The “Expanded” Anterior Transpetrosal Approach to the Upper Cerebellopontine Angle

Key Message: Anterior transpetrosal approach, also called the Kawase’s approach, is often criticized for providing a rather narrow window to the upper cerebellopontine angle. We demonstrate here two additional operative nuances, namely a sub trigeminal petrosectomy and skeletonization of the internal auditory canal. These subtle nuances can horizontally expand the traditional Kawase’s rhomboid. Upper cerebellopontine angle lesions pose significant surgical challenges. In particular, the meningiomas in this location tend to permeate into various crevices, infiltrate the dura, and often encase the neurovascular structures.[1] Their surgical extirpation, therefore, must aim to balance an optimal extent of tumor resection and preservation of the neurological functions. Both retro sigmoid and anterior transpetrosal approaches are commonly employed to access the lesions of this location.[2] The anterior transpetrosal approach was described by Kawase to access the upper cerebellopontine angle (CPA) through by drilling the triangular petrous apex by an epidural approach.[3] Several papers over the years have re-emphasized the value of this surgical approach.[4-6] The Kawase’s approach involves drilling of a rhomboidal part of the petrous apex delimited by the arcuate eminence posteriorly, the greater superficial petrosal nerve or petrosal segment of internal carotid artery (ICA) laterally, posterior edge of trigeminal nerve anteriorly and petrous ridge medially. Many authors have argued that this approach provided a narrow corridor, endangered the temporal lobe and underperformed when compared to the retrosigmoid approach with or without an intradural supramental tubercle drilling.[5,7,8] To maximize the benefit of the approach, Tripathi et al.[5] proposed the modified Dolenc Kawase’s approach to increase the superficial working freedom while Liu C et al.[9] recently reported for the first time in the literature the technical nuances of a true petrous apex resection to the reach the petroclival junction. The authors use the Kawase’s approach routinely in their practice and find that a couple of subtle modifications to the classical approach can circumvent many of its purported disadvantages. Objective This article describes the surgical technique of an expanded anterior transpetrosal approach (eATPA). In this technique, the traditional Kawase’s rhomboid is horizontally extended by two operative maneuvers 1) a sub-trigeminal petrous tip resection and 2) skeletonization of the proximal part of the internal auditory canal. Surgical technique/procedure The technique involves a pterional craniotomy with a slightly more temporal extension. The position is supine with a 45-degree head rotation and slight extension. Interfacial dissection exposes the zygomatic arch while preserving the frontalis branch of the facial nerve. We prefer a zygoma lowering to allow optimal temporalis muscle retraction. Goel had described a similar technique for middle fossa lesions to avoid a zygomatic osteotomy.[10] Sphenoid ridge is drilled till the meningo-orbital band. The dural transition of the frontal dura over the optic nerve is visualized and cerebrospinal fluid (CSF) is released from the chiasmatic cistern, a step developed by our team and called transdural cisternotomy. This relaxes the dura to allow further extradural work to continue. The middle meningeal artery is divided to start the dural peeling. Dura is peeled off from the V2 division till the arcuate eminence. The V3 is mobilized to expose the trigeminal impression. Kawase’s rhomboid is drilled. A sub trigeminal petrosectomy is performed beneath the V3 division while the IAC is skeletonized over the porus end, toward the petrous ridge. The superior petrosal sinus is divided and to gain a cranial exposure, the tentorium is divided after a limited durotomy over the temporal lobe. Tumor resection is completed. The potential sites for CSF leak are sealed with bone wax following hemostasis in the tumor bed. Fat obtained from the abdomen or anterolateral aspect of the right thigh is used to plug the dural defect at the petrous apex. Video link https://youtu.be/bn3baasId9k QR Code: Video audio transcript 0.11 In this video, the authors present the expanded anterior trans-petrosal approach, its technical nuances described through an illustrative case of anterior petrous meningioma. 0.35 As this picture shows the upper cerebellopontine angle (CP) angle can be approached from the middle cranial fossa site as well and this approach can be either medial to the fifth cranial nerve or lateral to the fifth cranial nerve. When this approach is medial to the fifth cranial nerve, it is called as pre- temporal trans-cavernous approach whereas the approach which comes lateral to fifth cranial nerve, through the apex of the petrous, it is called anterior trans-petrosal or the Kawase’s approach. 0.51 While the Kawase’s approach is a very versatile and elegant surgical approach, there are several criticisms ascribed to it, particularly with reference to the narrow corridor that it provides and cramped space as well as horizontal freedom of movements is concerned. 1.13 Clinical presentation: The illustrative case that we show here is a 35-year-old lady, who presented with headache for 6 months and right sided facial paresis 2 months. On examination she was conscious, oriented with 25% sensory numbness in the right V1 and V2 area and there was grade 2 House-Brackmann facial paresis on the right side, so all this feature suggested right CP angle syndrome. 1.37 Neuroimaging: On neuroimaging, in the computed tomographic scan shows right anterior petrosal lesion which is hyperdense; on magnetic resonance imaging this is homogenous and intense contrast enhancement the lesion is compressing the middle cerebellar peduncle and is located medial to 7–8th complex. We can also see there is another small meningioma on the left transverse sigmoid junctional area. So, this was the case of meningiomatosis with right anterior petrosal meningioma which was symptomatic. 