, 심대보

중앙대학교 의과대학 이비인후-두경부외과학교실¹ 연세대학교 의과대학 이비인후과교실²

문인석

, 김진

, 심대보

, 이원상

1Department of Otorhinolaryngology-Head & Neck Surgery, College of Medicine, Chung-Ang University,

2Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul, Korea

In Seok Moon, M.D.

, Jin Kim, M.D.

, Dae Bo Shim, M.D.

, and Won-Sang Lee, M.D., Ph.D.

내이, 중이, 외이 및 경정맥구를 침범한 전정신경초종

Vestibular Schwannoma Extended to Inner Ear, Middle Ear, and Jugula Fossa

▒ Introduction

Histologically, Vestibular schwannoma develops in the myelinated part of the vestibuo-cochlear (VIII) cranial nerve, often in the internal auditory canal (IAC). However, Schwann cells are also present in the modiolus, close to the spiral

ganglia²⁾, so schwannomas theoretically may arise in this area, the labyrinth.

Schwannoma confined to the labyrinth is called an intralabyrinthine schwannoma and become more frequently be reported with the introduction of magnetic resonance imaging (MRI). Falcioni et al⁶⁾reported 5 cases of veatibular

J Korean Skull Base Society 3 : 95~100, 2008

Intralabyrinthine schwannoma is rare and vestibular schwannoma extended into intralabyrinthine area is rarer. Until now, there have been no reports of schwannomas extending simultaneously in the inner ear, middle ear, and jugular foramen. We report the first experience of a vestibular schwannoma simultaneously involving the IAC, cochlea, vestibule, middle ear, external ear, and jugular foramen which removed via modified surgical technique called as ‘Rope-skipping’.

논문 접수일 : 2008년 10월 5일 심사 완료일 : 2008년 10월 20일

주소 : Department of Otorhinolaryngology, Yonsei University College of Medicine, 134 Sinchon-dong, Seodaemun-gu,

Seoul 120-752, Korea 전화 : +82-2-2228-3606 전송 : +82-2-393-0580 E-mail : [email protected]

Won-Sang Lee, MD, PhD

교신저자

schwannoma, labyrinth, facial nerve

Key Words

원저1 원저2 원저3 증례1 증례2 증례3 증례4 증례5 증례6 증례7

schwannomas which involved labyrinth and suggested that they should be distinguished from intralabyrinthine schwannomas because of the different clinical implications.

Shin et al¹²⁾ reported a case of vestibular schwannoma simultaneously involving the cochlea, vestibule, and IAC and named it canalolabyrinthine schwannoma.

Until now, there have been no reports on schwannomas simultaneously involving inner ear, middle ear, and jugular foramen. Here, we report the first experience of a vestibular schwannoma simultaneously involving the IAC, cochlea, vestibule, middle ear, external ear, and jugular foramen which removed via modified surgical technique called as

‘Rope-skipping’.

▒ Case Report

A 56-year old woman visited the Department of Otorhinolaryngology at Severance Hospital in Seoul, Korea.

She complained of progressive left-sided hearing loss over the past 2 years, which was accompanied by occasional otorrhea. She had no known history of medical illness. On otoscopic examination, a protruding mass within the left external auditory canal (EAC) was found. Punch biopsy

through the EAC was performed and was reported as epithelial hyperplasia. Pure tone audiometry revealed deafness of the left ear and normal hearing on the right ear.

She did not complain any vestibular disturbance, but bithermal caloric test showed a 73% canal paresis on the left ear and the rotator chair test showed decreased gain on a phase lead for the VOR.

The patient showed mild facial palsy (grade II according to the House-Brackmann scale) and the elctroneuronographic (ENoG) test showed a 59.4% degeneration rate of the left facial nerve. Lower cranial nerve (CN IX, X, XI, XII) deficit were not found.

Temporal bone CT scans showed an expansile mass with bony erosion in the left cerebellopontine angle (CPA) cistern that extended into left IAC, middle ear cavity (MEC), EAC, and jugular foramen (Fig. 1A). Erosion of the porus acousticus, posterior wall of petrous internal carotid artery (ICA), and mastoid segment of the facial canal were found.

A gadolinium enhanced MRI revealed an intensely enhanced left CPA cistern mass extending into the IAC, MEC, and EAC and jugular foramen. However, the labyrinthine extension was overlooked and its report was consistent with glomus jugulare paraganglioma on the first radiologic report

Preoperative imaging study

A. Temporal bone CT scan shows an expansile mass with bony erosion on left cerebellopntine angle(CPA) and extended into left internal auditory canal(IAC), middle ear cavity(MEC), and jugular foramen.

B&C. A gadolinium enhanced MRI revealed intensely enhanced left jugular foramen mass extending into CPA, IAC, MEA, EAC, and jugular fossa D. On preoperative vascular angiography for embolization, the tumor was not hypervascularized and feeding vessel was not found.

A B

C

D Fig. 1

(Fig. 1B&C). On preoperative vascular angiography for embolization, the tumor was not hypervascularized and the feeding vessel was not found (Fig. 1D). Re-evaluation of the preoperative MRI was done and it showed the presence of tumoral extension into the basal turn of the cochlea and semicircular canals (Fig 2). There was a strong possibility of vestibular schwannoma simultaneously involving the inner ear, MEC, EAC, and jugular foramen.

None of the conventional surgical techniques could completely remove the tumor and preserve facial function because the tumor mass involved the CPA, inner ear, middle ear, and jugular foramen. Therefore, the patient underwent mass excision via a combined type A infratemporal fossa (ITF) and transotic (TO) approach that involved the application of a modified facial nerve handling technique, which is called ‘rope-skipping’, to preserve facial function (Fig. 3).

