Polyvinyl alcohol (PVA) is one of the oldest particulate embolization materials available to provide inexpensive, permanent blood vessel obstruction. It is a water-soluble, colorless synthetic polymer made from polyvinyl acetate by partial or complete hydrolysis to remove acetic acid groups. The degree of hydroxylation determines the physical, chemical, and mechanical properties of PVA. 1 Normally, PVA is highly soluble in water, but is resistant to most organic solvents, making it useful in many industries, including paper, cosmetics, household sponges, food packaging, and medical apparatures.2 Grindlay reported the first medical use of PVA, in 1949 at the Mayo Clinic as a prosthesis following a pneumonectomy. Since then, it has found a variety of medical applications, such as heart surgery, skin grafts, embolization materials, artificial cartilage, artificial tear replacements, etc. Its non-toxic, inert characteristics have been well confirmed in the past few decades. Tadawasi et al. were the first to report the use of PVA as an embolization material in the mid-1970s. It is used to treat patients suffering from cervical cancer, hepatic angiosarcoma, vascular endothelioma of the neck and forehead, and arteriovenous malformations of the spine.
One of the most commonly used suppositories for PVA, which is not visible under the x-line, is usually mixed with contrast agents to make it visible under X-rays. Preparation of PVA particles first required their conversion into a foam capable of absorbing moisture and easily compressible. Historically, flaky or lumpy dry foam was removed to obtain irregular particles of varying sizes. Subsequently, the resulting flakes or particles were passed sequentially through a sieve with holes, separating them into different size specifications. Given the irregular structure of each individual particle, larger particles may also pass through small sieve holes, depending on the orientation in which they pass through the sieve. This explains the existence of different sizes in early particle preparation. PVAs offered today are formulations with irregular or spherical particles in a standardized size range, although there is still the possibility of varying sizes in aspherical formulations. This is a potential problem when using particulate PVAs, as the presence of smaller particles than expected may cause uncontrolled distal embolization (with tissue infarction), while the presence of larger particles than expected may cause proximal embolization (with potential recanalization).
PVA is extremely elastic and compressible, has an excellent memory, and can return to its original shape and size once it comes into contact with body fluids. 7 In fact, due to its inherent memory, PVA particles have the potential to swell about 4 to 15 times once they come into contact with a solution, and can therefore block blood vessels slightly larger than the inner diameter of the catheter. 7 In addition, when suspended in saline, the particles have a tendency to clump together. As a result, the effective size of the agent is usually larger than that of individual dried particles, which can lead to closer occlusion than expected. 8 This property may also increase the risk of microcatheter obstruction during delivery.
Since PVA particles adhere to the vessel wall, blood flow can be slowed. 9 This eventually leads to an inflammatory response, foreign body reaction, and thrombosis. PVA is a non-biodegradable embolic agent that has traditionally been thought to cause permanent vascular occlusion. Fibrosis results from thrombotic organization, loss of inflammatory infiltration, and connective tissue ingrowth. However, luminal recanalization after PVA embolization has also been reported, which may be due to thrombus resorption or capillary regrowth resulting from angiogenesis and angiogenesis within the organized thrombus.
Before using PVA as the embolization material, granular PVA should be redissolved to achieve radiographic visualization during administration for relaxation. This can be achieved by adding a contrast agent, 60% barium sulfate, or tantalum powder. To reduce particle aggregation, albumin, dextran, anhydrous ethanol, or absorbable gelatin foam can be added to brine. PVA embolization uses a blood flow guiding technique and is performed under DSA fluoroscopy guidance. Therefore, during embolization, it is necessary to administer under the supervision of DSA to quickly identify the timing of anterograde blood flow slowdown and vascular occlusion. Failure to recognize that the slowing of blood flow and the change in direction can increase the likelihood of non-target embolization due to the backflow of particles out of the target vessel. Considering the tendency of these particles to aggregate, arterial occlusion may occur faster than expected. In addition, it is recommended to flush the catheter frequently to minimize the possibility of catheter occlusion.
PVA is used where permanent embolization is required. Generally, this includes gastrointestinal or internal bleeding secondary to trauma, anticoagulation, etc.; therapeutic or preoperative tumor embolization; and uterine fibroid embolization (uterine artery embolization).
The reported complications associated with the use of PVA granules for embolization are usually related to the organ and pathology of the embolization, rather than the embolization agent itself. However, complications associated with PVA properties can occur, and are often a function of flow. As previously noted, PVA granules properties can cause granules to agglomerate, leading to proximal embolization, and potentially to subsequent recanalization and surgical failure. Avoiding granular agglomeration and non-targeted embolization requires attention to detail when preparing and delivering PVA.
1. Tubbs RK. Sequence distribution of partially hydrolyzed polyvinyl acetate. J Polym Sci Part A-1: Polym Chem.
2. Baker MI, Walsh SP, Schwartz Z, et al. A review of polyvinyl alcohol and its uses in cartilage and orthopedic applications. J Biomed Mater Res B Appl Biomater.
3. Grindlay JH, Clagett OT. A plastic sponge prosthesis for use after pneumonectomy; preliminary report of an experimental study. Proc Staff Meets Mayo Clin.
4. Tadavarthy SM, Knight L, Ovitt TW, et al. Therapeutic transcatheter arterial embolization. Radiology.
5. Tadavarthy SM, Moller JH, Amplatz K. Polyvinyl alcohol (Ivalon): a new embolic material. Am J Roentgenol Radium Ther Nucl Medina.
6. Siskin GP, Englander M, Stainken BF, et al. Embolic agents used for uterine fibroid embolization. AJR Am J Roentgenol.
7. Derdeyn CP, Moran CJ, Cross DT, et al. Polyvinyl alcohol particle size and suspension characteristics. Am J Neuroradiol.
8. Choe DH, Moon HH, Gyeong HK, et al. An experimental study of embolic effect according to infusion rate and concentration of suspension in transarterial particulate embolization. Invest Radiol.
9. Germano IM, Davis RL, Wilson CB, et al. Histopathological follow-up study of 66 cerebral arteriovenous malformations after therapeutic embolization with polyvinyl alcohol. J Neurosurg.
10. Castaneda-Zuniga WR, Sanchez R, Amplatz K. Experimental observations on short and long-term effects of arterial occlusion with Ivalon. Radiology.
11. White R, Stranberg JV, Gross G, et al. Therapeutic embolization with long-term occluding agents and their effects on embolized tissue. Radiology.
12. Link DP, Strandberg JD, Virmani R, et al. Histopathologic appearance of arterial occlusions with hydrogel and polyvinyl alcohol embolic material in domestic swine. J Vasc Interv Radiol.
13. Tomashefski JF, Cohen AM, Doershuk CF. Long-term histopathologic follow-up of bronchial arteries after therapeutic embolization with polyvinyl alcohol (Ivalon) in patients with cystic fibrosis. Hum Pathol.
