Carotid-Cavernous Fistula

Key Points at a Glance

Essentials of This Disease

• Carotid cavernous fistula (CCF) is an abnormal shunt between the carotid artery and the cavernous sinus.
• The triad of pulsatile exophthalmos, orbital bruit, and conjunctival chemosis (Dandy triad) is characteristic of direct CCF.
• In the Barrow classification, Type A corresponds to direct (high-flow) CCF, and Types B/C/D correspond to indirect (low-flow, dural) CCF.
• It occurs in approximately 0.2% of patients with traumatic brain injury and up to 4% of patients with skull base fractures.
• Indirect CCF has an insidious onset and is often misdiagnosed as conjunctivitis; diagnosis is reportedly delayed by an average of 234 days.
• Definitive diagnosis is made by DSA (digital subtraction angiography). CT/MRI play a supportive role.
• Endovascular treatment (coil embolization, balloon embolization) is the first-line therapy, with a success rate of 96.9% via the transvenous approach.

1. What is Carotid Cavernous Fistula?

Carotid cavernous fistula (CCF) is an abnormal vascular connection (arteriovenous shunt) between the internal carotid artery (ICA) or branches of the external carotid artery (ECA) and the venous channels of the cavernous sinus (CS). It is classified under ICD-10-CM code I77.0 (acquired arteriovenous fistula).

Classification

The Barrow classification is widely used for carotid cavernous fistulas.

Type	Feeding artery	Flow rate	Typical cause
Type A	Direct ICA (direct type)	High flow	Trauma, ICA aneurysm rupture
Type B	ICA dural branches only	Low flow	Idiopathic/dural type
Type C	ECA dural branches only	Low flow	Idiopathic/dural type
Type D	Both ICA and ECA	Low flow	Idiopathic/dural type (most common)

Indirect (dural) types refer to Types B/C/D. In a study by Preechawat et al. of 80 cases, Type B accounted for 14%, Type C for 15%, and Type D for 71% ⁷⁾, with Type D being the most common in spontaneous carotid-cavernous fistulas ⁹⁾.

Epidemiology

• Traumatic carotid-cavernous fistulas occur in 0.2% of patients with traumatic brain injury ¹⁾
• Up to 4% of patients with skull base fractures develop this condition
• Up to 24% of patients with ICA cavernous segment aneurysms develop carotid-cavernous fistulas
• Bilateral carotid-cavernous fistulas are rare but reported in up to 1% of traumatic cases
• Idiopathic carotid-cavernous fistulas account for up to 30% of all cases and are more common in postmenopausal women
• 75% of cases are caused by head trauma; the remaining 25% are idiopathic, more common in middle-aged women
• The average diagnostic delay for indirect carotid-cavernous fistulas is 234 days ⁷⁾

Q Can carotid-cavernous fistulas occur in both eyes, not just one?

A

Bilateral carotid-cavernous fistulas have been reported in up to 1% of traumatic cases. Spontaneous bilateral direct carotid-cavernous fistulas have also been reported in 35 cases in the literature ⁶⁾, and although rare, they can occur bilaterally.

2. Main Symptoms and Clinical Findings

Subjective Symptoms

The nature of symptoms differs greatly between direct type (high-flow, acute onset) and indirect type (low-flow, insidious onset).

Direct Type (Acute)

Pulsatile proptosis: Protrusion of the eye synchronized with the heartbeat. Characterized by sudden onset.

Orbital bruit: Pulsatile tinnitus audible to the patient. Also detectable by auscultation.

Orbital pain and headache: Severe pain in and around the orbit.

Diplopia: Due to extraocular muscle palsy or proptosis.

Visual loss: Associated with ocular ischemia or secondary glaucoma.

Indirect Type (Chronic)

Chronic conjunctival injection: Mild to moderate, slowly progressive.

Eyelid edema and swelling: Due to orbital venous stasis.

Diplopia and visual loss: Often mild and may go unnoticed.

Asymptomatic onset: In low-flow type, ocular symptoms are scarce, and patients may present only with “red eye” ⁹⁾.

