37 Surgical Management of the Cerebral Venous Sinuses
Surgery of meningiomas involving major dural sinuses challenges the surgeon with a dilemma: leave the invasive fragment and have a higher rate of recurrence, or attempt a total removal and have the venous circulation at risk. The current tendency is resection of the tumor mass outside the sinus wall (s) with coagulation of the remnant. For meningiomas with complete sinus occlusion, most authors advocate en bloc removal of the invaded portion based on the assumption that collateral venous pathways have developed in this scenario. Conventional wisdom states that complete removal of the invaded sinus is of little danger, and venous flow restoration is not needed. This, however, may not always be true. Other authors, although few, favor attempts at gross total removal with venous reconstruction. This latter attitude is our preference. Whatever approach is pursued, a clear understanding of the collateral venous anatomy and the degree of sinus invasion is warranted when surgery on the sinus is considered.
The outcomes, in terms of recurrence rate, morbidity, and mortality, of complete tumor removal in 100 of our patients (January 1980 to January 2001), including removal of the invaded portion of the dural venous sinus, with or without the restoration of venous circulation, were published in 2006.1 Meningiomas originated at the superior sagittal sinus in 92 of the cases (28 in the anterior, 48 in the middle, and 16 in the posterior third), the transverse sinus in five, and the confluence of sinus in three.
A simplified classification scheme based on the degree of dural sinus involvement was applied: type I: lesion attachment to the outer layer of the sinus wall; type II: tumor fragment inside the lateral recess; type III: invasion of the ipsilateral wall; type IV: invasion of the lateral wall and roof; types V and VI: complete sinus occlusion, with or without the contralateral wall free, respectively ( Fig. 37.1 ).
Lesions with type I invasion were treated by peeling the outer layer of the sinus wall. In cases of tumor sinus invasion types II to VI, two strategies were employed: a “nonreconstructive” (coagulation of the residual fragment or global resection) and a “reconstructive” one (suture, patch, or bypass).
Gross tumor removal was achieved in 93% of the cases and reconstruction of the sinus was attempted in 45 (65%) of the 69 cases with wall and lumen invasion. The overall recurrence rate in the study was 4%, with a follow-up ranging from 3 to 23 years (mean 8 years). The mortality rate was 3%, all cases due to brain swelling after en bloc resection of a type VI meningioma without venous restoration. Eight patients who harbored a lesion in the middle third portion of the superior sagittal sinus had permanent neurological worsening, likely due to local venous infarction. Six of these patients had not undergone a venous repair procedure. Venous reconstruction did not increase the morbidity and mortality rates in our series. From this study we concluded that (1) the relatively low recurrence rate of 4% favors attempts at complete removal, including the portion invading the sinus; (2) because the subgroup of patients without venous reconstruction displayed statistically significant clinical deterioration after surgery compared with the other subgroups (p = 0.02), venous flow restoration seems justified when not too risky ( Fig. 37.2 ).
Magnetic resonance imaging (MRI) scans with and without contrast medium are the key. MRI (T1-weighted sequences with and without gadolinium injection and T2 sequences) is more effective in delineating the tumor and differentiating it from surrounding structures. Gadolinium enhancement of the invaded dura allows the site of exposure to be predicted. However, it must be kept in mind that enhancement of the dura adjacent to the main tumor mass may indicate actual tumor invasion or may simply indicate hyperemia. Venous magnetic resonance offers additional useful information on venous system involvement. Magnetic resonance angiography is not adequate in providing a reliable depiction of the tumor vascularization and local hemodynamics. Therefore, angiography through the transfemoral route is of value before establishing the detailed surgical strategy.
Selective bilateral internal and external carotid subtraction angiography as well as vertebral angiography serve to determine the dural and cortical–pial supply ipsilateral or contralateral to the tumor. The arterial phase is useful to predict the difficulty of dissection of the capsule from the cortex. As we have shown in prior publications, dissection entails neurological risk when a pial vascular supply is identified.2,3 When meningeal supply is important, preoperative embolization may be of some value in producing tumor necrosis and dropping the operative risks to the patient by diminishing the blood loss that accompanies resection of these tumors.
The late venous phases with bilateral filling of the sagittal sinus are required for the full evaluation of sinus patency and collateral venous pathways. Oblique views can depict the superior sagittal sinus (SSS) throughout its entire course. Various degrees of sinus occlusion can be observed, from simple compression with narrowing of the sinus lumen to intraluminal defect to total occlusion. Complete occlusion may be assumed when segments of the sinus are not visible and collateral venous channels are present. The pattern of venous drainage and venous collateral channels must be established preoperatively to determine the surgical approach ( Fig. 37.2 ).
The patient is placed in the semisitting (lounging) position to allow a good venous return without increased intracranial pressure. Air embolism, although possible, is not a frequent risk because of the relatively high level of the intracranial venous pressure in these patients. The problem can be avoided or safely controlled in experienced surgical hands.
The operative exposure should be as extensive as necessary. The skin flap and craniotomy should extend across the midline to permit visualization of both sides of the sinus and ~3 cm outside the margins of the occluded sinus. However, such a large access should be reconsidered in the presence of scalp, pericranial, or diploic collateral venous pathways, which may be impaired during the approach.
Arterial feeders within the dura, especially those coming from middle meningeal arteries, should be coagulated or clipped before being cut.
The dura is incised in a circumferential manner around the margin of the tumor on the convexity and along the border of the corresponding portion of the superior sagittal sinus, taking care not to compromise the adjacent veins (bridging veins) to the sinus.
The microscope shows the division of the meningioma’s attachment to the lateral wall of the sinus and to the neighboring falx. The tumor is detached from these structures by using the cutting mode of the bipolar coagulation forceps, thus cutting off the tumor’s dural blood supply.
Intracapsular debulking is performed so that the remaining capsule of the tumor can be easily mobilized from the underlying cortex. Under the microscope, an extraarachnoidal plane of dissection must be carefully searched for and identified when possible. When absent, the plane of dissection becomes subpial due to pial incorporation into the tumor capsule3.
Sinus Surgery Procedure
Because there are frequent discrepancies between images and anatomical findings, the sinus should be explored through a short incision (~5 mm linear opening) to disclose any intrasinus fragment.
Temporary control of venous bleeding from the sinus and afferent veins is easily obtained by packing small pledgets of hemostatic material (Surgicel, Ethicon, Inc., Somerville, NJ) in the lumen and at the ostia of the afferent veins ( Fig. 37.3 and 37.4 ). Balloons should not be used because they do not pass easily through the sinus septa and may injure the sinus endothelium. Vascular clamps and aneurysm clips should be avoided as much as possible because they may injure the sinus walls and afferent veins.
Bridging veins, especially in the rolandic outflow area, should be preserved by dissecting them free from adjacent brain and tumor.
Venous reconstruction is performed using patches ( Fig. 37.3 ) or bypasses ( Figs. 37.5 and 37.6 ) with two hemirunning sutures (Prolene 8–0, Laboratoire ETHNOR, Neuilly/Seine, France). Although autologous vein would appear as the most suitable material for use as a patch, vein harvesting seems excessive for patching purposes only. The locally situated dura mater, fascia temporalis, and pericranium can be used; however, we favor the use of fascia temporalis when possible because it is strong, thin, and smooth and has a more rigid structure. When a bypass is performed, the graft should not be compressed by any surrounding structure, and measures to decrease the intracranial pressure should be taken to prevent it from kinking or stenosis.4