Chapter 2

Combined Surgical and Radiosurgical Treatment of Parasagittal and Falx Meningiomas with Superior Sagittal Sinus Invasion

Parasagittal and falx meningiomas make up a significant proportion of intracranial meningiomas, with reported rates ranging from 19.24 to 33.7%.1–4 In early studies, these meningiomas were classified based on whether or not they showed hyperostosis. An anatomic classification into anterior, middle, and posterior locations was first devised by Olivecrona.⁴ Anterior cases are located between the crista galli and the coronal suture, middle cases arise between the coronal and lambdoid sutures, and posterior cases are localized between the lambdoid suture and the torcular. Most of these lesions occur in the middle third, and the reported relative rates are 14.8 to 33.9%, 44.8 to 70.4%, and 9.2 to 29.6% in the anterior, middle, and posterior portions, respectively.^1,5–8

Superior sagittal sinus involvement is reported in a significant proportion of the cases, with Simpson⁹ noting a rate of 40%. The extent of venous involvement by the meningioma can range from invasion of the outer surface of the venous wall to complete invasion and obliteration of the sinus. Several authors have devised classification schemes for surgical decision making. The first detailed classification scheme of Krause was later modified by Merrem and then Bonnal and Brotchi.¹⁰ This widely cited classification scheme was in turn later modified by Hakuba to include eight subtypes. The latest, simplified version by Sindou and Alvernia¹¹ describes six types of parasagittal meningiomas classified according to the degree of sinus invasion:

The reported rates of these types are 31%, 8%, 11%, 13%, 5%, and 32%, respectively.^11,12

The anatomic classification into three segments along the anteroposterior axis is not merely of diagnostic significance but relates to the neurologic consequences of SSS closure at that segment. According to their terminal drainage, the superficial veins of the cerebral hemispheres are divided into superior sagittal, falcine, sphenoid, and tentorial groups.^13–15 These systems are interconnected by three large anastomotic veins: the vein of Trolard, the vein of Labbé, and the superficial sylvian vein. The superior sagittal group drains blood from both hemispheres into the SSS, the largest draining vein. The size of the SSS increases from anterior to posterior with the addition of veins from the frontal, parietal, and occipital lobes.^13–15 The terminal veins adjoin to form 1- to 2-cm free venous segments along the superior margin of the hemisphere in the subdural space. These terminal cortical veins can drain directly into the SSS or pass through lacunae before they drain into the sinus.¹⁴

The clinical consequences of acute occlusion, thrombosis, or sacrifice of the SSS were first documented in the first quarter of the 20th century,¹³ and it was soon concluded that the site of closure is the dominant factor in the patient’s neurologic outcome. Sacrifice of the anterior third is well tolerated, but some authors note that general slowing of the patient’s thought process and activity, or even akinetic mutism, are reported after such sacrifice, although these phenomena are rare.¹⁵ Sacrifice of the middle third causes hemiplegia, more prominent in the lower extremities, and akinesia.¹⁵ The posterior third is the largest portion and receives the straight sinus, and acute occlusion or surgical sacrifice of this portion carries a significant risk of fatal brain edema and increased intracranial pressure.

Although acute obliteration of the sinus is associated with such serious consequences, a more gradual closure during tumor growth is usually well tolerated. One must bear in mind that the gradual closure from tumor invasion is not merely a closure of the sinus. The living organism reacts actively to changes in the “interior milieu,” and gradual occlusion of the sinus is certainly accompanied by functional changes in venous drainage. Closure of the main drainage route does not necessarily lead to diversion of the venous drainage to other systems away from the SSS. In many cases, venous collaterals take over the role of the main channel, and sacrifice of these collaterals leads to morbidity similar to that of SSS sacrifice. Whether, or how much, the tumor contributes to venous drainage of the region is not known.16

Management Strategy

The goal in managing this type of “problem” meningioma is clear: keep the patient fully functional and prevent or provide long-term relief from problems associated with intracranial tumor growth. The availability of several alternative treatment possibilities indicates that there is still no single best form of treatment for meningiomas invading the SSS. The most straightforward treatment option is complete surgical excision. Meningiomas located in the anterior third are the least controversial with regard to treatment, and most authors recommend simple radical resection. Parasagittal meningiomas located in the middle third of the SSS are the most difficult to treat because of the abundance of afferent veins, the significant morbidity associated with their sacrifice, and the high risk of recurrence. Meningiomas in this group were early christened as “problem” meningiomas.² Total resection is technically demanding; it can be associated with significant morbidity in patients with invasion of the SSS. In some cases total resection is not possible. The general consensus for lesions that have limited sinus invasion is surgery followed by limited local reconstruction. Simple repair or patching with endogenous material (for example, muscle grafts) is adequate in most of these cases. If the invasion is more extensive, a radical excision necessitates venous reconstruction, but this entails a significant complication rate. Some authors have advocated more conservative resections to avoid this increased risk, but conservative approaches are associated with continued growth.

