The Clinical Application of Novel Mini Transoral Endoscopic Thyroidectomy to Avoid Numbness and Pain in Patients with Thyroidectomy

Background: Transoral endoscopic thyroidectomy has been gaining popularity as it allows patients to avoid a visible scar in the neck. However, there are still exiting disadvantages of traditional transoral endoscopic thyroidectomy (cid:0) including numbness in the lower jaw or excessive edema. Therefore, we designed and applied a novel Mini transoral endoscopic thyroidectomy on patients requiring for thyroidectomy. Patients and Methods: A total of 55 patients requiring for unilateral thyroidectomy who underwent novel Mini transoral endoscopic thyroidectomy (Mini group) were identied from August 2019 to December 2019. As a comparison, a matched cohort of 55 patients requiring for conventional transoral endoscopic thyroidectomy was also identied. The two groups were analyzed in terms of clinical characteristics, perioperative/operative clinical date and post-operative complications. Results: The hospitalization time of patients in the Mini group was obviously less than that in traditional group. Furthermore, the numbness of the lower jaw, nylon wire examination score, pressure needle puncture examination score, or numbness VAS score indicated that the degree of numbness of the jaw in Mini group is signicantly better than the traditional group. Moreover, the pain of the axillary incision using the pain VAS score method also showed that Mini group is signicantly better than the traditional group. The results of pain of the axillary incision using the VAS score method also showed that novel Mini group was signicantly better than that in the traditional group. Furthermore, dysfunction of mandibular muscles was observed in six of fty-ve patients in the traditional group, whereas no dysfunction of mandibular muscles observed in Mini group. At last, the degree of postoperative mandibular edema in Mini group was markedly slighter than that in traditional group. The post-operation infection rate was markedly lower in Mini group. Conclusion: The new novel Mini transoral endoscopic thyroidectomy is safe and feasible, and reduces the damage to the functional muscles such as the mandibular diaphragm and lower lip muscles, which signicantly reduces the numbness and edema of the mandible after surgery. Our novel Mini transoral endoscopic thyroidectomy


Background
Over the past two decades, transoral endoscopic thyroidectomy has gained popularity worldwide-likely born from a desire to avoid cosmetically displeasing scarring in such an exposed area [1] . The development of minimally invasive approaches to the thyroid gland went through many trials and tribulations. This process entailed a paradigm shift, away from the traditional transcervical thyroidectomy, toward a more re ned technique in an attempt to hide scarring and improve cosmetics in the neck region [2,3] . Of the currently available endoscopic techniques, the transoral endoscopic thyroidectomy vestibular approach provides a truly scarless approach with relatively direct access to the thyroid and reduced tissue dissection [2,4] .
More recently, there has been development of a technique known as the transoral endoscopic thyroidectomy vestibular approach [5] . This novel remote-access endoscopic technique for the excision of the thyroid gland has the bene ts and avoids the drawbacks of the other remote access procedures [6] . However, there are still some shortcomings in the commonly used surgical methods. For instance, the median incision is relatively large (2-3cm), part of the mental muscle and descending labial muscle need to be cut off, leading to larger injury surface. When the median incision is cut to both sides, it is very possible to damage the branches of the mental nerve of both sides. Postoperative numbness or complete loss of consciousness of the lower jaw will inevitably occur, which will generally take 2-3 months to completely recover [7] . After operation, it will affect the voluntary expression of subtle facial, the ne movement of the mouth and the pronunciation of some sounds. The swelling of postoperative mandible was obvious. When the specimen is larger, given that the specimen has to cross the chin, it is not easy to take out. During the operation, the needle hook is routinely used to puncture from the neck to help distract the banded muscle, and the drainage tube is routinely drawn from the neck, leaving ne scars or marks on the neck after operation. Intraoperative 10 mm endoscopy is easy to con ict with 5 mm Trocar on both sides. The prolonged compression of thin mental skin by 10 mm Trocar often leads to redness and swelling or subcutaneous ecchymosis. Moreover, there are still a program of disadvantages of traditional transoral endoscopic thyroid surgery,including numbness in the lower jaw or excessive edema [8] .
