Types of embolic materials

N-butyl cyanoacrylate is the most commonly used cerebral AVM embolic material, and is considered by some to be the most effective (Finfante and Wakhloo, 2007). While its drawbacks include tissue adhesiveness and optimization of polymerization time, the main advantage of this material is its permanency. The curative capability of n-BCA, seen both after initial embolization 

Owing to its non-adhesive nature and slower solidification characteristics, it has been suggested that this material can be delivered in a more sustained, controllable fashion with more nidal penetration and less chance of tissue adherence to the catheter (Velat et al, 2008). However, despite less tissue adhesion, there have been reported cases of the catheter tip becoming trapped in the delivered material during Onyx delivery (Weber et al, 2007). Also, it has been argued that with greater nidal penetration, there is a potential for increased complication rates due to subsequent increased venous occlusion. 

Delivering Onyx to a cerebral AVM requires some special considerations given the material s chemical and physical characteristics. Inclusion of DMSO within the delivery material requires that Onyx be injected very slowly. High speeds and large volumes of DMSO injection have been shown to cause vessel necrosis (Murayama et al, 1998). Also, Onyx requires the use of DMSO- 

1 Photograph depicting the soiidification of an ethyiene-vinyl alcohol copolymer in contact with saline. Reproduced with permission from Murayama (1998). Copyright (1998) Lippincott, Williams Wilkins. 

In a study by Fanning et al. (2007) 100 intracranial aneurysms were embolized with HydroCoils in conjunction with bare platinum coils, where a basket of bare platinum coils were positioned in the aneurysm, followed by the introduction of HydroCoils. The treatment group showed a 20% increase in the mean packing density when the same number of coils was used in the control 

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Clearly the differences between embolization microspheres available on the market have made the situation very complex for the users. Specific technical recommendations are necessary for each type of embolization materials and the use of such products... 

In general, there are four different types of embolic materials available balloons, particles, coils and liquids. 

Shape memory polymers make up another class of injectable biomaterials for vascular applications, yet are relatively new in the field of endovascular embolization. Shape memory polymers are chemically structured so that they are able to reversibly take on a different physical shape in response to some stimuli (Small et al, 2007). Usually these different shapes include a compact form and an expanded form of the polymer. In the case of endovascular embolization, the expanded polymer can be pre-formed to fit specific contours of an individual aneurysm (Ortega et al, 2007). Upon interacting with some type of stimuli, such as heat or cold, the material is compacted into a shape that can be delivered through a microcatheter. The process of using shape memory polymers to embolize an aneurysm is shown in Fig. 7.5, along with samples of expanded SMPs (Ortega et al, 2007). 

Five patterns of angiographic findings had been described by Kassarjian et al. [20]. Embolic material is selected depending on the vascular type. The first type, the most classical appearance, is early filling of abnormal vascular channels, stagnation of contrast material, and no evidence of a direct shunting (Fig. 23.5a-h). Type 2 shows high-flow nodules... 

The embolization is performed by arterial approach for types 1,2,3, and 5, and by transhepatic transvenous approach for portovenous shunts in type 4. Platinum fiber microcoils are generally safe in types 3,4 and 5, and permit the occlusion of the shunts. Glue (n-butyl-2-cyanoacrylate) is the most effective material in patients with direct arteriovenous and arterioportal shunting arising from multiple sources [21]. Medical antiangiogenesis drugs... 

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