Authors who have advocated subtotal resection of these meningiomas resect the tumor outside the sinus and leave the invading portion untouched.^3,17 Surgery is planned to restore or preserve function in an attempt to combine the lowest possible risk with the maximum benefit to the patient, based on the notion that most meningiomas are slow-growing tumors and even subtotal resection provides long, progression-free periods. However, most of these patients survive for long periods and therefore regrowth is inevitable after such conservative resections.^18–20 Recurrences are managed through repeated conservative resections until the sinus is obliterated, when total resection becomes an option. Although this idea may sound attractive, it is well known that the efficacy of surgery decreases and the complication rate increases with each repeated surgical intervention. The literature contains no solid scientific evidence on the long-term results of subtotal resection.

The high rate of regrowth after subtotal resection and the fact that complete surgical resection including the invaded structures is associated with lower rates of recurrence led several authors to develop techniques to resect the invaded sinus along with the tumor. As noted above, resecting part of a patent SSS can cause serious morbidity and mortality due to venous infarction and brain edema. Therefore, techniques have been developed to repair or reconstruct the sinus after the portion invaded by the meningioma is removed.^{5,6,10–12,21–29} Most recent studies, however, indicate that such aggressive approaches are not necessarily associated with good surgical results or low recurrence rates, and they are still associated with significant morbidity.²⁵

Such a venous reconstruction is a formidable surgical challenge, and the literature contains only a few large series of SSS reconstruction totaling fewer than 200 cases.

Bonnal and Brotchi¹⁰ were the leading authors advocating such procedures. In 1978, they published the results of 34 patients with SSS repair or reconstruction with venous allografts for parasagittal meningiomas. In nine patients, the surgeons were able to preserve the patency of the sinus without using a graft. In the other 25, they removed one or more walls of the SSS and then rebuilt the structure using a dural or venous graft. In one case, they needed to remove the entire SSS and then create a new sinus structure using a total vein graft.

Hakuba²³ also reported his results with 23 cases of para-sagittal meningiomas. In six patients, he totally removed the tumor and the sinus. Seventeen patients had sinus involvement and, after total tumor excision, Hakuba repaired the sinus wall or reconstructed the sinus with a vein graft. In this group, 29% of patients had postoperative paresis.

On two occasions, Sindou and his colleague^11,12 reported their experience with the aggressive management of para-sagittal meningiomas invading the SSS. The second study, of 100 meningiomas that invaded the dural sinuses, included 92 cases that were located in the SSS. Of these, 30.4% were in the anterior third in close relation to the precentral veins, 52.3% were in the middle third in relation to the postcentral veins, and 17.4% were in the posterior third.¹¹ The authors reported gross total removal in 93% of these patients (Simpson grade I or II) and radical excision combined with coagulation of a small amount of residual tumor (Simpson grade III) in the other 7%. The permanent neurologic morbidity rate was 8%, and the mortality rate was 3%. Looking back at those publications, one realizes that the techniques are not very efficient. In Bonnal and Brotchi’s series, the immediate postoperative control angiogram showed a patent SSS in 87% of the 34 patients. This rate was 66% in Hakuba’s²³ series and 64% in Sindou’s¹² 2001 series, indicating that, in up to a third of cases, the venous reconstruction did not work.

Similarly, the recurrence rates after radical resection are not very impressive either. Regardless of the form of surgical treatment, recurrence is common in patients with meningiomas invading the SSS. This high risk of recurrence was originally documented by Simpson’s9 landmark study, which indicated a recurrence rate of 5% for Simpson grade I and 17% for Simpson grade II resections. This is most likely due to microscopic residuals undetected at the time of surgery. Mathiesen and colleagues³⁰ reported microscopic residual meningioma growth in dural resection margins in 41% of “radical” Simpson grade I operations. Authors who have not attempted sinus reconstruction have reported similarly high rates of recurrence in patients in whom radical resections were possible. Jääskeläinen³¹ reported a recurrence rate of 21% after seemingly complete removal. At a mean follow-up of 25.4 years, Caroli and colleagues⁵ reported a 9.3% recurrence rate after Simpson grade I and a 42.9% recurrence after Simpson grade II resections. The mean time to recurrence was 6.8 years after grade I removal and 4.7 years after grade II or III resections. These results indicate that a more radical resection can decrease but not eliminate the risk of recurrence in patients with parasagittal meningiomas invading the SSS. One can also conclude that a more radical resection does not significantly delay the time to recurrence either. Based on these findings, it is not surprising that, even in the hands of masterful surgeons, radical resection combined with SSS reconstruction are associated with considerable rates of recurrence. In 2003, Brotchi’s research group²⁵ documented the long-term results for these cases. Of the 25 individuals who underwent partial or total SSS removal and sinus reconstruction, 15 had total tumor excision, and these patients had been followed for more than 10 years. Five of these 15 individuals (33%) developed a focal meningioma recurrence. The remaining 10 of the 25 patients underwent subtotal tumor excision, and eight of them had been followed for more than 10 years. Five of these eight patients (63%) developed local recurrence. Because of these outcomes, the authors questioned the efficacy of their approach and concluded that the optimal strategy for patients with meningiomas involving the SSS is gross tumor removal followed by monitoring, and radiosurgery if regrowth occurs.

