History

In 1874, “a 50-year-old woman developed paralysis of the arms, followed by the legs, then of respiration…and died after a few months. The autopsy revealed a nut-sized tumor of the inferior basilar gutter.” This case, presented by Hallopeau,⁸ may represent the first report of a petroclival meningioma in the literature. In the past, petroclival meningiomas were described only in postmortem studies.^9,10 In 1922, Cushing¹¹ acknowledged the difficulties in treating meningiomas of the clival region. He concluded his Cavendish lecture by saying, “The difficulties are admittedly great, sometimes insurmountable, and though the disappointments still are many, another generation of neurologic surgeons will unquestionably see them largely overcome.” The petroclival clival region is an anatomically complex area. It has an irregular bony topography and contains complex collection of blood vessels, cranial nerves, and related brain stem. Despite Cushing’s optimism, petroclival meningiomas remain the most demanding and formidable meningiomas to treat.

In 1927, Olivecrona¹² started his surgical exploration of clival meningiomas. He deemed them inoperable after an unacceptable experience with six patients. Early surgical experience with petroclival meningiomas was depressing. The reported surgical mortality exceeded 50%.^10,13,14 With the introduction of microsurgical techniques, Yasargil et al.⁵ reported more promising results in 1980, with a mortality rate of 10%. With improved three-dimensional understanding of microsurgical anatomy and advancement and refinement of skull base techniques and approaches, management of petroclival meningiomas has been accomplished with much lower morbidity and mortality rates according to the recent literature.

Natural History

The incidence of petroclival meningiomas is low compared to that of other skull base meningiomas. Petroclival meningiomas are known to be slowly growing. However, the literature on the growth rates and natural history of petroclival meningiomas is insufficient. Jääskeläinen et al.¹⁵ reported the growth rates of intracranial meningiomas among tumors with the same histologic grade. In 2003, Van Havenbergh et al.¹⁶ reported the results of a long-term clinical and radiologic follow-up study of 21 patients with petroclival meningiomas treated conservatively. The follow-up period was from 48 to 120 months (mean 82 months, median 85 months). During follow-up, radiologic tumor growth was documented in 76% of the patients, and clinical deterioration occurred in 63% of these patients. The mean growth rates were 1.16 mm/yr in diameter and 1.10 cm³/yr in volume. Rapid growth spurts were documented in small and medium-sized tumors. Small to medium-sized tumors tended to grow more than larger tumors. Therefore, active treatment was recommended for symptomatic patients with small or medium-sized tumors. The authors recommended surgical resection for younger and healthy patients and focused beam radiation therapy (stereotactic radiosurgery or radiotherapy) for elderly patients or unhealthy patients who cannot undergo surgery. The authors have the same recommendations for large growing asymptomatic tumors.

Recurrence Rate

It is difficult to compare the recurrence and regrowth rates in the published series due to the variation in the follow-up duration and the definition of the degree of resection. Recurrence rate depends on location, cavernous sinus involvement, brain stem infiltration, grade of resection, and histopathologic result.¹⁷ Mathiesen et al.¹⁸ provide comprehensive long-term results of resected skull base meningiomas. Recurrence rate after 5 years for Simpson grade I resection was 3.5%, for grade II resection was 4%, for grade III resection was 25%, and for grade IV to V resection 36% to 45%. After 15 years, recurrence rate for Simpson grade I resection was 7% to 10%, for grade II resection was 11% to 15%, for grade III resection was 37% to 43%, and for grade IV to V resection was 63% to 100%. Recurrence rate after 25 years for Simpson grade I resection was 13% to 16%, for grade II resection was 15% to 20%, and for grade III resection was 39% to 76%.

Recurrence rates for petroclival meningiomas in the published literature ranged from 0% to 42%^{2,3,5,7,17,19–24,26,30,31,65,66} (Table 40-1). Jung et al. followed 38 patients after subtotal resection of petroclival meningiomas for a mean period of 47.5 months. Radiographic evidence of tumor progression and recurrence occurred in 16 patients (42%). Among the previously mentioned factors, there were correlations among growth rate, old age, and occurrence of menopause.¹⁹

Clinical Picture

Clinical findings in patients with petroclival meningiomas can be related to four major etiologies: (1) involvement of cranial nerves, (2) cerebellar compression, (3) brain stem compression, and (4) increased intracranial pressure.^2,5,14 Presenting symptoms in petroclival meningiomas are nearly the same in all series reported in the literature. Cranial nerves affected, in order of greatest incidence, are V, VIII, VI, VII, IX, and X. Cranial nerves are affected by compression, stretching, incorporation into the tumor, or less frequently, invasion by the tumor. Other common neurologic findings include gait ataxia and motor and sensory deficits due to cerebellar and brain stem compression. Increased intracranial pressure, dementia, and change in visual acuity were frequently associated with hydrocephalus, secondary to aqueduct compression.

