INTRODUCTION

Venous sacrifice has always been a key problem in neurosurgery. For many years, surgery in and around the superior longitudinal and lateral sinuses has been debated in the literature.^1–6 Neurosurgeons understand the importance of Labbé, Trolard, and sylvian veins; they have learned to preserve the parasagittal bridging veins and have discovered the venous anastomotic channels, mainly with the advent of magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA). But in meningioma surgery, interest has focused more on arterial vascularization, arterial feeders, and preoperative embolization than on preoperative study of veins. However, most postoperative pitfalls in meningioma surgery, primarily in convexity and parasagittal meningiomas, have a venous origin, due to either a venous infarct or sacrifice of an anastomotic channel. Therefore, for some time we have directed much attention in preoperative angiography, MRI, and MRA toward the study of veins close to the meningioma or en route to it in a falcine location. We have also tested ourselves on the venous pathways and channels when a sinus was occluded without related neurologic signs.⁷ In this chapter, we consider convexity, parasagittal, and falcine meningiomas from the aspect of venous challenge.

GENERAL CONSIDERATIONS

The gold-standard treatment is complete removal of the tumor as well as the invaded dura and bone.⁸ But total removal should never be attempted without preservation of quality of life. Therefore, it is crucial to keep several principles in mind so as to plan the surgical opening adequately and to place the head of the patient in the best position to benefit from brain relaxation as described in the text that follows. At present, although we may rely on neuronavigation systems to avoid a wrong opening, it is also mandatory to enter in the computer program information on all the veins to preserve.

One of the greatest neurosurgical drawbacks is a brain retractor, which not only compresses the parenchyma but also alters venous drainage. It should be used cautiously and even avoided if possible.

Vein dissection and preservation under magnification cannot be performed in a bloody field. Clean surgery and a permanent hemostasis are required, which are not always easily achievable in hemorrhagic tumors such as meningiomas.

CONVEXITY MENINGIOMAS

Digital subtraction angiography (DSA) is important only if preoperative embolization is being considered, but it is an invasive diagnostic procedure with certain well known inherent risks. We therefore no longer recommend it, except if preoperative embolization is considered, or if we suspect some problem with cortex vascularization.

The patient is placed in a supine, lateral, or prone position according to the location of the meningioma (frontal, tempororolandic, or occipital). If the attachment to the dural convexity is wide, it is important to position the head in such a way that the meningioma is located in the upper part of the operative field.

After achieving a correct bone flap and cutting the dura all around the tumor, dissection from the brain may commence. However, keeping intact venous channels running close to the dura or inside in upper rolandic or in temporal locations may be a difficult challenge if one has not paid attention to those veins in the preoperative workup.

Convexity meningiomas rarely impair venous drainage but the second challenge is the dissection of the veins adhering to the tumor. The key is to stay extrapially as much as possible and to dissect the tumor in the arachnoidal plane. Many arachnoidal adhesions may be cut without coagulation (Fig. 22-1). Even bipolar coagulation is dangerous if it is too close to a vein. Meticulous dissection, never hurried, will successfully separate veins that initially seemed impossible to spare. It will keep the cortex intact in extrapial meningiomas but also preserve the integrity of the surrounding cortex in subpial tumors. Traction is applied to the tumor to lift it after progressive separation from the brain. This helps to cut arachnoid adhesions and coagulate away progressively arteries as small branches feeding the tumor, as well as veins that are more fragile and more delicate to dissect. The technique is recommended in all convexity locations, not only in the rolandic area, as brain softening from venous infarct may lead to disastrous consequences.

FIGURE 22-1 Convexity meningioma. Surgical views. A, Dissection starts in the arachnoidal plane. B, Meticulous dissection of the veins running over the meningioma. C, Complete removal with full patency of all veins.

PARASAGITTAL MENINGIOMAS

Surgery of parasagittal meningiomas may represent a true surgical challenge when the superior sagittal sinus (SSS) is involved. Moreover, the surgeon if often faced with bridging veins that must be preserved to prevent any massive postoperative neurologic deficit.

