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Carotid cavernous fistula (CCF) is an abnormal shunt from the carotid artery to the cavernous sinus. The symptomatology of CCFs is mainly a result of the effects on important neural and vascular structures in the cavernous sinus which include 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. This activity reviews the cause, pathophysiology, and presentation of CCF and highlights the role of the interprofessional team in its management. Objectives: Review the causes and types of carotid-cavernous fistula Describe the evaluation of a patient with carotid-cavernous fistula Summarize the treatment options for carotid-cavernous fistula Outline the importance of improving coordination among interprofessional team members to improve outcomes for patients affected by carotid-cavernous fistula Access free multiple choice questions on this topic.

Carotid cavernous fistula (CCFs) is an abnormal shunt from the carotid artery to the cavernous sinus.[1] The symptomatology of CCFs depends on the involvement of the important neural and vascular structures in the cavernous sinus. These structures include cranial nerves III (oculomotor nerve), IV (trochlear nerve), V1 (ophthalmic nerve), V2 (maxillary nerve), and VI (abducens nerve). 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, and High flow fistulas. Etiologically, they are classified as: Occurring following trauma, and Occurring spontaneously. Anatomical classification is most commonly used. The Barrow classification divides CCFs into: 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 results from the dural branches from the ICA and ECA [2] The patient's CCF flow velocity, venous anatomy, and symptom progression dictate 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 transsphenoidal procedure. 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, including hypertension. An alternative theory suggests that an increase in cavernous sinus pressure, such as that following thrombosis, increases the risk of tearing the dural arteries.[1]

Trauma, such as basilar skull fractures, projectile or slash injuries, or iatrogenic injuries, accounts for 70% to 75% of all CCFs. These are 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 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]

Obtaining an accurate history of symptom onset is important, as these can explain the etiology of CCFs. Traumatic high-flow, direct fistulas occur more acutely. The classical triad of proptosis, ocular bruit, and chemosis is common, but symptoms such as visual disturbances, orbital pain, and cranial nerve deficits can also be present.[4][5] Indirect, low-flow fistulas can be difficult to diagnose based on history, as they present more insidiously depending on the flow rate and may be relapsing and remitting.

Diagnostic tests and imaging for a CCF depend on the patient's symptoms and whether they present to the emergency room or the clinic. See Image. Carotid Cavernous Fistula, Symptoms and Diagnostic Tests. Tonometry and pneumotonometry may show an increased ocular pulse amplitude in the side of the carotid-cavernous fistula compared to the fellow eye.[3][6] A B-scan ultrasound or color Doppler shows a dilated superior ophthalmic vein (SOV) or orbital congestion. Patients suspected of having a CCF eventually undergo noninvasive imaging such as a standard CT (computed tomography) or MRI (magnetic resonance imaging) scan, which can show a dilated SOV, orbital congestion, or enlargement of the extraocular muscles. A CTA (computed tomography angiography) or MRA (magnetic resonance angiography) may also be utilized, as both imaging modalities are sensitive to detecting CCFs that result 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 reflux into cortical veins following an injection of CCA (common carotid artery), ECA, or ICA.[3]

Various options are available for managing 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 can be expected in 20% to 60% of cases.[1] Compression treatment: For low-flow fistulas, this conservative therapy is the least invasive alternative that involves compression of the cervical carotid multiple times a day for 4 to 6 weeks to promote thrombosis of the fistula. This is done by applying pressure to the neck with 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.[7] Surgical intervention is the most invasive but a definitive option. 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 it requires months to years to achieve complete obliteration.[8] Endovascular intervention is the first-line treatment for CCFs, with a cure rate exceeding 80%.[9] 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][5] 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.[10]

Differential diagnoses of CCF include: Non-specific orbital inflammation Orbital hemorrhage Orbital infection Orbital tumor Orbital vasculitis Cavernous sinus thrombosis, Thyroid disease, and Tumor with cavernous sinus involvement.

Successful embolization of a fistula results in thrombosis of the cavernous sinus over time, though closure can take weeks to months following radiosurgery. Symptoms, including chemosis, proptosis, and cranial nerve deficits, usually resolve within hours to days. Recovery of vision may depend on several factors, including the fistula flow, the timing of the intervention, and evidence of ischemic injury to 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.

Though most CCFs are not life-threatening, prompt treatment is necessary to prevent permanent injury to the involved eye. Even with spontaneous fistula closure, the patient may experience worsening symptoms due to cavernous sinus thrombosis. Complications related to endovascular embolization of CCFs are rare and include ophthalmoplegia, central retinal vein occlusion, ophthalmic artery occlusion, and cerebral infarction.[11] Embolization via the SOV route may be unsuccessful due to fragile or clotted veins, which can lead to complications such as vision loss.[12]

Issues of deterrence and patient education in the treatment of carotid cavernous fistula include: 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

Key facts to keep in mind about carotid cavernous fistula include: 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, intraocular pressure, ocular movements, and cranial nerves is vital.

Neuro-interventional, neuro-ophthalmic, and orbital surgical involvement in the patient's care is vital, as some patients may progress rapidly and require 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 fistula closure can be achieved with effective interprofessional teamwork.