RLN palsy can greatly diminish patients' quality of life. In addition to the hoarseness that occurs with unilateral RLN palsy, bilateral RLN palsy leads to dyspnea and often to life-threatening glottal obstruction. The preservation of the RLN is thus of great importance, and during every thyroidectomy, the intraoperative identification of the RLN is a mandatory security measure [1, 9, 14, 15]. Although the relationship between the RLN and the inferior thyroid artery is highly variable, the RLN usually runs posteriorly to the thyroid gland [4, 6, 7, 11, 12]. If the RLN is not found in the usual location, surgeons should consider the possibility of a non-RLN structure as an anatomic variation of the RLN [4, 11, 12]. The RLN has also been reported to run posteriorly to the thyroid gland [11, 12].

In our patient's case, the RLN was anterior to the thyroid tumor just behind the sternothyroid muscle; this RLN running course is very rare [16]. Hisham et al. reported that an anterior course of the RLN lying on the thyroid gland can often be encountered in reoperative procedures [16]. They noted that such an anterior course could be due to a previous mobilization or growth of remnants of the gland into a position beneath the nerve after the first procedure [16]. However, our patient's case had no previous cervical surgery including the thyroid. Normally, the left RLN runs along the tracheoesophageal groove, but the right RLN branches from the right vagus in front of the right subclavian artery and turns under the artery. It ascends obliquely from the right lateral side medially to enter the larynx at Berry's ligament. Thus, a tumor arising at the dorsal portion of the right thyroid lobe that progresses caudally may descend behind the right RLN. We suspect that this is the reason why our patient's RLN ran in front of the thyroid tumor. Thyroid surgeons should be aware that depending on the location of the tumor, the RLN may be compressed and take an unexpected route.

IONM is useful in thyroidectomies [9]. Although a visual identification of the RLN remains a gold standard in thyroid surgery, the use of neuromonitoring may help not only in the identification of nerves but also in the functional preservation of nerves, and its use reduces the incidence of RLN injury [1, 5, 8, 9, 15]. In the present patient, since an endotracheal tube integrated with surface electrodes was not performed because it is relatively expensive, palpation was performed to detect contraction of the PCA (the laryngeal twitch method). This method is a simple, readily available technique for any thyroid surgeon and can be performed with a variety of handheld, disposable, and widely available nerve stimulators [1]. However, this method requires the insertion of a finger deep to the posterior lamina and fascia overlying the vertebral column.

In our patient's surgery, a finger could not be inserted until a later timepoint, and the RLN could not be reliably identified earlier. If her RLN had been assumed to be located posterior to the thyroid tumor as is the usual anatomy (without the identification of the cord-like structure as the RLN), the RLN could have been injured during the surgery.

This case report emphasizes the importance of the intraoperative confirmation of the RLN during thyroid surgery. Although it would not have been possible to diagnose this RLN's running course variation reliably before surgery, surgeons should take extra care in similar cases, i.e., when a thyroid tumor is descending posteriorly up to the brachiocephalic artery.