Non-aggressive, sinus-type greater sphenoid wing dural arteriovenous fistula with shunt point in the laterocavernous sinus mimicking a cavernous sinus dural arteriovenous fistula converted to aggressive, non-sinus-type

Summary

Sphenoid wing dural arteriovenous fistulae (DAVFs) are rare. Although the imaging findings of greater sphenoid wing DAVFs may resemble those of cavernous sinus DAVFs (CSDAVFs), their respective presentations differ. Benign CSDAVFs rarely convert to the aggressive type. Conversely, as greater sphenoid wing DAVFs are often of the aggressive type, with intracranial cortical venous reflux and varices, treatment is recommended. Sphenoid wing DAVFs tend to be of the non-sinus type, and transarterial embolisation is often an effective endovascular treatment. We present a case of an asymptomatic greater sphenoid wing DAVF mimicking a CSDAVF that converted from a non-aggressive sinus-type to an aggressive non-sinus-type due to compartmentalisation and thrombotic occlusion. Transarterial embolisation with Onyx and a transarterial venous coil resulted in complete disappearance of the DAVF. Greater sphenoid wing DAVFs can be misdiagnosed as CSDAVFs and require accurate imaging evaluation and careful follow-up, even in asymptomatic or non-aggressive cases.

Background

The incidence of intracranial dural arteriovenous fistulae (DAVFs) is 0.15–1.044 per 100 000 person-years.^{1 2} Sphenoid wing DAVFs are rare, accounting for 2%–3% of all DAVFs³ and may show imaging findings similar to those of cavernous sinus DAVFs (CSDAVFs).⁴ It is reported that 2% of benign CSDAVFs convert into an aggressive type.⁵ Unlike CSDAVFs, greater sphenoid wing DAVFs tend to be of the aggressive type, with intracranial cortical venous reflux and varices. The aggressive type is reported to constitute 65% of greater sphenoid wing DAVFs, and treatment is often recommended.^{3 6} Transvenous embolisation (TVE), transarterial embolisation (TAE), direct surgery or combined therapy may be selected depending on the location of the shunt point and the access route available. Sphenoid wing DAVFs tend to take the form of non-sinus-type DAVFs³ and are generally difficult to treat with TVE; however, they may be treated with TAE or direct surgery.

Here, we present the case of a woman in her 70s with an asymptomatic greater sphenoid wing DAVF that converted from a non-aggressive, sinus-type to an aggressive, non-sinus-type due to compartmentalisation and thrombotic occlusion. This case was previously misdiagnosed as a benign CSDAVF based on initial magnetic resonance angiography (MRA) findings. As this patient had a single feeder, an accessory meningeal artery (AMA) and a drainage route limited to the intracranial veins from the left uncal vein, we performed a TAE using Onyx (Medtronic, Irvine, California, USA). This, in combination with a transarterial venous coil, resulted in the complete disappearance of the shunt.

Case presentation

A woman in her 70s underwent trans-sphenoidal surgery for a pituitary adenoma 20 years prior, and magnetic resonance imaging was performed irregularly several times thereafter. A DAVF was not detected on MRA 6 years ago. However, an MRA performed 5 years prior showed a high-signal area around the left internal carotid artery (ICA), suggesting the presence of a DAVF (figure 1A and B). This MRA finding was identified as a CSDAVF without an intracranial cortical venous reflux (figure 1A–D), and the patient was followed up assuming the presence of an asymptomatic benign CSDAVF. T2-weighted imaging and MRA performed just before treatment showed a DAVF adjacent to the left ICA, intracranial venous reflux with varices and one drainage route from the shunted pouch to the intracranial space (figure 1E–H). The left CS could not be visualised using MRA (figure 1F). The patient appeared to be consistently free of any cerebral haemorrhage or venous infarction, and no symptoms due to the DAVF were noted.

Figure 1. Magnetic resonance angiography (MRA) 5 years before transarterial embolisation (TAE) (A–D) and just before TAE (E–H). The shunt points, as detected on MRA, are at the same location at both time points (white arrows) (A, E). High signal areas are seen around the left internal carotid artery (black asterisks), which suggests shunt flow draining to the left cavernous sinus (CS) (white arrowheads) (B). An MRA 5 years before the TAE shows no left uncal vein or intracranial veins (C, D). In the MRA just before the TAE, there is no outflow of the shunt in the left CS (F). The MRA just before the TAE shows the left uncal vein (red arrowhead) (G) and intracranial veins (white dashed circle) (H).

