CHAPTER 37 The Posterior Petrosal Approach for the Treatment of Petroclival Meningiomas

INTRODUCTION

The posterior petrosal approach, as we describe it, is centered on the petrous bone, allowing exposure of the tumor from the middle fossa to the foramen magnum. We prefer this approach for a number of reasons: (1) there is minimal retraction of the temporal lobe and cerebellum; (2) the operative distance to the clivus is shortened when compared to the suboccipital approach; (3) the surgeon has a direct line of site to both the lesion and the anterior and lateral aspects of the brain stem; (4) the cochlea, labyrinth, and facial nerve are preserved; (5) the transverse and sigmoid sinuses, as well as the vein of Labbé and the basal and occipital veins, are preserved; (6) the tumor’s vascular supply is encountered early in the procedure; (7) multiple axes for dissection are provided; (8) tumor invading the petrous bone can be safely removed; and (9) it is easily combined with anterior approaches such as anterior petrosal, total petrosectomy, and transcondylar.

OPERATIVE TECHNIQUE

Patient Positioning

Patient positioning is one of the most important stages of this operation. The patient is placed supine with the head at the foot end of the operating table, allowing space and ease of movement for the seated surgeon. We also find it very useful to turn the table 180 degrees away from the anesthesiologist. This orientation gives the surgeon, his or her assistant, and the nurses involved in the operation the maximum space required to do their work. It is of critical importance that there is sufficient room to allow both the surgeon and his or her assistant to use both hands when operating as there will be points in the operation where the surgeon will require the use of both hands for the dissection while the assistant will be required to provide both irrigation and suction to the field. The table is flexed to a 20- to 30-degree elevation to allow the head to be slightly elevated above the trunk. The patient is positioned supine with the head turned to the opposite side and the ipsilateral shoulder raised slightly. This position will place the base of the petrous pyramid at the highest point in the surgical field. The neck position is carefully inspected to ensure that the contralateral jugular vein is not compressed. The head is then fixed in a three-point Mayfield headrest. The patient is secured to the operative table with a strap. During the operation, the surgeon’s line of sight can be adjusted by moving the table from side to side or up and down.

Before beginning the operation, electrophysiological monitoring is obtained by recording brain stem auditory evoked potentials and somatosensory evoked potentials bilaterally. Facial nerve function and localization are monitored through an electromyogram (EMG) from several groups of facial muscles on the ipsilateral side.

The skin incision is made extending from the zygoma anterior to the tragus, and extending in a curvilinear fashion behind the ear to below the mastoid process (Fig. 37-1). The skin flap is rotated anteriorly and inferiorly, and the temporal fascia is incised and reflected inferiorly in continuity with the sternocleidomastoid muscle. The temporalis muscle is cut along the superior edge of the incision and retracted inferiorly and anteriorly (Fig. 37-2). This flap will be used at the time of closure to cover the drilled surface of the temporal bone. Once these maneuvers are complete, the bony surfaces of the temporal fossa, mastoid, and lateral posterior fossa are exposed.

FIGURE 37-1 Patient’s position and skin incision for a right-sided posterior petrosal approach. The patient is in the supine position with a roll under the ipsilateral shoulder. The head is turned away from the side of the tumor with only slight elevation of the head.

(From Al-Mefty O. Operative Atlas of Meningiomas. Philadelphia: Lippincott-Raven, 1998. p. 288. Reproduced with permission.)

FIGURE 37-2 Soft tissue dissection. A muscular fascial flap is developed by keeping the temporal muscle fascia in continuity with the sternocleidomastoid.

(From Al-Mefty O. Operative Atlas of Meningiomas. Philadelphia: Lippincott-Raven, 1998. p. 314. Reproduced with permission.)

Four burr holes are placed straddling the transverse sinus, two in the posterior fossa and two supranteriorly. One hole is made just medial and inferior to the asterion opens into the posterior fossa below the transverse–sigmoid sinus junction. Another hole located at the squamal and mastoid junction of the temporal bond along the projection of the superior temporal line opens into the supratentorial compartment. A single bone flap covering the middle and posterior fossae is made using the foot attachment of a high-speed drill using the burr holes on either side of the sinus for access. The burr holes flanking the sinus are then connected using a rongeur or the drill. Caution should be taken during this step to avoid injury to the venous sinus wall during this step. The transverse–sigmoid sinus junction is exposed with the craniotomy. Care should also be taken when removing the bone flap because in many patients the bone is very adherent to the dura at the junction of the transverse and sigmoid sinus (Fig. 37-3).

FIGURE 37-3 Artist’s illustration of surgeon’s view: The temporal (TM) and sternomastoid muscles (SM) are elevated and retracted. A craniotome with foot attachment (1) is used to make the bony cut while a drill (2) is used to cross over the sinus. Inset: The sigmoid sinus (SS) is skeletonized and the petrous bone is drilled. F, fascia; FC, facial nerve; PFD, posterior fossa dura; SC, semicircular canal; TD, temporal dura.

(From Al-Mefty O, Schenk MP, Smith RR. Petroclival meningiomas. In: Rengachry SS, Wilkins RH, editors. Neurosurgical Operative Atlas, Vol. 1, No. 5. Baltimore: Williams and Wilkins, 1991. p. 318. Reproduced with permission of American Association of Neurological Surgeons.)