**2. Cerebral angiography**

Endovascular neurosurgery is based on cerebral angiography. It is well known that Portuguese neurologist Antonio Egas Moniz, the recipient of the Nobel Prize in Physiology and Medicine in 1949, developed and described cerebral angiography firstly in 1927 [6]. Before using cadaveric specimens of human to develop the technique, he had successfully obtained cerebral angiograms in dogs. His first cerebral angiography was performed in a 48-year-old patient with Parkinson's disease. The internal carotid artery (ICA) was ligated temporarily for 2 minutes and a 70% solution of strontium bromide was injected into the ICA at a dose of 13 to 14 ml. The middle and posterior cerebral arteries were demonstrated on his first film. Unfortunately, the patient died from thrombophlebitis 8 hours later. This invention ushered in the age of diagnostic and therapeutic angiography.

Cerebral angiography had a prominent role in defining neurosurgery as a specialty distinct from surgery. The cerebral angiography is based on X-ray imaging [7]. Contrast injection plus X-ray exposure combined with mask subtraction generates images of high resolution of the cerebral vasculature. In early angiogram systems, cut film and film cassettes were used, which required a technologist to exchange multiple cassettes to obtain series and angiography "runs". At that time, angiography generated radiopaque images of the cerebral vasculature and could be used to identify vessel occlusions and eventually identify vascular lesions [8]. Distortion and displacement of the vascular anatomy could be used for hematoma or tumor localization.

There has been an ongoing evolution of the cerebral angiography, first as a diagnostic tool but then the potential for intervening in vascular pathology became possible. Subsequently, the eventual introduction of braided catheters and hydrophilic wires, which allowed quick and safe catheterizations, set the foundation for intervention. Modern digital subtraction angiography (DSA) machines consist of an image intensifier and digital subtraction flat panel detectors that utilize a fraction of the radiation dosage for the acquisition of images of the finest detail [9]. The ability to rotate the image intensifier around the patient allowed the development of 3D rotational images [10].

Although cerebral angiography remains a mainstay in the diagnosis and endovascular treatment of cerebrospinal vascular disorders [11], several limitations of this technique are evident. X-ray based cerebral angiography cannot view neurovascular structures clearly in complex vascular lesions, lack resolution necessary to visualize small vessels and critical perforating vessels, which are essential to the treatment of many cerebrovascular disorders. As a real-time guide during therapy, intraluminal imaging with ultrasonography, maybe a resolution in the future. This technique will provide not only therapeutic guidance but also real-time documentation of the completeness of therapy.

### **3. Cerebral aneurysms**

Endovascular treatment of cerebral aneurysms had its start in neurosurgery. Werner et al. firstly reported successful electrothermic thrombosis of an intracranial aneurysm in 1941 [12]. With a transorbital puncture, "thirty feet of No. 34 gauge coin silver enameled wire was introduced into the aneurysm through a special needle" and "the wire was heated to an average temperature of 80°C for a total of 40 seconds. The aneurysm no longer bled when the needle was cleared at the conclusion of the operation" [12].

After these early attempts, particularly in the 1960s and early 1970s, several neurosurgeons and neuroradiologists sought therapeutic alternatives to conventional

#### *The History and Development of Endovascular Neurosurgery DOI: http://dx.doi.org/10.5772/intechopen.97139*

surgery [2]. Lacking devices suitable for safe navigation in the intracranial vasculature, their efforts originally concentrated on the extravascular route. Under radiographic guidance, thrombosis was initiated by passing electrical current to an electrode needle introduced within the aneurysm sac through a burr hole [13]. Mullan et al. described the treatment of intracranial aneurysms in a series of 12 patients, 10 of whom had presented with aneurysmal subarachnoid hemorrhage, by inducing electrothrombosis [13].

Until 1964, Luessenhop and Velasquez made the first endovascular attempt to treat a cerebral aneurysm [14]. They attempt to occlude a supraclinoid aneurysm with a silicone balloon. Subsequently, Serbinenko developed a balloon-mounted microcatheter with flow-directional capabilities for more effective intracranial catheterization [15]. He further developed detachable and nondetachable balloon catheters to make parent artery sacrifice or direct aneurysmal obliteration and to allow temporary balloon occlusion safe and reliable in the 1970s. His contributions gave birth to endovascular neurosurgery [15]. Balloon occlusion techniques were further used with a vast amount of clinical experience during the 1970s and 1980s [16–18].