Among all patients with carotid-cavernous fistula, 90% have proptosis, 90% have conjunctival chemosis, 50% have diplopia, up to 50% have visual impairment, and 5% have intracranial hemorrhage (ICH) ³⁾.

Clinical Findings (Findings Confirmed by Physician Examination)

Triad of direct carotid-cavernous fistula (Dandy triad):

1. Pulsatile exophthalmos
2. Orbital bruit
3. Chemosis

Vascular findings: Conjunctival congestion shows a tortuous and engorged vascular pattern called “caput Medusae.” Cork-screw (corkscrew) episcleral vessels converging toward the limbus are characteristic.

Elevated intraocular pressure: Reflects increased episcleral venous pressure (normal 8–10 mmHg) and can cause secondary open-angle glaucoma. There is positional variation, with elevation in the supine position. Persistent ocular ischemia may lead to neovascular glaucoma.

Ocular motility disorders: Diplopia due to palsy of the oculomotor (III), trochlear (IV), and abducens (VI) nerves.

Other findings: Eyelid edema and ptosis, papilledema, retinal vein dilation and tortuosity, central retinal vein occlusion (CRVO), ischemic optic neuropathy, choroidal detachment.

Diagnostic Pitfall

In dural carotid-cavernous fistulas that drain mainly into the inferior petrosal sinus with poor reflux into the superior ophthalmic vein, conjunctival congestion and edema may be minimal, making diagnosis difficult. Careful observation for the presence of corkscrew vessels is important.

Q Why is indirect carotid-cavernous fistula easily misdiagnosed as conjunctivitis?

A

Indirect type is low-flow and insidious in onset, so it often does not present with the classic triad (pulsatile exophthalmos, bruit, chemosis). Chronic conjunctival congestion may be the only symptom, leading to misdiagnosis as conjunctivitis, sinusitis, or orbital cellulitis ⁹⁾. Corkscrew episcleral vessels are a clue for differentiation.

3. Causes and Risk Factors

Traumatic (Most Common Cause)

• Closed head injury / skull base fracture: Most common cause. Caused by direct ICA laceration due to fracture or shear force, or rupture of the vessel wall due to a sudden increase in intraluminal pressure¹⁾
• Penetrating head injury: Stab wounds, gunshot wounds, etc.
• Iatrogenic: After intracranial surgery, transsphenoidal surgery, sinus surgery, or endovascular treatment
• Delayed onset: There are case reports of onset 13 days after trauma¹⁾; caution is needed not only immediately after trauma but also during follow-up

Idiopathic / Predisposing factors

• Rupture of ICA cavernous sinus aneurysm or ICA dissection
• Congenital arteriovenous malformation (AVM): May underlie dural carotid-cavernous fistula
• Predisposing diseases: Ehlers-Danlos syndrome, pseudoxanthoma elasticum, osteogenesis imperfecta, fibromuscular dysplasia
• Risk factors for indirect carotid-cavernous fistula: Hypertension, female sex, advanced age, diabetes. Hypertension and diabetes may trigger dural carotid-cavernous fistula.

Prevention / Daily care

Most carotid-cavernous fistulas are triggered by trauma or underlying diseases (hypertension, diabetes, connective tissue diseases). Proper control of hypertension and diabetes can reduce the risk of idiopathic carotid-cavernous fistula. If proptosis, conjunctival injection, or tinnitus appears after head trauma, promptly consult an ophthalmologist or neurologist.

4. Diagnosis and examination methods

Imaging studies

The characteristics of each modality are shown below.

Examination method	Main findings	Role / Features
CT/CTA	SOV enlargement, cavernous sinus enlargement, skull base fracture	Initial screening. Enlargement of the ipsilateral cavernous sinus and SOV dilation are “almost specific”
MRI/MRA	Flow void, orbital edema, SOV dilation	In carotid-cavernous fistula, CS blood flow becomes fast and is recognized as flow void. Useful for observing natural course and postoperative thrombosis
DSA	Exact location of fistula, feeding arteries, venous drainage pathways	Gold standard for definitive diagnosis

• Orbital Doppler ultrasound: Useful for confirming dilation of the superior ophthalmic vein (SOV) and blood flow reversal

Dynamic contrast-enhanced MRI: Shows early contrast enhancement of the cavernous sinus. In anterior drainage type, dilation and early enhancement of the superior ophthalmic vein are seen; in posterior drainage type, early enhancement of the pituitary venous plexus is seen. Useful as a non-invasive evaluation prior to DSA.