In present study, we aim to examine and describe our experience with a novel Mini transoral endoscopic thyroidectomy, outline the patient characteristics that make the transoral endoscopic approach feasible, detail the surgical technique, and will provide an overview to establish its e cacy and safety.

Methods
From August 2019 to December 2019, all patients who underwent thyroidectomy by the Department of Thyroid Surgery of the First Hospital of Wuhan were entered into a prospectively collected database. Our selection criteria for patients during this time period was as follows: 15-50 years of age, and thyroid mass size < 4 cm. Patients were excluded from this approach if they had a history of mandible or neck operation, lateral cervical lymph node or distant metastasis or a tumor located in the upper pole. A matched cohort of patients who underwent conventional transoral endoscopic thyroidectomy over this same time period was obtained from this prospective database by applying the same inclusion and exclusion criteria with 1:1 matching performed based on age and gender.

Data collection
Data were collected on patient demographics, operative details, post-operative outcomes and nal pathologic results. Time for central lymph node dissection was calculated from time of thyroid specimen removal to time of central lymph node specimen removal. Follow-up was standardized among both groups and was consistent with our practice at the time. The two groups were analyzed in terms of patient characteristics, operative clinical results and post-operative outcomes.

Statistical analysis
Statistical analysis was performed using SPSS 22.0 (SPSS, Chicago, IL, USA). The Chi-square test was employed for categorical variables and the Wilcoxon rank-sum test was used for continuous variables. A P value of <0.05 was considered statistically signi cant. The study was approved by The Ethical Committee of First Hospital of Wuhan.
Operative procedure of novel mini transoral endoscopic thyroid surgery The patient was placed in a supine position, and general anesthesia was induced with orotracheal intubation using a nerve monitoring tube(Fig1.). The neck was extended with a shoulder pillow. The oral cavity was disinfected with povidone in water, and skin preparation and draping were carried out in the usual manner. All papillary thyroid carcinoma has been con rmed via ne needle aspiration before surgery. Total endoscopic thyroid surgery procedure via oral vestibular approach: The oral cavity was sterilized 3 times with 0.5% iodophor and then rinsed with normal saline 3 times. After 0.5mm vertical incision taken from the inferior square of the orbicularis oris muscle of the lower lip, the oral mucosa was opened with a sharp knife, and then the 5mm Trocar was pierced directly from the incision to the middle of the chin and pressed close to the mandible as it passed through the chin. Through the subcutaneous puncture direction of the chin, rstly vertically downward, then forward below the platysma muscle, the 5mm Trocar was used to puncture several times in the thyroid cartilage region, with the subcutaneous space initially established. About 2.5-3cm distance from the median line, and about 2cm from the labial buccal and gingival sulcus, making oblique incision of 0.5cm small incision with sharp knife, then 5mmTrocar was directly pressed against the mandible on both sides of the incision and punctured in the direction of ipsilateral sternoclavicular joint. Ensure the Trocar con uent with the middle puncture tunnel at the lower level of the platysma muscle. The 5mm Trocar was lled with CO 2 with the gas pressure at 3mm Hg and the inlet ow rate at 15L/min. The electrocoagulation hook is entering from the right 5mmTrocar to cut open the loose fascia tissue below the thyroid cartilage, making the subcutaneous space gradually enlarged. The ultrasonic knife was used to further expand the space downward and bilaterally, and the sternocleidomastoid muscle was dissociated from the sternocleidomastoid muscle on both sides of the sternocleidomastoid muscle. After the construction of the cavity, the in ation pressure of CO 2 is adjusted to 6mm Hg, and the inlet ow rate of CO 2 is adjusted to 35L/min. The white line of the neck was cut with ultrasonic knife to expose the thyroid gland and cut the false capsule of the thyroid gland(Fig2.).
The 10mm incision was taken from the ipsilateral axillary fossa along the dermatoglyphic direction, and a blunt subcutaneous puncture device was used to puncture from the armpit along the super cial layer of the subcutaneous deep fascia to the cervical platysma muscle, close to one side of the sternocleidomastoid muscle to open the tunnel into the neck space, and then place 10mm Trocars in the armpit. Entering the endoscopic "bendable L-shaped" retractor to help retract the ribbon muscle(Fig3.).
