, or high thyroid lobe volume.

Keyword

Intraoperative nerve monitoring; Loss of signal; Nerve dissection; Recurrent laryngeal nerve; Thyroidectomy

Figure

• 

  Fig. 1 Flow diagram of the study. RLN, recurrent laryngeal nerve; TT, total thyroidectomy; L, lobectomy; NAR, nerve at risk; IONM, intraoperative nerve monitoring; LOS, loss of signal; EMG, electromyography.

• 

  Fig. 2 (A) Visual identification of the recurrent laryngeal nerve (RLN) at the lower border of the cricopharyngeal muscle and the posterior aspect of the upper parathyroid gland in the craniocaudal approach. (B) It shows RLN entrapment at the ligament of Berry (LOB). The RLN is shown at the tip of the handheld probe. Nerve monitoring was very helpful to map the course of the nerve between the fibrous and fascial layers of the LOB.

• 

  Fig. 3 Electromyographic (EMG) data showing repeated adverse EMG changes, combined event, and loss of signal. The blue line represents amplitude over time and the green line represents latency over time. In this patient, the recurrent laryngeal nerve had entrapment at the ligament of Berry and extralaryngeal branching, and the thyroid lobe volume was 40 cm3. EMG tracing shows a gradual decrease in the amplitude concordant with the increase in the latency period regarding the baseline values. The final amplitude was <100 µV. VN, vagal nerve.

• 

  Fig. 4 It shows the possible mechanisms of recurrent laryngeal nerve (RLN) injury during the anteromedial traction of an enlarged thyroid lobe during the lateral approach to the RLN. In the RLNs with entrapment at the ligament of Berry (LOB), a stretch injury may develop by direct distress of the stretching ligament on the RLN (A) or by pulling down the distal part of the RLN which is already excessively stretched through the LOB during anteromedial retraction of the thyroid lobe (B). This patient is not one of the patients who are operated on during the study period but we preferred to use this photograph as it is descriptive for possible RLN injury during the unavoidable excessive anteromedial traction of an enlarged thyroid lobe in the lateral approach. No RLN injury occurred in this patient.

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