INTRODUCTION
Most thyroid cancers are papillary thyroid carcinomas (PTCs), which have been reported to metastasize to cervical lymph nodes (LNs) in ~25%–33% of patients and to lateral LNs in ~5%–7% of patients [
1,
2]. Thus, the treatment of PTC should include removal of both the thyroid gland and metastatic LNs. Modified radical neck dissection (MRND), which includes all compartments from level II to V, is recommended, especially in patients with lateral LN metastasis beyond the border of the carotid artery [
3]. Conventionally, thyroid cancer has been treated by transcervical thyroidectomy with LN dissection. The development of endoscopic and robotic methods has led to the introduction of various types of remote access thyroid surgery. These methods result in minimal neck scarring, which is particularly important as thyroid cancers occur in women more frequently; in the 2017 national cancer statistics in Korea, thyroid cancer occurred in 6,035 men and 20,135 women (
https://www.cancer.go.kr). One of these methods, robotic thyroidectomy through the bilateral axillo-breast approach (BABA), using the da Vinci robotic surgical system, was introduced in 2008 [
4,
5].
Because the working space for thyroidectomy is relatively narrow, and instrument mobilization is restricted, endoscopic thyroidectomy is more difficult to perform than other endoscopic operations. However, endo-wrist actions during robotic operations can facilitate instrument movement compared with an endoscopic operation. Advances in robotic operation systems and surgeons’ skills have allowed the performance of more complicated procedures, such as robotic MRND. However, it remains unclear whether robotic MRND is technically and oncologically safe. Robotic MRND can be performed using a retroauricular, transaxillary, or BABA approach [
6-
12], each of which has several limitations. For example, accessing the contralateral LNs is troublesome using a retroauricular or transaxillary approach, whereas level IV dissection is difficult to perform using BABA [
8].
Although several studies have evaluated the safety of robotic MRND through BABA, those studies only evaluated the da Vinci S and da Vinci Si robotic systems [
7,
11,
12]. Unlike the da Vinci S and Si systems, which need a 12-mm trocar for the camera port, the da Vinci Xi system uses all 8-mm trocars, including for the camera port, and provides new endo-wrist instruments such as the vessel sealer extend and suction-irrigation tools. To our knowledge, no study has evaluated the safety of robotic MRND through BABA using the da Vinci Xi system. The present study therefore evaluated the technical and oncologic safety of robotic MRND through BABA using the da Vinci Xi system in comparison with conventional open MRND.
DISCUSSION
Because thyroid cancer mostly affects younger women and has a favorable prognosis, various remote access approaches have been developed to enhance cosmetic outcomes. Neck scars after conventional thyroidectomy are perceived to be less attractive and can reduce patient quality of life [
14,
15]. Patients with metastatic LNs in the lateral neck area require MRND, a more extensive surgical procedure than thyroidectomy [
3]. Open MRND requires a 10- to 15-cm-long transverse or hockey stick incision, often leading to an unfavorable thick and long neck scar. Because MRND requires more extensive dissection and is more difficult to perform than thyroidectomy, endoscopic or robotic MRND procedures are performed only at high-volume thyroid centers. Robotic surgical systems have facilitated more difficult procedures, providing a three-dimensional magnified view and enabling the multiarticulated EndoWrist function. Remote access approaches to robotic MRND, including transaxillary, retroauricular, and transoral approaches, as well as BABA, may result in scar-less surgery [
6,
9,
10,
15]. Each of these methods has advantages and limitations in effectively performing MRND. The transaxillary approach provides a view similar to the conventional open approach, as well as a relatively short operation time. However, accessing the upper neck area is relatively difficult, and contralateral MRND is impossible. Moreover, although rare, cases of brachial plexus injuries have been reported [
9]. The retroauricular approach can access the upper neck area and requires a smaller area for dissection. However, its operative view is in a direction opposite to that of the open procedure, and contralateral MRND is impossible [
8]. Although the transoral approach has been used to dissect lateral neck nodes [
15], this approach only allows selective dissection of level III or IV, making it oncologically unsafe at present. Robotic BABA provides a symmetric view, similar to the open approach, and bilateral MRND is possible. However, level IV dissection is relatively difficult because it has an inferior-tosuperior view, and the energy device has limited access to the inferior side of level IV or level VI [
10,
16].
To our knowledge, this study is the first to assess robotic MRND via BABA using a new robotic operating system, the da Vinci Xi. The results with this system were comparable to those using the da Vinci S or da Vinci Si system [
7,
12,
17]. Baseline clinical characteristics, including patient age, sex ratio, main tumor location, operation site, and tumor size, did not differ significantly in patients who underwent robotic and open surgery. The operation time was significantly longer in the robotic than in the open group (277.08±32.64 vs. 191.43±60.43 minutes, respectively;
P<0.01). However, when the operation time in the robotic group was subdivided into the flap elevation time (45.50±11.90 minutes) and console time after robot docking (200.33±26.86 minutes), the latter did not differ significantly from the time required for open surgery (
P=0.523). The rates of postoperative complications, including vocal cord palsy and hypoparathyroidism, were similar in the two groups. One patient in the open surgery group experienced permanent vocal cord palsy due to direct tumor invasion of the recurrent laryngeal nerve.
