Introduction

Clival and petroclival meningiomas represent ~2% of all intracranial meningiomas.1 Olivecrona2 is credited with being the first to attempt surgical resection of these tumors in 1927, but he later deemed them to be inoperable. Early surgical experience with petroclival meningiomas remained dismal, with mortality rates exceeding 50%,2–4 until the series published in the microsurgical era by Yasargil et al5 in 1980.

Classification schemes for these posterior fossa meningiomas have evolved since the initial description by Castellano and Ruggiero.6 Clival meningiomas have a dural attachment close to the midline along the upper two thirds of the clivus and displace the brain stem posteri-orly as they enlarge.7 Petroclival meningiomas also arise from the upper two thirds of the clivus but their dural attachment is centered on the petroclival junction.7 Their location is medial to the internal auditory meatus and posterior to the gasserian ganglion. As they enlarge, petroclival meningiomas displace the brain stem and basilar artery posteriorly and to the contralateral side. Petroclival meningiomas usually present as large tumors when they become symptomatic, and associated invasion of the posterior aspect of the cavernous sinus, parasellar region, tentorium, or foramen magnum is not uncommon.

Many surgical approaches have been used for the treatment of clival and petroclival meningiomas. The rationale for the use of each approach balances the need to limit brain retraction and allow for good visualization of the neural and vascular structures involved, while limiting any morbidity due to the approach. Early approaches described to remove these tumors were pterional, sub-temporal, or suboccipital.8–10 Skull base approaches have been developed to improve the access to these tumors by removing varying portions of the petrous bone. Anterior petrosectomy as well as various posterior petrosectomy approaches have been defined, some of which offer a presigmoid corridor to the tumor. Depending on the extent of the inferior extension of the tumor, lateral transcondylar approaches may also be necessary. Petroclival meningiomas are difficult tumors to resect, primarily because the cranial nerves are interposed between the surgeon and the tumor and because of the intimate relationship between the brain stem vascular supply and the tumor. Extended skull base approaches may be used to remove the tumor in one surgery, or separate approaches may be staged.

This chapter reviews the presenting symptoms, radiological characteristics, and surgical results of clival and petroclival meningiomas. Results and approaches pertaining to clival meningiomas are included in the description of petroclival meningiomas because they present the same surgical challenges, and current published series have consistently grouped them together.

Symptoms and Signs

Petroclival meningiomas predominantly affect middle-aged and older women, as is true of meningiomas in other locations. Exceptional cases have occurred in the pediatric population ( Table 29.1 ). The onset of these tumors is insidious, with patients developing headaches and gait problems. The onset of cranial nerve palsies is usually the first clinical sign, followed by cerebellar and brain stem compression signs. A slow onset of obstructive hydrocephalus may also be possible. Diagnosis is commonly made after the development of a cranial nerve palsy, at which point medical care is sought. Tumor size varies greatly at the time of diagnosis ( Table 29.1 ). The majority of patients in the largest studies have presented at the time of diagnosis with tumor diameters of 2 to 4 cm.11–13 The second most common group are tumors exceeding a diameter of 4 cm, whereas the discovery of small tumors remains the least common scenario.11–13

Cranial neuropathies are commonly present at time of diagnosis. Trigeminal nerve dysfunction is the most common and can present in the forms of trigeminal neural-gia, facial pain, or varying degrees of facial hypesthesia or frank anesthesia ( Table 29.1 ). Diplopia, hearing loss, and vertigo are also very common, followed in frequency by dysphonia, facial weakness, and dysphagia ( Table 29.1 ). Cranial neuropathies may not be isolated to the posterior fossa, and visual loss may occur with tumors that have significant cavernous sinus involvement through the Meckel cave.

Patients may be symptomatic for prolonged periods of time before the patient is imaged and the diagnosis is made ( Table 29.1 ). A low threshold should exist for imaging patients exhibiting compatible symptoms.

Natural History of Petroclival Meningiomas

Initial observational studies of clival and petroclival meningiomas suggested these tumors have insidious continuous growth with ultimately fatal outcomes, based on clinical and postmortem observations.1,6,14 More recent data derived from studying residual tumor growth after subtotal resection have suggested deaths are caused by tumor growth only in a minority of patients.8,13 Overall tumor recurrence or progression has been observed in as few as 13% of patients at 6 years in a large series of patients who were surgically treated with the use of adjuvant radiation upon indication of progression.11

The authors of some recent observational studies of untreated or subtotally resected petroclival meningiomas have observed growth rates ranging from 0.81 mm/year15 to 0.37 cm/year.16 The significance of these differences is unclear but may reflect the small number of cases involved. A great variability in growth patterns exists between different tumors, and growth patterns for individual tumors are not linear.15,16 An increase in tumor growth rate often precedes a clinical deterioration. An observational study of untreated petroclival meningiomas in 21 patients recorded a radiological tumor growth in 76% of patients at 4 years.15 This correlated with a functional decline in the majority of patients.15

An observational study of subtotally resected petroclival meningiomas demonstrated 42% of tumors showed radiological progression over 4 years with a faster growth pattern.16 The tumors’ mean doubling time was 8 years.16 Older patients and those who have gone through meno-pause seemed to have slower-growing tumors.16

Tumor growth of petroclival meningiomas remains unpredictable but is not universal. An absence of radiological tumor growth was noticed in 24% of patients over a 4-year observation period in untreated patients.15 After subtotal microsurgical resection, 58% of tumors did not grow over a period of 4 years.16 Thus conservative observation may be justified in asymptomatic elderly patients when close radiological follow-up can be performed.