In stark contrast, Sindou and Alvernia¹¹ reported a recurrence rate of 4% over a mean 8-year follow-up period (3–23 years). Such perfect results have not been replicated by any other master surgeon. Having analyzed the literature, we gave up the strategy of radical resection and reconstruction and started using a combination of surgery and the gamma knife.⁸ Our rationale is based on our previous good results with the combination of surgery and radiosurgery for meningiomas in other locations³² and the good results of other groups with this type of meningioma.⁷

The Role of Radiosurgery

The high complication rates of aggressive treatment strategies and the risk of recurrence after conservative treatment have created a need for alternative treatment strategies. Radiosurgical treatment of meningiomas has proven safe and effective, and this treatment modality for meningiomas has become very popular in recent years for the primary treatment of small meningiomas or as an adjuvant for residual or recurrent cases.^26,27 The reported tumor growth control rates range from 85 to 95%.²⁷ As in the case of cavernous sinus meningiomas, this relatively less-invasive treatment modality can potentially be used as an adjunct or alternative in patients with parasagittal meningiomas invading the SSS to achieve long-term control of tumor growth with little morbidity.²⁸

Currently there is no definitive evidence to show the superiority of aggressive or less invasive treatment paradigms. Only two studies have been published to test the hypothesis that the gamma knife can be used effectively to treat parasagittal meningiomas that invade the SSS. Kondziolka and colleagues⁷ conducted a multicenter study and documented treatment results for 23 such patients. Most of these meningiomas had invaded the middle or posterior region of the SSS, and the mean tumor volume was 10 cm³. Seventy-eight patients underwent radiosurgery as the primary therapy, with a 5-year actuarial tumor control rate of 93%, and none of the tumors smaller than 7.5 cc showed regrowth in the long term. For the 125 patients who had undergone surgery before gamma knife treatment, the 5-year control rate was only 60%. The authors reported that most cases of radiosurgery failure were due to remote tumor growth, as a precise definition of meningioma borders can be complicated in patients who have undergone previous surgery for SSS-invading meningiomas. In the 203 cases reported by Kondziolka and colleagues, the median marginal dose was 15 Gy. Sixteen percent of the patients developed symptomatic edema after radiosurgery. The authors analyzed the potential causes of this edema and found that the only factor correlated with this complication was previous neurologic deficit. In all cases, the edema resolved with medical therapy. The authors concluded that, in patients with a small meningioma (< 3 cm diameter) that has invaded the SSS but in whom the sinus is still patent, radiosurgery should be the primary surgical procedure. In patients in whom the tumor is larger, they recommend planned, second-stage radiosurgery.

In 2006, we reported our experience with gamma knife radiosurgery in 43 patients with parasagittal meningiomas that invaded the SSS.⁸ Twenty-eight patients had undergone previous resection, and the follow-up period after radiosurgery ranged from 24 to 86 months (median 46 months). The median dose was 15 Gy. During this follow-up, 22 tumors (51%) decreased in size, 16 (37%) remained volumetrically unchanged, and five (12%) grew. The overall rate of tumor control with radiosurgery was 88%. Based on a minimum of 2 years’ follow-up, our results show that radiosurgery provided successful tumor control in 13 of the 17 patients with recurrent meningiomas and 10 of the 11 patients with residual tumor tissue. The discrepancy relates to small tumor volumes in residual cases, resulting in possibly higher marginal doses. Our data also indicated that, at 2 years’ follow-up, gamma knife radiosurgery controlled tumor growth 100% in virgin cases. We found that radiosurgery was ineffective in two patients with malignant meningiomas. We therefore do not recommend radiosurgery as the first-line treatment for these cases. The overall recurrence rate for the 24 residual or recurrent meningiomas with a typical histology was 8%, a rate comparable to the recurrence rates reported after gross total resection. Our surgical strategy for these tumors in the earlier years was total excision with removal of the affected SSS wall and grafting for repair. However, in 1997 we changed our policy. We now remove the gross mass of the tumor, coagulate the infiltrated portion of the sinus wall, and then assess with MRI within the first 24 hours.

Total Removal of Parasagittal Meningiomas Involving the Superior Sagittal Sinus with Sinus Repair

General Considerations

Classification

Our surgical experience comprises a series of 160 meningiomas involving the major dural venous sinuses.^11,12,15,33 This experience has led us to adopt the following surgical strategies based on the classification of these meningiomas into six types,^{11,12,15,27,33} as shown in Fig. 2.1: