Acta Otolaryngol80: 410-414, 1975

AN EXTENDED APPROACH THROUGH THE MIDDLE CRANIAL FOSSA TO THE INTERNAL AUDITORY MEATUS AND THE CEREBELLO-PONTINE ANGLE Z. Bochenek and A. Kukwa

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From the ENT Department of the Medical Academy in Warsaw, Warsaw, Poland

(Received February 1, 1975)

accurate description of these operations come from William House, who in 1961demonstrated a technique of cutting part of the VIII nerve without damaging the function of the inner ear. Describing other techniques, House specified the exact indications for determining the approach to the meatus and the cerebellopontine angle in the cases of a neuroma of the VllTnerve according to localization of the tumour. According to this classification a tumour with a diameter of over 8 mm, or those extending beyond the area of the internal We describe an approach to the internal audi- acoustic meatus, should be removed by an aptory meatus and the region of the cerebello- proach through the labyrinth. Function of the pontine angle beneath the meninges of the mid- inner ear has a relative value in determining dle cranial fossa, after having drilled the upper the method of approach for removing the tupart of the pyramid and after cutting the mour mass. Thus the most important method, tentorium cerebelli. which permits the widest approach to the field' A submeningeal approach to the surface of of operation must allow for the following facthe pyramid through the middle cranial fossa tors: tumour size and location, continuity of has often been used in the past, particularly for the facial nerve and control of bleeding in the drainage of this area in the case of infection, case of damage to larger blood vessels. An exand also in head injuries. However, not until tended approach after section of the tentorium 1904 when R. H. Perry described the section of cerebelli, which was first suggested by Stiegthe VIII nerve in Meniere's disease, were vari- litz et al. in 1896 is not sufficient to view the ous specific techniques involving this region region of the cerebello-pontine angle adequadeveloped, among which is the operative ex- tely. In our opinion, the approach ad modum posure of the internal acoustic meatus and the House is also insufficient, especially in cases posterior cranial fossa by an approach through of removal of tumours in the region of the the middle cranial fossa. bulbus of the jugular vein, as those are loThe most extensive advocacy and the most calized medially in relation to the auditory-

Abstract. The submeningeal approach through the middle cranial fossa to the internal auditory meatus and cerebello-pontine angle after cutting the tentorium cerebelli is described. It is in some way similar to that used by Morrison & King. The approach is achieved by drilling the petrous bone to the level of the compact plate of the sigmoid sinus sulcus and to the lumen of the lateral semicircular canal. In this way it is possible to visualise safely the entire auditory-facialfasciculus, the region of the jugular foramen, the IX, X , XI, V and VI nerves as well as the lateral surface of the brainslem. I n m r qinionihis way should be and is preferable to the translabyrinthine approach through the mastoid process.

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Approach to internal auditory meatus and cerebello-pontine angle

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facial fasciculus. According to the description by Morrison & King (1973), Henderson uses an approach through the pyramid when removing tumours of the posterior cranial fossa, although details of this method are unclear. Our approach is similar to the combined approach used by Morrison & King (1973) but without the translabyrinthine part of the operation, We usually open the labyrint through the middle fossa, having the possibility to extend the approach in the direction of the sigmoid sinus. OPERATIVE TECHNIQUE Under general anesthesia, a 10 cm incision is made through all the tissues in the preauricular region just as in the approach through the middle cranial fossa. The entire surface of the squamous temporal bone is uncovered, and if the lambdoid suture is not readily seen in the area of the mastoid angle an additional incision is made in the post-auricular groove, beginning from the preceding incision and running in the direction of the mastoid process. Using a cutting burr, a plate of bone approximately 5.5 x3 cm is next removed. After exposing the meninges a 20 % solution of Mannitol is given i.v. approximately l.O/kg body weight. A fall in intra-cranial pressure is obtained after giving Mannitol, and this allows one separate of the meninges from the bone surface and to raise the temporal lobe in order to expose the petrous part of the temporal bone. The dura mater is separated from the anterior surface of the pyramid to the level of the sulcus of the superior petrosal sinus from above, and the hiatus of the facial canal from the front. The procedure here is for decompression of the VII nerve, according to Pulec (1966), or in exposing the internal auditory meatus for section of part of the VIII nerve according to Fisch (1970). Next, the superior petrosal sinus is gently dissected away from its sulcus, beginning from its orifice (to the sigmoidal sinus) and progressing in the direction of the pyramidal apex. Drilling the petrous bone is begun by first

Fig. 1

opening the mastoid antrum to the level of the compact plate of the slgmoidal sinus sulcus unveiling the lumen of the lateral semi-circular canal. Its course is a very important landmark in the successive steps of the operation. After opening the vestibule, the fundus may be readily located and the internal auditory meatus, which is not opened until a sufficient amount of bone has been removed for good visualization of the tumour. The removal of bone is begun laterally in relation to the internal auditory canal and progresses towards it. Such measures ensure greater safety with regard to the VII nerve due to the fact that even in opening the internal auditory canal the vestibular parts of the VIII nerve are located in the extreme lateral side in the fasciculus. After a sufficient amount of bone has been removed, the dura mater (tentorium cerebelli) is gently incised parallel to the upper border of the pyramid. Next, both flaps of meninges are separated and supported by suture threads. Acta Otolaryngol80

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Fig. 4

is possible to visualize the basilar artery and the brain stem. When the access to the tumour is sufficiently Such an approach gives us an exact view of the large and all the anatomical structures in the auditory-facial fasciculus, located in the field of internal auditory canal and the area of the angle operation. Inferiorly and somewhat laterally, have been identified, we may then proceed to the sigmoid sinus is seen together with the IX, remove the tumour. The decision whether to X and XI nerves, while supero-medially and remove the mass in fragments or in its entirety from the top the V, VI and sometimes the 111 depends on its size and vascularity. Quite often nerves. Somewhat deeper in relation to these it is possible to remove the tumour together structures is the cerebellum and the posterior with its capsule from the surrounding tissues inferior cerebellar artery. With further removal fairly readily. Blood vessels entering the of pyramidal bone in the direction of its apex it capsule or those already damaged earlier are coagulated by the use of a bipolar electrode. The separation of a large tumour is usually impossible, so that fragmentary removal is necessary, and in this way the access to the tumour is improved. After removal of the tumour mass and complete haemostasis it is necessary to check the integrity of all the nerves, particularly the facial nerve. The next step is to suture the edges of the incised meninges (tentorium cerebelli). Temporalis fascia is placed on the opened surface of the air space of the middle ear and petrous bone. By this means additional separation of the middle ear from the cranial cavity is achieved, which in turn guards against the liquorrhea and the possible spread of infection from the middle ear to Fig. 3 the meninges. A delay of 15-20 min is necesFig. 2

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Approach to internal auditory meatus and cerebello-pontine angle

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sary to allow for the dilatation of the temporal lobe. The removed plate of temporal bone is replaced in its former place and is sutured with Dacron. A rubber drain is placed into the epidural space for about 24 hours. Soft tissues are sutured in layers. In the postoperative period (2-3 days) Mannitol is given i.v. 1 g/kg body weight. All patients receive antibiotics prophylactically. DISCUSSION

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better than that passing through the mastoid process and the labyrinth, for the following reasons: 1. it gives a better orientation in the field of the operation, 2. it can be extended at any given moment, 3. it creates wider visualization of the area of the cerebello-pontine angle, which allows freer manoeuvering to achieve haemostasis and especially in haemorrhage from the posterior inferior cerebellar artery or its branches, 4. removal of part of the temporal bone can be used as the first step (decompression) in the case of large tumours in the posterior cranial fossa, 5 . it creates the possibility of visualization of all anatomical structures in this region from a better angle, 6 . it enables a wider and thus a better approach to the internal acoustic meatus and the auditory-facial fasciculus along its entire length, which is important in preserving the continuity of the VII nerve, 7. it creates facilities for decompression of the VII nerve, 8. communication with the middle ear is the same as in the approach through the labyrinth, but with this technique it is easier to separate these two spaces, namely the cranial fossa and the middle ear, by placing temporalis fascia or a fragment of fascia lata on the surface of the pyramid, 9. it is well tolerated by patients, 10. in the case of complications it is easy to achieve access to the operated region.

