Endovascular management has become the treatment of choice for carotid-cavernous fistulas regardless of the fistula type. The endovascular method offers numerous options that render it capable of treating each fistula type by choosing an adequate technique. This advantage along with the advancement in the field has led to fewer complications with higher success rate.
Key points
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The diagnosis of carotid-cavernous fistulas (CCFs) requires a high index of suspicion; a delay in treatment may lead to irreversible damage.
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Angiography remains the gold standard for diagnosing CCFs.
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The endovascular approach is the first-line treatment given the low complication rate and the favorable long-term outcome.
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The agents used for the endovascular management are balloons, coils, liquid embolic substances, and stents.
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Certain fistulas may require multiple agents or multiple sessions for complete closure.
Introduction
CCFs are arteriovenous malformations that result in shunting of the blood from the carotid artery to the cavernous sinus (CS). The pressure inside the CS increases, the draining vessels engorge, and the flow may get reversed leading to a myriad of clinical manifestation and mimicking many head and neck diseases. The management for most CCFs has shifted from open surgery to endovascular treatment. This novel therapy is still evolving in its approach, technique, and agents. The agents vary from balloons, to coils, to different liquid embolic substances, and recently, stents. The decision on the treatment modality is tailored to suit each patient depending on the risk factors and the characteristics of the fistula. This article reviews many aspects of the CCF while focusing on the endovascular management, which is the preferred treatment modality.
Introduction
CCFs are arteriovenous malformations that result in shunting of the blood from the carotid artery to the cavernous sinus (CS). The pressure inside the CS increases, the draining vessels engorge, and the flow may get reversed leading to a myriad of clinical manifestation and mimicking many head and neck diseases. The management for most CCFs has shifted from open surgery to endovascular treatment. This novel therapy is still evolving in its approach, technique, and agents. The agents vary from balloons, to coils, to different liquid embolic substances, and recently, stents. The decision on the treatment modality is tailored to suit each patient depending on the risk factors and the characteristics of the fistula. This article reviews many aspects of the CCF while focusing on the endovascular management, which is the preferred treatment modality.
Relevant anatomy
The CS is located lateral to the sella turcica, expanding from the superior orbital fissure to the apex of the petrous bone. The CS is neither a sinus nor cavernous per se, rather it is a reticulated structure, formed by an assembly of multiple thin-walled veins, as demonstrated by Parkinson and later by Hashimoto and colleagues. Therefore, the name lateral sellar compartment was proposed to be more accurate and to avoid any misinterpretation. The importance that this distinction brought has modified the CCF surgery (clipping a fistulous point) and more notably, the choice of embolic agent used to avoid compartmentalization, as discussed below (see Endovascular Treatment). The CS encloses important neurovascular structures responsible for the compliance of patients with fistula. The CS is divided into 4 compartments by the internal carotid artery (ICA), namely, medial, lateral, anteroinferior, and posterosuperior, in relation to the intracavernous portion of the ICA. The CS receives:
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Anteriorly: the superior and inferior ophthalmic veins
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Laterally: the superficial middle (sylvian) cerebral vein, the deep middle cerebral vein, and the sphenoparietal sinus
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Posteriorly: the superior and inferior petrosal veins drain the CS
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The basilary plexus, which is posterior in location, and the intercavernous sinus are examples of venous anastomoses that join the 2 CS.
The connection between the multiple pathways represents alternative routes for drainage when the CS becomes obstructed and also serves as multiple ports of entry to the CS when endovascular treatment is being performed.
Fistula classification and characteristics
CCF is sorted according to its cause, hemodynamic behavior, and angioarchitecture. Barrow and colleagues classified the CCFs in to 4 distinct types (A, B, C, and D) depending on the arterial supply. This classification is preferred because it encompasses indirectly the cause and the hemodynamic features; it also has a therapeutic implication.
Direct CCF
Type A or direct CCF is the most common type accounting for up to 80% of all CCFs. This type is a direct connection between the cavernous ICA and the CCF, mostly because of a tear in the carotid wall after trauma. Rupture could be due to the collision of the vessel against a bony fracture, shearing forces that act on the vessel wall, or increased intraluminal pressure after the distal compression of the vessel. Traumatic CCF can be bilateral in 2% of cases. If so, it is usually more deadly and more severe at presentation. The carotid disruption can result from blunt as well as penetrating head trauma, which explains the higher prevalence in young males. Direct CCF can be iatrogenic, following transsphenoidal surgery, endovascular procedures, and percutaneous trigeminal rhizotomy. This type of CCF can also be spontaneous in 20% cases, which happens when an ICA aneurysm spontaneously ruptures in the CS or when the patient has any disease that weakens the carotid wall predisposing it to rupture. It is important to be prudent when such diseases are present because of the increased risk of angiographic complications. Most Type A CCFs are high-flow lesions with minimal chance of spontaneous resolution.
