Carotid cavernous fistulas (CCFs) are an abnormal shunt from the carotid artery to the cavernous sinus. 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:
Etiologically, they are classified as:
Anatomically, which is the classification most commonly used, the Barrow classification is used:
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.
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. 
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.
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. Indirect, low-flow fistulas can be difficult to diagnose based on the 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.
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.
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 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. Embolization through the SOV route may not be successful due to fragile or clotted veins which can cause complications such as vision loss.
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)