Parasagittal meningiomas are tumors arising at the convexity of the hemisphere, just off the midline adjacent to SSS and falx, which may involve one, two, or three walls of the SSS with or without occlusion of its lumen. They have a predilection to arise where arachnoidal granulation tissue is the most pronounced⁹ and in 15% they invade the SSS.⁸ Simpson⁸ studied the possibilities of recurrence of intracranial meningiomas and reported that the infiltration of the SSS was a major reason for tumor recurrence. It is well established that the recurrence rate correlates significantly with the quality of the resection but is somewhat tempered by the knowledge that small tumor remnants may at times remain unchanged for several years. The goal is complete removal of the tumor, but the quality of life may be compromised by the surgery. Consequently, complete removal of parasagittal meningiomas by resection of the dural attachment involving the wall(s) of the SSS, and their reconstruction, represents a real surgical challenge. In the 1970s, several neurosurgeons described their surgical techniques for reconstruction of the SSS and collateral veins in dogs^4,10 or in patients with good clinical and radiologic results.^1,3 At the time, only computed tomography (CT) and conventional angiography were available. For the most part, classification of meningiomas was essentially based on surgical findings.

Today, MRI is the modality of choice for diagnosis and to obtain all the necessary information before surgery, especially as angiographic sequences (MRA) allow a precise study of the venous circulation. Indeed, surgery of parasagittal meningioma is mainly surgery and dissection of all the veins that surround the tumor: bridging and parasagittal veins, SSS, and collateral channels. MRA will show if the SSS is patent or not, will demonstrate the direction of the venous flow, and help achieve good planification of surgical technique.

CLASSIFICATION, DIAGNOSIS, AND PREOPERATIVE PLANNING

In 1978, we described a surgical classification with 8 subtypes of parasagittal meningiomas¹ but as a result of our experience during the last 20 years, we have simplified it into 5 categories (Table 22-1) that are more in accordance with our current surgical policy.¹¹ This classification is designed to help plan a rational surgical strategy.

TABLE 22-1 Classification of parasagittal meningiomas

Type I:	The meningioma is attached only to the outer surface of the sinus
Type II:	The meningioma enters the lateral recess of the SSS.
Type III:	The meningioma invades one SSS wall.
Type IV:	The meningioma invades two walls of a still patent sinus
Type V:	The meningioma spreads over the midline, invades the three walls with occlusion of the SSS.

Reproduced with permission from Hancq S, Balériaux D, Brotchi J. Surgical treatment of parasagittal meningiomas. Semin Neurosurg 2003;14(3):203–10.

As soon as the diagnosis of parasagittal meningioma is established via CT, the workup is completed with MRI, MRA, and in some cases DSA, the latter only if preoperative embolization is considered.

Before surgery, it is necessary to have thorough knowledge of venous anatomy. We visualize the sagittal sinus and determine if it is patent or partially or totally occluded. We evaluate the meningioma vascularization and its relationship with the cortex. We focus much attention on the cortical draining veins and on their relationship with the tumor, and observe where they enter the SSS.

The surgical strategy must take into account all of this vascular information. Whatever the percentage of SSS occlusion, all the draining veins must be spared to avoid clinical deficits such as hemiparesis (in the middle and posterior third of the SSS) or frontal edema (in the anterior third of the SSS).

CT provides a means to see bone invasion by the meningioma, but currently MRI with and without gadolinium is the most accurate radiologic exam to determine the configuration, size, and consistency of the tumor, and the relationship among the meningioma, the adjacent brain, and the blood vessels. But the gold-standard examination today is MRI combined with MRA, as we reported in 1996.⁷ MRA provides all the crucial information concerning the venous system without the invasiveness of the DSA: the degree of SSS invasion, the permeability or the thrombosis of the SSS, and the major pathways of collateral circulation on both sides. MRA is even superior to DSA because MRA detects blood flow in all directions simultaneously:

Moreover, the most important information provided by the MRA (which DSA cannot show) is the direction of flow in a given vascular structure by a special reconstructive procedure using 2D and 3D sequences. As the redistribution of the venous circulation is a frequent and important phenomenon in intracranial occlusive venous diseases of any type (thrombosis, tumoral invasion, etc.), this option is particularly valuable in certain situations because it gives a “pseudodynamic spell” to the otherwise static images. Conventional MRI and MRA are complementary and inseparable. Both types of images are necessary for diagnosis and preoperative classification of the meningioma type.

OPERATIVE APPROACH

The result of the neuroradiologic workup and especially of the venous study (sinus and collateral veins) significantly influences surgical strategy, which can be planned and performed safely. If a reconstruction of the SSS is to be performed (types III and IV), it is safer to do so in a second stage, as it is not wise to start a difficult vascular repair after a long surgical procedure for the removal of a large tumor.