Based on the location of the tumor’s dural attachment, Ichimura et al.²² created four subtypes of petroclival meningiomas: the upper clivus type, the cavernous sinus type, the tentorial type, and the petrous apex type. Trigeminal neuropathy was the most commonly found symptom (45%); there was no significant difference in the frequency of trigeminal neuropathy among the four types. The upper clivus type comprises tumors medial to the trigeminal nerve with the primary presentation of ataxia. The cavernous sinus type comprises tumors originating from the posterior cavernous sinus medial to the trigeminal nerve and extends into the posterior fossa, with the characteristic symptom being abducens nerve palsy. The tentorial type originates from the tentorium and the petroclival junction; it displaces the trigeminal nerve inferomedially. The petrous apex type of tumor attaches to the petrous apex lateral to the trigeminal nerve and pushes it superomedially. Trigeminal neuralgia was common in patients with the petrous apex and tentorial types.

Neuroradiologic Evaluation

Thorough evaluation of preoperative neuroimaging studies is of utmost importance in the management of petroclival meningiomas. Multimodality imaging methods are utilized to assess the tumor’s size, consistency, vascularity, location “zone” and extension of dural attachment, tumor–brain stem interface, degree of brain stem displacement encasement, displacement of the vertebrobasilar arterial system, and tumor extension into the cavernous sinus.²³

Computed tomography of the temporal bone is valuable in evaluating the anatomy of the inner ear, its relation to the jugular bulb, the “height of the jugular bulb,” and the degree of pneumatization of the mastoid bone. These data are helpful when transpetrosal approaches are contemplated. Tumor location zone can be identified from the temporal bone computed tomography.

Magnetic resonance imaging (MRI) T1-weighted images with and without contrast delineates the tumor and its relationships to the surrounding structures. MRI T2-weighted images are useful for assessment of the arachnoid cleavage plane, brain stem edema, and infiltration. Flow voids on MRI T2-weighted images can reveal the location of major vertebrobasilar vessels. The absence of a definite arachnoid cleavage plane between the tumor and the brain stem can make resection extremely challenging. This is one of the main obstacles preventing safe total resection of petroclival meningiomas. The lack of a definite arachnoid cleavage plane can be associated with brain stem pial infiltration. This can be predicted from preoperative MRI studies (Fig. 40-1) and has been associated with postoperative morbidity.^4,24–27 Understanding the venous anatomy can reduce related complications during surgical approaches for petroclival meningiomas. Magnetic resonance venogram can illustrate the variations of the torcula and the relative sizes and patency of the transverse and sigmoid sinuses on either side. In addition, the vein of Labbé (posterior temporal venous drainage) and its drainage area are often visualized. This information may be useful if a sigmoid sinus needs to be divided (lateral to the temporal venous drainage) during surgery.

FIGURE 40-1 T1- and T2-weighted MRI images revealing brain stem infiltration by a petroclival meningioma.

(From Abdel Aziz KM, Sanan A, van Loveren HR, et al. Petroclival meningiomas: predictive parameters for transpetrosal approaches. Neurosurgery. 2000;47(1):139-152.)

Cerebral angiography should be considered during the preoperative evaluation of petroclival meningiomas. Not only does it show the tumor’s blood supply, it also can indirectly demonstrate the tumor causing mass effect on the vertebrobasilar system and its branches. Petroclival meningiomas are supplied by the meningohypophysial trunk of the internal carotid artery, the posterior branch of the middle meningeal artery, the meningeal branch of the vertebral artery, the clivus artery from the carotid siphon, the petrosal branches of the meningeal arteries, and the ascending pharyngeal branches of the external carotid artery.²⁸ Angiography can also be used for preoperative tumor embolization to reduce surgical blood loss.

Anesthetic Considerations

Neuroanesthesia continues to evolve with recent advances in neurosurgical procedures and intraoperative monitoring. The goals of modern neuroanesthesia are to provide a stable hemodynamic condition, maintain cerebral perfusion pressure, allow optimum intraoperative monitoring, and leave no residual anesthetic effects to facilitate the postoperative assessment of patient’s neurologic condition.

Patient positioning may require maximal rotation of the patient’s head and neck. A reinforced (armored) endotracheal tube is preferred to prevent kinking of the endotracheal tube to maintain the airway.

Brain relaxation can be provided by the judicious use of mannitol (0.25 to 1.0 mg/kg) and furosemide (10 to 20 mg), hypertonic saline (NaCl 3%), and a lumbar drain. It is preferred to keep the patient normocapnic with maintained euvolemia. The ability to maintain and manipulate blood pressure in response to changes in monitoring parameters and surgical needs is crucial. Muscle relaxation is not utilized because of cranial nerve and motor tract monitoring. Most anesthesiologists use a narcotic-based technique, a remifentanil or sufentanil infusion for analgesia, and a low-solubility inhalational agent such as sevoflurane or an intravenous agent such as propofol for hypnosis. The hypnotic agents can be titrated based on bispectral index monitoring. This is especially useful when propofol is being used for long cases, because the context-sensitive half-life of propofol increases with the duration of use. Nitrous is not utilized with such a regimen. A phenylephrine drip is used to titrate the blood pressure to desired levels. Burst suppression can also be provided in conjunction with electroencephalogram monitoring.