Initially, the amount of 0.1ml carbon nanoparticles was injected into each side of the gland. After excision of anterior laryngeal lymph nodes and tapered lobes, with ultrasonic knife downward cutting of the isthmus was done to cut open berry ligament and adjust "bendable L-shaped" retractor to open the ribbon muscle above the cricothyroid joint, so as to expose the upper pole of the thyroid gland.
Electrocoagulation hook was used to cut open a small part of sternal thyroid muscle, soon after, endoscopic multi-functional separation forceps with nerve monitoring function was used to avoid the injury of external branch of superior laryngeal nerve with cricothyroid muscle tremor evaluation method. Then the branches of the upper polar vessels were cut off with ultrasonic knife. The V1 signal was measured in the area of carotid sheath, then the superior parathyroid gland was bluntly separated by endoscopy, with blood supply preserved in situ. The carotid sheath was cut open and the lymphoadipose tissue in the central region was dissociated medially. The recurrent laryngeal nerve was dissected below the inferior pole of the thyroid and the R1 signal was detected. Dissect with endoscopic ne separation forceps to bluntly separate the inferior parathyroid gland, and try to retain the blood supply of the inferior parathyroid gland in situ. If the inferior parathyroid gland cannot be preserved in situ, it can be actively removed and transplanted into the sternocleidomastoid muscle or deltoid muscle. Then go back to the laryngeal point and dissect the recurrent laryngeal nerve, continue to cut off part of the suspension ligament, bluntly separate the recurrent laryngeal nerve from the gland, and then completely remove the thyroid tissue near the cricothyroid joint attached to the trachea with an ultrasonic knife. Note that the head of the ultrasonic knife should maintain a distance above 3mm from the recurrent laryngeal nerve.
Next, the recurrent laryngeal nerve was dissected retrograde along the shape of the nerve with endoscopic separation forceps, and the nerve tunnel was opened to block remove from the rst and second layers of lymphoid adipose tissue in the ipsilateral central area, reaching the innominate artery and thymus below. Then preserve the specimen with a specimen bag. The specimen bag was removed from the axillary incision. Right thyroid cancer also requires a dissection of the third layer of central lymphoid adipose tissue, the lymph node behind the recurrent laryngeal nerve. With blunt separation close to the recurrent laryngeal nerve, cut and push with ultrasonic knife to remove the lymphoid adipose tissue in front of the esophagus, take out the free lymphoid adipose tissue from the back of the nerve and remove the whole piece as far as possible. At this time, we can use the "bendable L-shaped" retractor to push the common carotid artery outward to facilitate our next lower dissection (Fig4.).
The specimen was put into a specimen bag and removed from the axillary incision. Following up cleaning, the R2 signal and V2 signal were monitored and compared with R1 and V1 to see whether the signal was decreased. If the signal is not signi cantly reduced, the function of the recurrent laryngeal nerve is well protected. Rinse the operation eld with a large amount of distilled water, carefully check the hemostasis, suture the white line, place a high negative pressure drainage tube in the operation cavity, draw out from the axillary incision, and x the drainage tube in the skin layer. The 5mm Trocar on both sides of the oral vestibule and the 5mm Trocar in the middle were withdrawn in turn. The three 0.5cm oral mucosal incisions were intermittently sutured with absorbable lines, and each incision was sutured with two stitches. Finally, the oral cavity was sterilized 3 times with 0.5% iodophor and then rinsed with normal saline 3 times.

Results
Patient demographics and clinical characteristics are summarized in Table 1. The distribution of age, gender, and thyroid mass size did not differ signi cantly between the two groups. Furthermore, there was no signi cant difference in the postoperative pathological results, and the percent of malignant tumors between the two groups had no signi cant difference. In sum, the above clinical and pathological data con rm that it is feasible to compare the results of the two groups.
