Carotid-cavernous fistulas (CCF) are an abnormal communication between the carotid circulation and the cavernous sinus that alters the usual drainage flow.
According to flow parameters, they can be classified into direct high-flow CC fistulas, consisting of a defect in the wall of the internal carotid artery (ICA), causing a shunt between the ICA and the cavernous sinus (normally by a traumatic or spontaneous event for the ruptured cavernous segment aneurysm) and the indirect ones, low-flow CCF, which are equivalent to dural arteriovenous fistulas (dAVFs) of the cavernous sinus; they comprise about 35% of all dAVFs.
Barrow and his colleagues established the following classification scheme:
- Type A: direct communication between the cavernous segment of the ICA and the cavernous sinus.
- Type B: meningeal branches of the ICA to the cavernous sinus.
- Type C: meningeal branches of the external carotid artery (ECA) to the cavernous sinus.
- Type D: meningeal branches of both, the ICA and the ECA with the cavernous sinus.
Direct CCF correspond to Barrow’s type A, they are more likely to have significant symptoms and present acutely, and indirect CCF include types B, C and D; they are more common in postmenopausal women, often have a more insidious onset of symptoms and sometimes resolve spontaneously without treatment.
It is important to know the anatomy of the cavernous sinus complex:
- Pattern of venous drainage, according to their dominance, the CCF condition some symptoms:
- Anterior drainage: via the superior ophthalmic vein (SOV) and inferior ophthalmic vein results in chemosis, proptosis, conjunctival injection, eye pain and even loss of visual acuity ("Red-eyed shunt syndrome").
- Posterior drainage: via the superior petrosal sinus (SPS), inferior petrosal sinus (SPI) and basilar plexus results in a painful paralysis of the ocular motor nerve develops without congestive orbital characteristics (“white eye”), pulsatile tinnitus and bruit.
- Cortical drainage: via the sphenoparietal sinus or superficial cerebral vein, causing bleeding or ischemia due to rupture of the dilated cortical veins.
- Deep drainage to the internal cerebral vein can cause bleeding.
The two latter symptoms are dangerous drainage patterns that may have neurological symptoms.
- Regarding the ICA, the segment involved is the cavernous one, its main branches are the meningohypophyseal trunk, the inferolateral trunk and the McConell capsular artery.
The ACE branches most frequently involved in CCF are the middle meningeal artery, accessory meningeal, ascending pharyngeal.
- It contains the cranial nerves: III, IV, V1, V2, VI and it can cause them paralysis due to mass effect inside the cavernous sinus. The most frequently affected nerve is the abducens nerve since it is the closest to the ICA.