The incidence of transient hypoparathyroidism was significantly lower in the robotic group (16.7% vs. 53.6%, P=0.041). Regarding this interesting result, we suggest that following open total thyroidectomy, the naked parathyroid glands are exposed to fresh air during the neck dissection period. These glands may dry up, become cold, or experience oxidative damage during the MRND procedure. In robotic MRND, CO2 gas is insufflated during the entire surgical procedure, keeping the parathyroid glands moist and exposing them to less oxygen, thereby preventing oxidative damage. Moreover, preserving the microvascular structure of the parathyroid glands is easier during robotic surgery. However, these explanations are only hypothetical, and there is no objective evidence supporting them. Therefore, additional studies are required to confirm these hypotheses.
The hospital stay for thyroid surgery is usually longer in South Korea than in western countries because the medical insurance system in South Korea generally covers the cost of longer admissions for cancer patients [
18]. Our study found, however, that the mean hospital stay was shorter in the robotic group than in the open group (3.92±0.90 vs. 4.71±1.63 days, respectively;
P=0.056). The shorter hospital stay may be linked to the lower postoperative pain score and the significantly lower incidence of transient hypoparathyroidism in the robotic group. The use of BABA alone for remote access thyroidectomy, without neck dissection, has been regarded as not being “minimally invasive” as it requires a wider area of subcutaneous dissection than open surgery [
18,
19]. However, robotic MRND using BABA showed better performance, with excellent cosmetic and clinical outcomes, suggesting that robotic MRND is minimally invasive compared with open MRND.
Regarding oncologic outcomes, the mean number of retrieved LNs and retrieved LNs by neck levels did not differ between the two groups. Use of the da Vinci Xi system for robotic MRND may have several advantages. During robotic MRND using BABA, the visual field is blocked by the clavicle and the camera, making it difficult to access level IV or VI. This limited view of level IV can be overcome by encircling the lower breast using an elastic band, thereby elevating the subareolar height, expanding the visual field of the lower neck compartment [
16]. In the da Vinci Xi system, all four robotic arms, including the camera, can be inserted through an 8-mm trocar, allowing the camera and other arms to be changed freely. If another operating view is required, the camera port can be changed not only to another breast site, but to both axillary sites. This can enable dissection of the lower neck compartment, including levels IV and V, and the contralateral side of the neck. Another limitation of robotic MRND was the inability to articulate the ultrasonic shear device (Harmonic), limiting the approach of Harmonic ACE to the lower neck node levels. The da Vinci Xi system, however, allows use of the vessel sealer extend instrument and the bipolar energy coagulator with robot EndoWrist function [
17]. The flexible energy device enables safe dissection around all lateral neck node levels. As a result, the number of LNs retrieved in all LN areas did not differ significantly between the two groups [
13,
17]. The number of retrieved LNs in our study was smaller than in previous studies, which may have resulted from differences between pathologists.
A marker of the completeness of thyroid surgery is the sTg level, a reliable indicator of remnant thyroid tissue after total thyroidectomy [
19]. In our study, the sTg level and the proportion of patients with sTg levels <1 ng/mL (50.0% vs. 39.3%,
P=0.530) did not differ significantly between the two groups. Other studies measuring sTg concentrations showed the surgical completeness and safety of robotic MRND via BABA [
7,
11,
12].
This study has several limitations, including its single-center and retrospective design, which may have introduced selection bias. In addition, the sample size in both groups was small, and the follow-up period was too short to evaluate recurrence. Because of the limitations of robotic surgery, open surgery is recommended in patients with metastatic LNs invading adjacent structures, including the SCM muscle, trachea, or major vessels. Another disadvantage of robotic surgery is its cost, which is 3–4 times higher than that of open surgery in South Korea (10,000–12,000 vs. 2,500–3,000 USD). Furthermore, robotic surgery requires additional training, with few hospitals in South Korea currently performing robotic MRND via BABA.
In summary, this study is the first to report the results of robotic MRND via BABA using the da Vinci Xi system. This surgery not only provided excellent cosmetic results, but also surgical and oncologic outcomes comparable to those of open surgery, as well as lower rates of transient hypoparathyroidism. Although longer-term multicenter studies are required, robotic MRND using the da Vinci Xi system via BABA can be considered as an alternative surgical option with excellent cosmetic outcomes.