Carotid Cavernous Fistula

Article Author:
Gurkirat Kohli
Article Editor:
Bhupendra Patel
5/20/2020 10:00:18 PM
PubMed Link:
Carotid Cavernous Fistula


Carotid cavernous fistulas (CCFs) are an abnormal shunt from the carotid artery to the cavernous sinus.[1] The symptomatology of CCFs is mainly a result of the important neural and vascular structures in the cavernous sinus which involves cranial nerves III, IV, V1, V2, and VI. CCFs can be classified based on the hemodynamic properties, the etiology or the anatomy of the shunt.

Hemodynamically, the fistulas can be classified as:

  • Low flow fistulas 
  • High flow fistulas

Etiologically, they are classified as:

  • Occurring following trauma
  • Occurring spontaneously

Anatomically, which is the classification most commonly used, the Barrow classification[2] is used: 

  • Type A fistulas are direct connections between the internal carotid artery (ICA) and the cavernous sinus
  • Type B fistula results from dural branches of the ICA
  • Type C results from dural branches from the external carotid artery (ECA)
  • Type D result from dural branches from ICA and ECA

The flow velocity of the CCF, the venous anatomy, and progression of symptoms of the patient dictates the intervention used to treat the CCF.


Several theories have been proposed to account for CCF formation.

  • Direct CCFs are believed to occur secondary to a traumatic tear in the artery from a skull base fracture (see illustration), from the acceleration-deceleration force of a traumatic injury or from an iatrogenic injury following an endovascular intervention or a trans-sphenoidal approach. They can also occur spontaneously following an ICA aneurysm rupture or weakening of the arteries from a genetic condition.[1][3]
  • Indirect CCFs result from rupture of the dural branches of the carotid artery weakened by a defect such as a genetic condition or comorbidities such as hypertension. An alternative theory suggests that an increase in cavernous sinus pressure such as that which follows thrombosis increases the risk of the tear in the dural arteries.[1]


Trauma, such as basilar skull fractures, projectile or slash injuries, or iatrogenic injuries, account for 70% to 75% of all CCFs. These commonly present in young males and tend to be high flow, direct fistulas.[3]

Spontaneous CCFs represent 30% of all CCFs and result from aneurysm rupture or genetic conditions that predispose the patients to vascular injuries such as Ehlers-Danlos syndrome or fibromuscular dysplasia. They are most commonly seen in older females and result in low flow, type D indirect fistulas.[1][3]

History and Physical

Obtaining an accurate history of the onset of symptoms is important as they can explain the etiology of the CCFs. Traumatic high flow, direct fistulas occur more acutely.

The classical triad of symptoms of proptosis, ocular bruit, and chemosis are common, but symptoms such as visual disturbances, orbital pain, and cranial nerve deficits can also be present.[4] Indirect, low-flow fistulas can be difficult to diagnose based on history as they present more insidiously depending on the flow rate and can present in a relapsing and remitting manner.


Diagnostic tests and imaging for a CCF depend on the acuity of the symptoms and whether the patient presents to the emergency room or the clinic.

  • Tonometry and pneumotonometry may show a difference in ocular pressures with ocular pulse amplitudes related to the carotid-cavernous fistula.[3]
  • A B-scan ultrasound or color Doppler will show a dilated superior ophthalmic vein (SOV) or orbital congestion
  • Patients suspected of having a CCF eventually undergo noninvasive imaging such as a standard CT or MRI scan which can show a dilated SOV, orbital congestion, or enlargement of the extraocular muscles.
  • A CTA or MRA may also be utilized as both imaging modalities are sensitive in detecting CCFs resulting in visual symptoms.[1]
  • A cerebral angiogram is the gold standard test for diagnosing a CCF, which can show filling of the cavernous sinus through the fistula, drainage pattern of the fistula, and presence of reflex into cortical veins following an injection of CCA, ECA, or ICA.[3]

Treatment / Management

Various options are available for the management of CCFs depending on the flow rate. The goal is to achieve complete occlusion of the fistula while preserving normal ICA flow.

