Parasagittal meningiomas – literature review and a case report

1.1. Anatomy

The sagittal sinus has a triangular shape in coronal section and his size gradually increases as it extends posterior [1]. The superior sagittal sinus communicates with irregular venous cavities called lateral venous lacunae, which lie in the dura mater. In certain areas, the arachnoid projects into the venous sinuses to form the arachnoid villi. These are mushroom-shaped outpouchings of the subarachnoid space that invaginate into them allowing CSF to flow inside the sinuses. When they are very large, the villi can be perceived with naked eye and are called Pacchioni’s granulations. Sometimes these granulations may be seen on magnetic resonance imaging as a filling defect or a mass within a large dural sinus [2].

Parasagittal meningiomas have the dural attachment on the external layer of the SSS and invade the parasagittal angle displacing brain away from its normal position. Cushing and Eisenhardt, in their series of 295 meningiomas, found that the parasagittal location is the most common, 22% [3]. The frequency of parasagittal meningiomas among all meningiomas ranges in the literature between 16.8 and 25.6% [4]. Olivecrona classified parasagittal meningiomas taking into account their anatomic insertion along SSS. He divided the superior sagittal sinus into anterior, middle and posterior third having in mind the different consequences of sinus occlusion in each area [5]. Most frequently parasagittal meningiomas have the dural attachment in the middle third of the superior sagittal sinus (between coronal suture and lambdoid suture). This location is found in 37 - 70% of all parasagittal meningiomas. Along the first third of the SSS (from crista galli to the coronal suture) are located 15 - 42% of parasagittal meningiomas and only 9% to 16% of parasagittal tumors are located along the posterior third of the SSS (between the bregma and torcula) [6].

2.1. Signs and symptoms

The clinical picture of parasagittal meningiomas depends on the tumor location along the SSS. Thus, all tumors can produce headache, but meningiomas of the anterior third of the SSS often cause personality changes, tumors of the middle third of the SSS are often associated with Jacksonian seizures and progressive hemiparesis and those of the posterior third can cause hemianopsia [3-5].

It is generally accepted that, whilst the anterior third can usually be resected without morbidity, ligating the middle or posterior third of the sinus carries significant risk of venous infarction [6, 7].

There are also some other anatomic considerations that can be made regarding topographical differences among parasagittal meningiomas. Thus, the sagittal sinus is narrower in its anterior half and the veins entering the sinus are fewer in number and smaller than those behind the coronal suture, making the surgical approach easier in the anterior half. Moreover, the growth of tumors of the middle third of the parasagittal sinus against the paracentral lobule and the precentral/ postcentral gyri around the central sulcus makes them clinically evident early, explaining why they do not have the time to expand in size as do the tumors in the other two thirds [8, 9].

1.2. Surgical management

Surgery of meningiomas involving the sagittal sinus challenges the surgeon with a dilemma: to leave the invasive fragment having a higher rate of recurrence or to attempt total removal putting at risk the venous circulation [9, 10]. Current tendency nowadays is resection of the meningioma outside the walls of the sinus with coagulation of the tumor remnant, followed if needed by an “en bloc” removal of the residual tumor when complete sinus occlusion occurs [10, 11].

All neurosurgeons operating parasagittal meningiomas emphasize the importance of preserving the bridging veins [1, 8, 10], especially the ones of the group draining in the middle third of the sagittal sinus.

Another matter of almost general consensus is that surgeons have to avoid interrupt a sinus that is partially occluded. On the other hand, sometimes, a complete resection of a totally occluded segment of a sinus can lead to brain swelling and venous infarction if venous collateral circulation is affected. For this reason, a surgical intervention for a parasagittal meningioma that totally occludes the SSS must be carefully planned and performed, taking into account that even superficial or intra-diploic collaterals can be of paramount importance for the cerebral venous drainage [12, 13].

Even in extensive resections with sinus reconstruction or bypass that raised perioperative morbidity and mortality, local recurrence still remains a major problem [8, 9, 11]. Therefore, because of the potential morbidity of such cases and the efficacy of adjuvant radiosurgery for the management of residual tumors and recurrent meningiomas, surgeons have adopted lately a more conservative approach in the management of sinus invasion [14].

2.2. Outcome and results

In Olivecrona’s series, of 196 parasagittal meningiomas resected without sinus reconstruction, morbidity was 12.3%, half of which being attributed to venous damages [5]. The mortality rate was 10%, with significant differences depending on location: 12.8% for the middle third, 9% for the posterior third and 5.3% for the anterior third of the sinus. In Bonnal and Brotchi’s series of 21 cases, mortality was 4.7%, namely 1 patient [13]. In another recent report of 108 cases, brain swelling was found in nine patients (8.9%).

The postoperative mortality in cases with total tumor removal has obviously improved since the first attempts of complete resections performed several decades ago. Improvement in microsurgical techniques together with sinus repair when total tumor removal is performed has significantly changed the outcome of these patients. In Sindou series of 100 cases, mortality was 3%, three patients dying from postoperative brain swelling [11, 15]. These patients had extensive resection of the totally invaded segment of the sinus without venous flow restoration.

In the same series there were 15 sinus repairs with dura or fascia from which 13 were confirmed angiographically to be patent. In the authors experience, the preferred material was the thin and glossy fascia temporalis. When a synthetic graft was used, none of them remained patent in spite of anticoagulation therapy. In consequence, authors don’t recommend the use of synthetic grafts for repair of the venous system. If temporary occlusion of the sinus is required, the use of pledgets of Surgicel in the sinus lumen and at the ostia of the afferent veins is suggested. This technique is considered to be better that the use of aneurysm clips or balloons which were even found to damage the sinus walls. Silicone tubes used as shunts don’t pass well through the sinus lumen because of the presence of septae, especially in the middle third of the SSS [14-16].