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.

SSS SURGICAL STRATEGY

We prefer not to ligate SSS, even in the anterior third. Bilateral frontal edema may occur and except in the first 2 cm that we allow to scarify, we adopt a common policy all along the SSS.

In 1978, we showed the feasibility of SSS reconstruction and described our surgical technique.¹ That aggressive surgery has also been successful in the hands of others^{3–5,16–20} and also confirmed by us.² It may be successful in experienced hands only and it is currently a matter of debate with the revolution of brain imaging. In the 1970s, only CT and DSA were available, and in the 1980s conventional MRI, but we could not anticipate the venous anatomy as well as we do today and we were attempting tumor removal with opening of the SSS, resection of one or two walls, grafting the SSS, sometimes completely, without knowledge of the existence of collateral bypasses. Cortical venous rerouting in parasagittal meningiomas was already described in 1974,²¹ as well as the role of scalp veins as collateral pathways with parasagittal meningiomas occluding SSS.²² The question of grafting in totally occluded SSS with the help of sinus pressure monitoring has also been raised.¹⁹ With the new radiologic imaging, surgery can be meticulously prepared with preservation of cortical draining veins and bypasses and adjacent brain, keeping in mind the need to minimize or prevent neurologic deficit.⁷ The question of sinus grafting is again a matter of debate.

What Do We Recommend?

In types I and II, SSS grafting is not necessary. In type I, the attachment of the tumor to SSS can be coagulated with bipolar forceps and peeled until a clean, shiny dural surface is obtained, even by resection of the external dural sinus layer (Fig. 22-2). In type II, the lateral angle recess is progressively opened and a meningioma bud is very often removed. Then, as soon as it is cleaned, the opening is closed with a 6-0 nylon suture at the level of the angle while taking care not to narrow the SSS.

FIGURE 22-2 Convexity meningioma and grade I parasagittal meningioma. A, Preoperative: Axial T1 3D and coronal T1 gadolinium. The relationship between the meningioma and the right lateral wall of the superior longitudinal sinus is nicely shown. B, 2D phase-contrast: SSS is well seen and fully patent. C, Postoperative coronal T1 gadolinium demonstrates complete removal of both tumors and the preserved sinus.

In types III and IV, one or two sinus walls are invaded by the meningioma. Total resection involves the reconstruction of one or two walls with an autogenous vein graft. But the question today centers on the absolute need to do it, as we discuss in the text that follows.

In type III, one lateral sinus wall is invaded. This wall, as well as the intraluminal extension of the tumor, can be excised and replaced by a vein graft taken from the saphenous vein. When the wall resection is small, it may be possible to suture a simple piece of vein with a suitable tension, the two other sinus walls remaining sufficiently distant and stable to maintain an open SSS lumen.

In type IV, two sinus walls are invaded. The SSS is not completely occluded. The third wall, which is sound, receives venous inflow from the opposite side, since the SSS drains both hemispheres. It would be very dangerous to excise all three walls and to interrupt the SSS. If grafting has been decided on, it should have been prepared on the table at that stage. Then, the intrasinusal portion of the meningioma may be excised as well as the two invaded sinus walls, without touching the sound third wall, to preserve the rolandic vein inflow from the contralateral cortex (for technical details, see refs. 1 and 10). The vein graft, which consists of a segment of the internal saphenous vein, is longitudinally opened and prepared at the size of the sinus walls to be replaced. The internal valves of this vein determine the direction of blood flow. Great care should be taken not to place the graft in the wrong direction! A traumatic and very regular suture maintains watertight closure. When there is a rolandic vein opening in the third wall, it should be left open and blood loss grossly controlled by digital compression by the assistant on both openings of the SSS. When there is no contralateral main vein entering the sinus, the technique described by Hakuba can be helpful in massive bleeding.³ It consists of using a shunting extracorporeal tube, ballooned at each end, and inserted into SSS beyond each extremity of the tumoral invasion. That avoids air embolism or unnecessary bleeding. But, like Sindou,⁷ we prefer not to place any clip on the SSS, or any tube or balloon into the SSS because it can damage the endothelium and septa, with the risk of secondary thrombosis. We prefer the interrupted gentle and soft compression by the finger of the assistant helped by small pledgets of Surgicel. Then, it is important to keep the venous graft open by attaching it by a broad suture to a piece of dura, the extremities of which are sutured under tension to the dural edges and hinged to the bone. This maintains the triangular anatomic shape of the SSS, which is mandatory for patency. Local perfusion of saline–heparin solution is maintained during the suture and platelet antiaggregates are given orally long before and after surgery.

Type V parasagittal meningioma is discussed below.

Present Indications for SSS Reconstruction

Since 1978, other diagnostic tools have been available, such as MRI, which more accurately defines and visualizes the tumor but especially follows the precise evolution of a residual meningioma. It is now well established that a meningioma is a slowly growing tumor. Even if the resection is not totally performed, the residue can remain stable for years. Even if a regrowth occurs, it can be only a few millimeters per year with a progressive collateral circulation and progressive sinus thrombosis preventing any neurologic deficit. Interest in refined stereotactic radiosurgical techniques has also been reported.^23–25 With this new information, and even if we showed 30 years ago the feasibility of a sinus reconstruction, this surgery is not without risk and requires experienced neurosurgeons. Further, we observed 2 recurrences at 10 and 13 years after complete tumor removal and total SSS grafting, which raised the question of radical resection with SSS grafting. Both cases had a postoperative patent graft that came to late secondary occlusion due to tumor recurrence without any neurologic deficit. For this reason, we reviewed our position on the indication of the sinus reconstruction, which is not without risk. But avoiding the interruption of a partially occluded SSS is mandatory. The reconstruction of the sinus wall is now rarely performed in our center. If a parasagittal meningioma invades the sinus wall without occlusion of the SSS (types III and IV), we remove the extrasinusal meningioma and follow the residue via annual MRI and MRA (Fig. 22-3). If the residue regrows, a complementary gamma-knife procedure is performed to attempt to control the tumor before any second surgery. Of course, we need long follow-up to estimate the accuracy of that strategy. We now try not to touch the sinus until its complete obliteration. SSS receives blood from both hemispheres, but also from other dural, cortical, or diploic veins. Because of these anastomotic networks, clinical signs are frequently absent after SSS obstruction. Progressive gradual obstruction of the SSS may lead to a well developed collateral venous pathway²⁶ that must be kept intact in parasagittal meningioma surgery, which is our current approach with type V meningiomas (Fig. 22-4). Preoperatively, we carefully study the venous pathway and the venous flow direction and search for all collateral venous channels. We prepare a preoperative venous chart and plan to preserve all those channels at surgery. In this way, we may safely remove completely a type V parasagittal meningioma, with the occluded SSS, without the need of a venous graft. But great care is taken to keep intact all the collateral venous bypasses that have developed with time, shunting the occluded SSS without any neurologic warning. If any of those collateral veins is impaired, venous infarction and brain swelling almost always occur, which could explain rare severe brain swelling in patients treated by en bloc resection of a meningioma with occluded SSS without venous reconstruction.

FIGURE 22-3 Left parietal parasagittal meningioma type IV. A, Axial T2-weighted image: The tumor invades the lumen of the superior longitudinal sinus. B, Sagittal gadolinium-enhanced T1 image shows the extension of the tumor within the dural sinus that is almost completely obstructed. C, MRA: 3D Phase-contrast technique. A collateral diploic vein bridging the sinus is clearly demonstrated. That vein should absolutely be preserved during surgery because it bypasses the SSS. D, Axial T2: Postoperative control MRI. The SSS tumoral component has been left in place. E, Sagittal gadolinium-enhanced T1 image showing the partial removal of the tumor. F, Sagittal 2D phase- contrast MRI: Preservation of the collateral venous pathway.

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

FIGURE 22-4 Left parietal parasagittal meningioma type V. A, Axial gadolinium-enhanced T1-weighted image. B, Axial T2 image: The tumor invades the entire lumen of the dural sinus. A large intradiploic vein may be seen in the right frontal bone (arrow) but is much better visualized in C. C, Axial MRA obtained with a 3D phase-contrast technique. The bone flap should absolutely not cut the diploic contralateral vein coming from and draining the SSS.

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

In summary, the goal is complete removal of the tumor, but quality of life is challenged with surgery. During the last 10 years the principal evolution of our approach has been toward less aggressiveness in SSS reconstruction. When more than one wall is invaded, we favor resection of the tumor outside the SSS and yearly MRI follow-up. When the remaining bud is growing, we ask for radiosurgery. When the SSS is occluded, we may remove it without grafting at the condition to preserve all the collateral venous channels and natural bypasses, which should have been previously analyzed carefully via MRA.

FALCINE MENINGIOMAS

The problem is to safely arrive at the level of the falx. Patient positioning is also important and we follow exactly the procedure described in the preceding text for parasagittal meningiomas. Preoperative MRA or DSA will provide information on the location of the major bridging veins, thereby enabling us to adapt the bone opening according to those data. Further, the dura opening is delicate because of the bridging veins. Sometimes, we leave in place a piece of dura over a big vein when its separation seems too dangerous. Here, more than elsewhere, taking advantage of brain gravity by making the opening on the side down is of great importance. A problem frequently encountered is the opening of the interhemispheric fissure because of thick arachnoid adhesion between some large veins and the dura (Fig. 22-5). Under the microscope and with patience and precision, the white arachnoid sheet may be dissected, divided, and separated from the dura close to the midline, allowing us to achieve free space to control the falx above and below the meningioma. Thereafter, safe cutting the falx all around the tumor may begin, dividing also all feeders. Great care should be taken to avoid any injury on the contralateral hemisphere. Sometimes, the tumor is too large to be delivered between large bridging veins and it is therefore wise to make a piecemeal debulking or to divide the meningioma into several small pieces.

FIGURE 22-5 Falcine meningioma. Operative views with the operative side down, midline up, and major bridging parasagittal veins. A, Large veins block access to the falx. B, After arachnoid and pial dissection, a corridor has been made for safe approach to the falx and the meningioma.