Axillary channel-assisted TOETVA: An effective way to prevent mental nerve from iatrogenic injury?

Aim: To evaluate the protective effect of axillary channel-assisted (ACA) transoral endoscopic thyroidectomy vestibular approach on mental nerve. Materials and
Methods: From August 2018 to December 2020, 126 cases of thyroid micro-carcinoma patients who underwent endoscopic thyroidectomy were recruited retrospectively. Of those, 74 cases were performed with ACA trans-oral endoscopic thyroidectomy vestibular approach (ACA_TOETVA) (V and A group), 52 cases received standard TOETVA (V group). On postoperative day 1 (POD1), nylon monofilament test and numbness visual analogue scale score were conducted to evaluate the severity of numbness within the mental area, facial expression was tested to determine the motor function of lower mandible and the thickness of cutaneous and subcutaneous layers was measured with ultrasound. The other observation parameters including the time for operation and intraoperative blood loss were carefully collected.
Results: On POD1, nylon monofilament test showed that scores in the V and A group (2.9 ± 0.3) were significantly higher than V group (1.7 ± 0.5), P < 0.01, u = 254. The completion percentage of facial expression in the V and A group was 90.5% (67/74) and significantly higher than in V group (21.2%, 11/52), P < 0.01, χ2 = 62.35. The thickness increment of cutaneous and subcutaneous layer was 2.2 ± 1.2 mm in the V and A group, which was significantly less than in the V group (4.0 ± 1.2 mm), P < 0.01, u = 605. Compared with V group, the operation time (113.4 ± 22.3 min vs. 127.7 ± 25.6 min, u = 1262) and intraoperative blood loss (43.5 ± 13.4 ml vs. 51.0 ± 14.1 ml, u = 1355) were also significantly less in the V and A group. Conclusions: The ACA transoral endoscopic thyroidectomy possesses the protective effect on mental nerve and motor function of lower mandible and facilitates the operative procedures of TOETVA.

INTRODUCTION

Since the first transoral endoscopic thyroidectomy was reported by doctor Wilhelm and Metzig[1] from Germany in 2009, the procedure becomes much more popular in Asia than in Western countries because the euriprosopic or mesoprosopic type of face shapes is more common in Asian population,[2] which makes the transoral approach easier to be performed. In the past 10 years, with the constant efforts made by surgeons such as Nakajo A. from Japan, Anuwong A. from Thailand, Wang P. and Wu G. Y. from China, the procedure has been well refined and officially named as transoral endoscopic thyroidectomy via vestibular approach (TOETVA). In the meantime, the cosmetic effect and safety of TOETVA has also been widely acknowledged. However, people start to notice the ‘non-negligible’ fact of high prevalence of postoperative mental nerve injury (MNI), which described as 100% at most in some literatures,[3] and in some cases, the feeling of numbness could last even for 3–12 months.[4] Regarding the current situation of MNI research, on the one hand, this unique complication is getting more and more attentions, but on the other hand, the objective and quantified evaluations for severity of numbness are still missing, which leads to the absence of unanimous diagnostic criteria for MNI so far.

To prevent MNI, endoscopists have tried in many ways, including adjusting the location of center and lateral vestibular incisions,[5] intentionally dissecting and protecting the trunk of mantel nerve,[6] even transferring the vestibular incision to submental area.[78] However, the postoperative numbness still cannot be fully avoided.

In King et al.'s[9] report, 120 cases of mental nerves were dissected for their anatomic distributions on 60 human cadavers. Eight distinct distribution patterns of MN branches were discovered, especially in the type VIII, which was characterised by dense medial clustering branches, presents in up to 10% of all cases. Therefore, they believe that the transverse middle incision and large port are important reasons for iatrogenic MNI in classic TOETVA.

For this reason, we invented a modified approach, axillary channel-assisted transoral endoscopic thyroidectomy vestibular approach (ACA-TOETVA), with intention of diminishing the trauma related to vestibular channel by adding an additional axillary channel. Besides, the cosmetic merit of scarless neck offered by TOETVA could also be preserved well in ACA-TOETVA.

MATERIALS AND METHODS

General information

From August 2018 to November 2020, the clinical data of patients underwent endoscopic thyroid lobectomy with ipsilateral central compartment lymph node dissection via transoral approach due to unilateral thyroid micro-carcinoma were collected retrospectively in our institution. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the ethics board of Wuhan No. 1 hospital, and individual consent for this retrospective analysis was waived.

