Hearing status is one of the primary factors to consider when choosing the appropriate skull base approach for PC meningiomas. Assessment via pure tone audiogram and speech discrimination score helps classify the hearing as serviceable or nonserviceable. Serviceable hearing (<50 dB hearing loss or >50% speech discrimination score) corresponds to American Academy of Otolaryngology – Head and Neck Surgery class A/B and Gardner-Robertson class I/II and warrants choosing a skull base approach that preserves hearing [1, 3, 4]. It is especially relevant for transpetrosal approaches, which put the vestibulocochlear apparatus and cochlear nerve at risk of iatrogenic injury. The anterior transpetrosal approach carries a lower risk of hearing deterioration than the posterior transpetrosal approaches. Among the various posterior transpetrosal approaches, the retrolabyrinthine and transcrusal approaches may enable hearing preservation in contrast to the more extensive translabyrinthine, transotic, and transcochlear approaches [1, 3, 4].

It is vital to anticipate and prepare for a cerebral revascularization procedure in PC meningioma surgery where the intent of surgery is radical resection, especially in younger patients with recurrent and more aggressive tumors (WHO grade II/III) with a poor cerebrovascular reserve [14, 15]. In general, the approach to these tumors is subtotal with adjuvant radiation therapy if the cavernous cranial nerves are functionally intact. However, at recurrence following radiation therapy in the central skull base, aggressive surgical resection is considered. The common indications for a high-flow or high-capacitance extracranial-to-intracranial bypass include (1) acute vascular injury during the surgical procedure along with preoperative evidence of intolerance to sacrifice; (2) the desire to preserve cerebrovascular reserve in a young patient with long life expectancy; (3) the invasion of tumor into major intracranial arteries requiring sacrifice of the pivotal vessel to achieve radical resection, especially for malignant or aggressive tumors; (4) poor preoperative vascular reserve with symptoms of preoperative ischemia; and (5) high risk of intraoperative vessel injury due to tumor encasement or invasion, especially in cases with prior radiation or surgical treatments [14, 15]. Although the primary assessment tool for cerebrovascular reserve is the balloon occlusion test, the false-negative rate means up to 8% of patients can still be missed [14, 15]. Given this risk, the senior author prefers to augment cerebrovascular reserve via a revascularization procedure in younger patients with longer life expectancy after radical surgical resection. The risk of surgical complications in this subset of patients is relatively low (<5%).

The intricate relation of PC meningiomas with multiple cranial nerves and brainstem puts these vital neural structures at risk during surgical resection. Recently, strong evidence has emerged supporting the use of intraoperative electrophysiological monitoring for safe surgical resection and optimal functional outcome [16]. The senior author has made it a practice to utilize at least motor evoked potentials, somatosensory evoked potentials, brainstem auditory evoked response, and facial nerve monitoring in all cases of PC meningioma resection. Lower cranial nerve monitoring to assess the vagus, spinal accessory, and hypoglossal nerves is also employed when indicated. Finally, electroencephalography is used to assess the depth of anesthesia in cases where burst suppression is indicated while performing cerebral revascularization procedures. Carefully titrated and judicious use of safe anesthetic agents and muscle relaxants is essential to optimize the interpretation of electrophysiological monitoring and keep the intracranial pressure within a desirable range. Baseline potentials should always be obtained before and after patient positioning to assess the baseline neurological deficits and any iatrogenic deficits arising from patient positioning, which can be rectified appropriately [11].

The primary factors influencing the decision-making process in choosing an appropriate treatment strategy for patients with PC meningioma include age of the patient, functional status of the patient, whether the patient is symptomatic or asymptomatic, baseline hearing status, and radiological parameters such as tumor size, pattern of tumor extension and its epicenter, cavernous sinus involvement, and tumor-brainstem interface. Treatment strategies include the options of conservative management with close radiological surveillance, SRS , and surgical resection [1, 3, 4]. Because studies assessing the natural history of PC meningiomas [3] have demonstrated progressive increment in tumor dimensions leading to neurological decline and death if left untreated, watchful waiting is usually not employed as the first line of treatment in most cases if the lesion is symptomatic. Middle-aged or elderly asymptomatic patients with multiple comorbidities who have been incidentally diagnosed with small PC lesions suggestive of a benign meningioma may be an appropriate exception. In such cases, first follow-up imaging is done at 3–4 months to rule out an aggressive variant of tumor, which may warrant surgical exploration. If there is no significant interval change in tumor dimensions at the first follow-up, serial scans can be safely deferred to once a year. Objective decision-making can also be aided by calculation of the tumor growth index. These patients are generally advised to avoid hormonal replacement therapy, which may potentially accelerate the growth rate of these tumors and cause early onset of neurological symptoms.

SRS has emerged as an invaluable alternative/adjunct to surgical resection for these tumors [17, 18]. Although long-term data supporting its efficacy and safety are limited, its short-term results are reassuring. Many neurosurgeons across the globe have switched from aggressive radical tumor resection to more tailored safe tumor decompression and use of SRS as adjuvant therapy for better functional outcome. SRS can be used as primary therapy for small, minimally symptomatic, PC lesions suggestive of meningioma with primary involvement of cavernous sinus, especially in elderly patients with multiple comorbidities and limited life expectancy [17, 18]. SRS is more often employed as adjunct/adjuvant therapy in the modern microneurosurgical era, particularly for residual tumors along the cavernous sinus for patients with any age group, tumors with higher histological grade, and remnant tumors showing progressive growth on serial imaging [17, 18]. Another school of thought believes that small, benign WHO grade I residual tumors can be safely monitored using serial imaging because many have already been devascularized during bone drilling and dural coagulation, thereby reducing their growth potential [12, 19]. This strategy is especially used in younger patients who have a higher risk of long-term radiation toxicity.

