Carotid-cavernous fistula

A carotid-cavernous fistula is an abnormal communication between a carotid artery and the cavernous sinus. It is most commonly caused by trauma. The fistula leads to a high-pressure inflow of arterial blood into the venous sinuses, resulting in compression and damage to adjacent structures. The main symptom is diplopia, caused by compression injury of the oculomotor nerves. Other common symptoms include pulsatile tinnitus, exophthalmos, and headache. Diagnosis is established based on typical findings on CT/MRI or angiography (e.g., enlarged cavernous sinus). The preferred treatment method is endovascular occlusion of the fistula with balloons or coils.

• Direct (“high-flow”) carotid-cavernous fistula (most common)
  • Abnormal communication between the cavernous sinus and the intracavernous internal carotid artery
  • Typically rapid onset of symptoms
• Indirect (“low-flow” or “dural”) carotid-cavernous fistula
  • Abnormal communication between the cavernous sinus and branches of the internal and/or external carotid artery within the dura mater
  • Typically gradual onset of symptoms

References:^[1][2][3]

• Direct carotid-cavernous fistula
  • Secondary to head trauma
  • Spontaneous
• Indirect carotid-cavernous fistula
  • Secondary to cavernous carotid aneurysm rupture
  • Secondary to cavernous sinus thrombosis
  • Rarely, as a complication of diseases that affect arterial walls
  • Spontaneous

References:^[2][4]

• Arteriovenous fistula formation → high-pressure inflow of arterial blood into venous system → venous congestion
  • → Compression of cavernous sinus structures
    • Cranial nerves III, IV, and VI
    • 1^st and 2^nd branch of the trigeminal nerve (ophthalmic and maxillary nerves)
  • → Impaired venous drainage

Onset of symptoms may be abrupt or gradual, depending on whether the fistula is direct or indirect:

• Headache
• Orbital pain
• Diplopia, blurred vision
• Pulsatile tinnitus (fistula bruit)
• Signs of congestion
  • Unilateral or bilateral, pulsatile exophthalmos
  • Chemosis
  • Massive conjunctival congestion and hemorrhage, with potential bleeding in the retina and vitreous humor
  • Increase in intraocular pressure
  • Optic disc swelling

If not treated swiftly, carotid-cavernous fistulas may result in cerebral hemorrhage/infarction, intracranial hypertension, vision loss, or death!

References:^[1][2][5]

Initial studies help confirm the diagnosis.

• CT/MR (with or without angiography) may show:
  • Proptosis
  • Enlargement of the cavernous sinus
  • Expansion of the superior ophthalmic vein(s)
  • Skull fractures (if fistula is due to trauma)
  • Abnormal cavernous sinus flow
• Ultrasound with transcranial Doppler: shows increased blood flow
• Cerebral angiography
  • Gold standard for diagnosis (and treatment)
  • Visualization of feeding vessels and blood flow

References:^[1][2]

• Embolization using balloons or coils
  • Direct fistulas: transarterial approach
  • Indirect fistulas: transvenous approach
• Neurosurgery
  • Indicated if endovascular interventions fail or are not possible
  • Occlusion of the fistula via suturing or packing

References:^[2]