2:06 Position and incision: In this patient, we decided for an anterior trans-petrosal approach over a right retro sigmoid approach because this approach provides a direct and short route to the upper CP angle, and it also allows resection of bone and dura that is important for resection of meningioma. The head is turned to opposite side around 45 to 60° and the standard question mark incision is placed. We prefer zygoma lowering after inter-fascial dissection and we have moved away from orbito-zygomatic craniotomy for conducting such approach. 3:31 We can see right front-temporal craniotomy has been completed. The most important step is the division of middle meningeal artery. Care we need to be careful that we must divide the artery around 1 cm distal to the foramen spinosum because twig of artery could be feeding the greater superficial petrosal nerve (GSPN) and the geniculate ganglion. The next step is to peel the dura from the V2 as well as V3. V2–V3 inter space can be utilized for cavernous sinus haemostasias. By ante-grade dissection the petrous apex is exposed. This is the V3 division. V3 division is mobilized to expose the sub trigeminal petrous bone. This is the free edge of the petrous, there is a GSPN and arcuate eminence and this is line of internal auditory canal that is formed by bifurcation of GSPN and arcuate eminence. we can see that in this rhomboidal area petrosectomy is being performed with diamond drill and this drilling is done in small-small amount until we reach the inner cortical bone. It is very important that we expand the exposure of Kawase’s approach by two keys maneuver, one is skeletonization of internal auditory canal (IAC) that we can see here. It is very simple and easy to skeletonize the proximal part of IAM. However, the other important maneuver, sub trigeminal petrosectomy as is shown here. These two maneuver led to horizontal expansion of Kawase’s rhomboid. 3:42 Limited opening of temporal dura and division of tent by cutting across the superior petrosal sinus, also expand the surgical corridor vertically. 3:56 As we see here, we have landed right over the tumor. The tumor is debulked with ultrasonic aspirator. The tumor is quite firm. When the tumor is sufficiently debulked we go around the tumor and dissect it. 4:42 We can see the compressed brainstem and fifth cranial nerve. Similarly, 360° peritumoral dissection is conducted. Here we can see the area of dural adhesion. This is divided along with infiltrated dura and as the dissection is completed by going circumferentially around the tumor. We can free the tumor from any important attachment to the brainstem or cranial nerve or upper CP angle. And the tumor is then delivered out. We can see the compressed neuraxial structures at the tumor bed. The closure is conducted with the help of fat. 5:03 Postoperatively patient did well. She developed mild wound bulge post-operatively, otherwise she was doing well. Postoperative scan shows complete resection of the tumor and the petrous window that we obtained by the maneuver that we have shown, and she continues to do well at one year follow-up. The biopsy came out to be grade 1 meningothelial meningioma. 5:41 Conclusion: So in conclusion, the traditional anterior trans-petrosal approach could provide a narrow corridor but, several ways exist which can allow us to enlarge the surgical corridor and the current surgical illustration shows horizontal expansion of this window by adding sub trigeminal petrosectomy where the V3 division is elevated with the help of suction and the true petrous apex is resected and there is skeletonization done of the proximal segment of internal auditory canal and these two maneuver give us horizontal freedom as far as petrous bony window is concerned and additional division of tent and superior petrosal sinus can also provide the vertical expansion of surgical corridor. Conclusions In the authors’ experience, the e-ATPA allows an expansion of the rhomboidal bony window, providing a better horizontal working freedom in this area. This can improve our access to the prepontine area and ipsilateral Dorello’s canal while allowing an optimal control over a wider dural surface area to more effectively deal with meningiomas of this location. Pearls and pitfalls Case selection is very important. Meningiomas that extend lateral and inferior to the internal auditory meatus cannot be approached by this approach. The ideal situation is for an anterior petrosal meningioma or a petroclival meningioma that does not extend across the midline of the clivus. Patient’s head position determines the structures seen through the petrosectomy window and hence must be paid attention to. Brain relaxation is very important to reduce the temporal lobe retraction, venous complications and eventually the overall ease of the procedure. Our transdural cisternotomy technique is very useful. The middle meningeal artery division is a key step to begin the dural peeling to eventually expose the petrous apex. However, the artery must be divided around 1 cm beyond its entry from the foramen as a branch from the proximal portion may be feeding the geniculate ganglion. One should be mindful of the bare petrous carotid and its potential risks during this surgery. Mobilization of the V3 division is key to reach the sub trigeminal part of the petrous apex, the true petrous apex. It is important to direct the drill along the long axis of the true petrous apex, beneath the foramen Lacerum, until inferior petrosal sinus in encountered. Skeletonization of the IAC is best done starting from the petrous ridge and proceeding laterally along its anticipated line described by Garcia-Ibanez. The idea is to skeletonize the pours end, not the fundus end as the latter is more superficial and liable to be damaged. Moreover, the cochlea lies at a deeper level at this point. Waxing of the bony surfaces not only reduces bleeding, but also seals the potential sources of CSF leak. A tentorial incision cutting across the superior petrosal sinus expands the working space. Bath plugging technique employing fat obtained from the periumbilical area is an excellent repair technique to prevent CSF leaks. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.