Investigations

Digital subtraction angiography showed that the shunt point was located anterior to the left laterocavernous sinus (LCS), with a single left AMA feeder, reflux into the intracranial Trolard venous ring from the left uncal vein (figures2 3) and no reflux to the ipsilateral superficial middle cerebral vein (SMCV) flowing out into the sphenobasal vein. There was no connection between the left CS and LCS (figures2 3), and a transvenous approach to the left LCS appeared to be difficult. The patient was diagnosed with an aggressive non-sinus-type greater sphenoid wing DAVF.

Figure 2. Preoperative digital subtraction angiography of the left external carotid artery. The anteroposterior (A) and lateral views (B) demonstrate a dural arteriovenous fistula with feeders from the left accessory meningeal artery (white arrowheads). The fistula drains into the left uncal vein (black arrowheads) and intracranial veins (black arrow: laterocavernous sinus). Backflowing intracranial veins are accompanied by varices (white asterisks). The left laterocavernous sinus does not communicate with the left cavernous sinus. Schematic illustration of the present case (C). ACV, anterior communicating vein; AMA, accessory meningeal artery; BrV, bridging vein; BVR, basal vein of Rosenthal; CS, cavernous sinus; IPS, inferior petrosal sinus; LCS, laterocavernous sinus; lt, left; rt, right; SMCV, superficial middle cerebral vein; SpbV, sphenobasal vein; SS, straight sinus; SSS, superior sagittal sinus; UV, uncal vein.

Figure 3. Right lateral view of the preoperative three-dimensional rotational angiogram of the left accessory meningeal artery (white arrowheads) confirms that the shunt point (black dashed circle) is located at the anterior left laterocavernous sinus.

Treatment

A TAE was performed via the left AMA, which was the only feeding artery. Under general anaesthesia, an 8-Fr EMBOGUARD, 95-cm (Cerenovus, Miami, Florida, USA), was guided to the left external carotid artery (ECA) from the right femoral artery. Using a 3.2-Fr TACTICS PLUS 120-cm (Technocrat, Aichi, Japan) as an intermediate catheter, a 0.012-inch Marathon 165-cm microcatheter (Medtronic, Irvine, California, USA) was guided to the left AMA using a 0.010-inch TENROU 200-cm microguidewire (KANEKA MEDIX, Osaka, Japan), and a Marathon microcatheter was placed at the shunted pouch beyond the shunt point. One coil (i-ED coil 3–5 mm×15 cm; KANEKA MEDIX, Osaka, Japan) was placed in the left LCS (figure 4A and B), and the Marathon microcatheter was returned to the distal left AMA just before the shunt point. The left uncal vein, LCS and AMA were embolised with 0.3 cc of Onyx 18 (Medtronic) by inflating the EMBOGUARD balloon to block the blood flow to the left ECA (figure 4A and B).

Figure 4. Postoperative skull roentgenogram images (A, B) and digital subtraction angiography of the left external carotid artery (C, D). One coil is loosely placed inside the left laterocavernous sinus ((A) anteroposterior view, (B) lateral view). The Onyx cast has low visibility probably due to the small amount used (A, B). The anteroposterior (C) and lateral views (D) show complete disappearance of the dural arteriovenous fistula.

Outcome and follow-up

The TAE resulted in complete disappearance of the intracranial venous reflux and shunt (figure 4C and D). No treatment-related adverse events were observed, and no recurrence was noted on MRA at 3 months after treatment.

Discussion

We present the case of a greater sphenoid wing DAVF that initially mimicked a CSDAVF. It converted from a non-aggressive, sinus-type to an aggressive, non-sinus-type DAVF. We treated it with TAE using Onyx in combination with a transarterial venous coil, resulting in complete disappearance of the shunt.