Several major limitations of balloon occlusion technique are apparent. Aneurysmal catheterization was difficult without help of guidewire. The balloon shape often could not adequately filling an irregular aneurysm with leaving the fundus unprotected or creating a ball-valve effect of aneurysmal refilling. Therefore, the endovascular therapy of cerebral aneurysms shifted from balloon occlusion to free (pushable) platinum coil occlusion [2]. At this time, coil embolization for cerebral aneurysms is a dangerous procedure because of the inability to retrieve the pushed coils that migrated into the distal intracranial vasculature.

The innovation of electrolytic detachable coils by the Italian neurosurgeon Guido Guglielmi in the early 1990s updated the endovascular treatment of cerebral aneurysms [19, 20]. In the early 1980s, Guglielmi found accidental electrolytic detachment of the electrode tip while applying current to a stainless steel electrode inserted into an experimental aneurysm to promote electrothrombosis. After several years, he worked with Ivan Sepetka, an engineer at Target Therapeutics, Inc., to combine the two processes of endovascular electrolysis and electrothrombosis, which eventually resulted in the development of the present-day Guglielmi detachable coil (GDC; Boston Scientific/Target Therapeutics, Fremont CA) [21]. The Guglielmi detachable coil (GDC) can be re-positioned and examined before the coil was released electrolytically from its tether. On the other hand, the flexibility and softness of the coil enabled the safe filling of an irregular aneurysm with a low risk of rupture. The first intracranial aneurysm was treated using this new technology on April 12, 1990 [19]. The first multicenter GDC clinical trial result was published by Guglielmi et al. in 1992 [20]. Immediate complete occlusion was obtained in 81% of small-necked and 15% of wide-necked aneurysms with low procedure-related morbidity and mortality rates less than 5%. The GDC system was immediately accepted worldwide and became the focus of most published works on cerebral aneurysm management (**Figure 1**).

Despite the advantages of the GDC system, wide-necked and large aneurysms remained difficult to treat. New techniques were performed to keep the detached coils within the aneurysmal sac. Moret et al. was the pioneer of the "remodeling technique" using a balloon as a mechanical barrier to keep coils within the aneurysmal sac during its delivery (**Figure 2**) [22]. Moret et al. [22] published their results with use of the "balloon-remodeling technique" for the treatment of 56 cases of previously untreatable wide-necked cerebral aneurysms in 1997 with low morbidity and mortality rates.

An alternative approach to introduce a stent to maintain a patent lumen and provid a buttress to prevent coil herniation. After some early attempts of Wakhloo

#### **Figure 1.**

*A 46-year-old woman with a ruptured anterior communicating artery aneurysm was coiled with GDCs (Boston Scientific, USA) in 1998. A, frontal view of the left internal carotid artery injection. B, lateral view of the left internal carotid artery injection. Showing the aneurysm of the left anterior communicating artery (arrows). C, frontal view of the roadmap image of the left internal carotid artery injection showing the aneurysm (arrow). D, frontal view of the roadmap image after aneurysm coiling showing the disappearance of the aneurysm (arrow). E, frontal view of the left internal carotid artery injection after aneurysm coil embolization. F, lateral view of the left internal carotid artery injection after aneurysm coil embolization. Showing the aneurysm was completely occluded (arrows).*

et al. [23] and Geremia et al. [24], this stent-assisting technique has been further explored and expanded by an increasing number of neurosurgeons [25]. Neurosurgeons and neurointerventional radiologists at several centers began to borrow stents from the interventional cardiology at the same time and publish their case reports about treating wide-necked aneurysms with a combination of stents and coils (**Figure 3**). These stents were designed specifically for cardiac usage and were stiffer and more difficult to use in the tortuous neurovascular anatomy.

With the introduction of neurovascular stents, specifically designed for intracranial use (Neuroform stent, Boston Scientific Target), borrowing cardiac stents soon became unnecessary [26]. Although the use of stents required a regimen of

*The History and Development of Endovascular Neurosurgery DOI: http://dx.doi.org/10.5772/intechopen.97139*

#### **Figure 2.**

*A 37-year-old man presented with subarachnoid hemorrhage. A, frontal view of the left vertebral artery injection showing a basilar tip aneurysm (arrow). B, roadmap of the left vertebral artery injection showing the first orbit 3-D 7 mm × 13 cm coil and a 4 mm × 20 mm Hyperglide balloon catheter (Medtronic ev3, USA) (arrow). C, the left vertebral artery injection showing the aneurysm was completely occluded after subsequent coils (Microplex 6 mm × 15 cm,6 mm × 10 cm, 5 mm × 10 cm, orbit 5 mm × 15 cm, HydroCiol 3 mm × 7 cm, 2 mm × 4 cm, helix standard fiber 2 mm × 4 cm).*

