INTRODUCTION

Petroclival meningiomas are defined as arising at the petroclival junction from the upper two thirds of the clivus, medial to the trigeminal nerve. The more extensive sphenopetroclival additionally extend to the anterior cavernous sinus, sella turcica, and/or the sphenoid sinus. Their central location at the center of the cranial base, adjacent to important neurovascular structures, makes their surgical removal with acceptable mortality and morbidity rates extremely difficult. However, the natural history of petroclival meningiomas is characterized by progressive growth and neurologic deterioration, and an attempt at surgical removal is therefore justified.

Complete visualization of meningiomas and all adjacent vascular structures was once a must for making surgery more feasible and safer, and the literature was concerned with extensive cranial base approaches and their management. Malis, Mayberg, and Symon described the combined supra- and infratentorial approach, which involved the ligation of the transverse–sigmoid sinus. A combined retrosigmoid–subtemporal transtentorial approach with or without ligation of the sigmoid sinus was later introduced. As the main anatomic obstacle to a good exposure of the petroclival area is the temporal bone, approaches with partial or complete resection of the pyramid were later described. We introduced the intradural subtemporal approach with resection of the petrous apex. Kawase described an epidural subtemporal approach to the petrous apex. All of these lateral cranial base approaches provided a shorter distance to the tumor and surrounding neurovascular structures, improved visualization, and minimized brain retraction. Multiple modifications were later described differing mainly in the amount of temporal bone resection. However, the initial enthusiasm of performing extended approaches with wide bone resection was counteracted by the unacceptably high mortality and morbidity related to the surgical approach including a high rate of facial nerve palsy, hearing loss, and cerebrospinal fluid (CSF) leaks. Impingement or interruption of the basal temporal venous drainage also resulted in devastating consequences. Although these extensive approaches have contributed significantly to improve tumor respectability and patient outcome, growing experience and long-term follow-up directed us toward simpler and safer approaches to improve outcome and lessen the morbidity. The senior author’s concept has evolved over more than 25 years, through operation on 184 petroclival meningiomas. We currently manage large tumors with extension into the suprasellar and parasellar areas with involvement of the cavernous sinus, in stages using two simple approaches. Decompression of the brain stem is initially achieved by removal of the infratentorial tumor with a retrosigmoid suprameatal approach. The remaining supratentorial component is removed at a second stage with a frontotemporal approach.

The suboccipital retrosigmoid approach (SRA) is a safe and relatively simple approach to the cerebellopontine angle (CPA) and the petroclival area. It is related to a very low procedure-related morbidity rate^1–3 and therefore is among the most frequently utilized operative routes in neurosurgery.^4–6 The advantages of the approach are: it offers an excellent panoramic visualization to the whole CPA; it is a hearing-preserving technique that allows for a wide exposure of the tumor, whatever its size and pathologic type; and it offers increased safety when working in the vicinity of the brain stem. The dissection of the tumor at all stages is performed under direct visual control and the cranial nerves can be identified early both in their proximal and distal ends, thus increasing the chances for their preservation. If the SRA is combined with a resection of the petrous apex and incision of the tentorium, any petroclival lesions can be adequately exposed.^5,7–9 This retrosigmoid–suprameatal approach (RSMA), which was developed and introduced by the senior author in 1982, provides access to meningiomas of Meckel’s cave, petroclival area, and even the posterior cavernous sinus.^8,10 It avoids the risks related to alternative approaches, such as extensive petrous bone resection or retraction of the temporal lobe with the associated risks of damage to neural and vascular structures. Meningiomas extending to the foramen magnum level can be removed via a similar retrosigmoid craniectomy and a C1 hemilaminectomy/laminectomy.⁷

Potential drawbacks of the approach are the need of cerebellar retraction, as well as the relatively higher rate of postoperative headache. With current neuroanesthesia and some modifications of the original retrosigmoid approach, described in the chapter, these disadvantages are rather theoretical.³

SURGICAL APPROACH

Patient Positioning and Anesthesia Considerations

The position of the patient on the operating table—semi-sitting, lateral, or supine with the head rotated 90 degrees to the contralateral side^1,2,6,11—is a matter of surgeon’s preference and institutional tradition. We prefer the semi-sitting position,^3,12 which has several major advantages: (1) the surgeon can work bimanually because there is no need for constant suction and (2) the continuous irrigation of the operative field performed by the assistant obviates the need for frequent coagulation during tumor removal. The head is held with a three-point head fixation frame; then it is flexed and rotated approximately 30 degrees to the involved side, avoiding occlusion of venous jugular outflow or hyperflexion of the cervical spine (Fig. 39-1).

FIGURE 39-1 The head of the patient is fixed with the three-point head fixation frame, flexed, and rotated 30 degrees to the left side. The course of the venous sinuses (dark line); the parietomastoid, occipitomastoid, and lambdoid sutures; and the slightly curved skin incision (dotted line) are shown.

A drawback of this patient position is the risk of venous air embolism, paradoxic air embolism, tension pneumocephalus, or circulatory instability. However, in experienced hands these are not related to any lasting morbidity.^13,14 Transesophageal echocardiography is the most specific and sensitive method in detection of air embolism. However, the combined monitoring of end-tidal carbon dioxide and precordial Doppler echocardiography yield similar results.¹³ If immediate measures are carried out at the first sign of venous air embolism, the related morbidity is insignificant. Further, some studies have shown that the morbidity due to venous air embolism is similar in both the semi-sitting and supine positions.