After excluding the cases with previous operation involving submental, neck or facial area, 126 patients were recruited in total. Of those, 52 cases were performed with standard TOETVA (V group), and the other 74 cases were handled with ACA-TOETVA (V and A group). The same surgical team performed all the operations. There was no significant difference on gender, age, BMI, thyroid volume or tumour size between the two groups [Table 1].

Table 1

Pre-operative characters in patients with thyroid micro-carcinoma between two groups

Group	Gender		Age (years)	BMI	Thyroid volume (ml)	Tumour diameter (mm)
	Male, n (%)	Female, n (%)
V and A	4 (5.4)	70 (94.6)	38.0±9.4	20.6±2.4	25.1±5.2	6.8±2.0
V	2 (3.8)	50 (96.2)	37.1±10.1	20.3±2.3	24.9±5.8	6.9±1.9
u/χ2	0.0004		1823	1754	1790	1881
P	0.9839		0.6197	0.4001	0.5075	0.8292

BMI: Body mass index

Operation

Axillary channel-assisted transoral endoscopic thyroidectomy vestibular approach

Anaesthesia induction and preparation

Tracheal intubation was conducted using electromyographic endotracheal tube under the monitor of visual laryngoscope during general anaesthesia. Cefuroxime or clindamycin was given 30 min before operation as prophylactic antibiotic. The patient was placed in supine position, and the shoulders were lifted with cushion to make the neck slightly over stretched. The operator stood on the cranial side, and the oral vestibule was disinfected with 0.5% povidone-iodine and rinsed with normal saline alternately for 3 times.

Creation of transoral cervical channel

Five mm above the inferior labial frenulum, a vertical incision at length of 5 mm was made by scalpel [Figure 1], then small size Kelly clamp was used to gently dilate the submucosa space for- and down-ward. A 5 mm disposal Trocar with piercing mandrel was introduced aiming at the middle point of chin. ‘Drilling’ technique was conducted by rotating the Trocar clockwise or anti-clockwise to advance it along the surface of mandible and across the center of mental area. Then, ‘drilling’ was continued inferiorly to enter the superior layer of deep fascia of submental region [Figure 2]. When the plane of hyoid bone was reached, the piercing mandrel started to go superiorly and advanced between the platysma and superficial layer of the deep cervical fascia (SfDCF).

Figure 1

The vertical vestibular incision above inferior labial frenulum

Figure 2

The blunt dissection in ‘drilling’ fashion

Once the middle part of the thyroid cartilage was reached, the blunt puncture was performed for 5–8 times in a fan-shape area within the range of 60° to complete the creation of the first workspace. After that, on the lip side, at the sites above the middle points of the lines from the first premolar to the corner of mouth on each side, two oblique incisions of 5 mm in length were made using scalpel, and the disposable 5 mm Trocars with piercing mandrels were inserted and directed to the sternoclavicular joints on each side. The propelling was closely along the surface of the mandible, till two trocars arrived the precervical region. The bilateral cervical channels should be built in the same layer of center channel to ensure that three work channels will meet in the area of thyroid cartilage.

Three 5 mm Trocars were placed in established work channels respectively [Figure 3], the one in the middle was connected with CO2 insufflator and the pressure was set as 3 mmHg with a flow rate of 15 L/min. The camera was introduced through the central Trocar, and the electrocautery hook was on the right. The fascia was dissected under the direct vision at the beginning, and then, dissection was extended forward and laterally to enlarge the workspace. Through the left Trocar, a suction instrument was introduced to lift the flap up and clean the smoke and bleeding during dissecting. While the workspace was big enough, CO2 pressure was adjusted to 6 mmHg and the flow rate was set as 35 L/min. Dissection should be first conducted in the middle and then to the bilateral sides. If the procedure was performed in the right plane between the platsyma and SfDCF, the loosen fascia appearing as ‘white roof and white floor’ could be seen. The dissection should be caudally expanded to the sternal notch and widen to the lateral boarder of sternocleidomastoid muscles on both sides.

Figure 3

The placement of three 5 mm Trocars in oral vestibule

Creation of axilla-cervical channel

Within axillary fossa, a 10 mm incision was made according to skin texture on the ipsilateral anterior axillary line and then a disposable blunt subcutaneous dissector was introduced and passed from the arm-pit to the cervical region through the plane of SfDCF [Figure 4]. On the site where is cranial to the sternum head of sternocleidomastoid muscle, the blunt dissector entered into the established workspace and formed ‘the axillary-cervical channel (ACC)’ which was 1 cm in diameter and compatible for 10 mm Trocar [Figure 5]. With the help of ACC, flexible L-shape or ‘golden finger’ retractor became available. Instead of stay suture, flexible retractor was used to push the strap muscle aside, lift up the flap and make a better operation field.

