**2. History of treatment for intracranial aneurysms**

The history of craniotomy clipping for cerebral aneurysms is long. Dandy WE reported clipping surgery using a V-shaped malleable clip in 1937 [1]. Many papers have been published since 1959 when Mount LA et al. reported a procedure using the highly operable Selverstone clamp [2]. Since then, craniotomy clipping results have improved with the advent of the latest cerebral aneurysm clips and surgeon skill improvements. Many neurosurgeons have accepted this as a highly reliable long-term procedure with a low recurrence rate for unruptured and ruptured cerebral aneurysms [3–5]. The most significant advantage of this treatment is that it immediately

removes the cerebral aneurysm from the general circulatory system, leading to a very low probability of rupture or rerupture. On the other hand, it is necessarily a relatively invasive procedure because it involves skin and muscle incisions, craniotomy, and subdural brain manipulation, making it a burdensome procedure for patients with medical complications and the elderly. Minimally invasive surgical techniques centered on key hole surgery have been developed to solve this problem, and patient satisfaction has improved, and it has also been reported to reduce the frequency of cerebral vasospasm in subarachnoid hemorrhage cases and to improve treatment prognosis [6–9].

Endovascular treatment as a counterpart to cranial clipping as a treatment for cerebral aneurysms was reported as early as 1832. It was intended to occlude the aneurysm by wire insertion or electrothrombosis. Still, it was not used to occlude intracranial arteries. The most significant disadvantages of endovascular treatment are its high rate of complications such as distal embolism, high mortality rate, and the long time required for occlusion [10]. Subsequently, treatment of large and giant cavernous sinus internal carotid artery aneurysms using a detachable balloon was reported by Serbienko and colleagues. Since then, many good treatment results have been reported with improvements and performance enhancements by Romadanov, Debrun, Hieshima, and Taki [11–14]. Conversely, they are challenging to apply to intradural cerebral aneurysms and new devices have been awaited.

Endovascular treatment of cerebral aneurysms has made great strides since the introduction of the Guglielmi Detachable Coil (GDC) in 1991 [15]. Compared to conventional devices, this is an electrically detachable platinum coil, easy to operate, and incredibly soft, making it less invasive to the aneurysm wall, enabling safer and more reliable endovascular treatment of intracranial aneurysms. The GDC received FDA approval in 1995. Since then, the GDC has become a widely used treatment for cerebral aneurysms. The International Subarachnoid Aneurysm Trial (ISAT), a randomized controlled trial of coil embolization versus surgical clipping for ruptured cerebral arterial aneurysms, was published in 2002 [16]. The results showed that in patients in whom endovascular coiling and neurosurgical clipping were the treatment of choice for ruptured intracranial aneurysms, the 1-year disability-free survival rate was significantly better with endovascular coiling. The long-term risk of rebleeding from treated aneurysms was also lower for both treatment modalities but was suggested to be slightly more frequent with endovascular coiling [16]. Since the publication of this report, coil embolization has become a more aggressive option for ruptured and unruptured cerebral aneurysms, especially in Europe and the United States. Furthermore, the Barrow Ruptured Aneurysm Trial (BRAT), which compared coil embolization and surgical clipping to treat ruptured cerebral aneurysms, confirmed that the treatment prognoses for both procedures were comparable [17, 18]. In a report from Australia covering cases from 2008 to 2018 based on the Australian National Hospital Morbidity database, endovascular treatment for cerebral aneurysms accounted for 58.4% of all cases [19]. Furthermore, the Nationwide Inpatient Sample database from 2002 to 2012 reported that in a total of 23,053 patients with unruptured cerebral aneurysms, coil embolization was the procedure of choice in approximately 73% of cases [20]. Opportunities for endovascular treatment options for cerebral aneurysms, coupled with advances in the technology of the devices and surgeons, will continue to increase in proportion.

*Perspective Chapter: Role of Direct Surgery for Recurrent Aneurysms after Endovascular Treatment DOI: http://dx.doi.org/10.5772/intechopen.112076*
