widely in neurosurgery and probably have a place in the management of a small proportion of lesions affecting the orbit. Specifically, the following disorders will be discussed: carotid-cavernous sinus fistulas, arteriovenous malformations, distensible venous anomalies, preoperative embolization of tumors, and aneurysms.

CAROTID-CAVERNOUS SINUS FISTULAS

Carotid-cavernous fistulas (CCF) are the commonest lesions encountered by the orbital specialist that lend themselves to interventional radiological techniques. These fistulas (CCF) have been classified in several ways, and this classification has some bearing on the therapeutic approach employed (if treatment is required). The most useful classification in terms of interventional radiological techniques employed is that of Barrow et al. (1), who organizes CCFs into four types.

Type A: direct shunts between the internal carotid artery (ICA) and the cavernous sinus (often traumatic in origin, sometimes the result of rupture of an ICA, and of high flow).

Type B: a shunt between meningeal branches of the ICA and the cavernous sinus.

Type C: a shunt between the meningeal branches of the external carotid artery (ECA) and the cavernous sinus.

Type D: a shunt between meningeal branches of both the ICA and ECA.

Type B, C, and D fistulas (often called dural fistulas) are often ‘‘spontaneous’’ and more often low flow. Type D tends to be more frequent than the purer forms of B and C. Additionally, a fistula may be supplied by meningeal branches of the ICA and ECA from one or both sides. The clinical signs may be (a) ipsilateral to the meningeal branches that supply the fistula; (b) contralateral, usually when the superior ophthalmic vein on the side of the fistula has thrombosed and the fistula drains to the opposite side of the cavernous sinus via intercavernous connections,

or (c) bilateral, depending on the anatomy of the intercavernous sinus and the meningeal branches of supply.

The anatomy of the fistula is important in planning the therapeutic approach to each patient, and the only way to get an accurate assessment of the anatomy is with selective bilateral internal and external carotid angiography. The patient may be treated during the same angiography session provided the anatomy allows for occlusion of the fistula by endovascular techniques.

The majority of Type A fistulas occur in the setting of trauma. Interventional radiological techniques have been successful in the majority of these cases, without the need for neurosurgical or orbital surgical approaches. The aim is to close the fistulous connection whilst maintaining the patency of the ICA. This is usually achieved with detachable balloons, which are floated into the fistula via a catheter in the ICA, filled to occlude the fistula, and then detached from the catheter (Fig. 1). If an arterial approach is not possible, a transvenous approach is an alternative, usually via the inferior petrosal sinus reached via the internal jugular vein. For transvenous approaches, thrombogenic coils (Fig. 2) are most commonly employed to fill and thrombose the cavernous sinus and thereby obliterate the fistula.

Type C and D fistulas may be treated by trans arterial embolization of the external carotid artery branches of supply. Liquid or particulate matter may be used. In Type D fistulas, this may be enough to reduce the flow in the fistula and thrombose it without direct closure of the ICA branches, although often the fistula will persist. Selective embolization of meningeal branches of the ICA is usually not possible.

The transvenous approach to CCFs via the superior ophthalmic vein (SOV) is now well established and involves the orbital surgeon directly in the management of these patients. Patients benefiting from this approach are those where other trans arterial and transvenous approaches have failed. Some have suggested the technique be employed primarily, but where a fistula can be successfully treated by the radiologist alone, without the need for a surgical procedure, it would seem sensible to use that approach first.

Figure 2 A thrombogenic coil being released from the end of a catheter.

The SOV approach was first described in the literature by our institution, the Royal Melbourne Hospital, in 1983

(2). A patient with a longstanding high flow Type D carotidcavernous fistula had a direct approach made to it via exposure of an enlarged SOV in the anterior-superior orbit, using stainless steel coils to thrombose the fistula. Since that time, we and others have used the technique and published a series of patients successfully treated this way (3–7).