• DSA (4-vessel angiography): For dural carotid-cavernous fistula, angiography of both ICA and ECA is necessary. It identifies the location of the fistula, feeding arteries, flow rate, and full venous drainage pattern, essential for treatment planning

Differential Diagnosis

Main diseases to differentiate from carotid-cavernous fistula:

• Cavernous sinus thrombosis: Often preceded by fever or infection
• Thyroid eye disease (Graves ophthalmopathy): Particularly similar in bilateral cases ⁶⁾
• Tolosa-Hunt syndrome / Orbital inflammatory pseudotumor: Inflammatory diseases. Steroid-responsive
• Superior orbital fissure syndrome / Orbital apex syndrome
• Retrobulbar hemorrhage

Caution for misdiagnosis

Carotid-cavernous fistula is sometimes misdiagnosed as conjunctivitis, sinusitis, or orbital cellulitis ⁹⁾. Especially in indirect type, because the classic triad is absent, if corkscrew vessels are found in treatment-resistant “chronic ocular congestion,” carotid-cavernous fistula should be actively suspected and imaging performed.

Q Why is cerebral angiography (DSA) necessary for definitive diagnosis of carotid-cavernous fistula?

A

CT and MRI can suggest enlargement of the cavernous sinus or dilation of the SOV, but cannot identify the exact location of the fistula, the type of feeding arteries (ICA branches, ECA branches), or the details of venous drainage pathways. Only DSA can confirm these and enable treatment planning, including the route for coil or balloon placement. For dural carotid-cavernous fistulas, four-vessel angiography is necessary.

5. Standard treatment

The treatment strategy for carotid-cavernous fistula is determined by the type, severity, and progression of symptoms. First, referral to a neurosurgeon is necessary, and ophthalmology manages ocular symptoms and follow-up.

Indications for observation and spontaneous closure

Indirect type carotid-cavernous fistulas with low shunt flow and mild ocular symptoms may be expected to close spontaneously.

• Spontaneous closure rate of dural type carotid-cavernous fistula is less than 50%
• Up to 70% of indirect type carotid-cavernous fistulas have been reported to close spontaneously ⁶⁾
• Direct type carotid-cavernous fistulas rarely close spontaneously after 3 weeks
• In mild cases, healing may occur with carotid compression maneuvers.

Endovascular Treatment (First-Line)

Endovascular treatment is performed when there is sustained elevated intraocular pressure, vision loss, diplopia, risk of cerebral hemorrhage/subarachnoid hemorrhage, or when spontaneous closure is not expected.

Coil embolization: Filling the cavernous sinus with detachable coils. Applicable to both direct and indirect types.

• Transvenous approach: Safest and most effective for indirect carotid-cavernous fistulas. The most common route is the inferior petrosal sinus (IPS) ²⁾. If IPS is unavailable, consider SOV, inferior ophthalmic vein (IOV), superior petrosal sinus, pterygoid plexus, or contralateral SOV/IPS.
• The success rate of transvenous embolization reaches 96.9% ⁴⁾.

Balloon embolization: Occludes the fistula with a balloon while preserving the ICA. Successful in over 90% of cases ¹⁾. However, the supply of detachable balloons is currently limited ³⁾.

Liquid embolic agents: Onyx (ethylene-vinyl alcohol copolymer), n-BCA (histoacryl glue). In high-flow direct fistulas, caution is needed regarding glue reflux and distal migration ³⁾.

Transorbital approach: Alternative technique when transvenous routes are unavailable.

• Dyna-CT-guided direct SOV puncture: Allows three-dimensional depth adjustment and is less affected by orbital bone interference than ultrasound or fluoroscopy ⁸⁾.
• For endoscopic transorbital approach (ETOA), see the “Latest Research” section.