The removal of tumours of the VIII nerve extending beyond the internal acoustic meatus and for tumours of the cerebello-pontine angle is performed through a different approach from those which have been previously described. This modification creates a new and improved possibility for surgical intervention in the region of the cerebello-pontine angle. Thus the removal of the upper part of the pyramid up to the level of the bony plate of the sigmoid sinus laterally and to the lumen of the horizontal semicircular canal medially, enables the visualization of the entire auditory-facial fasciculus, the bulbus of the jugular vein, the IX, X, XI, V, VI and I11 nerves. In this way it is possible to visualize the anterior surface of the cerebellum and the lateral recess of the fourth ventricle, as well as the lateral surface of the brain stem. The anterior inferior cerebellar artery is also well seen along its entire length from the basilar artery to its loop in the area of the orifice of the internal acoustic meatus. The approach described was used exceptionally only in the situation when, according to House (1964, the approach through the middle cranial fossa was found to be insufficient during the course of the operation. This was the case when the tumour was found to be larger than RESUME anticipated and extended beyond the internal acoustic meatus. It is considered that this Les auteurs decrivent la voie submeningeale de la fosse ckrebrale moyenne pour aborder le conduit auditif interne should always be the routine approach when et I’angle ponto-cerebelleux, aprks I’incision de la tente the tumour is over 8 mm of diameter and de- du cervelet. La voie resemble un peu a celle utilisee mands a wider approach. This approach to the par Morrison et King. On proctde a fraiser le rocher jusqu’au niveau de la lame compacte de la gouttiere internal acoustic meatus and the anterior part sigmoide et jusqu’a la lumikre du canal semi-circulaire of the posterior cranial fossa is considered to be externe. On obtient ainsi en toute securite - une vue Acta Otolaryngol80

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suffisamment large sur le fascicule acoustico-facial, la region du trou dechire posterieur, les nerfs IX, X, XI, V, VI et la partie laterale du tronc cerebral. Les auteurs trouvent cette voie preferable B la voie trans-labyrintique a travers la mastoide.

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ZU SAMMENFASSUNG Der submeningeale Zugang durch die mittlere Schadelgrube zum inneren Gehorgang und zum Kleinhirnbruckenwinkel nach der Inzision des Tentorium cerebelli wird beschrieben. Dieser Zugang entspricht in gewisser Weise dem, der von Morrison und King benutzt wird. Der Zugang wird durch das Bohren des Felsenbeins bis zum Niveau der Lamina compacta des Sulcus sinus sigmoidei und zum Lumen des Canalis semicircularis lateralis erreicht. Auf diese Weise ist es ohne Gefahr moglich, den ganzen Fasciculus acustico-facialis, die Gegend des Foramen jugulare, den N . IX, X, XI, V und VI sowie auch die laterale Flache des Hirnstamms sichtbar zu machen. Unserer Meinung nach ubertrifft der beschriebene Zugang den translabyrintharen Zugang durch den Mastoid.

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REFERENCES Fisch, U. 1970. Transtemporal surgery of internal auditory canal. Adv Otorhinolaryngol 17, 203. House, W. F. 1964. Transtemporal bone microsurgical removal of acoustic neuromas. Arch Otolaryngol 80, 599. Morrison, A. W. & King, T. T. 1973. Experiences with a translabyrinthine-transtentorial approach to the cerebello-pontine angle. Technical note. J Neurosurg 38, 382. Perry, R. H. 1904. A case of tinnitus and vertigo treated by division of the auditory nerve. J Laryngol Otol19, 402. Pulec, J . L. 1966. Total decompression of the facial nerve. Laryngoscope 76, 1015. Stieglitz, L., Gerster, A. G. & Lilienthal, H. 1896. A study of three cases of tumor of the brain in which operation was performed-one recovery, two deaths. Am J Med Sci 1 1 1 , 509.

Z . Bochenek, M . D . Dept. of Otolaryngology Medical Academy of Warsaw Filtrowa 4412 Warsaw Poland

An extended approach through the middle cranial fossa to the internal auditory meatus and the cerebello-pontine angle.

The submeningeal approach through the middle cranial fossa to the internal auditory meatus and cerebello-pontine angle after cutting the tentorium cer...
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