13.1 Key Learning Points

• 
  

  Vascular injury in skull base surgery is best managed by avoidance.

  
  
• 
  

  Excellent understanding of the relevant anatomy and a thorough study of the pathologic anatomy is critical for avoiding vascular injuries.

  
  
• 
  

  The petrous and cavernous portions of the internal carotid artery are of primary concern in middle fossa approaches.

  
  
• 
  

  The critical step in safely operating along the middle fossa and cavernous sinus is proximal and distal control of the carotid artery.

  
  
• 
  

  Branches from the petrous or cavernous segment of the internal carotid artery are noncritical, except for a persistent trigeminal artery or an early origin of the ophthalmic artery from the cavernous segment with a poor retinal collateral supply.

  
  
• 
  

  A previously irradiated internal carotid artery develops radiation-induced angiopathy, characterized by diminution of the muscular layer and fragility of the vessel wall, which makes the vessel more susceptible to rupture during dissection.

  
  
• 
  

  Carotid artery sacrifice may lead to morbidity and mortality despite reassuring temporary occlusion testing.

  
  
• 
  

  If arterial injury is suspected intraoperatively, catheter angiography should be performed.

  
  
• 
  

  If the initial angiogram is negative, repeat, delayed angiography is needed to ensure there is no delayed pseudoaneurysm development.

  
  
• 
  

  Revascularization should always be considered and applied over a permanent occlusion of the carotid, particularly for cases in which no detailed temporary occlusion study with cerebral blood flow was performed.

  
  
• 
  

  Endovascular reconstruction of an iatrogenically injured petrous and cavernous carotid arteries with vessel preservation can be accomplished with the use of covered stents. Flow-diverting devices are being increasingly used, but they do not provide immediate protection of the lesion and therefore in locations where there are no critical branches, a covered stent is a more optimal solution.

  
  
• 
  

  If permanent carotid occlusion is deemed necessary, microsurgical clipping immediately proximal to the ophthalmic artery origin is the preferred method of vascular sacrifice. This strategy prevents thrombus formation and subsequent embolization from the occluded vessel and is possible through the exposure from the middle fossa approach.

13.2 Introduction

Vascular injuries are one of the most feared complications of skull base surgery with potentially devastating hemorrhagic or ischemic complications. Skull base surgeons should enter every skull base operation with a plan to avoid vascular injury and a separate plan to manage it, should it occur. Indeed, the best management of vascular injuries is avoidance, which is best accomplished with a thorough understanding of the normal and pathologic anatomy. Skull base anatomy requires an in-depth three-dimensional understanding of critical neurovascular structures, which is best mastered through considerable time spent in the dissection lab. If one idea could be imparted from this chapter, it should be a call to those seeking the trust and responsibility of caring for patients with skull base pathology, to spend the time in the dissection lab to learn skull base anatomy and its many variations. Regardless of the approach or technology used, this is the skull base surgeon’s best tool in avoiding vascular injuries. When dealing with pathology, however, it is insufficient, as the “normal” anatomy is frequently distorted. It must be combined with a detailed preoperative study of the pathologic anatomy. In the case of skull base tumors, this should include magnetic resonance imaging (MRI), computed tomography (CT), and vascular imaging. We have found dynamic computed tomography angiography (CTA) particularly useful in studying vascular anatomy (Fig. 13.1). ¹

13.3 Vascular Control and Injury Avoidance

Skull base approaches based on or including a middle fossa dissection are valuable for a variety of skull base pathologies. The key to safely working along the middle fossa is control of the internal carotid artery. The internal carotid artery enters the intracranial compartment from the neck via the carotid canal in the temporal bone (Fig. 13.2). It then travels along the petrous portion of the temporal bone in the middle cranial fossa before ascending into the cavernous sinus between the foramen lacerum and petrolingual ligament. Within the carotid canal of the petrous bone, the carotid artery travels in a lateral to medial direction as it proceeds from posterior to anterior. The middle meningeal artery arising from the foramen spinosum is a reliable landmark in the middle fossa dissection. Once it is identified, the greater superficial petrosal nerve, which overlies the carotid artery, can be found just medially. The textbook representation is for the carotid artery to be entirely within a bony canal; however, bony dehiscence is not uncommon and extreme care must be taken to avoid injury of an exposed carotid artery.