Ophthalmic Symptomatic Treatment

• High intraocular pressure: Use ocular hypotensive agents such as dorzolamide-timolol fixed combination eye drops ⁹⁾.
• Without improvement in underlying hemodynamics, intraocular pressure control is limited.

Prognosis

• If a direct carotid-cavernous fistula is left untreated, it can lead to life-threatening outcomes such as cavernous sinus rupture, cerebral hemorrhage, and subarachnoid hemorrhage.
• The main causes of blindness are secondary glaucoma and central retinal vein occlusion.
• In successfully treated cases, symptom improvement is good: recovery of intraocular pressure from 31 to 12 mmHg and visual acuity from 0.04 to 0.9 has been reported ³⁾.
• Recurrence after closure and healing is occasionally observed.

Caution regarding cortical venous reflux (CVR)

When arterial blood refluxes into the cortical venous system on the brain surface (cortical venous reflux; CVR), the risk of cerebral hemorrhage, brain edema, and venous infarction increases. The annual bleeding rate of untreated dural arteriovenous fistulas with CVR is reported to reach 13% ⁷⁾, and urgent endovascular treatment is necessary.

Q Can an indirect carotid-cavernous fistula heal on its own?

A

The spontaneous closure rate of dural carotid-cavernous fistulas is less than 50%, and up to 70% of indirect (low-flow) types are reported to close spontaneously ⁶⁾. However, when accompanied by cortical venous reflux (CVR), the risk of cerebral hemorrhage is high, and spontaneous closure cannot be awaited. The feasibility of observation is determined after evaluating the venous drainage pathway by DSA.

6. Pathophysiology and detailed mechanism of onset

Anatomy of the cavernous sinus

The cavernous sinus is a paired dural venous sinus located lateral to the sella turcica.

• Course of cranial nerves: In the lateral wall, from top to bottom, III (oculomotor), IV (trochlear), V1 (ophthalmic), and V2 (maxillary) nerves run. VI (abducens) runs lateral to the ICA within the CS lumen.
• ICA cavernous segment: Enters the sinus at the petrolingual ligament and exits at the proximal dural ring.
• Branches of the ICA: Meningohypophyseal trunk (MHT), inferolateral trunk (ILT), and McConnell’s capsular artery.
• Venous drainage pathways: Orbit (SOV/IOV), Sylvian fissure, anterior and middle cranial fossae (sphenoparietal sinus), posterior cranial fossa (basilar venous plexus, superior and inferior petrosal sinuses), and pterygoid venous plexus.
• The left and right cavernous sinuses are connected by the anterior and posterior intercavernous sinuses.
• The orbital veins have no valves, so reflux easily occurs when pressure increases.

Mechanism from shunt formation to ocular symptoms

When arterial blood flows directly into the CS without passing through capillaries, the CS pressure increases.

• Anterior drainage type: Increased CS pressure → blood reflux into SOV → SOV dilation → orbital congestion, increased intraocular pressure, proptosis, and mass effect due to enlargement of extraocular muscles.
• Cortical venous reflux (CVR) type: Arterial blood reflux into the sylvian vein and brainstem venous system → cortical venous hypertension → increased risk of ICH, brain edema, and venous infarction³⁾.

When a dural carotid-cavernous fistula mainly drains into the inferior petrosal sinus and anterior drainage is poor, conjunctival injection and edema may be inconspicuous, making diagnosis difficult.

Mechanism of spontaneous closure

The following mechanisms are involved in spontaneous closure after partial embolization³⁾:

1. Small fistula size
2. Hypotension
3. Venous stasis due to decreased arteriovenous pressure gradient
4. ICA spasm or dissection during DSA or treatment
5. Increased ICP due to ICH
6. Thrombogenic effect of contrast media (endothelial damage, promotion of leukocyte adhesion, promotion of erythrocyte aggregation)
7. Lack of posterior drainage

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7. Latest Research and Future Perspectives (Research Stage Reports)

For Patients: Please Read Carefully

The following content is currently in the research stage or under clinical trials and is not standard treatment available at general hospitals. It is reference information for professionals regarding future medical developments.

