Embolizing materials

Cardioembolism Cardioembolism accounts for approximately 30% of all stroke and 25-30% of strokes in the young (age <45 years)." AF accounts for a large proportion of these strokes (15-25%). Symptoms may be suggestive, but they are not diagnostic. Repetitive, stereotyped, transient ischemic attacks (TIAs) are unusual in embolic stroke. The classic presentation for cardioembolism is the sudden onset of maximal symptoms. The size of the embolic material determines, in part, the course of the embolic material. Small emboli can cause retinal ischemic or lacunar symptoms. Posterior cerebral artery territory infarcts, in particular, are often due to cardiac embolism. This predilection is not completely consistent across the various cardiac structural abnormalities that predispose to stroke, and may be due to patterns of blood flow associated with specific cardiac pathologies. 

Removal of balloon-occlusive EPDs is preceded by aspiration of 50-60 ml of blood using a dedicated catheter. Filter-based EPDs are removed using a dedicated retrieval catheter. Difficulties in advancing the retrieval catheter through the stent are at time eliminated by having the patient rotate his/her neck. Rarely, the filter can become obstructed by large amounts of embolic material and blood flow in the ICA is interrupted. Facile technique and optimal antiplatelet therapy prevent this complication in most cases. 

Paradoxical embolism can occur in a patent foramen ovale with a right to left shunt. Embolic material arising from the pelvic or leg veins or elsewhere in the venous system may bypass the pulmonary system and reach the cerebral arteries (Braun et al. 2004). 

Komemushi A, Tanigawa N, Okuda Y, et al. A new liquid embolic material for liver tumors. Acta Radiol 2002 43(2) 186-191. Murdoch L-A. Dimethyl sulfoxide (DMSO) an overview. Can J Hasp Pharm 1982 35(3) 79-85. 

J. D. Folts, Deleterious hemodynamic effects of thrombotic/embolic materials on the distal myocardial vasculature, Cardiovasc Res 42, 6-7 (1999). 

Merrill Birdno, Brent Vernon. Mechanical optimization of an arteriovenous malformation embolization material a predictive model analysis. Annals of Biomedical Engineering. 2005 33(2) 191-201. 

Matsumaru, Y., Hyodo, A., Nose, T., Ito, S., Hirano, T. Ohashi, S. (1996) Application of thermosensitive polymers as a new embolic material for intravascular neurosurgery. Journal of Biomaterials Science — Polymer Edition, 1, 795-804. 

Abstract This chapter focuses on the vascular applications of injectable biomatetials. Two clinically relevant vascular conditions, cerebral arteriovenous malformations and intracranial aneurysm, will be discussed in terms of endovascular embolization. This chapter then outlines available embolic materials used to treat each condition, as well as highlighting new injectable biomaterials developed for embolization purposes. 

Key words endovascular embolization, arteriovenous malformations, aneurysms, 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... 

Onyx Liquid Embolic System, manufactured by ev3, is a non-adhesive precipitating embolic material formulated from ethylene-vinyl alcohol copolymer dissolved in the organic solvent dimethylsulfoxide (DMSO). The copolymer is formed with ethylene, which is a hydrophobic subunit, and vinyl alcohol, which is hydrophilic. This mixture is dissolved in DMSO and micronized tantalum particles are added for radio-opacity. Once the solution is injected, DMSO rapidly diffuses away into the blood and the copolymer precipitates to create a spongy solid (He et ah, 2005). Figure 7.1 depicts a similar ethylene and vinyl alcohol copolymer as it solidifies when coming into contact with saline (Murayama et al, 1998). 

Embolic materials for both intracranial AVMs and aneurysms have come a long way since the first endovascular embolization procedure was carried out. Much advancement to this branch of neurosurgery came about because of an emphasis on development of equipment that was better suited to endovascular techniques. Some of these inventions include flow-directed microcatheters, endovascular balloons, and re-designed stents. Owing to a greater capacity to perform endovascular techniques with suitable equipment, the development of better embolic materials has followed. Now, there are a variety of techniques and materials that endovascular neurosurgeons have at their disposal, all of which provide a variety of benefits, yet have considerable drawbacks. Efforts are always being made to improve current materials and techniques, as well as to... 

Shape memory polymers, as well as the other developmental embolic materials discussed here, represent insight into future procedures that may revolutionize the practice of endovascular embolization in order to better treat critical vascular conditions. 

In addition to the conventional uses of PLLA and its copolymers as microspheres or micro-capsules for drug delivery systems, PLLA microspheres or microcapsules have recently been approved by the FDA for the restoration and correction of facial fat loss caused by the human immunodeficiency virus (HIV)/AIDS without acute side effects [41]. Moreover, PLLA microspheres have been applied as embolization materials to control arterial malformation, haemorrhage and tumours without complications [41]. 

Ensure availability of equipment and resources Adequate fluoroscopy/DSA, availability of catheters, guidewires, large inventory of coils and embolic materials. 

Choice of embolic material/method is paramount and must be based on the target vascular territory and the desired effect. Ability to reach distal vascular beds. For example, emergent non-selective embolization of a large vascular territory is best accomplished with a potentially temporary occlusive agent such as Gelfoam. 

Carefiilly estimate volume of embolic material quantity to be used (excess leads to overflow reflux). 

Beware of causes of reflux of embolic material which can cause non-target embolization ... 

Maintain tactile feedback during embolic material injection or coils deployment and void forceful contrast injections. 

Rosenwasser RH, Berenstein A, Nelson PK, Setton A, Jafar JJ, Marotta T (1993) Safety of embolic materials [comment]. J Neurosurg 79 153-155... 

Embolotherapy is a major aspect of Interventional Radiology and, as such, there are an increasing number of indications, ongoing research, and new developments. Numerous materials have been used for embolization and, recently, many new embolic agents, and devices have been developed. In this chapter we review the most common materials used in daily practice of most interventional radiologists. In this two-volume textbook, each chapter discusses separately the optimal embolic materials related to the corresponding clinical indications. We will also refer the readers to Chap. 10.6 in volume I, and Chap. 17 in Volume II, discussing future development in embolic materials. 

The key decision in the performance of any embolization procedure is the choice of agent. Based on their physical and chemical properties, embolic agents can induce mechanical occlusion of the vessels provoke the formation of thrombus by inflammatory reactions or destroy the endothelium leading to thrombosis. In this section, we will discuss the particulate agents, liquid agents and metallic embolic materials. 

Tadavarthy SM, Moller JH, Amplatz K (1975) Polyvinyl alcohol (Ivalon) a new embolic material. AJR Am J Roentgenol 125 609-616... 

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