#### **Figure 3.**

*A vertebral artery aneurysm treated with coronary artery stent and coiling in 1990s. A, 3-D angiogram of the right vertebral artery injection showing a dissecting aneurysm of vertebral artery-inferior posterior cerebellar artery (arrow). B, angiogram of the right vertebral artery injection showing a microwire was passed through the aneurysm for navigation of a BX coronary artery stent (Medtronic, USA). C, angiogram of the right vertebral artery injection showing the aneurysm was coiled with assistance of a 3.0 mm × 18 mm BX coronary artery stent (Medtronic, USA)(arrow). D, angiogram of the right vertebral artery injection showing the aneurysm was completely occluded (arrow).*

#### **Figure 4.**

*A 62-year-old woman presented with an incidental paraclinoid aneurysm of the internal carotid artery. A, 3-D reconstruction of the right internal carotid artery injection showing the 6 mm × 6 mm paraclinoid aneurysm of the internal carotid artery (arrow), which was treated with 4 mm × 30 mm Neuroform stent and coils. B, the unsubtracted image showing the Neuroform stent (black arrow) and the first 3-D coil (white arrow). C, oblique view of the right internal carotid artery injection after treatment showing the aneurysm was occluded completely (arrow).*

antiplatelet medication adding to the risk of the procedure itself as well as risks associated with the recovery period, these risks were quickly accommodated by interventionalists and improved overall occlusion rates as decreased the aneurysm recurrence (**Figure 4**) [27].

Bioactive coils were explored by some manufacturers to promote thrombus formation and endothelialization. However, these modified coils were shown to have limited efficacy and no clear advantage over pure platinum coils when used alone [28]. The use of polymers was also explored by some authors to treat cerebral aneurysms, but the increased risk and patient morbidity derailed this strategy and prevented its widespread acceptance [29].

It was firstly confirmed by the International Subarachnoid Aneurysm Trial (ISAT) that more and more aneurysm patients were being treated worldwide with the introduction of detachable coils and various intracranial stents [30]. An overall decreased risk of death and morbidity in the endovascular group treated with detachable coils when compared to those treated with open surgery were found [30]. The worldwide treatment of both ruptured and unruptured aneurysms by detachable coils quickly has surpassed open surgery as the primary treatment modality. Covered stents already are used successfully in the treatment of cerebral aneurysms, iatrogenic pseudoaneurysms, and carotid-cavernous fistulas (CCF) [31, 32].

#### **4. Flow diverter**

The introduction of flow diverter had a dramatic effect on the management of cerebral aneurysms. The concept of flow diverter was initially explored by Wakhloo in 2014, but Nelson and colleagues developed the first commercially available flow diverter [33]. Flow diverter introduced the concept of a more physiological therapy for aneurysms, focusing on treating the parent vessel without the requirement of entering the aneurysm dome [34]. With data that indicated complete occlusion rates that approached 90% at follow-up in systematic review, treatment recommendations for selected intracranial aneurysms was made [35]. Even giant aneurysms, in the past managed with balloon test occlusion and vessel sacrifice or complex bypasses, can now be managed with flow diverter with great efficacy and considerably lower morbidity [36, 37] (**Figure 5**). Moreover, the indications for flow diversion have been extended to smaller aneurysms that are usually treated with coiling, stent-coiling, or clipping [38].

**Figure 5.**

*A 58-year-old woman presented with visual deficit caused by a giant supraclinoid aneurysm of the internal carotid artery, which was treated by flow diverter. a, right internal carotid artery (ICA) angiogram (anteroposterior) demonstrating a giant aneurysm of the supraclinoid internal carotid artery. b, right ICA angiogram (anteroposterior) after pipeline flex flow diverter and coil embolization showing nearly complete occlusion of the aneurysm. c, right ICA angiogram (anteroposterior) at 1-year follow-up showing complete occlusion of the aneurysm.*

Cerebral aneurysms, both ruptured and unruptured, can be treated with flow diverters [3]. Research into surface modification of devices to mitigate or negate the need for anticoagulation or antiplatelet medications is actively being pursued [3]. However, careful must be always taken in evaluating benefits and risks. In a recent paper by Gory et al., a total of 21.8% of interventions experienced at least 1 morbidity during the 12-month follow-up [39]. Among the serious events, 5.9% were considered permanent and related to the procedure. Moreover sixty-six (16%) of the 412 interventions had a complication, and 10 of them caused a neurological deficit [40].