Treatment with Flow Diverter Devices (FDD)

Flow diverter devices (FDD) are an approach that redirects blood flow from the ICA lumen to gradually reduce blood flow to the fistula.

A systematic review by Stamatopoulos et al. (2022) included 16 studies with 38 patients, of which 94.7% had Barrow type A direct carotid-cavernous fistulas ⁵⁾. Clinical improvement was achieved in 92.1% (35/38), with an immediate complete occlusion rate of 44.7% and a long-term occlusion rate reaching 100%. The FDD-related neurological complication rate was 2.6% (1/38).

Main usage forms and outcomes:

Usage Form	Number of Cases	Remarks
FDD alone	4 cases	Immediate complete occlusion rate 100%
FDD + embolic material	11 cases	Immediate complete occlusion rate 45.4%
Multiple FDDs	6 cases	—
Multiple FDDs + embolic material	17 cases	—

Postoperative antiplatelet therapy (DAT: aspirin 100 mg + clopidogrel 75 mg) was administered in 84.2% of cases ⁵⁾. Further evidence building through multicenter prospective studies remains a challenge.

Endoscopic transorbital approach (ETOA)

For indirect carotid-cavernous fistulas where conventional transvenous routes are unusable due to thrombosis, the world’s first treatment using an endoscopic transorbital approach (ETOA) was reported in 2025.

Wong et al. (2025) successfully treated a 65-year-old man with a Barrow type D indirect carotid-cavernous fistula by accessing the cavernous sinus directly from the orbit via ETOA and occluding it with Floseal injection ⁴⁾. Complete occlusion was confirmed on DSA at 1 month.

Advantages of ETOA: small incision, minimally invasive, short hospital stay, direct access to the cavernous sinus. The reported success rate of transorbital approaches (including direct SOV puncture) is 89.9% (30 studies, 140 patients) ⁴⁾.

Spontaneous closure strategy after partial treatment

Cases have been reported where residual shunts closed spontaneously after partial endovascular treatment (blocking only forward drainage), attracting attention as a minimally invasive approach for high-risk cases ³⁾. The management principle is short-interval clinical and imaging monitoring, with prompt additional treatment if symptoms worsen.

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8. References

1. Mahmoodkhani M, Askariardehjani N. Post-traumatic carotid-cavernous fistula. Heliyon. 2023;9:e14778.
2. Rotim A, Kalousek V, Raguz M, et al. Transvenous approach for indirect carotid-cavernous fistula using detachable coils: a case report and review of treatment options. Acta Clin Croat. 2022;61:555-559.
3. Liao WJ, Hsiao CY, Chen CH, Tseng YY, Yang TC. Spontaneous resolution of an aggressive direct carotid cavernous fistula following partial transvenous embolization treatment: a case report and review of literatures. Medicina. 2024;60:2011.
4. Wong DK, Chan NN, Ng BC, Mak CH. Endoscopic transorbital approach to managing indirect carotid cavernous fistula: a novel technique. Surg Neurol Int. 2025;16:532.
5. Stamatopoulos T, Anagnostou E, Plakas S, et al. Treatment of carotid cavernous sinus fistulas with flow diverters: a case report and systematic review. Interv Neuroradiol. 2022;28:70-83.
6. Pellegrini F, Zappacosta A, Cirone D, Ciabattoni C, Lee AG. A case of spontaneous bilateral direct carotid-cavernous fistula. Cureus. 2022;14:e24634.
7. Sharma R, Ponder C, Kamran M, et al. Bilateral carotid-cavernous fistula: a diagnostic and therapeutic challenge. J Investig Med High Impact Case Rep. 2022;10:1-6.
8. Min XF, Yuan G, Si GY, Xu YN. Direct puncture the superior ophthalmic vein guiding by Dyna-CT to obliterating a traumatic carotid-cavernous sinus fistula: a case report and literature review. Medicine. 2022;101:e31560.
9. Sarkis Y, Worden A, Schreiber T, Lapitz A. High index of suspicion: diagnosing a carotid-cavernous fistula. BMJ Case Rep. 2023;16:e253473.