Exposure of the SOV is usually readily accomplished via an upper eyelid crease or sub-brow incision (Fig. 3a). The SOV

Figure 1 (Facing page) A left lateral internal carotid angiogram demonstrates rapid filling of a carotid cavernous fistula. (b) After placement of a detachable balloon (partially obscuring the ICA), the fistula no longer fills the cavernous sinus with dye. (c) Left lateral plain skull x-ray shows the balloon in the cavernous sinus filled with contrast medium.

anastomoses usually with the angular and supraorbital veins in the superomedial lid and anterior orbit, and the best place to find the SOV is just below the trochlea of the superior oblique. In longstanding and high flow fistulas, there may be very large veins in the eyelid itself and these may be very tortuous. It may be difficult to tell which direction is towards the cavernous sinus in these cases. Once the vein is isolated, vascular tape or loops are passed beneath it to help control the blood flow while a venotomy is made and a catheter fed into the vein (Fig. 3b). A guide wire is then passed along the SOV to the cavernous sinus, a catheter passed over it, and an injection of dye made to ascertain the exact position of the catheter. Thrombogenic coils are then deposited in the cavernous sinus, starting posteriorly and moving anteriorly. A check carotid angiogram is made to determine if there is still any flow in the fistula. The catheter is removed and the SOV may be ligated.

For fistulas with bilateral drainage (through both SOVs), one SOV may be used to access both sides of the cavernous sinus, provided that the intercavernous sinus(es) is large enough to negotiate from one to the other side. Both sides may then be embolized (Fig. 4).

This technique may be limited by aberrant anatomy of the SOV. In some cases, the SOV may not extend to the anterior orbit, presumably because of prior partial thrombosis, or variant anatomy (Fig. 5). The entire SOV may thrombose prior to the technique being employed. We have managed a patient whose predominant drainage of the fistula via cerebral veins was thought to be a risk; however, prior to the patient reaching the procedure room, the SOV had thrombosed, thus protecting the eye but making access via the SOV impossible.

Some authors have preferred to perform this technique in the operating room rather than the angiography suite, arguing the need for all the equipment available in the operating room. We have found it quite feasible to have all the necessary equipment moved to the angiography suite, which has the advantage of having available, all the sophisticated angiography equipment and avoids dependence on less

sophisticated portable angiographic equipment. One exceptional case of ours had to be treated in the operating room because of extreme obesity. The patient’s weight exceeded that allowable on the angiography table and direct puncture of the femoral vessels could not be achieved, so that the carotid and jugular vessels had to be exposed in the neck, as well as exposing the SOV in the anterior orbit. His fistula was successfully treated.

Many patients will temporarily worsen after embolization of their CCF. This same worsening is seen in spontaneous thrombosis of the SOV in some cases of CCF (8). In the majority of these treated and spontaneously resolving cases, the signs resolve over days to weeks.

In patients who cannot be adequately treated in these ways, neurosurgical approaches remain an option. Direct puncture of the cavernous sinus at craniotomy may be used to gain access for embolization, and techniques to reach the cavernous sinus using cerebral veins have also been described. Closure of the ICA above and below the feeding vessels may be a last resort, and interventional radiological techniques may be used for this, using trial occlusions to assess the adequacy of the circle of Willis before permanently occluding the ICA.

There have also been reports of transcutaneous puncture of the deep SOV (9) or even cavernous sinus via the orbit where other techniques have failed. Clearly, there is a significant risk of hemorrhage within the orbit or cranial cavity.

Figure 4 (Facing page) (a) An anterior venous phase carotid angiogram of a patient with a bilateral Type D carotid-cavernous sinus fistula. There is filling of both superior ophthalmic veins via the cavernous sinuses, connected by a prominent intercavernous sinus. (b) A guide wire has been placed via the left superior ophthalmic vein into the left cavernous sinus and then across into the right cavernous sinus via an intercavernous sinus. (c) Lateral view of the guide wire seen in (b). (d) An antero-posterior view after placement of thrombogenic coils in the right and left cavernous sinuses. (e) Right lateral internal carotid angiogram shows no filling of either superior ophthalmic vein after successful embolization.