Once the location of the carotid artery is established, control is sought. Although it should be included in the prepared field, the cervical carotid artery is not needed for obtaining control. Instead, we have adopted the Wascher and Spetzler technique of placing a small Fogarty balloon within the carotid canal. ² If there is not already a complete uncovering of the bony canal, the bone is often paper thin at its most anterior aspect just prior to entering the cavernous sinus, and enough room to insert the Fogarty balloon is easily exposed with a diamond drill bit under copious irrigation or with a sharp dissector with its blunt end facing toward the canal. For dissection within the cavernous sinus, distal control is established at the clinoidal segment of the carotid artery after removal of the anterior clinoid process.

Another important anatomical consideration for managing vascular complications of the petrous and cavernous carotid is the lack of critical branches. The petrous carotid artery is inconsistent in the number and type of branches, and not infrequently there are no branches at all. Branches that do occur from the petrous carotid are the caroticotympanic branch, vidian artery, and periosteal arteries. The cavernous portion of the carotid artery supplies branches to the surrounding dura, tentorium, and redundant supply to the hypophysis. ^{3 ,​ 4 ,​ 5 ,​ 6} Although these small branches may not provide a critical function, they may be implicated in the injury as they may avulse from the carotid artery leading to brisk arterial bleeding and if unrecognized, eventual pseudoaneurysm development. ⁷ In the rare cases involving a persistent trigeminal artery, the surgeon must be wary of this critical arteries origin anywhere between the petrous and cavernous carotid artery segments.

13.4 Related Pathologies

• 
  

  Neoplastic:

  
  
  
  
  • 
    

    Meningioma:

    
    
    
    
    • 
      

      Cavernous sinus.

      
      
    • 
      

      Petroclival.

      
      
    • 
      

      Middle fossa.

    
    
  • 
    

    Schwannoma:

    
    
    
    
    • 
      

      Trigeminal.

      
      
    • 
      

      Vestibular.

    
    
  • 
    

    Pituitary adenoma.

    
    
  • 
    

    Chordoma.

    
    
  • 
    

    Chondrosarcoma.

  
  
• 
  

  Vascular:

  
  
  
  
  • 
    

    Posterior circulation aneurysm.

    
    
  • 
    

    Brainstem cavernous malformations.

  
  
• 
  

  Nonneoplastic:

  
  
  
  
  • 
    

    Petrous apex cholesterol granuloma.

    
    
  • 
    

    Tegmen defect.

  
  
• 
  

  Infectious:

  
  
  
  
  • 
    

    Mucormycosis.

    
    
  • 
    

    Aspergillosis.

13.5 Case Example

A 69-year-old female previously underwent surgery and radiation of a petrous meningioma at an outside institution (Fig. 13.3). She presented with tumor progression and worsening facial function and underwent a transtemporal approach for re-resection. The petrous ridge was severely hyperostotic and drilled extensively. During drilling brisk arterial bleeding was encountered, which was controlled with gentle packing with Gelfoam. Surgery was completed and a complete resection accomplished. Following surgery, she was taken for catheter angiography, which showed a subtle irregularity without definitive pseudoaneurysm formation or contrast extravasation (Fig. 13.3b). The patient remained at her neurologic baseline with stable facial nerve function. Given the concern for arterial injury, despite the apparent reassuring initial angiogram, follow-up CTA and then catheter angiography was performed at postoperative days 3 and 7, respectively. On the follow-up angiogram there was a clear pseudoaneurysm formation (Fig. 13.3c). The pseudoaneurysm was successfully treated endovascularly with a covered coronary stent, the Graftmaster Jostent (Abbott Vascular, Santa Clara, California, USA) which remained widely patent on 8-month follow-up (Fig. 13.3d).