**1. Introduction**

26 Will-be-set-by-IN-TECH

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#### **1.1. Epidemiology**

Internal carotid artery (ICA) and vertebral artery (VA) aneurysms are most frequent aneurysmatic lesions. Especially intracranial aneurysms are pathologic focal dilatations of the cerebrovasculature that are prone to rupture. These vascular abnormalities are classified by presumed pathogenesis. Saccular, berry, or congenital aneurysms constitute 90% of all cerebral aneurysms and are located at the major branch points of large arteries. Dolichoectatic, fusiform, or arteriosclerotic aneurysms account for 7% of all cerebral aneurysms. Infectious or mycotic aneurysms are situated peripherally and comprise 0.5% of all cerebral aneurysms. Other peripheral lesions include neoplastic aneurysms, rare sequelae of embolized tumor fragments, and traumatic aneurysms. Saccular intracranial aneurysms are situated in the anterior circulation in 85-95% of cases, whereas dolichoectatic aneurysms predominantly the vertebrobasilar system. Multiple saccular aneurysms are noted in 20-30% of patients with cerebral aneurysms. Aneurysmal rupture can result most often in subarachnoid hemorrhage, but may also present as intraparenchymal, intraventricular, or subdural hemorrhage. Giant saccular aneurysms, defined as greater than 25 mm in diameter, may cause SAH, but these lesions more frequently produce mass effect and may result in distal thromboembolism.

On the other hand, extracranial internal carotid and vertebral artery aneurysms usually may present with cerebral embolism, transient ischemic attack, cerebrovascular insufficiency, continued enlargement with compression syndrome, vessel occlusion or hemorrhage. Aneurysms may be also often asymptomatic until the time of rupture. In the past, most of these aneurysms were treated surgically. Surgery, however, is often difficult because of the

© 2012 Vulev and Klepanec, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

location and the damaged arterial wall and may result in sacrifice of the internal carotid or vertebral artery. Vertebral artery (VA) aneurysms constitute 0.5 to 3% of intracranial aneurysms and 20% of posterior circulation aneurysms [1]. The causes of aneurysms are multiple and may occur following trauma, mycotic infection, as a result of atherosclerosis, tumor invasion or radiation necrosis or iatrogenic. Among these, dysplastic lesions appeared to be the main cause of extracranial internal carotid artery aneurysms, associated or not with spontaneous dissection. VA aneurysms include VA-PICA (posterior inferior cerebellar artery) aneurysms, vertebro-basilar junction aneurysms, distal PICA aneurysms and those aneurysms located along the distal VA. Dissecting aneurysms of the intradural vertebral arteries often present with subarachnoid haemorrhage. A second episode of bleeding (rebleeding) is common and deadly. Rebleeding rates were estimated at 71% of cases with subsequent re-rupture of the aneurysms in 57% [2]. Ruptured posterior circulation aneurysms are technically difficult to expose and clip and their management and surgical outcomes are poorer as compared to anterior circulation aneurysms [3]. They often need expertise with various skull base approaches to improve the exposure, to minimize brain retraction and to achieve better outcome. Certain subset of posterior circulation aneurysms are considered at even higher risk for surgery due to their location and the size, prompting recourse to other modalities of therapy.

#### **1.2. Diagnostic imaging**

Early diagnosis and evaluation of anatomical characteristics of the internal carotid and vertebral artery aneurysms are essential in terms of surgical or endovascular treatment planning.

Ultrasound imaging is initially useful in the diagnostic process for cases with suspicion for extracranial internal carotid artery aneurysm palpable pulsatile mass at neck region. It serves for determination of the size and extension of the aneurysm. Although ultrasound is a valuable diagnostic tool for definition of anechoic structure and pulsation of the aneurysm, it may become insufficient in defining thrombosed aneurysm, relation of the aneurysm with its neighboring structures. Duplex ultrasound scanning is the most simple investigation in the detection of vertebral and extracranial internal carotid artery aneurysms, but this may fail if the lesion is located high, especially if the patient has a short neck or when the examination is focused on stenosis diagnostic and if the size of the aneurysm is small.

In diagnosing and characterizing the aneurysms, DSA is still the gold standard imaging method. But, since DSA is an invasive method, persistant neurological complications can develop and that´s why nowadays it is mostly used just for endovascular treatment. DSA most often provides the diagnosis of the lesion, specifies the localization, and detects any associated lesion, stenosis, or wall irregularities inducing a carotid dysplasia. The disadvantage of DSA is showing only the patent lumen and the risk of complications associated with invasive catheterization. Therefore, recently noninvasive or minimally invasive methods, such as CT angiography and MR angiography are more popular to detect and demonstrate the aneurysms.

Contrast enhanced CT scanning with three-dimensional reconstructions allows analysis of the aneurysm and assesses the possible existence of a false lumen channel, representing the existence of a previous dysplastic or traumatic dissection. Analysis of the slices at the osseous window allows the assessment of the distance between the upper limit of the aneurysm and the temporal bone. Currently, contrast enhanced CT scanning with reconstruction is the most sophisticated examination available and gives the most information. CT angiography (CTA) has advantages such as easy and rapid applicability, being a minimally invasive method, having no manifest complication besides contrast medium allergy, capability of rotating the images 360° [4]. The most important advantage of CT angiography is its capability of evaluating images on preferred planes and angles on the screen. Therefore, superimposed vessel images in DSA making it hard to evaluate are easily evaluated with CT angiography. Moreover, capability of rotating the CT angiographic images on preferred planes and angles helps the surgeon or interventional radiologist in orientation to approach the aneurysm and in the treatment planning (Figure 1). Contrary, CT angiography has some limitations. Differentiation of small aneurysms from neighboring bones is not possible each time and CT angiography is not capable of showing the collateral circulation as seen in DSA [5]. Both arteries and veins are visible in CT angiography and sometimes it is not easy to differentiate either of them. CT angiography has also limitations in the postoperative management of aneuryms, especially in patients receiving coil embolisation because of coil artefacts.

