Venous Considerations in Skull Base Surgery

20 Venous Considerations in Skull Base Surgery

Chandranath Sen and Carolina Benjamin

Summary

Given the varied configurations of the venous system in both the normal and pathologic states, it is crucial to take venous anatomy into consideration when performing complex skull base surgery. In order to have a thorough understanding of the venous drainage for a particular case, dedicated imaging such as computed tomography venogram (CTV), magnetic resonance venogram (MRV), or diagnostic angiography is necessary. The best strategy remains avoidance of injury. Unlike arteries, veins are delicate and more easily susceptible to injury and therefore special attention has to be paid to this avoidance. This can be achieved by recognizing the relevant anatomy preoperatively and choosing the most direct and safest approach accordingly. However, in the case of sinus injury or involvement by the tumor, skull base surgeons must be prepared to repair and reconstruct major venous structures. Finally, surgeons must also be able to recognize and manage iatrogenic venous sinus thromboses in the postoperative setting.

Keywords: Venous complications, venous sinus thrombosis, venous thrombosis, venous sinus injury, venous sinus repair

20.1 Key Learning Points

●Skull base approaches often traverse important venous structures such as temporal lobe draining veins, the petrosal vein, the torcula, the sigmoid sinuses, and the jugular bulbs.

●Although the venous system can be assessed using magnetic resonance venogram (MRV) or computed tomography venogram (CTV), the only dynamic modality for understanding the venous outflow is an actual catheter-based angiogram. The optimal surgical approach can be planned while mitigating the risk of venous injury.

●Intraoperative techniques that can be used to maximize exposure of the tumor while preserving veins and sinuses include:

–Arachnoid dissection to release the veins from the surface of the brain and the dural base.

–When accessing the clivus, it may be advantageous to work on both sides of the sigmoid sinus.

–Strategic placement of subtemporal retractors (e.g., placing a retractor underneath the posterior leaflet of a divided tentorium to elevate it with the temporal lobe can be used to prevent occlusion or avulsion of temporal lobe veins in a presigmoid transpetrosal approach).

●Venous sinuses or veins can be accidentally lacerated. Immediate repair and reconstruction have to be considered on an individual basis given that by the time brain edema or hemorrhage sets in, it is too late.

●If division of a dominant sigmoid or transverse sinus is contemplated, measurement of the intrasinus pressure on both sides of a temporary clip at the proposed site of ligation is helpful to predict the safety of such ligation.

●Patch grafts and venous interposition grafts are options to be considered in repairing sinus injuries.

●Postoperative sinus thrombosis after skull base surgery is rarely symptomatic and does not require intervention. However, occasionally patient may develop elevated intracranial pressure and may need a shunt or therapeutic anticoagulation.

20.2 Introduction

Venous sinuses and cerebral draining veins may be involved by tumors or may be encountered during the approach to most skull base tumors. Inadvertent injury to these structures can result in serious problems such as bleeding, air embolism, venous infarct, and intraparenchymal hemorrhage leading to intracranial hypertension requiring intervention. All of these can produce neurological deficits that range from asymptomatic to severe (Fig. 20.1 and Fig. 20.2). In addition, excessive manipulation of these venous structures can result in thrombosis. Brain retraction coupled with sacrifice of some cortical veins can further complicate the situation, such as under the temporal lobe and in the sylvian fissure. Avoidance of venous injury is the best strategy. However, the surgeon needs to be aware of the options available for recognizing and dealing with these problems, should they arise.

Fig. 20.1 (a) Axial and (b) coronal preoperative magnetic resonance imaging (MRI) of a patient with an olfactory groove meningioma. The superior sagittal sinus was ligated and transected distally for a subfrontal approach for the resection of this tumor. (c) Axial noncontrast computed tomography (CT) demonstrating the postoperative venous infarct with hemorrhagic conversion that was symptomatic and required a decompressive hemicraniectomy. It was discovered that the patient had Factor V Leiden mutation and therefore was hypercoagulable. (d) Postoperative magnetic resonance venogram (MRV) revealing the propagation of the superior sagittal sinus thrombosis (arrow) after sinus ligation.

Fig. 20.2 (a) Sagittal, (b) axial, and (c) coronal preoperative magnetic resonance imaging (MRI) of a patient with a clival meningioma with suprasellar extension who underwent a transtemporal approach for resection. (d) Axial computed tomography (CT) images revealing a symptomatic hemorrhagic temporal lobe venous infarct which developed postoperatively.