Figure 4

Creation of axillary cervical channel

Figure 5

Trocars placement after the establishment of vestibular and axillary channels

Thyroidectomy and lymph nodes dissection

After opening the linea alba cervicalis, the pyramidal lobe and prelaryngeal lymph nodes were removed first. By pushing the strap muscles laterally with flexible retractor, the upper polar was sufficiently exposed, and the current (1–2 mA) delivered by stimulator probe of neuromonitor was used to detect the cricothyroid muscular tremor[10] within the area where superior thyroid vessel was planed to be divided. Once the lateral branch of superior laryngeal nerve was identified, protective dissection should be conducted under direct vision. Blunt dissection was used to locate the superior parathyroid, the small vessels distributed on the surface of it were cauterised by bio-polar device and then parathyroid was pushed to deeper position. After finding recurrent laryngeal nerve (RLN) at the entrance point to larynx, the ligament of berry was cut off; sequentially, along the RLN, unilateral thyroid lobe, lymph nodes and fat tissues in the central section were en bloc removed. Because only the patients with papillary micro-carcinoma were recruited in our study, the standard thyroid lobectomy, isthmus resection and ipsilateral central section lymph node dissection were performed in all of our cases. If the tumour located in the right lobe, the lymph nodes posterior to RLN should also be removed. In such cases, the L-shape or golden finger flexible retractor was used to push the common carotid artery aside, which could greatly facilitate the dissection manoeuvre in prevertebral fascia layer. However, cautions should be taken because too deep dissection might cause inadvertent injury to vagus and cervical sympathetic nerve.

Specimen extraction, drainage placement and wound closure: The specimen bag was taken out via axillary incision. The operation field was carefully checked for bleeding and irrigated with amount of distilled water. A drainage tube was placed superficial to the strap muscle and pulled out from new created orifice, which is close to the axillary incision, and drainage was fixed with suture. Absorbable sutures were used to close the three 5-mm vestibular incisions, 1 or 2 stitches for each [Figure 6]. The 10 mm incision of axilla was re-approximated with medical Histoacryl. At last, the oral cavity was rinsed with 0.5% povidone-iodine and normal saline alternately for three times.

Figure 6

Closure of three 5mm incisions in oral vestibule

Transoral endoscopic thyroidectomy vestibular approach

Creation of workspace

Five mm above the inferior labial frenulum, a 2–2.5 cm horizontal or roof-like incision was made by electrocautery instrument, the cutting was then continued caudally and downward. After partly dividing the depressor labii inferioris, the advancing was continued along the mandible, and part of bilateral mentalis was cut off. Electrocautery was bent at an angle of 60° in order to pass the curve of mental region. A blunt dissector was inserted through the space created before. After passing over the chin, its’ tip went down for 1.5–2.0 cm, then went superficially, under the plane of platysma, it reached the region of thyroid cartilage. Next, we started to create the precervical workspace with dissector in three different directions—suprasternal fossa, left and right sternoclavicular joint. A 10 mm Trocar was placed in the central channel. The procedures of establishing of bilateral vestibular incisions and channels were same as we described in 2.2.1. The workspace was maintained with CO2 insufflation, and the parameter of air pressure and flow rate was settled at 6 mmHg and 35 L/min, respectively.

Operation field exposure

On the skin covered the cricothyroid joint, a V-shape retractor was penetrated and used for retracting the ipsilateral strap muscle to enhance the visibility of the thyroid and lymph nodes.

Specimen extraction

A disposable specimen bag was put through 10 mm Trocar. After loading, the outlet of central work channel was widened by electric cutting or blunt dilation according to the size of specimen before extraction.

Incision closure

The central incision was interruptedly sutured for about 10 stiches. One or 2 stitches was put for each of two lateral incisions. Other procedures were same as ACA-TOETVA. The schematic diagram for two approaches is shown in Figure 7.

Figure 7

Schematic diagram for two approaches

Observation parameters

Evaluation for mental nerve injury

The Semmes-Weinstein monofilament test that was first introduced by Kumar et al.,[11] was referred to evaluate the loss of protective sensation. On postoperative day 1 (POD1), the tip of nylon monofilament weighted 2 g was used to streak over the skin of chin for 10 times, and patients were asked to close their eyes and report if is there any sensation of touch during the test. According to their reports on the times of positive sensation, the cutaneous sensory function of mental region was classified as normal, impaired and loss [Table 2 and Figure 8].

