CCF is an abnormal arterio-venous communication between the carotid arteries and cavernous sinus (CS) [1]. It is seen mostly in young males in the third decade of life [2]. CCFs can occur either spontaneously or following trauma. Depending on the flow rate across the fistula, they can be classified as either high or low flow CCF. They can be direct when there is communication between the ICA and CS or indirect when meningeal branches of the carotid arteries communicate with the CS. Barrow’s classification includes four types of fistulas, Type A to D. The fistulas between the intra-cavernous ICA and CS are high flow direct fistulas and are classified as type A. Those fistulas in which there is communication between the meningeal branches of ICA, ECA or both and CS constitute types B, C and D respectively and these are low flow indirect fistulas [3]. Most of these fistulas, about 69-77% occur following trauma. Iatrogenic intervention and collagen vascular disorders are other causes of direct fistulas. [2,3]. Anteriorly draining fistulas present with orbital bruit, proptosis, chemosis, abducens nerve palsy, conjunctival injection, diplopia, pain, red eye, ocular foreign body sensation, blurred vision, and headache. Neurologic symptoms are seen with posteriorly draining fistulas such as confusion, expressive aphasia and diplopia from isolated ocular motor nerve pareses [4,5].
Orbital Doppler Ultrasonography (US), computed tomography (CT), magnetic resonance imaging (MRI) and digital subtraction angiography (DSA) are the imaging modalities used for diagnosis of CCF. Orbital Doppler US shows arterialization with low resistance flow, reversal of flow or thrombosis in the SOV. CT and MRI reveal proptosis, dilated tortuous SOV, enlarged ipsilateral CS with bulging of its lateral wall and extra-ocular muscle thickening. Non-contrast cranial CT scan can detect skull fractures. Other findings like orbital oedema and abnormal flow voids in CS that correspond to shunted blood on spin-echo sequences are better visualized on MRI. 3D TOF MRA detects CCF accurately by depicting flow-related enhancement in the involved CS as well as the arterial feeders in an indirect fistula. DSA is used for diagnostic confirmation, anatomical evaluation and classification of CCF [2,5].
Conservative management is indicated for small asymptomatic low flow stable fistulae. In other cases, an endovascular approach is used to close the fistulous connection. Detachable balloons, platinum coils, liquid embolizing agents (N n-butyl cyanoacrylate, ethylene-vinyl alcohol copolymer), stents or a combination may be used for embolization [4,5].