250 Aneurysm

location and the damaged arterial wall and may result in sacrifice of the internal carotid or vertebral artery. Vertebral artery (VA) aneurysms constitute 0.5 to 3% of intracranial aneurysms and 20% of posterior circulation aneurysms [1]. The causes of aneurysms are multiple and may occur following trauma, mycotic infection, as a result of atherosclerosis, tumor invasion or radiation necrosis or iatrogenic. Among these, dysplastic lesions appeared to be the main cause of extracranial internal carotid artery aneurysms, associated or not with spontaneous dissection. VA aneurysms include VA-PICA (posterior inferior cerebellar artery) aneurysms, vertebro-basilar junction aneurysms, distal PICA aneurysms and those aneurysms located along the distal VA. Dissecting aneurysms of the intradural vertebral arteries often present with subarachnoid haemorrhage. A second episode of bleeding (rebleeding) is common and deadly. Rebleeding rates were estimated at 71% of cases with subsequent re-rupture of the aneurysms in 57% [2]. Ruptured posterior circulation aneurysms are technically difficult to expose and clip and their management and surgical outcomes are poorer as compared to anterior circulation aneurysms [3]. They often need expertise with various skull base approaches to improve the exposure, to minimize brain retraction and to achieve better outcome. Certain subset of posterior circulation aneurysms are considered at even higher risk for surgery due to their location and the size,

Early diagnosis and evaluation of anatomical characteristics of the internal carotid and vertebral artery aneurysms are essential in terms of surgical or endovascular treatment

Ultrasound imaging is initially useful in the diagnostic process for cases with suspicion for extracranial internal carotid artery aneurysm palpable pulsatile mass at neck region. It serves for determination of the size and extension of the aneurysm. Although ultrasound is a valuable diagnostic tool for definition of anechoic structure and pulsation of the aneurysm, it may become insufficient in defining thrombosed aneurysm, relation of the aneurysm with its neighboring structures. Duplex ultrasound scanning is the most simple investigation in the detection of vertebral and extracranial internal carotid artery aneurysms, but this may fail if the lesion is located high, especially if the patient has a short neck or when the examination is

In diagnosing and characterizing the aneurysms, DSA is still the gold standard imaging method. But, since DSA is an invasive method, persistant neurological complications can develop and that´s why nowadays it is mostly used just for endovascular treatment. DSA most often provides the diagnosis of the lesion, specifies the localization, and detects any associated lesion, stenosis, or wall irregularities inducing a carotid dysplasia. The disadvantage of DSA is showing only the patent lumen and the risk of complications associated with invasive catheterization. Therefore, recently noninvasive or minimally invasive methods, such as CT angiography and MR angiography are more popular to detect

focused on stenosis diagnostic and if the size of the aneurysm is small.

prompting recourse to other modalities of therapy.

**1.2. Diagnostic imaging** 

and demonstrate the aneurysms.

planning.

**Figure 1.** Maximum intensity projection (A) and virtual rendering technique (B) reconstructions of aneurysm of left intradural part of vertebral artery.

Magnetic resonance angiography (MRA) is a non-invasive method that can visualize vascular structures without a need for contrast medium injection or radiation. MRA can manifest the thrombosed portions of aneurysms, residual lumina and flow characteristics. MRA is particularly useful in suspicion of carotid artery dissection due to its characteristic of detecting the old blood in dissected area. MRA and CT angiography mainly replaced the

conventional angiography. Promiment factors that emphasize superiority of MRA to arteriography are that it excludes the risk of stroke associated with angiography and also possible access site complications and it gives information about the surrounding tissues. MRA also provides reconstruction and rotation of images of intracranial circulation and evaluation of collateral circulation better than angiography.

#### **1.3. Endovascular treatment**

The current treatment options include surgical treatment and endovascular treatment, but these are not without significant problems [6]. For instance, a randomised, multicentre trial compared the safety and efficacy of endovascular coiling with standard neurosurgical clipping for intracranial aneurysms found that the outcome in terms of survival free of disability at 1 year is significantly better with endovascular coiling [7]. In addition, neurosurgery is associated with significantly longer length of stay and significantly higher total hospital charges [8]. Surgical treatment of extracranial internal carotid artery aneurysms located near skull base is technically challenging with high morbidity and mortality rates. In addition, surgical approach often requires an extended cervicotomy, mandibular subluxation, resection of the styloid process, and sometimes a transection of the external auditory canal with resection of the mastoid and vaginal process of the styloid bone to expose the first vertical intrapetrous segment of the ICA and risk of cranial nerve injury. Over the past decades, with advances in technologies, endovascular therapy is becoming the first-line treatment in the treatment of internal carotid and vertebral artery aneurysms and offers a minimally invasive alternative to open surgery.

Endovascular treatment options includes covered stent placement, flow diverting device (FDD) placement, parent vessel sacrifice with detachable balloons and coils, coil embolisation of the aneurysm with or without a stent placement. Endovascular techniques are usually performed via a femoral access route with placement of either covered stent, FDD or stent extending from the normal artery site to the distal vessel beyond the aneurysm. Despite the trend toward endovascular treatment the rate of recurrence and complications can be high.

This article describes current possibilities in endovascular treatment of vertebral and internal carotid artery aneurysms, with special focus on covered stents with our experience and description of used techniques in the treatment of internal carotid and vertebral artery aneurysms.