Indirect CCF
Type B, C, and D CCFs are indirect fistulas that arise from meningeal branches of the ICA or the external carotid artery (ECA). Type B is the least frequent; it arises from the meningeal branches of the ICA. Type C arises from the meningeal branches of the ECA, and Type D arises from meningeal branches of both the ICA and the ECA; it is the most frequent indirect type of CCF. The indirect fistulas, also named dural fistulas, most commonly arise spontaneously but can occur after trauma. These fistulas are frequently nourished by the internal maxillary artery, the middle meningeal artery, the meningohypophyseal trunks, and the capsular arteries. The underlying mechanism that leads to the formation of these fistulas remains unknown. It has been postulated that thrombosis of the microscopic venous vessels or partial thrombosis of the sinus leads to high pressure and rupture of the thin-walled dural vessel that traverses the sinus. Reported predisposing factors are pregnancy, diabetes mellitus, collagen vascular disease, arterial hypertension, and phlebitis. As with spontaneous direct CCF, arterial wall defect may also lead to spontaneous indirect CCF formation after minor strains. Indirect fistulas occur in postmenopausal women most frequently, but can occur at any age including infancy. Some reported indirect CCFs were considered to be congenital. A subset type of indirect CCF is the posttraumatic CCF, and it differs from the spontaneous ones by having a single vessel for blood supply. Unlike direct fistulas, indirect fistulas can have contralateral feeders and require bilateral angiography of the ICA and ECA. Dural fistulas are low-flow lesions, have gradual onset, and may resolve spontaneously or by manual carotid compression in up to 30% to 50% of cases. Table 1 highlights the main difference between direct and indirect fistulas. Indirect fistulas, when fed by ICA branches, are hazardous and less amenable to transarterial embolization.
| Direct CCF | Indirect CCF | |
|---|---|---|
| Type | A | B, C, D |
| Arterial source | Cavernous ICA | ICA/ECA meningeal branches |
| Single feeder | Multiple feeders a | |
| Etiology | Traumatic>spontaneous | Spontaneous>traumatic |
| Epidemiology | Young individuals 75%–80% of fistulas | Elderly women 15%–20% of fistulas |
| Hemodynamic features | High flow | Low flow |
| Presentation | Abrupt onset | Gradual onset |
| Resolution | Spontaneous uncommon | Spontaneous common |
| Diagnostic angiography | Unilateral is enough | Bilateral to exclude contralateral |
| Treatment route | Intra-arterial: favored b | Intravenous: favored |
| Cure rate | 80%–99% | 80%–90% c |
a Can be single in case of trauma.
b Some favor the transvenous route because of easier manipulation of the coil catheter.
c More than 90% cure for indirect CCF has been reported when combined treatment is used.
Pathophysiology and clinical presentation
The short-circuiting of the arterial blood increases the pressure in the CS leading to flow reversal. The flow then may follow any draining pattern producing venous hypertension and/or thrombosis. The signs and symptoms depend on the drainage pathway, the presence of collaterals, and finally the size and location of the CCF. Table 2 lists the symptoms with their underlying physiopathology. The most frequent complains are in the orbital region. Anterior drainage leads to orbital vein congestion and transudation of fluids, increased intraocular pressure, impaired retinal perfusion, and rupture of dilated veins. The patient may present with symptoms ranging from subconjunctival hemorrhage to visual loss. Whether the vision loss improves or not is difficult to predict, but as a general rule, minor defects improve with better chance than severe ones. Chances of recovery decrease if the superior ophthalmic vein (SOV) is already thrombosed or the central retinal vein has been damaged by the time of the diagnosis. Lateral drainage in the sphenoparietal sinus leads to cortical venous hypertension, which is associated with intracranial hemorrhage and neurologic deficits. The risk is lower in posttraumatic young patients in whom the venous system is still resilient. Posterior drainage can have cranial nerve palsies as the only ocular finding. External hemorrhage such as epistaxis is rare but fatal; it has been reported in 2% of CCF cases, sometimes requiring emergent carotid sacrifice. The clinical presentation of direct and indirect CCF overlaps; however, the onset of symptoms and the severity differ. Direct fistulas are high-flow lesions and present classically with proptosis, chemosis, orbital bruits, and headache. Vision loss has been reported in up to 50% of cases. Less common presentations include intracerebral or subarachnoid hemorrhage in 5% of patients and exteriorized bleeding in 3% of cases. Indirect CCFs have relapsing and remitting symptoms often with an insidious course that tends to delay the diagnosis. Proptosis, chemosis, and glaucoma are the most notable findings. An important feature of the disease is the dynamicity of the venous drainage. When venous pathways become thrombosed, the outflow changes in direction, which may account for the relapsing and remitting symptoms of the indirect CCF, or sometimes for the spontaneous resolution of symptoms. Hence the need to follow patients with angiography when curative treatment was not achieved; clinical resolution might be due to the change in course of the venous circulation perhaps to a more risky location.
