Introduction

Carotid-cavernous fistulas (CCFs) are a form of arteriovenous fistulas that have an abnormal connection between the C4 segment of the carotid artery proper, internal carotid artery (ICA) or external carotid artery (ECA) branch, and the cavernous sinus (CS). Compared to other types of arteriovenous fistulas, CCF can present with acute findings that warrant immediate recognition and treatment. These lesions come in slow-flow (type B–D) and high-flow (type A) varieties and can be difficult to treat with microsurgical or endovascular techniques. Currently, most of these lesions are treated by endovascular approaches.

Major controversies in decision making addressed in this chapter include:

1. 
   

   Is treatment indicated?

   
   
2. 
   

   Is an endovascular arterial or venous approach ideal for CCF?

   
   
3. 
   

   Is there a role for open microsurgery and radiation therapy in the treatment of CCF?

   
   
4. 
   

   What is the best treatment for a CCF that develops after the placement of a pipeline embolization device (PED; Medtronic, Minneapolis, MN)?

Whether to Treat

High-flow CCFs (type A) always warrant emergent treatment because the patient′s vision is at risk ( 1 in algorithm ). Slow-flow fistulas (types B–D) resulting in headaches, chemosis, proptosis, or visual disturbance should also be treated ( 2–4 in algorithm ). Patients with incidentally found (i.e., asymptomatic) lesions that do not show radiographic signs of high-risk features can be observed or treated conservatively. Any change in symptoms should prompt repeat angiographic imaging and treatment. Patients with fistulas who are undergoing observation should have routine eye examinations to exclude papilledema and raised intraorbital pressure. High-risk CCF features observed on digital subtraction angiography (DSA) include cortical venous reflux, venous hypertension, occluded distant venous outflow, cavernous sinus varix, pseudoaneurysm, and CCF that develop post-PED placement.

Halbach et al retrospectively reported the complication rates for 155 patients with CCF (127 direct, 28 indirect). They noted that hemorrhage was a complication in 10.2% of direct (ICA to cavernous sinus) fistulas (hemorrhage location breakdown is as follows: intracerebral 3.1%, subarachnoid 3.1%, epistaxis 3.1%, and otorrhagia 0.8%). Increased intracranial pressure was present in 7.7% of fistulas overall (direct type had an 8.7% incidence, whereas the indirect [ICA or ECA branch to cavernous sinus] type had a 3.6% incidence). Decreased visual acuity was noted in 31% of patients (direct type had a 32.3% incidence; the indirect type had a 25% incidence). Blindness occurred in 4.5% of patients (direct type incidence 3.1%; indirect type incidence 10.7%). Rapidly progressive proptosis occurred in 1.6% (direct type). Cerebral ischemia occurred in 0.8% (direct type). Fatalities were noted in 3.2% of patients (all in the direct type fistulas group).

Anatomical Considerations

Contrary to popular portrayal in schematic illustrations, the CS is not just a large, blood-filled venous sac. Rather, it should be thought of as a connection of dural lakes in a trabeculated manner. This portrayal has access implications when treating these lesions. The main function of the CS is the distribution of venous blood drainage of the cerebrum, brainstem, face, eye, orbit, nasopharynx, mastoid, and middle ear. The cavernous area has cranial nerve VI freely coursing through the center of the sinus (i.e., it is the most medial nerve within the CS). Cranial nerves III, IV, and V are located in the outer dural leaflet. The carotid siphon runs through the sinus, and the meningeal and clival branches of the inferolateral trunk and meningo-hypophyseal vessels supply this area. The ICA can be tortuous and have an acute siphon or stenosis further complicating endovascular treatment. The ICA enters the posterior cavernous sinus above the foramen lacerum. The petrolingual ligament can be found here. The bony floor of the CS is the middle cranial fossa, and the bony medial wall is the sella turcica. The posterior wall contains Gruber′s ligament where the cranial nerve VI enters the sinus at Dorello′s canal. Near the clinoid process, the ICA has a proximal and distal dural ring with a small potential subarachnoid space (i.e., the carotid cave). Removal of the anterior clinoid process and optic strut can expose the anterosuperior portion of the CS (i.e., the anterior clinoid triangle with the optic nerve medially and cranial nerve III laterally). ECA branches that may be involved in CCF arise from the internal maxillary artery and the middle meningeal artery (MMA). The most common branch, the vidian artery, anastomoses through the foramen lacerum with the inferolateral trunk of the ICA.

The CS is a major path for venous blood distribution from the brain, skull base, and face. It is connected to the basilar venous plexus, superior petrosal sinus, inferior petrosal sinus (IPS), sphenoparietal sinus, middle meningeal vein, superior ophthalmic vein, and the contralateral CS.

Pathophysiology

Traumatic direct CCF (type A) arises as a consequence of trauma to the central skull base or the CS segment of the ICA. The fistula can cause a direct connection between the ICA and the CS. Trauma accounts for 75% of CCF cases. CCF can develop by a direct tear of the ICA or one of its branches. Type A fistulas can also be caused iatrogenically during cavernous, carotid artery, or transsphenoidal surgery and can also result from endovascular procedures involving PED placement (see later).

Spontaneous direct (type A) or indirect (types B–D) CCFs occur predominantly in patients with underlying vascular disease. Rupture of a cavernous ICA aneurysm is the most common cause. Other causes include genetic disorders with weak connective tissues (e.g., fibro-muscular dysplasia, osteogenesis imperfecta, Ehlers–Danlos syndrome type IV, or moyamoya). In patients without cavernous ICA aneurysms or predisposing congenital factors, CCFs are thought to develop due to an increase in pressure within the draining venous structures that causes small breaks in arterial dural vessels of the CS. Spontaneous indirect (type B–D) CCFs are typically supplied by dural branches of the ICA.

Types B–D fistulas are theorized to result from microtrauma, congenital connections, and sinus thrombosis, similar to mechanisms responsible for the development of other dural arteriovenous fistulas (DAVF). Surgical procedures and radiation can also result in fistula formation.

Classification

The Barrow Classification System is the most frequently used categorization and divides CCF into four types. Type A is a direct fistula. Types B–D represent types of indirect DAVF.

• 
  

  Type A: This type is classically described as a high-flow direct communication between the ICA siphon at the level of the C4 segment and the CS (▶ Fig. 61.1a ).

  
  
• 
  

  Type B: These are slow-flow lesions from meningeal branches of the ICA, such as the inferolateral trunk, and meningo-hypophyseal vessels (▶ Fig. 61.1b ).

  
  
• 
  

  Type C: These are slow-flow lesions arising from ECA branches communicating with the CS. Typically, a branch of the MMA is involved (▶ Fig. 61.1c ).

  
  
• 
  

  Type D: This type represents slow-flow lesions involving ICA and/or ECA meningeal branches (▶ Fig. 61.1d ).

Workup

Related posts:

54 Spetzler–Martin Grade III Arteriovenous Malformations 56 Brainstem Arteriovenous Malformations 58 Spinal Arteriovenous Malformations 57 Cerebellar Arteriovenous Malformations 59 Pial Arteriovenous Fistulas 60 Dural Arteriovenous Fistulas

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