Microsurgery can cure most intracranial dural arteriovenous fistulae of the sinus and non-sinus type

In non-sinus-type fistule, the institutional strategy was to interrupt the arterialized leptomeningeal vein, shortly after the dural entry/exit point without attacking the meningeal feeding arteries or excising the arterialized dura. Because these draining veins have inverted flow, the occlusion at their dural origin is not followed by further venous congestion [8, 16, 22, 40, 43, 45]. After occlusion, the draining vein thromboses without significant hemodynamical changes due to downstream veins that already have resumed the draining of functional cerebral areas. We achieved an overall occlusion rate of non-sinus-type fistulae in 97.6%. The permanent surgery-associated morbidity rate for the whole series was 7.1%, and for the non-sinus-type fistulae 4.8% (n = 2). The induced neurological deficits could be considered to be minor. Neuronavigation, using CT angiographic data, proved to be helpful for intraoperative identification of the first segment of the leptomeningeal-draining vein [18]. An increasing number of publications support this concept and report comparable occlusion and morbidity rates [8, 16, 18, 22, 40]. Experiences with the endovascular management of non-sinus-type dAVFs likewise have been reported, but in many series the occlusion rate is lower and the complication rate higher [46]. With transarterial embolization, using particles or N-butyl-2-cyanoacrylate occlusion rates between 28% and 33% could be achieved [40, 43]. Better results were obtained by Agid et al., who achieved angiographic cure in 63.6% [1]. First experiences indicate that transarterial embolization with Onyx has the potential to yield higher occlusion rates. Jiang et al. report an occlusion rate of 68.4% [47]. In the series of Carlson et al. and Nogueira et al., the occlusion rate was even higher with 80% and 83%, respectively [5, 28]. Exceptionally good results were reported by Rossitti, who achieved a 100% occlusion rate [31]. Retrograde transvenous routes are rarely used in non-sinus-type fistulas due to the assumable high risk of rupture of the already fragile leptomeningeal-draining vein [9, 26, 44]. Some combined transarterial and transvenous techniques. In a very recent paper, an occlusion rate of 96% had been reported in 25 patients [19]. However, it remained unclear if true non-sinus-type fistulas were treated in this series because an involvement of the sinus was described for all cases. Complication rates of 9%, occasionally of up to 21%, and even fatalities have been reported in contemporary endovascular series [19, 41, 45, 46, 48]. In consequence, we propose that microsurgical interruption of the draining vein should be the treatment of first choice in all patients with non-sinus-type dAVFs. This especially holds true because the leptomeningeal-draining vein is easily accessible by standard neurosurgical approaches in most instances [25]. The very recent papers of Rossitti and Kirsch et al. indicate that advanced endovascular techniques yield results which are comparable to surgical results. Possibly, our proposal has to be re-evaluated with further up-coming endovascular series. Arterial embolization to mitigate blood loss during surgery is proposed by some [18, 30]. However, in non-sinus-type fistulae we never experienced brisk bleeding during coagulation or clipping of the leptomeningeal vein, and therefore question the usefulness of preoperative arterial embolization.

In sinus-type fistulae of sinuses, which are easily accessible by surgery (sigmoid/transverse sinus, superior sagittal sinus), our institutional strategy was to expose the arterialized segment of the sinus, to incise the wall minimally and to pack the sinus with oxidized cellulose until cessation of arterial blood flow. We achieved an overall occlusion rate of 100%, without major morbidity and mortality, and a minor morbidity rate of 10%. These results are in line with the few other surgical series [10, 17]. In these surgical series, sinus packing was achieved with microcoils after sinus puncture. If sinus packing with coils is more advantageous than minimal sinus wall incision and packing with oxidized cellulose will remain a matter of discussion [17]. Possible arguments against sinus packing with coils are the higher costs and the need for intraoperative angiography or patient transfer [29, 30]. In the authors’ opinion, there is rarely the need for microsurgical excision of the diseased sinus segment for control of the dAVF [3, 8, 30]. Furthermore, excision of the arterialized sinus could lead to complications as reported in the literature and witnessed in one case of our series [38]. Van Dijk et al., who only disconnected the cortical venous reflux from the arterialized sinus, proposed a new surgical concept [44]. However, taken the assumed pathophysiology of sinus-type dAVFs, recruitment of new leptomeningeal veins seems possible [14, 39]. Furthermore, the assumption of van Dijk and co-workers that intradural disconnection of the arterialized cortical vein is less risky than sinus packing, which represents a completely extradural operation, could be challenged. In sinus-type fistulae, the retrograde transvenous embolization yields results, which are comparable to surgical sinus packing, with an obliteration rate of 81% to 87.5%, and a permanent morbidity rate of 4% [19, 32]. Transarterial embolization with particles or glue often yields poorer results. Recently, transarterial embolization using Onyx has been proposed for the management of sinus-type fistulae [36]. The reported occlusion rate was 78%. Another endovascular option is conversion of an aggressive into a non-aggressive fistula type by recanalization of the thrombosed sinus, but only single cases have been reported so far [13, 27]. The comparable results of microsurgery and retrograde transvenous embolization do not allow the definition of the superior therapeutic option, but the lower invasiveness favors transvenous embolization as the first treatment option. However, microsurgery should be considered early if transvenous embolization fails.

The cavernous sinus is not easily accessible by microsurgery and sinus packing is not without risk for the cranial nerves [42]. Furthermore, cavernous sinus fistulae could either be bilaterally fed from the carotid arteries or could extend to the contralateral side via the intercavernous sinus, making unilateral sinus packing often ineffective. Thus, cavernous sinus dAVFs are the domain of endovascular interventions [6]. In the rare cases in which the cavernous sinus cannot be reached transvenously, surgery is indicated to provide access to the cavernous sinus via the petrosal vein [15], or the superior ophthalmic vein [49] for retrograde catheterization. In one case, we disconnected the arterialized leptomeningeal-draining vein and thereby successfully increased the intracavernous pressure, which “opened” the blocked petrous sinus for successful retrograde embolization, which is a strategy that has not been reported so far. Very rarely, embolization proved to be not possible, as witnessed in one patient, and microsurgical sinus packing remains the only treatment option.