Geibprasert et al classified sphenoid wing DAVFs into ventral epidural or osteo (cartilaginous) epidural groups.⁷ They stated that this group developed a cortical venous reflux when the epidural space was thrombosed. It is speculated that greater sphenoid wing DAVFs have tenuous connections to their epidural space (such as the CS) and close connections with spaces that communicate directly with the SMCV, resulting in an earlier cortical venous reflux.⁸ In the present case, the left CS was considered an outflow channel (figure 1A and B), and no intracranial venous reflux was observed (figure 1C and D). It is suggested that at the time of the DAVF onset, there was a connection between the left LCS and CS, and most of the shunt flow may have exited via the left CS. It is possible that the high venous pressure caused compartmentalisation and thrombotic occlusion of a part of the left CS (figure 1E–H). Apparently, the shunt from the left CS did not flow out, causing an intracranial venous reflux (figure 1F–H). This suggests that greater sphenoid wing DAVFs with shunt points at the LCS that once had a connection between the LCS and CS may initially be of the non-aggressive type and may convert to the aggressive type over time. This may coincide with a change from a sinus-type to a non-sinus-type DAVF. In contrast, greater sphenoid wing DAVFs that originally have no connection between the LCS and CS may be an aggressive type from onset. Gailloud et al reported that 63.5% of cases had no connection between the CS and LCS.⁹ In addition, imaging findings of greater sphenoid wing DAVFs with shunt points at the LCS during the connection between the LCS and CS may be very similar to those of CSDAVFs, and it is plausible that there are greater sphenoid wing DAVFs that have been misdiagnosed and treated as CSDAVFs. As the vein of the foramen ovale is an emissary vein from the CS to the pterygoid venous plexus, DAVFs around the foramen ovale, in addition to those at the LCS, may mimic CSDAVFs.⁴ Kiyosue et al reported the location of shunted pouches in CSDAVFs.¹⁰ Their results demonstrate that all patients had shunted pouches either posterior to the CS alone or posterior to the CS and at other sites, and no patients exhibited shunted pouches exclusively laterally or medially to the CS. The possibility of greater sphenoid wing DAVFs should be considered in cases where the shunted pouches are not located posterior to the CS, as in the present case.

Several reports of endovascular treatment of greater sphenoid wing DAVFs reveal a strategy similar to that used for other DAVFs. If an approach from the veins to the shunt point is possible, TVE is considered. In cases of drainage into the superior ophthalmic vein (SOV), reaching the shunt point near the SOV by directly puncturing the SOV,¹¹ via the CS¹² and via the facial vein¹³ has been reported. As it is difficult to perform TVE for non-sinus-type greater sphenoid wing DAVFs, several TAE methods have been reported. Sahu et al described a TAE using the pressure cooker technique with Onyx.¹⁴ In addition to TAE with liquid embolic agents, Shi et al reported TAE with Onyx combined with transarterial coil placement in a shunted pouch to reduce the high-flow arterial input.⁸ Fukuda et al reported on the use of TAE from the optimal artery using n-butyl cyanoacrylate after the embolisation of non-optimal feeders with coils,¹⁵ while Inoue et al used transarterial venous coil embolisation.¹⁶ If the shunt remains after TAE, an additional TVE is considered, if possible.¹⁵ If complete disappearance of the shunt cannot be achieved by TAE and TVE, direct surgery is considered.⁶

In the present case, although we first considered TVE, there was no connection between the left CS and LCS, and no other venous approach route was used for TVE. Therefore, we performed a transarterial approach using the left AMA, which was the only feeding artery. If the microcatheter had not been guided to the venous side beyond the shunt point, we would have embolised from the distal AMA to the draining vein with Onyx. However, as the microcatheter was guided to the venous side beyond the shunt point during TAE, we were concerned about incomplete obliteration after transarterial coil embolisation alone and about the onset of adverse events due to tight coil packing. Therefore, before performing Onyx embolisation, we placed one coil in the left LCS to promote thrombosis, prevent Onyx backflow into the intracranial veins and reduce the amount of Onyx used. Owing to the presence of only one coil, we embolised the shunt using a small amount of Onyx. This treatment strategy is similar to that reported by Shi et al.⁸ There have been reports of temporary facial nerve paralysis caused by Onyx migration into the petrous branch of the middle meningeal artery.¹⁴ We speculate that reducing the amount of Onyx used can minimise the risk of Onyx migration to potentially dangerous anastomoses and other related complications.

In conclusion, greater sphenoid wing DAVF is a rare neurovascular disease and can mimic CSDAVFs. A non-aggressive type greater sphenoid wing DAVF can convert to an aggressive type. It can be misdiagnosed as CSDAVFs and require accurate imaging evaluations or careful follow-up, even in asymptomatic or non-aggressive types.

Patient’s perspective.

I didn't have any symptoms and didn't really understand my disease, but I'm glad that it healed without any problems.

Learning points.

• Greater sphenoid wing dural arteriovenous fistula (DAVF) is a rare neurovascular disease that tends to be of a non-sinus and aggressive type with an intracranial cortical venous reflux and varices.

• Some greater sphenoid wing DAVFs convert from being non-aggressive to aggressive owing to compartmentalisation and thrombotic occlusion.

• Image findings of greater sphenoid wing DAVFs with shunt points at the laterocavernous sinus may resemble those of cavernous sinus (CS) DAVFs if there is a connection between the laterocavernous sinus and CS.

• Greater sphenoid wing DAVFs can be misdiagnosed as a CSDAVF and require careful follow-up and accurate imaging diagnosis, even in asymptomatic or non-aggressive types.