Cavernous Cartoid Fistulas (CCF)
CCF represent abnormal connections between the internal (ICA) and external carotid arteries (ECA) and the cavernous sinus (CS) or its dura. Barrow has divided CCF into indirect and direct categories. Indirect or type A fistulas involve direct connections between the ICA and CS via a hole in the cavernous ICA. Indirect or dural CCF are subcategorized into types B, C, and D. Type B is supplies by dural branches of the cavernous ICA. Type C is supplied by dural branches of the ECA. Type D has both dural supply from the ICA and ECA. Venous drainage may be anterior via the SOV or posterior via the (IPS) and superior petrosal sinus (SPS). Contralateral venous drainage may also occur via the circular sinus. The latter situation can create contralateral symptoms.
Direct CCF may result from trauma, rupture of a cavernous carotid aneurysms, or from a tear in the wall of a congenitally weak cavernous ICA secondary to collagen vascular disease. Indirect CCF are usually spontaneous and idiopathic.
Clinical signs and symptoms depend upon the venous drainage. Anterior drainage via the SOV can present with exophthalmos, chemosis, proptosis, and decreased visual acuity. Cranial nerve palsies, epitaxis, headache, bruit, and tinnitus may be present with either anterior or posterior drainage. Rare cases with subarachnoid hemorrhage. As stated above, contralateral signs and symptoms may occur if drainage to the opposite cavernous sinus via the circular sinus is excessive.
CT and MRI can demonstrate the dilated SOV and proptotic eye. Angiography reveals the exact arterial and venous anatomy. Fistula flow may be so rapid that the fistula site cannot be identified. In such cases, if arteriography can be done with simultaneous carotid compression. If a posterior communicating artery is present the fistula site may become more recognizable as blood flows from the posterior circulation towards the anterior circulation.
Many CCF will close spontaneously. This is more common for indirect type fistulas. Those lesions that present with worsening proptosis, pial venous drainage, deteriorating vision, epitaxis, increased intracranial pressure, glaucoma, and ophthalmoplegia require urgent or semi-urgent attention. Carotid compression therapy may be tried. It is more effective with indirect CCF. Transarterial embolization using coils or detachable silicon balloons is generally reserved for direct fistulas where the rent in the cavernous ICA can be crossed with a catheter so that these devices can be deposited on the venous side to occlude the hole in the artery. Transvenous approaches such as that described in the above case or by selectively catheterizing the SOV via a surgical cut down or transfemoral/transfacial approach can be used for either direct or indirect CCF. Even in cases where the IPS cannot be identified on the arteriogram it can generally be selectively catheterized and navigated. Transarterial embolization for indirect fistulas is not recommended. Without obliterating the recruit new arterial supply which is often less accessible and more complicated than the initially supplying the CCF.