INTRODUCTION

Meningiomas are one of the most commonly seen lesions of the petroclival and clival regions. Approaches to the cerebellopontine angle, the petroclival region, and the ventral aspect of the brain are technically challenging in neurosurgery. Initially these tumors were thought to be “inoperable,” as surgical attempts to remove them were associated with high rates of morbidity and mortality in the early series. More recently, skull-base surgery has undergone a remarkable evolution with resulting progress in radiodiagnostic techniques, intraoperative neurophysiologic monitoring, and better investigation of the microsurgical anatomy of this region. As a result, surgical management of these tumors has been evolving, leading to better outcome and a marked reduction in surgical morbidity and mortality.^1–9 However, radical excision of these tumors via all the modern skull-base surgery techniques is discouraging even in the hands of experienced cranial base surgeons.^1,4,10 Moreover, many surgeons changed their philosophy of treatment approach from radical to conservative because of the good results achieved with adjuvant radiosurgery and probably also because complex surgery may have a paramount impact on the patients’ health.^1,4,10

Small operative corridors and proximity to neurovascular structures can make the petroclival region one of the most difficult areas to access. This has led to the development of several different techniques designed to minimize morbidity that may potentially obtain a surgical cure with complete resection. The choice of approach must achieve a balance between adequate exposure and minimizing surgical morbidity. When optimal and safer exposure of this area is obtained, injury to the surrounding key neural and vascular structures will be greatly reduced.

THE ADVENTURE THROUGH THE OPTIMAL APPROACH

The term “petroclival meningioma” was defined as meningiomas having their point of origin at the upper ⅔ of the clivus and petrous apex, medial to the trigeminal nerve. Extension to the medial tentorium, Meckel’s cave, middle cranial fossa, parasellar area, petrosal and cavernous sinuses, and cranial nerve (CN) foramina may be seen. Traditionally, major routes used to reach these areas are the middle cranial fossa (subtemporal),^2,11–15 transpetrosal,^1,9,16,17 suboccipital retrosigmoid,^18–22 and combined approaches.^23–26 Each method has its advocates, and comparable results have been reported in the literature.

The so-called subtemporal approach was originally adapted by Drake for elimination of basilar aneurysms and modified later by many authors.^12,15,27 It is possible to reach the upper clival, tentorial notch, and petrous apex region by this method. For petroclival meningiomas, approach through the middle fossa is a fascinating proposition because it affords immediate visibility and complete control of the supratentorial tumor bulge. In our experience, however, it is also a highly hazardous route. Retraction of the temporal lobe can cause some heavy postoperative morbidity, especially on the dominant side. Access to the posterior fossa also remains narrow and tedious, affording insufficient command of CNs below the trigeminal nerve. Because of this subtotal excision is more possible with this approach, especially if the tumor is reaching downward through the lower clivus.

The classical retrosigmoid approach,^18–22 with unroofing of the transverse and sigmoid sinuses to keep them out of the surgical field and moderate, readily tolerated, cerebellar retraction affords the simplest access to the region of the cerebellopontine angle and lateral clivus. However, it is difficult to resect tumors that are implanted all the way to the dura of the cavernous sinus and sella turcica and those that involve Meckel’s cave and tentorium to encase CN III and/or the internal carotid artery. In addition, the retrosigmoid approach does not provide a direct view of the brain stem–tumor interface. Another drawback may be found in the fact that the surgeon must conduct the whole phase of removal through the fissures made by the tentorium and by CNs V, VII–VIII, and IX–XI, all of which may be contused in the process.

HISTORY OF THE TRANSPETROSAL APPROACH

A combined supra–infratentorial presigmoid transpetrosal approach without sigmoid sinus division embodies some important refinements of the original approach developed by Hakuba and his associates. Hakuba and co-workers²⁸ first described in the neurosurgical literature the surgical technique and results of the transpetrosal transtentorial route, used in eight patients with a retrochiasmatic craniopharyngioma. Again, in 1988 Hakuba¹⁶ described his experience using the transpetrosal approach for surgery of clivus meningeomas. In the same year, Al-Mefty and co-workers⁹ and Samii and Ammirati²⁹ independently described their experience with the technique and results of the transpetrosal approach. Al-Mefty reported on 13 patients with a petroclival meningioma treated using what he called the “petrosal” approach. He described the petrosal approach for petroclival meningiomas in which the retrolabyrinthine transtentorial approach was used to preserve hearing. They approached lesions through the petrosal corridor by making a craniotomy of temporo-occipital bone above the tentorium and suboccipital bone below the tentorium, centered on the posterior petrous ridge. Samii²⁹ described nine patients treated with a “combined supra–infratentorial pre-sigmoid sinus avenue” approach. Further reports on the use of the presigmoid transpetrosal approach to tumors of the clivus with some technical modifications came from Sekhar^30,31 and Fukushima¹⁷ based on their extensive experience in skull-base surgery. Kawase and co-workers³² described the anterior transpetrosal–transtentorial approach to aneurysms of the lower basilar artery. This anterior petrosal approach was later used to remove petroclival tumors.^33,34 Like the retrolabyrinthine posterior petrosal approach, the anterior petrosal approach preserves hearing and facial nevre function, even though the exposure is limited. According to the amount of petrous bone drilling there are three variations of the transpetrosal approach: (1) the retrolabyrinthine approach with preservation of hearing, (2) the translabyrinthine technique with more extensive resection of the petrous bone and sacrifice of hearing, and (3) the transcochlear approach with radical petrous bone removal, sacrifice of hearing, and rerouting of the facial nerve.^35,36

ADVANTAGES OF THE PETROSAL APPROACH

The transpetrosal approach is an elegant and less dangerous way to reach (and possibly remove) petroclival meningiomas that involve a large portion of the skull base from the lower clivus to the parasellar area. The transpetrosal approach reduces the impediment of the bony structures to deep seated lesions at the cerebellopontine angle, the petroclival region, and the upper and middle ventral brain stem, thus shortening and minimizing the necessity for brain retraction.

The transpetrosal approach shortens the working distance and provides excellent exposure of the deepest part of the cranial base from a direct viewing angle to allow easy resection of tumors, cysts, and even vascular lesions in the cerebellopontine angle, the petroclival regions, and the ventral aspect of the brain stem. The access afforded by the retrosigmoid or subtemporal routes is too restricted unless one is willing to face a two-stage operation, for which we feel no particular inclination. Unlike the suboccipital retrosigmoid approach, little or no cerebellar traction is required even when the tumor is huge. Indeed, with proper positioning of the patient to allow the cerebellum and pons to fall away with gravity, and adequate drainage of cerebrospinal fluid (CSF) during a presigmoid approach, retractors are not needed during surgery. It allows the surgeon to work about 2 cm closer to the tumor than would be possible through the retrosigmoid approach and in front of the brain stem.