Facial nerve reconstruction using a split hypoglossal nerve in treating unilateral facial palsy after acoustic neuroma removal

정효진, 고승현, 이원상, 문인석

연세대학교 의과대학 이비인후과학교실

Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul,

Hyo-Jin Chung, MD, Seung-Hyun Koh, MD, Won-Sang Lee, MD, PhD, In Seok Moon, MD, PhD

Facial nerve reconstruction using a split hypoglossal nerve in treating unilateral facial palsy after acoustic neuroma removal

J Korean Skull Base Society 6권 2호 : 28~33, 2011

Two patients underwent split hypoglossal-facial nerve anastomosis(anastomosis of a split hypoglossal nerve to the facial nerve) for treatment of unilateral facial palsy. All patients previously had undergone removals of a large acoustic neuroma. Facial nerve had been resected and immediately reconstructed in one patient. In the other patient, facial nerve had been anatomically preserved at the first operation and the interval between tumor resection and reconstruction was 10 months. Postoperative recovery of facial movement was good and the degree of hypoglossal nerve atrophy on the operated side was graded mild or moderate in all cases during an average follow-up period of 1.2 years. It was concluded that split hypoglossal-facial nerve anastomosis results in good facial reanimation and may reduce the degree of hemiglossal atrophy in comparison with the classic hypoglossal-facial nerve anastomosis.

논문 접수일 : 2011년 11월 10일 심사 완료일 : 2011년 11월 30일

주소 : Department of Otorhinolaryngology, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Korea

Tel : 82-2-2228-3606 Fax : 82-2-393-0580 E-mail : [email protected]

Won-Sang Lee, MD. PhD

교신저자

facial nerve paralysis, split hypoglossal-facial anastomosis, tongue atrophy

Key Words 종설1

원저1 증례1 증례2 증례3 증례4

▒ Introduction

Neural reconstruction of facial paralysis typically involves epineural anastomosis from a donor motor nerve. The ipsilateral hypoglossal nerve has been the popular option.¹⁾ The traditional hypoglossal-facial nerve anastomosis procedure is effective in establishing facial tone, rest symmetry, and some movement, but it may later be associated with lack of movement and the progressive atrophy of ipsilateral tongue.²⁾Split hypoglossal-facial nerve neurorrhapy, a modified surgical technique has been developed as a potential solution to reduce significant morbidity.^3-5) We report two cases of facial nerve reconstruction after vestibular schwannoma surgery with split hypoglossal nerve because using the split hypoglossal nerve may allow a restoration of facial function while preserving tongue function.

▒ Case presentation

Case 1

A twenty-year-old male patient visited our clinic with unilateral complete facial palsy on the right side. He previously had undergone removal of a ipsilateral giant acoustic neuroma, preserving facial nerve anatomically 10 months ago, but immediate facial palsy developed at that time and showed no interval change for 10 months. Upon systemic review, the patient had dead hearing on the right ear as a result of previous operation. Facial palsy was graded House-Brackmann grade V, showing no movement in forehead, incomplete closure in eye, and slight movement in mouth (Fig. 1A & B). There were no other specific findings upon physical examination and the patient’s lower cranial functions were also intact. Preoperative electromyography was performed and the results showed an abnormal myogenic potential for the right frontalis, nasalis, and oris muscle. Distant recruitment pattern was observed for right

Pre- and post- operative facial expression

A, B. Preoperatively facial palsy was graded as House-Brackmann grade V, showing incomplete closure in eye, and slight movement in mouth.

C, D. Postoperatively facial palsy was graded as House-Brackmann grade III, showing closure in eye with minimal effort, moderate movement in mouth angle.

E. Mild tongue atrophy was noted.

Fig. 1

A B

C D E

frontalis and oculi muscle, and reduced recruitment pattern was noted for right nasalis and oris muscle.

Facial nerve reconstruction with split hypoglossal nerve was performed to allow restoration of facial function with maximal preservation of tongue function. The hypoglossal nerve was split longitudinally. For each side, the nerve’s response was measured intraoperatively by recording the compound action potential of the tongue muscle. The split nerve showing lesser response was selected for anastomosis.

The facial nerve was transected at the proximal side to stylomastoid foramen, and its distal part underwent a direct anastomosis with the selected half of the hypoglossal nerve.

(Fig. 2 & 3)

After 6 months following the surgery, the patient started showing a recovery of facial function and after 2 years follow-up, he showed a moderate degree of facial dysfunction (H-B grade III) as a final result. The patient was able to close

his eyes, and movement was seen in the mouth angle, but mild tongue atrophy was noted.(Fig.1C-E) Also, upon maximal protrusion of his tongue, there was aligned movement in his upper eyelid.

Case 2

A Fifty-six-year old female patient with vestibular shwannoma who underwent gamma knife surgery(GKS) as the initial treatment 12 years ago, visited our clinic with mild unilateral facial weakness and disequilibrium for several months. Upon resting, she showed facial symmetry, but there was a slight asymmetry in her mouth movement upon maximal effort. She showed complete closure in her eyes.