Upon the above, evaluation of surgical data was adopted between the two groups. As shown in Table1, in the novel Mini group, operative time was not signi cantly longer than that in the conventional group. Moreover, the specimen removal time did not differ between the two groups, suggesting that Mini surgery does not increase the complexity of the operation. Notably, the hospitalization time of patients in the novel Mini group was obviously less than that in conventional group. In conclusion, compared with traditional surgery, Mini surgery reduces the length of hospital stay without increasing the complexity of the operation. Numbness of the lower jaw, pain, mandibular muscles dysfunction and mandibular edema are the most common side effect after thyroidectomy. Firstly, in order to evaluate and compare the numbness of the lower jaw of the patients between the two groups, in the rst day post-operation, appearance of numbness of the jaw, the nylon lament check score, pressure needle puncture examination score, or numbness VAS score were administrated and results indicated that the degree of numbness of the jaw in novel Mini group is signi cantly better than the conventional group(P < 0.01). Moreover, the pain of the axillary incision was evaluated using the pain VAS score method, and the results also showed that novel Mini group was signi cantly better than that in the conventional group(P < 0.001). Furthermore, in terms of mandibular muscles dysfunction, dysfunction of mandibular muscles was observed in six of fty-ve patients in the conventional group, whereas no dysfunction of mandibular muscles observed in Mini group(P < 0.001). At last, the results of post-operation mandibular edema between two groups indicated that degree of mandibular edema postoperative in Mini group was markedly slighter than that in the conventional group, whereas there was no difference between the two groups pre-surgery. In sum, patients in novel Mini group generally showed no signi cant numbness in the lower jaw, no signi cant pain in the axillary incision, and the degree of edema in the lower jaw was slighter in Mini group.
In terms of surgical results and severe complication, as shown tin Table 2, there were no signi cant differences in RLN palsy, transient hypocalcemia, and subcutaneous emphysema between the novel Mini group and the conventional group. Intriguingly, post-operation infection was observed in two of fty-ve patients in the conventional group, whereas no post-operation infection observed in Mini group(P < 0.001), which is attributed to the minor incisions and wounds in Mini transoral endoscopic thyroidectomy ( Fig. 5.).
Additionally, this approach has been improved to make the incision in the mouth smaller, reduce the damage to the surrounding tissues, edema and numbness in the lower jaw post-surgery. In order to make up for the loss of surgical operation space, another small incision was made in the armpit as an auxiliary. However, the small incision was clinically veri ed to have little effect on aesthetics, and did not add additional surgical pain and postoperative complications.
Of note, the novel Mini method reduces the incision in the oral cavity and has a high degree of matching with trocar, which reduces the risk of infection caused by second-class incisions. Furthermore, the improved surgical method did not increase the risk of infection and reduced the postoperative infection and effects on taste and smell when the disinfection time was reduced and the concentration and dosage of iodophor disinfection were reduced.

Discussion
There is an increasing number of transoral endoscopic thyroidectomy being performed worldwide [9,10] . With its ability to be completely scarless and with the most short and direct path to the thyroid, transoral endoscopic thyroidectomy vestibular approach is a logical next step in the evolution of endoscopic thyroid surgery [11] . In present study, we designed and adopted a novel Mini transoral endoscopic thyroidectomy in patients with thyroidectomy. The most important priority in evaluating and adopting a new surgical procedure is its safety. The conventional transoral endoscopic thyroidectomy has been reported to be safe [12] . However, there is still a lot of room for improvement in the traditional methods and techniques being used now [13,14] . Hence, in this study we evaluated the safety and e cacy of novel Mini transoral endoscopic thyroidectomy in the rst 45 patients, focusing on safety and complications.
First, our series of study compares the safety and e cacy of novel Mini transoral endoscopic thyroidectomy with conventional transoral endoscopic thyroidectomy speci cally for patients with thyroidectomy. Similar to previously published trials comparing endoscopic and open thyroidectomy [15] , Mini transoral endoscopic thyroidectomy did not have a signi cantly longer overall operative time compared with conventional transoral endoscopic thyroidectomy. This is in large part due to time spent inserting ports and establishing the working space with ne laparoscopic instruments. Outside of operative time, it is critical that any new technique be at least equivalent to the standard of care in terms of outcome. In our cohort, the Mini transoral endoscopic thyroidectomy group had less post-operation hospitalization compared to the conventional transoral endoscopic thyroidectomy.