| Clinical Symptoms | Underlying Physiopathology | Frequency (%) |
|---|---|---|
| Orbital findings | Proptosis/corneal damage: increased orbital pressure Pain: impaired aqueous humor return, increased IOP (glaucoma) Impaired vision: ischemic retinopathy, ischemic optic neuropathy Diplopia: cranial nerve palsies Chemosis: venous congestion a Subconjunctival hemorrhage: rupture arterialized veins | Very frequent >50 |
| External bleeding | Otorrhagia: ruptured ear canal veins Epistaxis: drainage in the sphenoid sinus with consequent rupture | 3 |
| Intracranial bleeding Subarachnoid bleeding | Cerebral cortical venous hypertension | 5 |
| Headache | Bleeding, venous hypertension, trigeminal dysfunction | >30 |
a The tortuosity of the vessels suggests CCF as the cause rather than conjunctivitis, episcleritis, or thyroid disorder.
Workup
The best initial tests used when CCF fistula is suspected for the reasons mentioned above are computed tomography (CT) or magnetic resonance (MR). These tests can confirm the clinical symptoms by visualizing the proptosis, the cerebral edema, and the cerebral hemorrhage. Signs and symptoms that suggest CCF are the following: enlargement of the extraocular muscles; engorgement of the SOV; dilatation of the facial vein; expansion of the ipsilateral CS, which can be described as pseudoaneurysmal (bulging) or sinusoidal (less bulging); presence of venous aneurysm; and enlargement of pial and cortical veins. CT adds the benefit of detecting bone fracture, whereas MR offers the advantage of detecting flow voids in the CS as well as the orbital edema when present. CT angiography (CTA) and MR angiography (MRA) are considered similar in accuracy, but in a recent study, CTA outperformed MRA in detecting the fistula when it was located in segment 4 or 5 of the ICA. Doppler flow can assist in the diagnosis by looking for increased flow, decreased resistance, and the presence of orbital bruits. Digital subtraction angiography (DSA) remains the gold standard in the diagnosis of CCF, because many diseases might be confused with CCF on the CT scan. Recently, in a case report, a prominent bulging of the SOV on the CT scan was diagnosed as a CCF before the DSA revealed a direct fistula between the ICA and the SOV bypassing the CCF. The DSA is required to evaluate the angioarchitecture of the fistula, assess the feeding arteries, and plan the intervention. DSA can provide information on flow velocity, steel phenomenon, associated vascular injuries, collaterals, and high-risk pathways ; it can also reveal small dural feeding arteries missed on the CTA. To better evaluate the high-flow lesion, the Mehringer-Hieshima maneuver is used to control the flow by slowly injecting the ipsilateral ICA while gentle manual compression is applied to the artery. Following the occlusion, the results should be carefully interpreted because a worsening of the steel phenomenon is possible; this may give the impression of a false-negative balloon occlusion test (BOT). Another well-known maneuver is the Huber maneuver, which helps in identifying the distal extent of the fistula by manually compressing the ICA while injecting the ipsilateral vertebral artery. The retrograde flow through the posterior communicating artery fills the fistula distally. Before initiating treatment, tolerance of carotid occlusion should be assessed. This assessment is usually done via the BOT or the single-photon emission computed tomography. The latter seems to be more sensitive because it can predict major stroke after carotid occlusion in patients with positive result of BOT. The diagnosis of CCF in the setting of a patient with trauma can be challenging and even more problematic when the patient is comatose. To allow early diagnosis, Schiavi and colleagues suggested monitoring the increase in the jugular venous oxygen saturation. Finally, based on certain angiographic or clinical findings, the fistula can be considered as lethal and an emergent aggressive treatment can be lifesaving and necessary to improve the outcome. These indications are detailed in Table 3 .
| Angiographic Indications | |
|---|---|
| Findings | Future Risk |
| Pseudoaneurysm | SAH |
| Large varix of the cavernous sinus | SAH |
| Venous drainage to cortical veins | Hemorrhagic venous infarction |
| Thrombosis of distant venous outflow pathways | Hemorrhagic venous infarction |
| Clinical Indicators | |
|---|---|
| Presentation | Mechanism |
| Epistaxis/Otorrhagia | External bleeding due to venous hypertension or pseudoaneurysmal varix |
| Headache, diplopia | Increased intracranial pressure from cortical venous hypertension |
| Rapidly progressive proptosis Diminished visual acuity | Obstruction of venous outflow pathway to the orbit |
| TIA/stroke |
|
Related posts:
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Endovascular Treatment of Basilar Aneurysms
Cerebral Vasospasm
Endovascular Management and Treatment of Acute Ischemic Stroke
Endovascular Management of Intracranial Atherosclerosis
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