Upon systemic review, the patient had dead hearing on the left ear after previous GKS. Also, vestibular function test showed a reduced vestibular function on the left side. There were no other specific findings upon physical examination Fig. 2

A

B

C

D

E

A. Schematic drawing of split hypoglossal-facial anastomosis B. Preparation of facial nerve (VII) and split of hypoglossal nerve (XII) C. Anterior cut of XII using sharp scalpel and superior division of XII

brought superiorly to proximal VII

D. Superior division of XII anastomosed to proximal VII E. Postoperative illustrations

and the patient’s lower cranial functions were also intact. MR imaging detected about 3cm sized tumor which had mulitcystic component.(Fig. 4A & B) Preoperatively, the tumor was diagnosed as vestibular schwannoma and was planned to remove via transcochlear approach. However, during the surgery, the facial nerve schwannoma was seen to extend from the IAC to the geniculate ganglion. Surgery was paused and after obtaining consents from the guardian, facial nerve origin schawannoma containing facial nerve

components was completely removed and split hypoglossal- facial nerve anastomosis was performed. 25 days after the surgery, ENoG result was 72.7%, facial palsy was graded House-Brackmann grade V.(Fig. 5A & B) 4 months following the surgery, there was no forehead wrinkling but eye closure was possible upon maximal effort and nasolabial fold was observed, showing recovery of facial palsy as House- Brackmann grade IV. On 12 months follow up after surgery, MR imaging showed complete tumor removal status and

Intraoperative findings

A. Transection of facial nerve at the proximal to stylomastoid foramen(arrow head) B. XII was split with sharp scalpel(black arrow)

C. Post-anastomosis state of VII and XII. Facial nerve trunk(arrow head), split upper portion of CN XII(black arrow), descending portion of CN XII(white arrow) is seen.

A B C

Fig. 3

Pre- and post- operative MRI findings

A, B. Preoperatively enhanced axial and coronal view. 3x3cm sized tumor which had multicystic component

A B

D

C Fig. 4

showed no signs of recurrence.(Fig. 4 C & D) Facial function showed further improvement with House-Brackmann grade III showing eye closure upon minimal effort and slight movement in mouth and tongue movement was almost normal and showed mild atrophy. (Fig. 5C-E)

▒ Discussion

Hypoglossal-facial nerve neurorrhapy is an accepted and widely used technique for neural rehabilitation of permanent facial nerve injuries. However, the traditional hypoglossal- facial nerve transfer (end-to-end anastomosis) is often associated with significant tongue morbidities due to immobility and atrophy of the ipsilateral side. To avoid or reduce hemiglossal dysfunction, some modified techniques have been developed,^{6, 7)}A modified technique, end-to-side hypoglossal-facial nerve anastomosis, is quick and preserves tongue function completely, but the quality of recovery is

variable and needs a longer length of remnant facial nerve.⁸⁾ The split hypoglossal-facial nerve anastomosis involves equal split of the hypoglossal nerve and then the superior nerve bundle is rotated superiorly so that anastomosis may be performed with the facial nerve trunk.⁹⁾ The most clinically significant benefit of this alternative approach is the reduced morbidity seen in the ipsilateral tongue and stable favorable facial recovery. This technique is also not fettered by length of remnant facial nerve. Although some minor deficits may persist, these dificits seem reduced when compared to total hypoglossal sacrifice, thereby allowing compensation of the patients to play a significant role in improved function.

Previous studies reported that the nature of interwoven axonal paths through the hypoglossal nerve and the axons not traveling in strict linear paths through the epineurium.¹⁰⁾ Sequential neuronal cross-sectional studies have shown variable and often twisting axonal paths through the nerve,

Post- operative facial expression

A, B. 1 month postoperatively, facial palsy was graded as House- Brackmann grade V, showing incomplete closure in eye and definite deviation in mouth at maximal effort.

C, D. 11 months postoperatively, facial palsy was graded as House- Brackmann grade III, showing closure in eye with minimal effort, moderate movement in mouth angle.

E. Mild tongue atrophy was noted.

Fig. 5

A B

C D E

therefore, if the nerve is split, many axons would likely be transected in the process. The ideal 50/50 distribution may eventually become a 30/30/40 distribution where, hypothetically, 40% of the axons are lost.⁷⁾The exact amount of axonal loss is purely supposition as this information is not attainable without cross-sectional studies of the reinnervated nerve.

In our case, postoperatively the patient showed moderate dysfunction(grade III) and his mastication function and pronunciation function were well preserved with only moderate tongue atrophy and it was much milder than that seen in complete hypoglossal nerve transection.

This is thought to be due to the regeneration ability of nerve fibers, and even though there may be only an initial distribution of 30/30 and 40% of nerve fiber are lost immediately after the surgery, this may increase up to 40/40 or 50/50 as time passes on along with the reinnervation.

Among two cases, the case of acoustic tumor removal and XII-VII anastomosis performed simultaneously started to show recovery after 3 months and showed H-B G III after 8 months. This was faster compared to the case of the delayed neurorrhaphy after tumor surgery, which recovery started after 6 months and showed H-B G III after 1 year.

Regeneration follows Wallerian degeneration in the injured facial nerve. At this time, grafts may also be needed to allow for appropriate reinnervation,¹¹⁾because it is supported by Schwann cells through growth factors release. Thus, when anastomosis is performed right after the nerve injury, which means immediate operation after Wallerian degeneration, it constantly receives signals from the proximal motor fiber, even though it may be a different nerve. This may cause less degeneration and also faster initiation of the recovery process after degeneration.

Therefore, we reached to the idea that this technique may provide a favorable alternative to the traditional method of complete hypoglossal sacrifice.

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