After removal of the schwannoma in the EAC and MEC, posterior canal wall of the EAC was drilled. The fallopian canal was skeletonized from the labyrinthine segment to the stylomastoid foramen and was exposed in the neck to its entry into the parotid gland. After removing the bony shell of the fallopian canal, the nerve was freed from the surrounding bone and mobilized for gentle lateral retraction. The basal

turn of cochlea and labyrinth were opened, the tumor was impacted in them (Fig. 4A). After tumor removal, a labyrinthectomy was performed and all of the turns of the cochlea were drilled to expose the internal carotid artery. The lower cranial nerves (CNs) were identified in the neck and

Gadolinium enhanced MRI coronal view showed the presence of tumoral extension into the basal turn of the cochlea(Arrow).

A B

Fig. 2

Mass excision via a combined modified ITF type A and transcochlear approach applying the rope-skipping technique.

This technique makes it easier to remove the mass around the facial nerve with minimal trauma to the feeding vessels. The position of the facial nerve could be changed according to the surgeon’s convenience

Fig. 3

followed proximally toward the pars nervosa in the foramen.

The sigmoid sinus was ligated and incised to rule out jugular paraganglioma and to open the jugular bulb to expose the jugular foramen. There was no evidence of tumor in jugular vein. The tumor of the jugular bulb was dissected out of its bed, and special care was taken to ensure that all of it was removed from the hypotympanum (Fig 4B). Then, the jugular bulb was packed with adipose and muscle tissue. The posteriror fossa dura was incised and the tumor was debulked and completely removed. To prevent CSF leakage, the mastoid cavity was filled with abdominal fat.

The postoperative course was uneventful. One year later, there was no evidence of recurrence (Fig. 5), and the facial nerve function showed a grade II (Fig. 6).

▒ Discussion

The reported frequency of intralabyrinthine schwannoma has increased with the development of MRI over the last few years. In some articles, pure intralabyrinthine schwannomas have been listed with labyrinthine involvement by vestibular schwannomas5, 8, 9, 10). We think that the vestibular schwannomas involving inner ear should be distinguished from ISs because of differing clinical implications and, probably, the different site of origin, which is in agreement with Falcioni et al⁶⁾and Zbar et al¹⁴⁾. In fact, although it is not possible to definitively identify the origin of a schwannoma with IAC and inner ear involvement⁴⁾, the hypothesis of progressive involvement of the labyrinth during the growth of a vestibular schwannoma seems to be more reasonable.

Intraoperative findings

A. The lateral semicircular canal was opened, the tumor impacted in it(arrow).

B. After complete removal of tumor. The facial nerve (arrow) is totally decompressed from the labyrinthine portion to the stylomastoid foramen.

C. The pathology of tumor was confirmed as schwannoma.

A B C

Postoperative MRI findings One year later, the MRI showed no recurrence of tumor. Operated site was filled with abdominal fat (arrow).

A B

Fig. 5

This is supported by the fact that cochlear involvement is more frequent than vestibular involvement. This difference can be explained by the presence of the weakest part of the fundus, the cribriform area, between the IAC and the cochlea¹⁾. In rare cases, tumors involving the inner ear can exhibit further growth into the middle ear, through the oval window or the round window. Because of the natural barrier represented by the footplate, the round window route is more probable and has been reported more frequently in the literature^{1, 11, 13)}. In our patients, Labyrinthine invasion was clearly visible on MRI (Fig. 2). The tumor seemed to completely fill the inner ear, with a small component protruding into the middle ear cleft through the round window. Then the tumor penetrated the tympanic mambrane and filled with EAC. To the direction of the jugular fossa, we assumed that the vestibular schwannoma extended in the CPA direction first, and then extended to the jugular fossa through jugular foremen along to glossophryngeal nerve or vagus nerve route.

In treating vestibular schwannomas involving the inner ear, no hearing preservation procedure is feasible. Therefore, the middle cranial fossa approach, which was originally meant to preserve hearing, does not make sense and it

cannot handle the jugular foramen lesion. The retrosigmoid approach, which does not allow access to the inner ear, is contraindicated in the presence of intralabyrinthine tumoral extension. The classic Translabyrinthine approach allows opening and control of the vestibule and semicircular canal while the cochlea remains inaccessible.

TO approach can handle the cochlea as well as vestibule⁷⁾, but requires skeletonization and preservation of the bony fallopian canal. It is hard to preserve the bony canal during the procedure and has limitations in accessing the deeper portion like the jugular fossa. ITF type A requires the transposition of the facial nerve and supply good surgical view³⁾, but this technique causes transient paralysis. The transcochlear approach requires posterior transposition of the facial nerve and exhibits no better than HB grade III postoperatively, which is mostly due to the loss of vascular supply.

We removed the tumor in the inner ear, middle ear, and jugular foramen with combined type A ITF and TO approach with modified facial nerve handling technique, which is called the ‘rope-skippng’technique. The major benefit of the rope- skipping technique is minimal trauma to the feeding vessels of the facial nerve, while other benefits include a wide

Postoperative findings of facial function.

One year later, favorable facial function (HB grade II) were noted.

A B

Fig. 6

surgical field, direct root of the cerebellopontine angle, and an easier approach to the jugular foramen without facial nerve transposition. The position of the facial nerve can change according to the surgeon’s convenience (Fig. 3).

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