New techniques also bring with them approach speci c complications [15,16] . For instance, the increased risk of infection from transforming a clean procedure to a clean contaminated operation were key concerns following the introduction of conventional transoral endoscopic thyroid surgery [17] . In the present study, there was no signi cant difference in the pathological results, and the occurrence of malignant tumors between the two groups was not signi cantly different. In the novel Mini transoral endoscopic thyroidectomy group, operative time was not signi cantly longer than that in the conventional transoral endoscopic thyroidectomy group. Moreover, the specimen removal time did not differ between the novel Mini transoral endoscopic thyroidectomy group and the conventional transoral endoscopic thyroidectomy group.
Axillary pain and numbness of the chin after conventional transoral endoscopic thyroidectomy are important reasons affecting the effect of surgery outcome [18,19] . More importantly, the nylon wire examination score, pressure needle puncture examination score, or numbness VAS score indicated that the degree of numbness of the jaw in novel Mini transoral endoscopic thyroidectomy group is signi cantly better than the conventional transoral endoscopic thyroidectomy group. Moreover, the pain of the axillary incision using the pain VAS score method also showed that novel Mini transoral endoscopic thyroidectomy group is signi cantly better than the conventional transoral endoscopic thyroidectomy group. Patients in novel Mini transoral endoscopic thyroidectomy group generally showed no signi cant numbness in the lower jaw, no signi cant pain in the axillary incision, and the degree of edema in the lower jaw was slight. Many advantages of novel Mini transoral endoscopic thyroidectomy have led to this result. For instance, without cutting off any muscles in the mandible, the cavity was constructed by direct puncture with three 0.5cmTrocar, which caused slight injury to the oral cavity and mandible. The middle 0.5cmtrocar was punctured from the midline and the bilateral 0.5 cm trocar was punctured from the 2.5-3cm away the midline to avoid the anatomical area of the mental nerve and prevent the injury of the mental nerve. After operation, there was almost no sensation of numbness and loss of consciousness in the lower jaw. After operation, it will not affect the voluntary expression of facial micro expression, the ne movement of mouth and pronunciation. The swelling of mandible was alleviated obviously after operation. One cm incision was made along the dermatoglyphics from the ipsilateral axilla of the lesion. The subcutaneous tunnel from the armpit to the neck was established with the endoscopic visual separation rod made by Schneider. After the specimen was put into the specimen bag during the operation, the specimen was dragged out from the subcutaneous tunnel to the armpit to be easier to take out. During the operation, 10 mm trocar can be placed from the axillary incision, and then from the armpit into the endoscopic retractor (extensible "L" type) to help retract the banded muscle. The drainage tube can be drawn from the axillary incision, so the neck does not leave any puncture holes or micro-incisions, which can achieve "really no marks". During the operation, 5 mm endoscopy is not easy to con ict with 5 mm Trocar on both sides. 5 mm Trocar is more likely to pass through the chin subcutaneous with mild mental skin compression, producing mild skin redness, swelling or subcutaneous ecchymosis. Intraoperative trocar from the axillary into the separation forceps or grasping forceps to help separate or pull tissues or organs, such as anatomy of parathyroid glands, can help to pull parathyroid glands, conducive to our ne in situ preservation of parathyroid glands and blood supply [20] . During the operation, the trocar from the axilla can enter the suction tube, so that the smoke produced during the operation can be sucked out from the side, and the fog of the endoscopic lens can be improved obviously. During the operation, trocar can be performed from the axilla, by which we can more clearly observe the situation of the superior thyroid pole and the anatomy of the superior laryngeal nerve. As such, our results indicated that novel mini transoral thyroid surgery is a safe technique when performed by experienced surgeons.
In conclusion, the new novel Mini transoral endoscopic thyroidectomy is safe and feasible, and reduces the damage to the functional muscles such as the mandibular diaphragm and lower lip muscles, signi cantly reduces the numbness and edema of the mandible after surgery, and reduces the impact on the expression muscle activity. Our novel Mini transoral endoscopic thyroidectomy is a feasible and safe option for select patients who require thyroidectomy, when compared with conventional transoral endoscopic thyroidectomy, and can be a viable alternative for patients wishing to avoid numbness and pain.
Abbreviations VAS: Visual Analogue Score; RLN: recurrent laryngeal nerve Declarations Ethics approval and consent to participate All the patients were over the age of 16 with the informed consent of the patients.

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