Intraoperative Neurophysiologic Monitoring

Intraoperative neurophysiologic monitoring has been utilized to minimize neurologic morbidity from operative manipulations. Intraoperative monitoring has been effective in localizing cranial nerves, which helps guide the neurosurgeon during dissection. This facilitates safe tumor resection with cranial nerve preservation.

The following modalities are generally used:

Monitoring of cranial nerves III to VII and IX to XII is performed by recording electromyogram activity from the appropriately innervated muscles via an intraoperative stimulation probe. Again, muscle relaxants cannot be utilized during cranial nerve monitoring.

Goals of Surgical Management

Neurosurgeons must weigh the increased morbidity produced by aggressive surgery against the natural history of residual tumor, particularly in older patients. The optimal therapeutic strategy for each patient involves various considerations. These include prognostic factors, applicability of other options such as radiosurgery, and consequences of the outcome on the patient’s quality of life. Evaluating the surgical results of petroclival meningioma removal requires special considerations. Grading schemes used for convexity meningiomas cannot be used to evaluate the excision of petroclival meningiomas. It is extremely difficult to achieve total excision of a petroclival meningioma, including excision of its dural attachment, its dural tail, and the involved bone. Therefore, it is impractical to apply the Simpson grading system to assess the degree of resection of petroclival meningiomas.²⁹

Untreated petroclival meningiomas produce morbidity from the continuous brain stem compression (Fig. 40-2). Therefore, our primary goal is brain stem decompression to restore clinical function with either total or subtotal excision. We have developed a grading scale that evaluates the extent of resection and the degree of brain stem reexpansion. The extent of resection is considered maximal if the tumor is grossly removed. Brain stem reexpansion is maximal if the brain stem regains its normal contour and position (Table 40-2).

FIGURE 40-2 MRI revealing brain stem compression. A, Less than 25% compression. B, From 25% to 50% compression. C, More than 50% compression.

(From Abdel Aziz KM, Sanan A, van Loveren HR, et al. Petroclival meningiomas: predictive parameters for transpetrosal approaches. Neurosurgery. 2000;47(1):139-152.)

Table 40-2 Grading Scale for Excision of Petroclival Meningiomas

Petroclival meningiomas grow very slowly, and they may have a tendency to invade the brain stem, cranial nerves, and the basilar artery and its perforators. For tumors with neurovascular invasion, we prefer performing an excision of the tumor that leaves the parts infiltrating the neurovascular structures undisturbed, rather than attempting total excision of the tumor, which may leave the patient with a major neurologic deficit. Devascularization of the residual capsule of a petroclival meningioma may result in limited growth for a long period.^3,30

The ideal goal of surgery is complete resection of the tumor without causing additional deficits to the patient. Preoperative imaging shows the extent of the tumor, its relationship to adjoining nerves and major blood vessels, and the lack or presence of an arachnoid cleavage plane. For petroclival meningiomas, the surgeon must constantly weigh the benefits of complete resection, the risk of morbidity by injury to vital structures and the natural history of potentially residual tumor. To keep morbidity to a minimum, other alternatives to surgery include safe debulking (incomplete, subtotal resection) and stereotactic radiosurgery or stereotactic radiotherapy.

Surgical Approaches

Petroclival meningiomas have been mainly exposed through the petrous portion of the temporal bone. Petrosal approaches have a distinctive advantage for exposure of the petroclival region compared to the other conventional approaches.^{1,2,24,31–37} The variety of names for the petrosal approaches fall into one of two categories: anterior or posterior petrosectomy.³³ The two approaches can be combined (i.e., combined petrosal approach), or they can be used as part of a more elaborate surgical exposure. We prefer to collaborate with the neuro-otologists to perform the temporal bone drilling. However, some neurosurgeons prefer to perform the whole approach in either one or two stages without a neuro-otologist. On the basis of surgical experience and anatomic dissections, we have designed an algorithm to predict the extent of resection possible via transpetrosal approaches.²³ The extent of exposure achieved via the anterior petrosal approach is from cranial nerve III down to the IAC (Fig. 40-3A). The extent of exposure achieved via the posterior petrosal (retrolabyrinthine) approach was from cranial nerve IV to the upper border of the jugular tubercle (Fig. 40-3B). Some pioneers achieved successful results through the lateral suboccipital “retrosigmoid” approach.^38–40

FIGURE 40-3

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