Surgical resection has been the standard of care for PC meningiomas in the present microneurosurgical era, although the aggressiveness of tumor resection has decreased over the past two decades in an effort to reduce iatrogenic neurological deficits. Surgery is primarily considered for young, symptomatic patients with rapidly growing tumors and no/minimal systemic comorbidities, patients with larger tumors causing brainstem compression and multiple cranial neuropathies, and cases where the diagnosis of benign lesion is in doubt [1, 3, 4]. The aim of the surgical intervention is maximal safe resection (complete if possible) of tumor without causing undue traction to surrounding neurovascular structures to minimize iatrogenic neurological deficits. The goals of surgery include establishing the histological diagnosis, achieving brainstem and cranial nerves decompression to facilitate improvement in functional outcome, and reducing tumor volume to smaller dimensions making it compatible to SRS adjuvant therapy (especially tumors extending into cavernous sinus). Intraoperative assessment of the tumor-brainstem interface is critical, as overzealous attempts at radically removing firm and adherent tumors stuck to brainstem may lead to catastrophic sequelae. Lastly, use of neuroendoscopy, neuronavigation, and electrophysiological monitoring intraoperatively can contribute toward a safe surgery and optimal patient outcome [11].

The basic tenets of skull base surgery include optimal patient positioning to help gravity-assisted retraction; use of intraoperative lumbar drain to facilitate brain relaxation for easy access to the tumor, moving from one anatomical landmark to another to ensure precise surgical exposure and maximal use of the operative corridor; early devascularization of the tumor via drilling of involved bone and coagulating tumor feeders along the involved dura mater; and maintaining the arachnoid plane between the tumor and the surrounding vital neurovascular structures. The rationale for choosing each skull base approach optimizes the balance between iatrogenic morbidity due to the approach and the need to limit brain retraction for good visualization of neurovascular structures involved. Broadly speaking, the surgical approaches to the PC region are divided into transfacial and transcranial approaches (Fig. 7.2) [11]. Transfacial approaches can utilize transoral, transsphenoidal, or transmaxillary surgical corridors for accessing the PC region. Advances in the realm of neuroendoscopy, the availability of precise neuronavigation systems, and development of better hemostatic agents have provided a much-needed boost to efforts to resect large PC meningiomas via minimally invasive transfacial approaches. At present, however, the data to support long-term safety and efficacy for this purpose are lacking.

On the contrary, transcranial approaches have stood the test of time for resecting PC meningiomas safely. They are further subdivided based on the surgical trajectory taken to reach the PC region: anterior/anterolateral and lateral/posterolateral approaches [1, 3, 4, 11]. The principal anterior approach is the transbasal transplanum transclival approach, which has traditionally been used for extensive and more midline tumors such as clival chordoma and craniopharyngioma , especially involving anterior and middle cranial fossa. Access to the petroclival region is limited for tumors involving the inferior half of the clivus and extending lateral to the internal acoustic meatus. Cavernous sinus and Meckel’s cave involvement further limits surgical access via this approach. Anterolateral approaches include the pterional, orbitozygomatic, and transzygomatic subtemporal/pretemporal approaches [1, 3, 4, 11]. They are primarily utilized for tumors with their epicenters/tumor bulk in the supratentorial compartment, which are difficult to access via lateral/posterolateral approaches. The primary disadvantages to these approaches are limited access to tumor extending to the contralateral side across ventral brainstem, utilization of a long surgical access route to the tumor, and working in a narrow operative corridor between the optic apparatus, oculomotor nerves, and carotid vessels. Detailed description of these anterior/anterolateral approaches is beyond the scope of this chapter.

Lateral/posterolateral approaches include the transpetrosal and suboccipital approaches [1, 3, 4, 11]. Transpetrosal approaches are the workhorse for accessing PC tumors. They include anterior, posterior, and combined transpetrosal approaches , which are the primary focus of this chapter. The primary advantages of transpetrosal approaches over anterior/anterolateral approaches are wider, shorter, and direct access to the tumor and a much better surgical trajectory to access tumors extending across the midline along ventral brainstem. Limitations include the higher risk for retraction injury to the temporal lobe with consequent seizures and dysphasia, facial weakness, hearing loss, cerebrospinal fluid rhinorrhea, and iatrogenic injury to sigmoid sinus, transverse sinus, and vein of Labbé leading to venous infarcts. The decision to use either of these approaches is governed by tumor size and extent, preoperative hearing status, and surgeon’s preference [1, 3, 4, 11]. The retrosigmoid suboccipital approach (Fig. 7.1) is yet another option to resect lesions in PC region, although it is limited by the supratentorial extension of the tumor and contralateral extension across the ventral aspect of brainstem. The interposition of facial and cochlear cranial nerves between the tumor and the surgeon further limits the surgical freedom. The retrosigmoid suboccipital approach may also be used as a second-stage procedure after an anterior transpetrosal approach to resect the residual tumor lateral to the internal acoustic meatus and along the ventral brainstem. By choosing this surgical strategy, many neurosurgeons have been able to reduce the rate of iatrogenic complications arising from much more extensive combined (anterior and posterior) transpetrosal approaches (see below). Far/extreme lateral approaches can also be combined with retrosigmoid suboccipital approaches for tumors extending along lower third of the clivus and contralaterally along the ventral brainstem to optimize the surgical trajectory with limited brainstem traction [1, 3, 4, 11]. In addition, suprameatal extension of the conventional retrosigmoid suboccipital approach enhances the surgical access to Meckel’s cave, an area commonly involved by these tumors (Fig. 7.1). The suboccipital approaches are described in depth elsewhere [1, 3, 4, 11].