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.

Division of the tentorium materially reduces the need for retracting the cerebellum and temporal lobe, preserves drainage of the vein of Labbé, and creates an excellent exposure, opening an unimpeded vista from the lower CNs to the sella. In addition, division of the tentorium provides excellent exposure of the supratentorial and infratentorial compartments, and creates ample space by minimal traction of the brain in the craniectomy window. In particular, it affords control of the whole intracranial course of CNs III and IV with less risk of injuring those structures. The trunk of the basilar artery and its branches are eventually well exposed, as are the contralateral V and III CNs and the pituitary stalk. The approach requires good knowledge of petrous bone anatomy to spare the labyrinth and facial nerve. It also requires a good deal of patience and meticulousness because, like the retrosigmoid approach, this approach forces one to work lateral to CNs V–XI as well as between them. In the long run, however, it is rewarding.

KEYHOLE APPROACH AND SMALL OPENING OF THE BONE

A combined supra–infratentorial presigmoid transpetrosal approach is well described in the literature.^1,9,16,17,28 For this approach, the patient is placed under general endotracheal anesthesia and positioned supine with the head rotated to the side opposite the lesion and fixed in a three-pin head frame (Fig. 40-1). The vertex is lowered as much as possible to allow a good view of the lesion without having to retract the temporal lobe. A small, reverse, hook-shaped supraretroauricular incision is made beginning above the ear and finishing 1 cm distal to the mastoid process (see Fig. 40-1). After the skin and subcutaneous tissue are incised, they are separated in one layer from the muscle layer. The muscles and periosteum are incised in the same fashion and dissected to expose the underlying bone.

FIGURE 40-1 Position of the patient in the keyhole presigmoid approach. The patient is supine with the head rotated to the opposite of the lesion and fixed with a three-pin head frame. A small reverse hook-shaped supraretroauricular incision is performed. M, tip of the mastoid process.

A combined supra–infratentorial craniotomy is a part of transpetrosal approach described by several authors.^9,16,17,28 Burr holes are made on each side of the transverse sinus and the temporal bone and then a portion of the occipital bone above and as well as below the tentorium are cut between burr holes with craniotome. As a result a craniotomy flap is raised. A triangular bony area in the petrosal bone in front of this exposed surface is then left. The tumor to be approached is located under this presigmoidal triangle and can be approached upon opening of the dura. What the surgeon actually needs is this space (Fig. 40-2).

FIGURE 40-2 The area that is needed for exposure is a small presigmoid petrosal triangle (black arrow) beneath the temporal lobe. A, Intraoperative; B, skull view. The yellow arrow shows the described craniotomy area behind the presigmoid petrosal triangle. M, tip of the mastoid; S, sigmoid sinus; P, superior petrosal sinus; B, burr hole; T, transverse sinus.

Thus in recent cases we used a different technique called the presigmoid keyhole approach in which we did not perform a craniotomy, in contrast with the preceding discussion.³⁷ For this keyhole presigmoid transpetrosal approach, after the incision and dissection of the skin, muscle, and periosteum and exposing the petrosal bone, a posterior petrosectomy is performed without a preceding craniotomy (Fig. 40-3A). The petrosectomy stage of the presigmoid keyhole approach is identical to that of the conventional combined approach, only with the execption that it is not performed after craniotomy as in the combined approach.

FIGURE 40-3 A, After complete drilling of the mastoid process of petrosal bone. Transverse and sigmoid sinuses are skeletonized and a triangular area anterior to sigmoid sinus is exposed. A thin shell of bone is left over the sinuses that is later elevated with a dissector (B). S, sigmoid sinus; PSD, presigmoid dura; TD, temporal dura.

A posterior petrosectomy starts with a mastoidectomy with the use of a high-speed drill. The sigmoid sinus is completely unroofed under the surgical microscope. A suction-irrigator should be used for temporal bone procedures to keep the field free of bone dust and the underlying structures cool. A thin shell of bone can be left on the sigmoid and can later be elevated with a free elevator (Fig. 40-3B). For the posterior petrosectomy, this is followed by a drilling of bone with a sufficient exposure of the presigmoid dura from the superior petrosal sinus to the level of the jugular bulb, while preserving the integrity of the facial canal as well as middle and inner ear structures³⁸ (Fig. 40-4). Petrosectomy should be wide, fully defining the sigmoid and transverse sinuses; it is also important to fully delineate the sinodural angle, the angle defined by the sigmoid sinus with the middle and presigmoid posterior fossa.

FIGURE 40-4 The extent of bone drilling is approximately 3 × 4 cm, which is wide enough for fully delineating the sinuses and presigmoidal area.

After completion of the extradural bone removal, the temporal dura is incised parallel to the floor of the temporal fossa in the anterior portion of vein of Labbé (Fig. 40-5). The presigmoid dura covering the posterior fossa is then incised up to the superior petrosal sinus, which is coagulated or obliterated using small hemoclips and severed (Fig. 40-6). CSF is released from the cerebellopontine angle cistern. The temporal lobe is slightly elevated and the tentorium is transected completely, parallel to the petrous bone, in the direction of the trochlear nerve (Fig. 40-7). Preservation of the Vein of Labbé during elevation of the temporal lobe and during cutting of the tentorium is very important. After the tentorium has been cut completely, the transverse and sigmoid sinuses and the remaining part of the tentorium can be retracted with self-retaining retractors. The ambient cistern and crus cerebri are then exposed.

FIGURE 40-5 After finishing the work with the bone, the temporal dura is opened parallel to the floor of the temporal fossa. S, sigmoid sinus; PSD, presigmoid dura; TD, temporal dura; P, superior petrosal sinus. After the temporal dura, the posterior fossa dura in front of the presigmoid sinus is also opened.

FIGURE 40-6 Intraoperative view of two different patients showing the petrosal sinus cut. After opening of the temporal and presigmoid dura separately, the superior petrosal sinus is obliterated by clipping with hemoclips (A) or coagulation with bipolar cautery after ligation with sutures (B) and cut. Arrows show both ends of superior petrosal sinus. T, temporal lobe; C, cerebellum.

FIGURE 40-7 The temporal lobe is slightly elevated retractors (arrow) and the tentorium is divided parallel to the petrous bone toward the trochlear nerve. Attention should be given to not damage the trochlear nerve and vein of Labbé at this stage of the operation. T, tumor; TN, trochlear nerve; TEN, tentorium.

After tumor removal, the dura is closed with a fascial graft. The mastoid bony defect is then packed with a fat graft, Gelfoam, and thrombin/fibrinogen sealant to prevent CSF leakage. Primary closure of the muscle, subcutaneous tissue, and skin is performed. The cosmetic result is fair (Fig. 40-8A) and the postoperative bony defect is small (Fig. 40-8B).

FIGURE 40-8 The presigmoid keyhole approach yields a good cosmetic result (A). The limited bone opening is well appreciated on 3-dimensional CT reconstructions from outside

(B) and inside (C) the skull.

The objectives of this keyhole approach may be explained by several facts: First, there are some disadvantages of the transpetrosal approach, some of which may be related to the extent of bone removal. The operating time is often prolonged by adding a craniotomy to the long-lasting drilling of the petrous pyramid. In addition, a significant number of new neurologic deficits occur due to sinus injury, and craniotomy that is passing over the sinus may increase this undesirable event. The transverse and sigmoid sinus dura may be adherent to the inner table of the cranium and separation from the bone may injure sinuses. Finally, a CSF fistula and the prolonged operation time increase the risk of infection.

On the other hand, the need for craniotomy flap is supposed to be its additional benefit for retraction of the temporal lobe and cerebellum. However, the retraction can be performed through the drilled petrosal bone and by cutting the tentorium and superior petrosal sinus without the need for craniotomy. Adding a craniotomy does not give an additional benefit for retraction, nor does it increase the working area at the petroclival region, because the veins of this area especially the Labbé vein, inhibit further retraction.

In our view, in approaching to these tumors, further craniotomy or craniectomy besides the drilled bone is an unnecessary procedure that can potentiate unwanted postoperative complications, as ideal exposure could be achieved and the tumor itself is accessible during the resection (Fig. 40-9). In our experience, the reasons for failure to resect totally were not due to a small opening of bone but the fibrous nature of the tumor, adherence to brain stem, perforating artery and/or cranial nerve encasement, cavernous sinus invasion, and bradycardia during resection.

FIGURE 40-9 A, Axial, coronal, and sagittal contrast-enhancing brain MRIs of a 45-year-old woman showing a left petroclival meningioma.

B, Early postoperative MRIs demonstrate total resection with the presigmoid key-hole approach.