Cases of patients with DAVF and sinus stenosis have been literately reported before[1, 3, 6, 8]. Multiple factors are believed involving the development of DAVF, but their true etiology is still unidentified Sinus thrombosis is deemed to be the most common reason for venous hypertension and ultimately dAVF formation, but the cause–effect relationship is still under investigation[9, 10]. We believed that the DAVF with bilateral sigmoid sinus stenosis in this patient would be caused by idiopathic intracranial hypertension. Bateman et al. first proposed that a disordered positive biofeedback mechanism may be present in idiopathic intracranial hypertension where elevated CSF pressure compresses the venous sinuses, leading to further venous hypertension and further elevation of CSF pressure. Abnormal high venous pressure against vessel walls established pathological connection between dural arteries and cerebral veins, resulting in DAVF appearance. Meanwhile, venous hypertension could cause venous blood congestion resulting in local tissue hypoxia, which promotes angiogenesis by releasing angiogenic factors[1, 12] .
Almost 66% of type IIa + b DAVF could cause intracranial hypertension, but bilateral venous congestion caused by transverse sinus stenosis leads to further venous hypertension and further elevation of intracranial hypertension. As a result, the management of sinus stenosis and DAVF were of equal prominence in this case. A series of cases about DAVF with ispilateral sinus stenosis cured by stenting were reported. Renieri et al. demonstrated two patients with Cognard classification type II DAVF and ispilateral transverse sinus stenosis had improvement after deploying a stent across the stenosis to compress both the stenosis and fistula. In these cases, the location of sinus stenosis were close to the opening of fistula so that deploying a stent could both recanalization of sinus and closure of the fistula opening. In our patient, however, compression and alleviation of the fistula was not achieved because the stent failed to cover the opening of DAVF. Further embolization was needed for DAVF.
Different treatment options have been proposed to address DAVF, including endovascular embolization, surgery and radiosurgery[7, 12, 14]. Directly removing the fistula, which has a high obliteration rate, is reputed to be unsafe due to the risks associated with open surgery. Although the affected left sigmoid sinus was obliterated, incidental surgical damage of transverse sinus would cause irreversible impairment. Transvenous embolization of DAVF have been reported to be successful in the region of cavernous sinus or transverse sinus[12, 14]. However, this approach was not feasible in this case considering it was difficult for a microcatheter to pass through the stent and it was possible that Onyx reflux could cause occlude the sinus. Optimal arterial routines, right middle meningeal artery, have been occluded in previous transarterial embolization. Therefore, we decided to embolize the fistula through contralateral middle meningeal artery. The rate of success is far lower after previously failed embolization due to occlusion of main feeder. However, fistula could still be embolized in a sole approach considering the primary benefit of Onyx is the ability to perform a slow, large-volume, controlled injection[15, 16]. Large amount of Onyx can result in filling of the fistulous network and allow for reflux into either intracranial or extracranial feeding arteries in a single catheterizations and embolization. Cognard et al. reported 18 cases of DAVF were completely obliterated after embolization of only one feeder in only one-time administration. Although contralateral middle meningeal artery was distal to the lesion and its diameter is smaller compared with left middle meningeal artery and right occipital artery, cured fistula was almost achieved via this routine.
We also found the evaluation results of sigmoid sinus stenosis between cerebral angiography and magnetic resonance venography (MRV) were inconsistence. In venous stage, cerebral digital subtraction angiography (DSA) demonstrated engorgement of cortical veins with filling defects in bilateral sigmoid sinus. In magnetic resonance venography (MRV), however, images showed poor signal intensity in right transverse-sigmoid sinus, but segmented filling defect in left transverse sinus. The differences between DSA and MRV could be caused by relevant insufficient injection volume of contrast in DSA because of overflow of cortical veins and relevant inadequate filling of transverse-sigmoid sinus. It is a technical dilemma of whether nor not increasing injection volume of contrast in patients with both DAVF and sinus stenosis considering the potential risk of hemorrhage when overload injection[11, 18]. This is no trials concerning the optimal parameters of contrast media injector when performed in patients with DAVF and sinus stenosis, so further studies are needed. In addition, the disagreements about the stenosis also were problematic when we were choosing stenting in left or right side sinus. Based on the result of MRV, the segmented stenosis in left transverse sigmoid seemed to be easier for recanalization, but previous two efforts proved that the sinus of left side was not accessible in this patient. Considering prior performances, surprising success of opening right side remind us it is worth the effort to try on other side if opening one side was difficult.