Intracranial Venous Revascularization

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32 Intracranial Venous Revascularization

Introduction

Ignoring the cerebral venous system (CVS) during surgery would entail disastrous consequences; therefore, thorough knowledge of venous anatomy and physiology is of prime importance in intracranial neurosurgery.18

There is no doubt that many harmful events after intracranial surgery are related to iatrogenic venous damages. They manifest as locally developed edema, regional or diffuse brain swelling—some being fatal because of uncontrollable intracranial hypertension—or devastating hemorrhagic infarcts that are erroneously attributed to so-called defaults in hemostasis.

Tumors—especially meningiomas—that invade major dural sinuses (superior sagittal sinus, torcular, transverse sinus) confront the surgeon with a dilemma: leave the fragment invading the sinus and experience a relatively high risk of recurrence, or attempt total removal with or without venous reconstruction and expose the patient to a potentially greater operative danger. Radical removal implies preservation or repair of the venous circulation.

Given that 20% of the patients presenting with intracranial hypertension due to venous thrombosis develop threatening manifestations, restoration of the venous flow may contribute to the cure of these diseases.

Before surgery a detailed preoperative study, including venous angio-MR, and, if necessary, DSA with late venous phases, helps to determine optimal surgical strategy. A sustained effort to respect the venous system, especially the so-called “dangerous veins,” is an obligation for the surgeon. Reconstruction or restoration of the venous circulation, especially the major dural sinuses, may be of importance in particular situations.

The “dangerous” venous structures

The Dural Venous Sinuses

The superior sagittal sinus (SSS), a major dural sinus, has three parts. The anterior third receives the prefrontal afferent veins (Figure 32–1). It is generally admitted that its sacrifice is well tolerated. Actually, severe mental disorders, personality changes, or loss of recent memory with a general slowing of thought processes and activity, or even akinetic mutism, may occur if sacrificed. The mid-third receives the voluminous cortical veins of the central group. Interruption of this portion entails high risks of (bilateral) hemiplegia and akinesia. The posterior third, as well as the torcular Herophili, which receives the straight sinus, drains a considerable amount of blood. Interruption would inevitably provoke potentially fatal intracranial hypertension.

The lateral sinuses (LS) ensure symmetric drainage in only 20% of the cases. In extreme cases, one LS (most often the right one) may drain the SSS in totality and the other the straight sinus.

The transverse sinus (TS) may be atretic on one side, the remaining sigmoid sinus (SS) draining the inferior cerebral veins (i.e., the Labbé system). The SS drains the posterior fossa; it receives the superior and the inferior petrosal sinuses. When the sigmoid segment of the LS is atretic, the TS with its affluents drains toward the opposite side.

All of these anatomical configurations have surgical implications and must be taken into account before considering interrupting sinuses.911

The Deep Veins of the Brain

The deep veins of the brain drain toward the venous confluent of Galen (Figure 32–2). The term venous confluent is appropriate since, in addition to the two internal cerebral veins, the Galenic system receives the two basilar veins of Rosenthal, and also veins from the corpus callosum, the cerebellum (mainly the vermian precentral vein), and the occipital cortex.

A good knowledge of deep veins is important for surgery in the lateral ventricles, third ventricle, and pineal region. There is general agreement that the sacrifice of the vein of Galen or of one of its main tributaries should be considered high risk, although animal experiments and a few reported clinical observations have shown otherwise.

Regarding the precentral vermian vein, it is generally accepted, and we agree, that its sacrifice to approach the pineal region is without danger.13

The Superficial Veins

Any of the superficial veins of a certain caliber presumably have a functional role. The superficial veins belong to three “systems”: the midline afferents to the SSS, the inferior cerebral afferents to the TS, and the superficial sylvian afferents to the cavernous sinus (Figure 32–3). These three systems are strongly interconnected, but there is considerable variability among patients. The main anastomotic veins are Trolard to the SSS, Labbé to the TS, and great superficial sylvian, all of them bearing important surgical implications.

Intracranial approaches, especially skull base ones, must be prepared taking into account the organization of the superficial venous system (see Figure 32–3).7,13,14

Avoidance of venous occlusions during surgery

The role played by venous occlusions during surgery in the occurrence of postoperative hemorrhagic infarcts is undeniable.13,7 Retraction of the brain provokes local congestion by compressing the cortical venous network, reduction in venous flow by stretching the bridging veins, and thrombosis of veins if compression of the retractor is prolonged.15 Excessive brain retraction can be avoided by specially designed approaches and limited opening of the dura, obeying two principles, including the minimally invasive opening and bone removal associated with craniotomy at the base of the skull. Keyhole approaches or limited opening of the dura prevent excessive retraction and consequently avulsing veins.

A bridge vein acting as a limitation may occur. To be preserved, the vein has to be dissected free from the arachnoid and cortex at a length of 10 to 20 mm.16 When an important vein ruptures, its reconstruction may be considered either by resuturing or by using the silicone tubing technique.17

Wounds made in a vein wall are common. Rather than coagulating the vein, hemostasis can be attempted by simply wrapping the wall with a small piece of Surgicel (Johnson and Johnson Medical, Viroflay, France). If this is insufficient, a very localized microcoagulation with a sharp bipolar forceps or by placing a single suture with a 10-0 nylon thread is recommended. In cases with a large defect, a patching repair can be performed.18,19 In all cases, whatever the technique used, hemostasis quality has to be checked by jugular compression at the neck.

Tumors invading the major dural sinuses

The study of long-term results in our series of 100 consecutive patients affected by meningiomas involving a major dural sinus, and in whom we attempted radical removal and venous repair,20 led us to the following conclusions. The low recurrence rate of 4% in our series, followed over a 3- to 23-year period (mean 8 years), supports resecting not only the tumor portion outside the sinus, but also the fragment invading the sinus. When radical removal is attempted, we consider venous reconstruction mandatory when the sinus is incompletely occluded, and potentially useful even in cases with complete occlusion. The goal is to restore the flow that might be compromised by impairment of the compensatory collateral channels (Figure 32–4). The traditional belief that radical removal of meningiomas with a totally occluded sinus is not dangerous must be reconsidered.2124 In our series, the three patients who died (all three from brain swelling) had a meningioma that totally occluded the sinus and was wholly removed without any restoration of the sinus circulation.20

This is not surprising, as surgical access basically involves the destruction of some to all of the collateral pathways that naturally developed to compensate the sinus occlusion. Therefore, restoring the venous circulation at end of surgery may reduce brain swelling. Furthermore, patching or bypassing did not increase the morbidity rate in our series.20

To guide in surgical decision making, we introduced a meningioma classification comprised of six types according to degree of sinus invasion1,22 (Figure 32–5). This simplified classification was developed after the ones introduced by Merrem,25 Krause,26 and Bonnal and Brotchi.27