Preoperative Evaluation

Magnetic resonance imaging (MRI) of the brain with and without contrast enhancement remains the examination of choice for diagnosis of clival and petroclival meningiomas. The radiological characteristics of these tumors are similar to those of meningiomas in other locations. They typically present as isointense extraaxial lesions on T1-weighted sequences and are of variable intensity on T2-weighted sequences. Upon gadolinium administration, clival and petroclival meningiomas enhance homogeneously, and a dural tail may be observed ( Fig. 29.1A,B ). Fat suppression imaging techniques may be useful in differentiating tumor involvement of bone from normal marrow in selected cases.

The presence of brain stem edema should be noted and raise concerns for pial invasion, which is reported in about one third of cases ( Table 29.2 ). The relationships of the basilar artery, jugular tubercle, cavernous sinus, parasellar region, and internal auditory meatus should be noted. Extension of the tumor into the cavernous sinus seems to be very common ( Table 29.2 ). The tumor may also extend past the tentorium cerebelli ( Fig. 29.2 ), whereas the involvement of the internal acoustic meatus has not been reported with as much frequency ( Table 29.2 ). Extension of the tumor to the midline of the clivus probably occurs in ~20% of cases and makes surgical resection more difficult. The basilar artery appears to be encased in the tumor in many cases, based on MRI criteria, which does not preclude the existence of intact arachnoid planes at time of surgery.

A fine-cut computed tomographic (CT) scan of the skull base can be used to identify extension of the tumor into the internal auditory meatus or Meckel cave as well as any potential bony involvement, the incidence of which has not been consistently reported ( Table 29.2 ). An assessment of the exposure provided by various posterior petrosal approaches is possible.

A four-vessel cerebral angiogram may help in the surgical planning to identify venous sinus patency, anatomy of temporal draining veins, and tumor blood supply. Embolization of the tumor necessitates access to direct feeders from the posterior circulation as well as access to the meningohypophyseal trunk of the internal carotid artery. Given the logistic difficulty and associated risks with embolization of meningiomas in this location, the senior author rarely performs this before surgical resection, regardless of the size of the tumor. An angiogram with a balloon test occlusion of the carotid artery may be necessary in cases of young patients with symptomatic cavernous sinus involvement in which a high-flow bypass is contemplated before a radical resection.

Surgical Approaches

As already indicated, the surgical resection of clival and petroclival meningiomas was associated with dismal results until the microneurosurgical era. The central location of the tumors medial to the cranial nerve foramina and the intimate relationship to the brain stem and its vasculature explain the surgical difficulties encountered ( Fig. 29.3 ).

The first surgical attempts at resection were performed through the pterional and suboccipital approaches. These approaches provide access to the tumor with a narrow central corridor, and dissection of the tumor in its periphery under direct visualization is limited. Skull base approaches provide a more direct route to the tumor and may extend the exposure with a better anterior view of the brain stem ( Fig. 29.4 ).

Electrophysiological monitoring in the surgical re-section of petroclival meningiomas includes somato-sensory evoked potentials, electroencephalography, motor evoked potentials, facial nerve monitoring, and brain stem auditory evoked responses. In cases in which lower cranial nerve involvement is suspected, an electromyographic endotracheal tube can be used for cranial nerve (CN) X monitoring, and electrodes placed into the sternocleidomastoid muscle can provide monitoring for CN XI.

An anterior petrosectomy may be combined with a pterional or subtemporal approach (extended middle fossa approach) to provide better access to the tumor in its infratentorial compartment. An extradural approach should be used up to the outer layer (dura propria) of the lateral wall of the cavernous sinus, which is elevated extradurally to the gasserian ganglion and the inferior aspect of V3 to the foramen ovale. Bony removal is limited to the Kawase triangle, limited anteriorly by V3, laterally by the greater superficial petrosal nerve and internal carotid artery, posteriorly by the internal acoustic canal, and medially by the petrous edge. The dural opening should then be parallel to the base of the temporal lobe followed by ligation of the superior petrosal sinus anterior to the drainage of the vein of Labbé. The tentorium is divided, offering a combined supra- and infratentorial access. The infratentorial component of the tumor can be removed above the internal acoustic meatus, and the approach provides a good view of the anterior surface of the brain stem.17 An anterior petrosectomy is useful in cases of tumors crossing the midline or when the central clival depression needs to be accessed.17,18 An increased risk of injury to the trigeminal nerve is possible because of its central location in the surgical corridor. The potential morbidity of the approach consists of cerebrospinal fluid (CSF) leaks, hearing loss, decreased tearing, and facial nerve palsy, as well as injury to the temporal lobe secondary to the use of brain retraction or sacrifice of the superior petrosal sinus.

The posterior petrosal approaches expose the middle fossa as well as the posterior fossa in a presigmoid fashion and address the tumor laterally and inferior to the internal acoustic meatus ( Figs. 29.3, 29.5, and 29.6 ). Varying degrees of temporal bone can be removed (retrolabyrinthine, translabyrinthine, or transcochlear approaches) based on the patient’s preoperative hearing status ( Fig. 29.4 ). A retrolabyrinthine approach preserves hearing by leaving the otologic structures intact. A translabyrinthine approach involves drilling of the semicircular canals for a more anterior trajectory to the tumor, with sacrifice of hearing. A transcochlear approach involves drilling of all otologic structures as well as transposing the facial nerve posteriorly to maximize the surgical view. The translabyrinthine and transcochlear approaches are reserved for patients who do not have serviceable hearing (speech discrimination score inferior to 50% or hearing loss greater than 50 dB on formal audiogram testing). The superior petrosal sinus is sacrificed in all posterior petrosal approaches ( Fig. 29.6 ), but care should be taken to preserve the drainage of the vein of Labbé. The tentorium should only be divided anterior to the drainage of the vein of Labbé, which may drain directly into the sigmoid sinus or the superior petrosal sinus. Potential complications of the approach include CSF leaks, hearing loss, or facial nerve paresis. Posterior petrosal approaches offer a more direct trajectory to the tumor with minimal retraction on the temporal lobe and cerebellar hemispheres. Earlier interruption of the tumor’s blood supply is also feasible due to a more anterior surgical trajectory.

A combined petrosal approach offers the supratentorial access with an anterior petrosectomy and the infratentorial retrolabyrinthine presigmoid access. A complete petrosectomy combines the anterior and posterior petrosectomy with a labyrinthectomy as well as drilling of the cochlea and ossicles of the middle ear.

The choice of approach depends on the extent of the tumor based on preoperative imaging as well as the status of the patient’s cranial nerves, especially hearing. The use of extensive skull base approaches increases the morbidity of the approach in petroclival meningioma surgery. Specific morbidity due to the posterior petrosal approaches consists of a risk of CSF leakage, hearing loss, and facial nerve palsy. CSF leaks are more prominent in the posterior petrosal approaches than in anterior approaches but can be treated with temporary drainage in most cases.17 At the time of closure, the dura should be closed, and a fascia lata graft may be necessary. Packing the defect created by the mastoidectomy with fat is often necessary, and care should be taken not to create mass effect on the dura. Hearing preservation has been reported in up to 92% of patients with petroclival meningiomas treated with a posterior retrolabyrinthine petrosal approach.17,19 Partial resection of the posterior and superior semicircular canals may still preserve hearing20–22 and improve midline access,22 obviating the need to perform a full translabyrinthine approach. A transcochlear approach improves midline exposure at a higher risk of permanent facial palsy secondary to ischemia of the nerve if the nerve is translocated.18,23 Because of the high incidence of facial nerve palsies in these approaches and the opportunity to access the midline structures through an anterior petrosectomy, the usefulness of the translabyrinthine and transcochlear approach in the context of petroclival meningiomas has been questioned.17,22

Venous anatomy may alter the effectiveness of a posterior petrosal approach. A high jugular bulb may limit the size of the presigmoid corridor, severely limiting the benefit of the approach.17 Variations in the draining of the vein of Labbé also alter the posterior extent of the cut through the tentorium. Preoperative evaluation of the venous structures with the help of magnetic resonance venography (MRV) and computed tomographic angiography (CTA) can more accurately predict the usefulness of posterior petrosal approaches in specific cases.17

Regardless of the approach used, tumor removal is performed in a piecemeal fashion. Inspection of the inferior part of the tumor should permit visualization of the vertebral artery, posterior inferior cerebellar artery, and cranial nerves IX through XI ( Fig. 29.7 ). The fourth and fifth cranial nerves are usually displaced toward the superior end of the tumor ( Fig. 29.8 ). The sixth cranial nerve is usually displaced medially to the tumor and is encountered in the later stages of the dissection. The seventh and eighth cranial nerve complex may be displaced laterally to the tumor or can be embedded in the tumor ( Fig. 29.9 ). Careful piecemeal resection of the tumor can be accomplished with microscissors, and cranial nerves and vascular branches to the brain stem should be preserved. Coagulation should be avoided in the close vicinity of the brain stem, and copious irrigation may be preferable to accomplish hemostasis.8 A complete resection of the tumor against the brain stem may be dangerous in cases where the tumor is adherent or has parasitized the blood supply to the brain stem.

Several authors, including the senior author, still advocate the use of a suboccipital retrosigmoid craniotomy for petroclival meningiomas without supratentorial extent because they believe there to be typically less morbidity due to the approach.8,9 A difference in postoperative morbidity has not been demonstrated in published series with the use of any of these approaches.