Introduction 

   Dural arteriovenous fistulas (dAVFs) may be found in any dural structure, but they are most commonly found in the region of the transverse, sigmoid, and cavernous sinuses. DAVFs at the superior sagittal sinus (SSS) account for 8%~11% of intracranial dAVFs.¹⁰⁾ Because of the midline location of the SSS, eloquent venous drainage, and multiple bilateral arterial feeders, endovascular treatment alone often fails to eliminate the fistula.⁶⁾ Surgical extirpation of the dAVF should not be recommended for all cases because of the considerable risks involved. In a subgroup of patients who had a dAVF with patent sinus drainage and retrograde leptomeningeal venous drainage (Borden Type II, Corgnard Type IIb and IIa+b),¹²⁾ simple disconnection of the cortical venous reflux resulted in a similar outcome to the method of completely obliterating the fistula.⁴⁾¹¹⁾ The authors report on a case of dAVF at the SSS with retrograde leptomeningeal venous drainage, which were selectively disconnected using an aneurysmal clip under intraoperative Doppler monitoring. 

Case Report 

   A 74-year-old man with a history of hypertension presented with suddenly developed left-side visual field defect (Fig. 1) and mild left-side weakness. There was no history of trauma. Computed tomography showed subtle low density in the right occipital area with prominent enhanced vascular structure. Magnetic resonance imaging (MRI) also showed infarction in the right parietooccipital lobe and multiple tortuous vascular structures in the same area with gyral enhancement (Fig. 2). Digital subtraction angiography (DSA) revealed a dAVF of SSS and a scalp arteriovenous malformation (AVM) at the right parietooccipital region. The dAVF was fed by multiple branches of the middle meningeal artery (MMA), and the scalp AVM was fed by both the superficial temporal artery (STA) and the occipital artery. Drainage took place through a cortical vein; otherwise, the SSS drainage pattern was normal (Fig. 3 and 4). 
   The patient elected to undergo surgical treatment for the dAVF. The prominent branches of the STA were cauterized, and bleeding from the edge of the craniotomy was controlled promptly using bone wax. Several feeding vessels arising from the MMA were assertively cauterized. After medial reflection of the dura, reddish edematous brain and arterialized tortuous cortical veins were found. A major retrograde cortical vein adjacent to the SSS was verified using intraoperative Doppler (Fig. 5). The major cortical draining vein was occluded as closely as possible to the SSS using an aneurysmal clip (Fig. 6). After occlusion with the clip, retrograde venous drainage flow stopped. Postoperatively, the visual field defect vanished, and the left hemiparesis was fully ameliorated (Fig. 7). Postoperative DSA and MRI showed no abnormal venous drainage (Fig. 8). 

Discussion 

   Intracranial dAVFs are very rare and account for 10~15% of all intracranial arteriovenous malformations.⁴⁾¹²⁾ Lawton et al. reported a hypothesis regarding its pathogenesis, which was that venous hypertension eventually led to formation of dAVMs (Fig. 9).⁹⁾ DAVFs at the SSS account for only 8~11% of intracranial dAVFs.¹⁰⁾ In contrast to dAVFs in other sites with a female predominance, dAVFs of the SSS have a slight male predominance.²⁾³⁾ Because of their midline location, eloquent venous drainage, and multiple bilateral arterial feeders, dAVFs at the SSS are difficult to alleviate completely compared with dAVFs at the other sites. A complete radioanatomically certified cure by transvenous endovascular embolization alone was achieved in only about 50% or less of dAVFs at the SSS.⁵⁾ Resection of sinus wall and adjacent dura mater at the entrance of the fistula-draining vein present a serious risk for later thrombosis, thus dramatically increasing the risk of further harm due to complications from the surgical treatment.²⁾ 
   The clinical behavior of dAVFs is highly correlated with their venous drainage pattern. Corgnard et al. introduced a reviewed classification for dAVFs based on the fistulous venous drainage.¹²⁾ According to their classification, a type IIb presents with reflux into cortical veins, and a type IIa+b presents with reflux into the sinus and cortical veins. Selective disconnection of the cortical venous reflux can eliminate most of the clinical symptoms of dAVFs. Van Dijk et al. reported that selective disconnection of the cortical venous reflux in cranial dural AVFs was simpler, safer and had less risk of complication from significant blood loss.¹¹⁾ 
   Intraoperative Doppler for spinal dAVFs has been used and described in some reports.⁸⁾ Because venous hypertension can lead to venous congestion, clinical symptoms, such as myelopathy and weakness, develop with spinal dAVFs. A goal in treating a spinal dAVF is the elimination of the venous congestion of the spinal cord.⁷⁾ Surgical ligation of the intrathecal arterialized draining vein using intraoperative Doppler can repair these dAVFs with minimal risk of complications.¹⁾ 
   The authors used aneurysmal clip for surgical ligation. Intraoperative Doppler is used to confirm preclipping retrograde venous flow in cranial dAVFs and to verify postclipping venous flow pattern. For minimal manipulation around the eloquent brain cortex, the authors used aneurysmal clip rather than vessel coagulation and disconnection method. Vessel coagulation and disconnection requires additional surgical manipulation that can lead to cortical injury. Using aneurysmal clip is safer and time saving but the clip can induce paramagnetic artifacts when MRI is taken. 
   Treatment with this relatively safe and simple method should be recommended for patients with high intraoperative risk and old age. 

Conclusion 

   We report a case of dAVFs at the SSS with patent sinus drainage and retrograde leptomeningeal venous drainage, which were selectively disconnected using aneurysmal clips under intraoperative Doppler monitoring. During a two year follow-up neurological symptoms vanished and no further progression of the dAVF has been found. This method of converting an aggressive dAVF to a benign form is relatively safe and simple. Therefore treatment with this relatively safe, simple, and effective method could be recommended for patients with high intraoperative risk and old age. 

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