  • Spontaneous closure: In indirect low flow fistulas, spontaneous closure due to thrombosis of the cavernous sinus can be expected in 20% to 60% of the cases.[1]
  • Compression treatment: For low flow fistulas, conservative therapy is the least invasive alternative that involves compression of the cervical carotid for 4 to 6 weeks to promote thrombosis of the fistula. This is done by applying pressure to the neck by the opposite hand since any cortical ischemia resulting from the compression would cause the hand to fall away from the neck. Closure with conservative management can be expected in only 30% of all cases.[5]
  • Surgical intervention is the most invasive, but definitive option available. With a success rate of 31% to 79%, surgical options include suturing or clipping the fistula, packing the cavernous sinus or ligating the ICA.[1] Radiosurgery is also an option for low flow indirect fistulas. Obliteration of the fistula can be achieved in 75% to 100% of cases. However, radiosurgery is not a treatment option for acute, urgent cases because of latency of months to years before complete obliteration is achieved.[6]
  • Endovascular intervention is the first line treatment of CCFs with a cure rate of greater than 80%.[7] For direct high flow CCFs, the trans-arterial route is preferred. Following access to the ICA, the fistula can be embolized using coils or a liquid embolization material. Other options include placement of a covered stent graft in the ICA or an endovascular arterial sacrifice.[3] For indirect CCFs, the transvenous route is preferred due to the risk of embolic stroke with trans-arterial access of the arterial feeders. The cavernous sinus can be accessed via the inferior petrosal sinus or from the facial vein to the superior ophthalmic vein.[3][4] In cases with venous thrombosis or increased tortuosity of the vasculature, access to the cavernous sinus can be obtained through direct cannulation of the superior ophthalmic vein following surgical exposure.[8]

Differential Diagnosis

  • Non-specific orbital inflammation
  • Orbital hemorrhage
  • Orbital infection
  • Orbital tumor
  • Orbital vasculitis
  • Thyroid disease
  • Tumor with cavernous sinus involvement

Clinical examination, accurate history, and relevant investigations will yield the correct diagnosis.


Successful embolization of a fistula results in thrombosis of the cavernous sinus over time although it can take weeks to months for closure to occur following radiosurgery. Symptoms including chemosis, proptosis, and cranial nerve deficits will resolve within hours to days. Recovery of vision may depend on several factors including the flow of the fistula, the timing of the intervention, and evidence of ischemic injury of the optic nerve or retina. Recurrence of the CCF is rare, but patients can be followed up with a posttreatment angiogram to confirm the complete obliteration of the fistula.


Since most CCFs are not life-threatening, prompt treatment is necessary to prevent permanent injury to the involved eye. Even with the spontaneous closure of a fistula, the patient may experience worsening symptoms as the cavernous sinus thromboses. Although complications related to endovascular embolization of CCFs are rare complications such as ophthalmoplegia, central retinal vein occlusion, ophthalmic artery occlusion, and cerebral infarction have been reported.[9] Embolization through the SOV route may not be successful due to fragile or clotted veins which can cause complications such as vision loss.[10]

Deterrence and Patient Education

  • Avoid contact sports
  • Control high blood pressure
  • Maintain regular follow up with an ophthalmologist 
  • Report to the emergency room for worsening symptoms
  • Obtain post-treatment imaging to determine closure of the fistula

Pearls and Other Issues

  • Maintain a high level of suspicion for a carotid-cavernous fistula following high-velocity trauma when symptoms of blurry vision, eye and face pain, double vision and ptosis develop some days or even weeks after the trauma. 
  • Type A fistulas (high-flow, post-traumatic fistulas) always need intervention to close the fistula.
  • Spontaneous closure may occur in Type B, C, and D fistulas.
  • Neuro-ophthalmic assessment of vision, pressures, ocular movements, assessment of the cranial nerves is vital.

Enhancing Healthcare Team Outcomes

Neuro-interventional, neuro-ophthalmic, and orbital surgical involvement in the patient's care is vital as some of these patients may progress rapidly and need urgent intervention. Orbital surgeons should be familiar with the technique of superior ophthalmic vein cannulation to assist with the neuro-intervention when needed. A high rate of successful closure of the fistulas can be achieved with proper interprofessional teamwork. (Level V)

  • Contributed by Professor Bhupendra C K Patel MD, FRCS
    (Move Mouse on Image to Enlarge)
    • Image 7131 Not availableImage 7131 Not available
      Contributed by Professor Bhupendra C K Patel MD, FRCS


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