20.3 Venous Anatomy

Although the venous drainage at the skull base follows a general pattern, normal variations can exist.

20.3.1 Temporal Lobe Draining Veins

Cortical veins from the basal temporal lobe drain into the lateral tentorial sinus which then joins the transverse sinus. Cortical veins from the lateral temporal lobe can drain directly into the transverse sinus or can also drain into tentorial venous lakes for a short course prior to draining into the transverse sinus (Fig. 20.3). The anastomotic vein of Labbe typically drains to the transverse sinus directly but can occasionally drain into the lateral tentorial sinus.¹ ^, ² ^, ³ Many skull base approaches require manipulation of or transection of the tentorium, which can lead to significant bleeding. Excessive coagulation of the tentorium can lead to compromise of the venous drainage of the temporal lobe leading to temporal lobe venous infarct as mentioned above.

Fig. 20.3 Anatomic dissection illustrating the venous drainage of the temporal lobe (a) with and (b) without the tentorium in place. Lateral and basal temporal draining veins tend to drain into venous lakes in the tentorium; seen here prior to draining into the transverse sinus. Coagulation of these lakes intraoperatively for skull base approaches can lead to venous compromise.

20.3.2 The Petrosal Vein

The petrosal vein is composed of multiple tributaries that come together and drain into the superior petrosal sinus. The petrosal vein drains the lateral aspect of the cerebellum and the brainstem into the superior petrosal sinus which joins the transverse sinus to form the sigmoid sinus.⁴ ^, ⁵ ^, ⁶ ^, ⁷ Although complication secondary to sacrifice of the superior petrosal vein is thought to be rare, there are reports of an incidence of up to 30%. The reported complications can range from mild cerebellar edema, peduncular hallucinosis, hearing loss, and cranial nerve palsies to more serious complications such as cerebellar venous infarct (with possible hemorrhagic conversion), midbrain or pontine infarct, acute hydrocephalus, or death.² ^, ⁸ ^, ⁹ ^, ¹⁰ ^, ¹¹ ^, ¹² ^, ¹³ ^, ¹⁴ Given that some of these complications can be very serious and even fatal, sacrifice of this vein should be avoided as much as possible.¹⁵

20.3.3 Torcula

The sinuses converge at the torcula in various configurations, which is best characterized on conventional angiogram or CTV. Anatomic studies show that the most common configuration is that the superior sagittal sinus (SSS) drains predominantly to the right transverse sinus (TS). The second most common configuration is that the SSS duplicates into right and left channels but still drains to a single transverse sinus. Another configuration seen is that the SSS drains to a true confluence of sinuses and then splits into bilateral transverse sinuses. The least commonly seen configuration is when the SSS drains predominantly to the left transverse sinus.3 ^, ⁶ ^, ¹⁶ ^, ¹⁷ ^, ¹⁸ ^, ¹⁹ The drainage pattern of the SSS at the torcula becomes important in the preoperative planning of skull base approaches.

20.3.4 Sigmoid Sinuses and Jugular Bulb

The venous structures surrounding the vertebral artery in the suboccipital region form a complex network that is highly interconnected and has been likened to the cavernous sinus, hence the term the “suboccipital cavernous sinus.” This venous plexus connects to the jugular bulb via the anterior, posterior, and lateral condylar emissary veins.² ^, ³ ^, ⁶ This relationship of the sigmoid sinus and jugular bulb with condylar emissary vein becomes important in cases of sigmoid or jugular bulb occlusion. In these cases, the condylar emissary acts as the alternate pathway for venous drainage and therefore care must be taken to preserve this vein during skull base approaches.

20.4 Avoidance of Injury

20.4.1 Understanding the Relevant Anatomy

The surgeon must have a thorough understanding of the relationship between the tumor and venous structures. There are several ways of assessing the venous system including MRV, CTV, and digital subtraction angiography (DSA). The only dynamic modality for understanding the venous outflow is an actual catheter-based angiogram or venogram. Interventionalists are becoming increasingly adept and comfortable with exploring the venous anatomy, which typically involves retrograde access from the ipsilateral internal jugular vein. We suspect this will become increasingly common as new techniques to assess venous flow or pressure, in combination with the ability to place venous stents, becomes mainstream.

