It is generally believed that the combination of brain arteriovenous malformation BAVMs and intracranial aneurysms (IAs) is associated with higher hemorrhage rates at presentation and higher rehemorrhage rates and thus with a more aggressive course and natural history.

There is wide variation in the literature on the prevalence of BAVM-associated aneurysms (range 2.7%-58%), with 10%-20% being most often cited in the largest case series.

Possible involvement of SOX-17 and RBBP8, genes involved in cell cycle progression, deserves further investigation ¹⁾.

The risk of intracranial hemorrhage in patients with unruptured BAVMs and coexisting IAs has been reported to be 7% annually, compared with 2%-4% annually for those with BAVM alone.

Several different classification systems have been applied in an attempt to better understand the natural history of this combination of lesions and implications for treatment. Independent of the classification used, it is clear that a few subtypes of aneurysms have a direct hemodynamic correlation with the BAVM itself. This is exemplified by the fact that the presence of a distal flow-related or an intranidal aneurysm appears to be associated with an increased hemorrhage risk, when compared with an aneurysm located on a vessel with no direct supply to the BAVM nidus.

Debate still exists regarding the etiology of the association between those two vascular lesions, the subsequent implications for patients' risk of hemorrhagic stroke, and finally the determination of which patients warrant treatment and when.

The ultimate goals of the treatment of a BAVM associated with an IA are to prevent hemorrhage, avoid stepwise neurological deterioration, and eliminate the mortality risk associated with recurrent hemorrhagic events. The treatment is only justifiable if the risks associated with an intervention are lower than or equivalent to the long-term risks of disability or mortality caused by the lesion itself. When faced with this difficult decision, a few questions need to be answered by the treating neurosurgeon: What is the mode of presentation? What is the symptomatic lesion? Which one of the lesions bled? What is the relationship between the BAVM and IA? Is it possible to safely treat both BAVM and IA? ²⁾.

AAA was a significant risk factor for hemorrhage and was associated with a poor outcome. It seems worthwhile to consider whether the aneurysm itself is a risk factor or only an epiphenomenon of severely altered hemodynamics induced by these special arteriovenous malformations AVMs and therefore only the most common site of rupture. As the complication rate was low for aneurysm occlusion, Platz et al., recommend treating these aneurysms whenever possible. Furthermore, obliteration of the AVM should be strived for as this subtype may be associated with an increased risk of hemorrhage ³⁾.