Table 2

Nylon monofilament test

	Normal	Impaired	Loss
Times of positive sensation	7-10	1-6	0
Points	3	2	1

Figure 8

Nylon monofilament test

Numbness visual analogue scale score

On POD1, numbness visual analogue scale (VAS) score was evaluated with a silk thread at length of 10 cm, on which the one end represents no numbness at all (0 point), and the other end represents extremely numbness (10 points). Patients were told to choose the position on the thread according to their feelings for severity of numbness.

Evaluation for motor function of mandibular muscle

On POD1, all the patients were asked for making facial expressions including ‘pouting’ and ‘cheek blowing’; the results of able or fail to perform were recorded.

Evaluation for subcutaneous oedema in mental region

The thickness increment of skin and subcutaneous layer of mental region was measured by Doppler ultrasonic detector on the day before operation and POD1.

Operative outcomes

The duration of entire operation, time for creation of workspace (defined as the duration from opening skin of neck to starting thyroidectomy), time for specimen extraction (defined as the duration from finishing of packing up the specimen to pulling the bag out of the work channel), time for closure of incisions (defined as the duration of closure all the incisions including axillary and vestibular incisions), intraoperative bleeding volume (ml), postoperative drainage volume (ml), and postoperative length of stay (d).

Statistical analysis

Software package Prism 7.0 for Mac OS X (GraphPad Software, USA) was used for statistical analysis. The quantitative data were expressed as mean ± standard deviation and were analysed with Mann–Whitney test due to its’ non-normal distribution. The count data were expressed as percentage (%), and Chi-square or Yate's continuity correct Chi-square was used for analysis. P < 0.05 was considered statistically significant.

RESULTS

Quantitative evaluation for numbness in mental region

Figure 9 shows nylon monofilament test and numbness VAS scores.

Figure 9

Scores of nylon monofilament test and numbness visual analogue scale

On POD1, nylon monofilament test showed that scores in V and A group (2.9 ± 0.3) were significantly higher than in V group (1.7 ± 0.5), P < 0.0001, u = 254. On POD1, numbness VAS evaluation showed that not only the incidence of postoperative numbness in V and A group (17.6%) was significant less than in V group (100%), P = 0.0038, χ2 = 8.376, but the scores in V and A group (1.7 ± 1.3) were also significantly lower than in V group (5.0 ± 1.7), P < 0.0001 and u = 298.5

Subcutaneous oedema in mental region

Figures 10 and 11 shows thickness increment of cutaneous and subcutaneous layer in V and V and A group.

Figure 10

Postoperative thickness of cutaneous and subcutaneous layer in TOETVA

Figure 11

Postoperative thickness of cutaneous and subcutaneous layer in axillary channel assisted_TOETVA

After operation, the cutaneous and subcutaneous layer became thicker than before in both groups. However, the thickness increment in V and A group is 2.2 ± 1.2 mm, which is significantly less than in V group (4.0 ± 1.2 mm), P < 0.01, u = 605.

The intraoperative parameters and postoperative complications were compared between V and A group and V group

On the aspect of procedure related time consumption, all kinds of durations in VandA group were significant shorter than in V group. Furthermore, the parameters reflect the severity of surgical trauma, including intraoperative bleeding, and postoperative drainage were all significantly less in V and A group. There was no significant difference regarding the rate of postoperative complications between two groups. The incidence of subcutaneous ecchymosis is higher in V group (7.7%) than in V and A group (0%), although the P value did not reach, but very close to the significant level (0.056) [Table 3].

Table 3

The comparison of operative outcomes between V and A group and V group

	V and A Group (n=74)	V Group (n=52)	P	u/χ 2
Operative duration (min)	113.4±22.3*	127.7±25.6	0.0009	1262
Time for workspace creation (min)	3.3±0.9*	10.1±1.7	<0.0001	0
Time for incisions closure (s)	155.4±28.0*	383.1±56.0	<0.0001	0
Time for specimen extraction (s)	133.6±40.2*	288.9±136.2	<0.0001	239
Drainage (ml)	43.5±13.4*	51.0±14.1	0.0045	1355
Bleeding (ml)	21.1±4.3*	24.0±5.5	0.0007	1247
Post-operative LOS (days)	2.5±0.8*	4.5±0.9	<0.0001	184.5
Facial expression test, n (%)	67 (90.5)*	11 (21.2)	<0.0001	62.35
Post-operative complications, n (%)
Hoarseness	1 (1.4)	1 (1.9)	0.64	0.2219
Ecchymosis	0	4 (7.7)	0.056	3.643
Hematoma	0	1 (1.9)	0.86	0.0317
Infection	0	0

