Abnormal communication between the cavernous sinus and the carotid arterial system.
Aetiology
Direct CCFs (Barrow type A):
High-flow fistulas characterized by a direct connection between the internal carotid artery (ICA) and the cavernous sinus
- Traumatic in origin (M/C)
- Rupture of ICA aneurysm within cavernous sinus
- Ehlers–Danlos syndrome type IV
- Iatrogenic intervention: transarterial endovascular intervention, internal carotid endarterectomy, percutaneous treatment of trigeminal neuralgia, trans-sphenoidal resection of a pituitary tumour, and maxillofacial surgery
Dural CCFs (Barrow types B, C, and D):
Low-flow fistulas that consist of communications between the cavernous sinus and cavernous arterial branches
- Hypertension
- Fibromuscular dysplasia
- Ehlers–Danlos type IV
- Dissection of the ICA
Classification
Barrow classification:
Anatomical classification
- 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
Clinical features
Classical triad:
- Pulsatile proptosis
- Chemosis
- Bruit

Anteriorly draining fistulas:
More likely to cause ocular symptoms
- Subjective bruit
- Diplopia
- Tearing
- Red eye
- Ocular foreign body sensation
- Blurred vision
- Headache
Posteriorly draining fistulas:
May develop neurologic symptoms
- Confusion
- Expressive aphasia
- Diplopia (from isolated ocular motor nerve pareses)
Diagnosis
Pneumotonometry:
Valuable diagnostic tool
- Difference in ocular pulse amplitudes (difference between systolic and diastolic IOP) of 1.6 mm Hg between the two eyes (100% sensitive & 93% specific for a CCF)

Orbital ultrasound:
Can be used to exclude mimickers of CCF, including orbital tumours, dysthyroid orbitopathy, orbital inflammation, and scleritis.
- Dilated superior ophthalmic vein (SOV)
- Evidence of orbital congestion with enlarged extraocular muscles
Colour Doppler:
Evaluates flow velocity and direction, thus indicating arterial flow in the orbital veins in cases of CCF
- Flow reversal in the SOV: Suggestive of a CCF
Computed tomographic angiography (CTA) or magnetic resonance angiography (MRA):
- Unilateral/bilateral enlargement of the SOV (suggestive of CCF)
- Orbital congestion
- Enlargement of the extraocular muscles and periorbital fat
- Convexity of the lateral wall of the cavernous sinus

Digital subtraction angiography (DSA):
Gold standard for classification and diagnosis of CCF and can be both diagnostic and therapeutic

Differential diagnosis:
- Non-specific orbital inflammation
- Orbital hemorrhage
- Orbital infection
- Orbital tumor
- Orbital vasculitis
- Thyroid disease
- Tumor with cavernous sinus involvement
Management
Direct CCF:
- Endovascular intervention (first-line treatment):
- Detachable balloons, coils, liquid embolic agents, or a combination of these tools.
Dural CCFs:
Often resolve spontaneously, low-risk cases may be managed conservatively.
- Endovascular intervention or stereotactic radiosurgery (when invasive treatment is warranted)
