Traditionally, two approaches have been utilized to access the rostral basilar artery (BA) for clipping aneurysms. These are: 1) the subtemporal approach pioneered by Canadian neurosurgeon Charles George Drake and 2) the transsylvian or pterional approach popularized by Turkish neurosurgeon Mahmut Gazi Yasargil. Both of these approaches have assets and liabilities, and both have modifications to expand the surgical field of view. Some rostral BA aneurysms and some patients with aneurysms of both the anterior and posterior circulation requiring clip ligation may benefit from a combined transsylvian and subtemporal (half-and-half) exposure. In this chapter, we describe our version of that approach, which provides access to both anterior and posterior circulation aneurysms. We detail neuroanesthesia considerations, patient positioning, bone drilling, subarachnoid dissection, and clip placement. Also included is an illustrative case.

Numerous areas of skull base neurosurgery and interventional neuroradiology overlap. Interventional neuroradiology techniques can often be employed in combination with open skull base surgery to provide solutions to complex cerebrovascular and oncological problems. This chapter describes the indications for, and technical nuances of, combined microsurgical and endovascular treatment of cerebrovascular and skull base disease. In particular, three major disease states are discussed: intracranial aneurysms, arteriovenous malformations of the brain and dura, and skull base tumors.

Data on the prevalence of intracranial aneurysms in the general population come from autopsy and from angiography series. A recent review found that the prevalence of intracranial aneurysms for adults without a history of subarachnoid hemorrhage (SAH) is approximately 2%, with a male to female ratio of approximately 1 to 1.3. The same analysis found that the prevalence of aneurysms increases with age, peaking in the 69–79 year age group. Nearly half of all intracranial aneurysms become symptomatic during the patient's lifetime, usually presenting as subarachnoid hemorrhage. In North America, approximately 28,000 cases of aneurysmal SAH occur each year, mostly in adults.

As opposed to fusiform aneurysms, which are encountered in the extracranial peripheral vasculature, intracranial aneurysms are typically saccular in morphology. Intracranial aneurysms possess a well-defined neck and sac distinct from the lumen of the parent vessel and are frequently located at proximal intracranial arterial branching points. Although the pathophysiology of intracranial aneurysms is controversial, they are thought to arise from defects (congenital or acquired) in the muscularis media. Once an aneurysm has developed, conditions such as hypertension and tobacco smoking will likely increase the risk of rupture, leading to SAH. Certain conditions (e.g., autosomal dominant polycystic kidney disease, Ehlers-Danlos syndrome type IV, Alpha-1 Antitrypsin Deficiency (A-1ATD)) are associated with the formation of cerebral aneurysms, presumably from the predisposition for the development of focal weak spots in vessel walls near arterial branch points.

Intracranial aneurysms are a relatively common disorder with an autopsy prevalence of 2% to 5% in the general population. Nearly half of these aneurysms become symptomatic during the patient's lifetime, usually presenting as subarachnoid hemorrhage (SAH). In North America, approximately 28 000 cases of aneurysmal SAH occur each year, mostly in adults. As opposed to the fusiform aneurysms that are encountered in the extracranial peripheral vasculature, intracranial aneurysms are typically saccular with a well-defined neck and sac distinct from the lumen of the parent vessel, frequently at proximal intracranial arterial branching points. Although the pathophysiology of intracranial aneurysms is controversial, they are thought to arise from defects in the muscularis media which may be congenital or acquired. Once these aneurysms have developed, conditions like hypertension and tobacco smoking may increase the risk of rupture, leading to SAH. Unruptured aneurysms are believed to bleed at varying rates according to multiple factors, including their diameter at the time of diagnosis. Although evidence suggests that intracranial aneurysms are less likely to bleed if they are less than 7 to 10 mm, both angiographic and direct intraoperative observational studies have demonstrated that even smaller aneurysms may rupture. About 40% to 50% of patients die within the first month as a result of the initial hemorrhage and its complications. Of those who survive, approximately 20% succumb to rebleeding in the ensuing 2 weeks (50% in 6 months) if the aneurysms are not treated, with the highest rate of recurrent hemorrhage (4%) during the first 24 hours after initial rupture.