*Stands for comparing with V group, the difference is significant (P<0.05). LOS: Length of stay

DISCUSSION

MNI with different severity occurs in standard TOETVA frequently, which often presents as postoperative numbness in mental area and lower lip. However, the incidences of MNI are highly varied in different reports, such as Wilheim and Metzig[12] descried a high prevalence of 75% in his series, and incidence is even as high as 100% in Nakajo's report.[13] On contrary, extremely low percentages were also mentioned by some authors. For instances, only 0.7% was reported in Anuwong et al.'s[14] paper, and Tae et al.,[3] described even no MNI in his study at all. We believe that the reason for such huge difference is largely because the diagnosis of MNI was based on the presentation of postoperative numbness, but to which degree of numbness should be defined as MNI was quite different among the studies. Clearly, so far, there is no unanimous quantified standard for evaluation of numb severity occurred in mental region. To quantitatively measure the severity of numbness, we used subjective VAS scores and discovered that actually, all the patients after standard TOETVA had more or less symptom of numbness, but the scores in V group were quite varied (from 1 to 9), at average level of 5.0 ± 1.7. Ascribing the minimal loss of sensation to MNI was the reason for the high prevalence (100% in V group) in our study. Furthermore, in order to provide more objective evidence of changes of cutaneous perception due to endoscopic thyroidectomy, we referred to Semmes-Weinstein monofilament test that had been designed by Kumar et al.'S[11] in 1998, to evaluate the loss of protective sensation in diabetic patients. The nylon monofilament test shows that the scores reflect extent of loss sensation in V group was 1.7 ± 0.5. To best of our knowledge, this is the first paper to report quantified data in regard to numbness severity after TOETVA.

According to the anatomic course and distribution of mental nerve, an effective way to prevent mental nerve from iatrogenic injury is setting the central vestibular incision just above and close to the inferior labial frenulum, and placing two 5 mm incisions laterally enough at the opposite of the first premolar on the lip side.[14] Equally importantly, the using of large size Trocar, excessively squeezing or over dissecting in mental region should be also avoided.[3] In our ACA-TOETVA, at first, because the manoeuvre of specimen extraction was altered to ACC, the length of central vestibular incision could be reduced from 2.5 cm to 0.5 cm. Second, there was no longer needs for extensive dissection with electric energy during the phase of creating workspace. Third, the impact of blindly pulling and squeezing on central vestibular channel was completely excluded by this approach. Our study shows, with assistant of axillary channel, the percentage of postoperative numbness is only 17.57% (13/74), and score of VAS is 1.7 ± 1.3, and score of nylon monofilament test is 2.9 ± 0.3, which are all significantly superior to the standard vestibular approach and offer much better postoperative experiences to patients. Besides, Li et al.[6] discovered that even with the effort of actively protective dissection of the trunk of mental nerve, the postoperative numbness within cervical and mental region still exists. Therefore, they believe the occurrence of numbness also results from flap dissection and subcutaneous oedema. In our study, ultrasound was used to objectively measure the thickness increment of cutaneous and subcutaneous layer, and the result shows V and A group (2.2 ± 1.2 mm) was significantly lower than V group (4.0 ± 1.2 mm). The less severity of subcutaneous oedema might be part of the reason for milder or even no symptom of postoperative numbness. Thus, when comparison was made between two approaches, both objective test (VAS, nylon monofilament test) and subjective measurement (ultrasound) exhibit the protective effect of ACA-TOETVA on mental nerve.

In standard TOETVA, during dissecting of flap through the central vestibular opening, at least part of the depressor labii inferioris and mentalis will be divided,[15] which lead to the facial expressions, like ‘pouting’ and ‘blowing’ were not able to be correctly implement. On POD1, 78.8% of patients in our V group were incapable of conducting the expressional actions mentioned above. Contrarily, instead of sharp dissection, we employed blunt dissection in ‘drilling’ fashion during creation of workspace in V and A group to prevent mentalis to be divided. Therefore, the completion rate of expression tests reached 90.5%, and obviously superior to V group. In short, due to the assisted axillary approach, the tissue damage caused by vestibular incision and flap dissection was minimised, which endows ACA-TOETVA with better protective effects on mentalis and mental nerve.

