Study on Clinical Application of Nerve Monitor in Parotid Tumor Surgery

XU Liang-peng JIA Bao-jun AO Jian-hua QU Dan-yang SHENG Yan-jiao

【Abstract】Objective The purpose of the study is to explore the application value of the nerve monitor adopted to pinpoint facial nerves before anatomization during a parotid tumor surgery. Methods Facial nerves of 36 patients were pinpointed by N800 nerve monitor produced by Shandong Weigao Group Medical Polymer Co. Ltd before being anatomized and exposed in parotid surgeries in order to protect the corresponding facial nerve branch and complete the related surgery. Results All the facial nerves of the 36 patients were located precisely and 108 related facial nerves were successfully anatomized and protected without any damage. Conclusion Pinpointing the facial nerve branch with a nerve monitor before anatomization promotes not only the efficiency of the surgery but also the safety of it and is proved to be more significant in a secondary surgery.

【key words 】Parotid Tumor； Facial Nerve； Nerve Monitor

【CLC】R739.8 【Document code】B【Article number】1004-4949（2014）01-0237-01

Parotid gland tumor，which accounts for 80% of salivary gland tumor and 30% of head and neck tumor， often needs to be excised by surgery. Face-lift incision is needed during the parotidectomy surgery. Besides， the parotid gland is closely connected to facial nerve in various ways[1].Separating the facial nerve， as a result， is the key step in a parotid tumor surgery. There are different approaches to dissecting facial nerves [2] ，but all of them have their own risks. In order to minimize the potential risks， our department has introduced nerve monitor since 2011. And we adopt the nerve monitor in parotid gland tumor surgery to pinpoint the facial nerve branch before anatomizing， exposing and preserving them. We have applied this method to 36 cases of parotid gland surgery and have achieved satisfying achievements.

Case Report：

1 Materials and methods

1.1 Clinical Materials

There are 36 patients in total with 21 males and 15 females aged from 25 years old to 76 years old. The average age is 45.5 years old. Among the 36 cases， there are 25 pleomorphic adenoma， 4 Warthin tumor， 3 monomorphic adenoma， 2 basal cell adenoma， 1 adenoid cystic carcinoma of the parotid gland and 1 mucoepidermoid carcinoma of parotid. All facial nerves of these patients were reserved. Surgical parotid procedures were performed on all the patients， including 30 superficial lobe parotidectomies， 4 deep lobe paratidectomies， and 2 enlargement lobe parotidectomies. Of all the patients， 2 have experienced a surgery before but suffered a recurrence of parotid gland tumor then..

1.2 Anesthesia

All the patients were conducted endotracheal intubation after general anesthesia through intravenous administration.

1.3 Nerve Monitor

N800 neural monitor produced by Shandong Weigao Group Medical Polymer Company Limited was applied. After successful anesthesia， the negative stimulating electrode and the reference electrode were inserted and fixed into the subcutaneous， which is controlled by respective flank facial nerve branch， before connected to N800 EMG monitor. Check carefully to see whether the position of vocal contact surface of electrode and resistance is conformed to the requirements and make adjustment when needed. DC stimulating current ranges from 0 to 3 mA， the duration of the stimulating current varies from 50 to 250μs monophasic wave， and stimulating frequency is 4 times / s. The operation can start out once the verification is completed.

1.4 Surgical methods

Performed in a conventional way， the parotid surgery should start with an incision on platyma， widening the incision and exposeing the superficial lobe envelope， applying the stimulating probe when the leading edge of the superficial lobe of the parotid gland is found. Pinpoint the facial nerve branch area with the single-pole stimulator until the synchronized beep （4/s） is heard. After precise anatomization， the corresponding facial nerve branch will be exposed soon， and the various facial nerve branches that matters in the surgery， by further exploration， will be pinpointed and should be well protected. The parotid gland tumor and its peripheral parotid gland tissues then can be removed without influencing the facial nerves. （fig 1-3）

2 Results

The facial nerve branches of all the 36 patients were successfully detected and dissected. At the same time， postoperative facial paralysis symptom happened to ten of them. Given that symptom was caused by intraoperative traction， they all recovered in three or six months. The other 15 patients were free of the postoperative symptom of facial paralysis after surgery.

3 Discussions

3.1 The importance of dissecting facial nerves in parotid gland surgery.

The relationship between the facial nerve as well as its branches and the parotid gland is significant in parotid gland surgery[3]. Parotid gland， surrounded by fascia sheath formed by deep cervical fascia， is clinically divided into shallow and deep lobes by branches of the facial nerve. Facial nerve branches， usually walk in the substance are stored in the deep surface of the superficial lobe of parotid gland， the layer in which other branches also live. Facial nerves and gland lobules are separated by loose connective tissue， which makes it easier to expose and protect facial nerves when remove the parotid gland. In parotid tumor resection， facial nerves should be dissected and maintained as far as possible， especially the zygomatic and marginal mandibular branch， which play important roles in facial functions and expressions. Mandibular margin， 1 cm above or beneath the the edge of mandible， has long process， and is easy to be damaged in the surgery， making it the most preferable as the branch to be dissected. Neck branch dominated platysma， however， is less significant in surgery. Studies have shown that resection of benign parotid facial nerve dysfunction accounts for 10 % to 60%[4]. Effective intraoperative protection and treatment of facial nerves and the prevention of postoperative paralysis have been regarded as an important project that maxillofacial surgeons have been devoting to for a long time.

