Parasagittal and Falx Meningiomas

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CHAPTER 24 Parasagittal and Falx Meningiomas

Peter M. Black, Jacob. Zauberman

INTRODUCTION

Parasagittal meningiomas are interesting because of the technical challenges they present in resection and the changing concepts of their general management. Their usual location is in eloquent cortex, and the increasingly conservative surgical management is paradigmatic of a changing approach to meningiomas in general. Aggressive resection of these tumors means opening the superior sagittal sinus (SSS), removing tumor from within it, and somehow reconstituting the sinus. This has been advocated by some as the preferred surgical goal when the sinus is only partially occluded, with sinus repair and venous grafting when necessary.¹^–³ In the past, surgical techniques for assessing and safely grafting the sinus have been described.^1,⁴

Recently there has been a different approach to these meningiomas. Resection of the sinus, although leading to lower rate of recurrence, increases the risk of hemorrhage, SSS thrombosis, or venous infarction leading to brain edema and neurologic deterioration. This approach has therefore been modified in recent years, with increasing use of radiosurgery as adjunctive treatment for residual tumors after resection of most of the meningioma.⁵ We have recently evaluated patients who underwent parasagittal meningioma resection at our institution. Our general approach to these tumors was to resect all tumor and dura involved outside the SSS, and closely follow the residual tumor in the sinus. Tumor progression was treated with radiosurgery.

Falx meningiomas are less complicated because they do not invade the SSS. For these, the major issues are localization and resection without injury to the adjacent brain. Often this is eloquent cortex, making the approach very important. This chapter addresses surgical selection, surgical technique, management of the sagittal sinus, recurrence and radiation therapy, and outcomes for parasagittal and falx meningiomas.

SURGICAL SELECTION

In our series, one quarter of parasagittal tumor patients were asymptomatic. If patients were asymptomatic, older than 65 years of age, or had tumor less than 3 cm in diameter we followed them with annual magnetic resonance (MR) scans. We treated only if there was demonstrated growth.

Three quarters of our patients with parasagittal meningiomas were symptomatic; because of their symptoms and the size of their tumors, they were treated with surgical resection. The most common symptoms were headache (about one third), weakness or other motor findings (about one third), and seizures (about a third). The motor findings demonstrate the tendency of these tumors to grow in the middle third of the sagittal sinus.

SURGICAL TECHNIQUES

Preoperative Planning

The imaging revolution that is part of contemporary neuroscience has been important in planning for meningioma surgery as well. An accurate assessment of the relationship between meningioma and brain; of the relationship to the sagittal sinus; and of the veins can all be achieved with the present imaging techniques. Recently the ability to perform functional imaging has added to this capacity.

Positioning

Our approach and positioning are chosen based on the segment of the SSS involved. The general concept is to have eloquent cortex fall away from the tumor by gravity. Patients with tumors involving the anterior third of the SSS are therefore positioned supine with the head flexed. Patients with tumors involving the middle third are positioned with the head turned to the side of the tumor so that gravity causes the brain to fall away from the tumor ⁶ (Fig. 24-1). This usually eliminates the need for brain retraction. Patients with tumors involving the posterior third are positioned prone so that the motor cortex falls away by gravity.

FIGURE 24-1 A, Coronal view of a parasagittal. B, Postoperative view; the tumor was removed from the wall of the sinus without difficulty.

Procedure

Our craniotomy is usually performed in two stages: The elevation of a bone flap on the side of the tumor to avoid crossing the sinus in the initial opening; and then the stripping of dura and elevation of a flap on the other side of the sinus. This avoids potential sinus injury early in the opening and with the present plating systems does not compromise the bone closure. In the dural opening, we try to open just over tumor and not the brain; otherwise there may be brain herniation around the tumor.

The veins associated with these tumors must be preserved at all costs.^7,⁸ The safe surgery of parasagittal meningiomas is surgery of the veins that are associated with them. We undermine veins or gently dissect them off the tumor surface as we are debulking the tumor.

We begin tumor resection by internally debulking using Cavitron or loop cautery, doing our best to avoid retraction on the brain. We then separate the tumor from the brain circumferentially. Tumor invading the SSS is cauterized on the wall of the SSS. If the tumor is just in the wall of the sinus it is removed and the sinus is sutured as the tumor is removed; however, we do not try to reconstruct the sinus with a vein or other graft. Figure 24-2 shows an example of a large parasagittal meningioma removed using these techniques.

FIGURE 24-2 A large parasagittal meningioma invading the sinus in which the sinus was resected. The patient had no deficit postoperatively (B). It was an atypical meningioma. A, Preoperative transaxial MR. B, Postoperative transaxial MR; the tumor and the sinus are resected and the patient has no deficit.

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