On the other hand, additional axillary channel could facilitate manoeuvres under endoscopy. As we all know, compared with traditional open approach, TOETVA undoubtedly increases the time consumption of operation. Anuwong et al.'s[5] data shows the average duration for unilateral lobectomy is 85 ± 22.4 min. Fernandez-Ranvier et al.,[16] collected the data of 222 TOETVA cases from 5 European clinics and come up with the average duration of 161.8 ± 42.4 min. Because the patients recruited in our study were limited to the micro-carcinoma, therefore, the unilateral central section lymph node dissection is mandatory in our procedures. The average time in our V group is 127.7 ± 25.6 min, which is longer than Anuwong et al.'s report (only lobectomy), but very similar to 112.1 ± 16.6 min in Li et al.'s paper,[6] in which lobectomy with central section lymph node dissections were performed as we did. Whereas, after adding an axillary channel, the duration for entire operation was significantly shortened to 113.4 ± 22.3 min. By analysis of the subsets of procedure related durations, we discovered that the time for workspace creation, incisions closure and specimen extraction were all decreased when compared with V group. In classic TOETVA, the creation of workspace is started with opening the vestibular mucosa and cutting part of mentalis at first, and then, the dissection should be extended to the inferior boarder of mandible. The tunnel to the submental region could be only created after previous preparations. But in ACA-TOETVA, middle cervical and axillary cervical tunnel were both created in drilling fashion, without additional dissections. As long as the proper plane was adopted, the establishment of subcutaneous tunnel could be done very quickly. So, in our study, the time for working space creation in V and A group is significantly shorter than V group (3.3 + 0.9 min vs. 10.1 + 1.7 min, P < 0.0001). These data suggested that, by means of altering to blunt dissection during workspace creation, saving time for incisions closure due to shortened central vestibular incision, and facilitation of specimen extraction, the ACA-TOETVA could effectively reduce the time consumption of entire operation. Besides, the three vestibular channels at 5 mm diameter could tightly surround the Trocars without gas leakage, consequently improved the exposure of operative field, and contributed to the reduction of operation time as well.

In the specialties with sophisticated technique of TOETVA, the volume of intraoperative bleeding stays low. In literatures, the haemorrhage during operation is about 18 ml to 39 ml.[451617] The average blood loss in our V group is 24.0 + 5.5 ml, and within the range described in previous reports. However, in VandA group, the volume decreased to 21.1 + 4.3 ml, and the difference has reached the significant level (P = 0.0007, u = 1247). We believe that because of the introduction of extra retract instrument via the axillary cervical channel, the flexible retractor such as ‘L shape’ or ‘golden finger’ could assist in retracting the strap muscles away, or elevate the skin flap, or push carotid artery laterally, which in turn, not only facilitates the exposure and resection of thyroid and lymph node, but also maintains the clearance of operative field and precision of manoeuvres in a limited workspace. Therefore, when the intraoperative bleeding, a common used parameter for operative trauma, was compared between two procedures, ACA-TOETVA exhibit its’ superiority too.

Disadvantage and flaws: (1) In ACA-TOETVA, an extra trauma has to be made on patients due to the establishment of additional axillary channel and incision; (2) Performing flap dissection in precervical area with ‘drilling’ skill and ensuring the convergence of four work channels within the right plane is not easy. It probably prolongs the learning curve for surgeons without experience in endoscopic thyroidectomy. (3) Different from the electrocautery dissection in standard TOETVA, in our procedure, the reduced 5 mm submental channel was built with blunt ‘drill’ technique, which is only easier to be performed in patients with flat curve of the bone structure of chin. Therefore, the applicability of this procedure might be limited to Asian patients. (4) Our research is retrospective, and the cases are not abundant. To confirm the advantages of ACA-TOETVA, some randomised prospective clinic trails are still needed.

CONCLUSIONS

By creating an additional axillary cervical channel, ACA-TOETVA reduces the trauma caused by workspace establishment and specimen extraction, and has better protective effects on mentalis and mental never. On the other hand, with the help of extra assistant instrument, the operation time and loss of blood was decreased, and the manoeuvre under endoscopy could be facilitated.

Financial support and sponsorship

Natural Science Foundation of Hubei Province (Grant: 2018CFC831).

Conflicts of interest

There are no conflicts of interest.