3.2 Advantages of the nerve monitor in the facial nerve anatomy application

Nerve monitoring technology was at the very beginning， applied in the protection of facial nerves and was introduced to China comparatively later than other countries[5]. N400 nerve monitor is a kind of evoking EMG instrument， which， via pulse current， stimulating facial nerves so as to evoke its corresponding muscle to practice electromyography activity. And by inserting multi-channel electrodes into the muscle or the surface of the muscle， the equipment can collect and record the information of the compound muscle action， namely electromyography. The stimulating current intensity varies from 0. 01 to 3.00mA and can be selected according to specific circumstances. The stimulating electrode may be optionally unipolar or bipolar with its pulse duration up to 3.1 ms. The monitor is equipped with four EMG electromyography channel， built-in stimulator and a sonorous speaker. N400 is the ideal equipment especially when the surgery is close to motor neurons or mixed nerves. The stimulator of this machine can be used to trace the influencing branch fibers so as to locate and identify nerves and accelerate the surgical process.

When nerves are stimulated by single machine or electricity， they will evoke the response of facial muscles EMG activity， which serves as the proof to determine the process of the anatomy of facial nerves. Although the application of the nerve monitor plays a significant role in the protection of the facial nerve， it can not be used continuously during the surgery and its damage also can not be completely avoided. In secondary or multiple surgeries[6]， due to the partial adhesion， and the already changed normal anatomical structures， it is more likely to make damage to nerves. Pinpointing facial nerves with nerve monitor before anatomizing would save a lot of time and would not damage nerve if the monitor is gently applied. Find the nerve and continue to dissect until it is completely separated from the parotid gland. Expose the operating area of facial nerves and remove the parotid tumor. Such a procedure can greatly reduce the risk of intraoperative facial nerve branch injury and can also lower the complexity to seek the nerve especially when the facial nerve is anatomically varied. This surgical approach can avoid the possible damage caused by unreasoning anatomization， and can also overcome the shortcomings of pure and simple monitoring， so that has greatly improved the security of the operation especially in the parotid full cut and secondary surgery.

3.3 Details of nerve monitor that should be paid attention to in parotid gland surgery application

3.3.1 Electrodes installation and fixation

In parotid gland surgery， receiving electrodes should be respectively inserted into muscles dominated by facial nerves in lateral supraorbital area，zygomatic are， upper lip and lower lip. Referring electrodes are generally inserted into the muscle tissue of zygomatic space. The device should be monitored after connection， to ensure its working order during the surgery， as a result， the wires should be checked to see if they are all connected correctly and if the instrument is in its working status. Electrodes inserted into the body should be fixed properly lest the accidental detachment during operation leaving the corresponding nerve monitoring uncompleted.

3.3.2 Interference problems

The nerve monitor is a very sophisticated device， making it easy to be interfered in the monitoring process by additional current stimulation， such as electric knife， mobile phone. If that happens， the monitor display will break off or in disorder. All kinds of possible interference should be shielded before the surgery or used alternately during the surgery.

3.3.3 Scope of application

In parotid gland surgery， monitoring the facial nerve is the best way to prevent hospital injury in that this approach can greatly reduce the possibility of facial nerve injury in surgery[7]. But for patients who have already had symptoms of nerve injury or paralysis ， it is inappropriate to apply nerve monitor to them for they cannot receive current stimulation nor make corresponding reaction， which will affecting the analysis and decision of surgeon.

References

[1] Tweedie DJ， Jacob A. Surgery of the Parotid Gland： Evolution of Techniques， nomenclature and a revised classification system [J]. Clin Otolaryngol， 2009， 34（4）： 303-308.

[2] Zou Zhi， Liu Kai. Effects of Different Anatomical Methods on Facial Nerve Function [J]. Progress In Modern Biomedicine， 2010， 10（11）：2117-2119

[3] Zhang Xuehui， XiaoPing. Clinical Significance of Facial Nerve Dissection in Parotid Surgery [J].Chinese Medical Herald， 2008， 5（24）：219-220.

[4] Wu Liehong，Clinical Study of Regional Excision of Benign Parotid Gland Tumor [J]. Chinese Journal of Otorhinolaryngology of Integrated Traditional and Western Medicine.2008， 16（2）：137.

[5] Pan Kai， GebhartzC，KrausD. Application and Evaluation of Neural Detector in thyroid surgery [J]. Chinese Journal of General Surgery.2003， 18（12）：731-732.

[6] Jiang Futing， Zhang Xiliang. The Application of Nerve Monitor before Anatomization of Recurrent Laryngeal Nerve in Thyroid Surgery [J].Shandong Medical Journal，2010，50（44）：108-109.

[7] Ding Ruifang， Wang Lili. Experience of Applying Nerve Monitor in Nerve Micro-Surgery [J] Nursing Journal of Chinese People's Liberation Army.2010， 10（11）：2117-2119.