Example 1: A 40-year-old female presented with facial numbness from a clival meningioma. As part of her workup, she also had an MRV performed (Fig. 20.4a, b). The images suggested narrowing of a portion of the right transverse sinus (blue arrow). A preoperative cerebral arteriogram (Fig. 20.4c, d) confirmed the area of stenosis on MRV (blue arrow). The temporal lobe drainage (via two major veins, green arrows) was coming into the transverse-sigmoid junction that ultimately drained into the jugular bulb. Therefore, during the performance of a presigmoid supra- and infratentorial approach, it was imperative to avoid injury to the sinus which was the predominant pathway for draining the temporal lobe.

Fig. 20.4 (a) Coronal and (b) three-dimensional reconstruction of the preoperative magnetic resonance venogram (MRV) for a patient undergoing combined supratentorial and infratentorial approach for resection of a clival meningioma. These images revealed a suggested stenosis (blue arrows) which prompted a formal cerebral angiogram for further elucidation of the venous outflow. (c) Anteroposterior (AP) and (d) lateral views of the cerebral angiogram demonstrate that rather than a mere stenosis, there is an actual occlusion and discontinuity (blue arrows) in the transverse sinus which is not clear on the MRV. Furthermore, it reveals two major temporal lobe draining veins (green arrows) that converge at the sigmoid sinus and drain into the jugular bulb. It was, therefore, critical to avoid injury to the sigmoid sinus which can be compromised during this approach.

Example 2: A 37-year-old female suffered from palsy of the right hypoglossal nerve with atrophy of the right half of the tongue. Further workup with a cerebral arteriogram showed that the right jugular bulb and internal jugular veins were the dominant venous drainage (Fig. 20.5). Direct surgery for removing the tumor could jeopardize the large jugular bulb. Also, given that she had a complete hypoglossal palsy, surgery was not considered and she was treated with stereotactic radiosurgery.

Fig. 20.5 (a) Axial magnetic resonance imaging (MRI), (b) coronal MRI, and (c) axial noncontrast computed tomography (CT) revealing an expansile lesion in the right hypoglossal canal (green arrow) with extension to the upper cervical region. Note the jugular bulb immediately superior to the tumor (blue arrow) which would have been at risk with surgery. Anteroposterior (AP) views of a cerebral angiogram of the (d) right carotid and (e) left carotid injections illustrating that the right-sided transverse and sigmoid sinus and the right internal jugular veins were dominant and the left-sided venous system was small. Given that this patient already had a fixed deficit (complete hypoglossal nerve palsy) which was unlikely to improve, surgery was not recommended and she was referred for stereotactic radiosurgery.

20.4.2 Using Alternate Approaches

Detailed study of the venous anatomy can reveal variations that may require a change in the planned approach. This becomes particularly important in cases involving an occluded sinus when collateral venous channels have to be carefully preserved.

Example case: A 63-year-old male had a dumbbell schwannoma arising from the left tenth cranial nerve (Fig. 20.6a–c). A preoperative angiogram showed the left transverse and sigmoid sinus were the dominant venous outflow but the jugular bulb was occluded by the tumor. The venous drainage was via the condylar emissary vein (Fig. 20.6d). A transtemporal approach was initially planned for a one-stage removal of the intracranial and extracranial portions of the tumor. However, on reviewing the angiogram this approach would carry a high risk of injuring the condylar emissary vein with possibly serious consequences. It was therefore decided to perform the resection in two separate stages. A preauricular infratemporal approach was carried out in the first stage to allow resection of the extracranial and foraminal portion of the tumor. At a second stage, a retrosigmoid craniectomy was performed to remove the remaining posterior fossa portion of the tumor (Fig. 20.6e). In this way, the venous drainage was safely avoided and preserved.

Fig. 20.6 (a) Axial postcontrast, (b) axial T2, and (c) sagittal T2 preoperative magnetic resonance imaging (MRI) of patient with an intracranial and extracranial dumbbell schwannoma arising from the tenth cranial nerve. (d) Preoperative angiogram was performed revealing that the left transverse and sigmoid sinuses were the dominant outflow but due to an occlusion of the jugular bulb, the drainage was being diverted through a condylar emissary vein (arrow). (e) Noncontrast head computed tomography (CT) demonstrating the surgical approach to this tumor. Given the risk of injury to the condylar emissary vein in a transtemporal approach, the surgical plan was changed to a two-stage resection, that is, a preauricular infratemporal approach first (green arrow) followed by a retrosigmoid approach (blue arrow).