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Review |
1 All authors: Division of Vascular and Interventional Radiology, Institute for Vascular Health and Disease, Albany Medical College, A-113, 47 New Scotland Ave., Albany, NY 12208.
Received December 22, 1999;
accepted after revision February 10, 2000.
Address correspondence to G. P. Siskin.
Introduction
 Top Introduction Polyvinyl AlcoholThe Role of Polyvinyl...GelfoamThe Role of Gelfoam...ConclusionReferences |
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The technique and materials used during uterine fibroid embolization are often part of an interventional radiologist's standard repertoire. Once percutaneous access is gained in the common femoral artery, the right- and left-sided uterine arteries are selectively catheterized. An embolic agent is then injected into the vessels, resulting in arterial occlusion and fibroid infarction (Fig. 1A,1B,1C,1D,1E). Polyvinyl alcohol has been the most commonly used embolic agent during uterine fibroid embolization and has been associated with the clinical and imaging success touted by proponents of the procedure [2,3,4,5,6]. At the same time, some investigators promote Gelfoam (Pharmacia and Upjohn, Kalamazoo, MI) as an alternative agent because, historically, it has been associated with clinical success, fertility preservation, and the ability of the uterus to maintain a full-term gestation after embolization [7,8].
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Many interventional radiologists have successfully included uterine fibroid embolization as an integral part of their daily practice. As both gynecologists and patients seek information about embolization, they often ask questions about the historical uses of embolic agents, the clinical success of uterine fibroid embolization with selected embolic agents, and the potential complications related to the procedure and embolic agent. With this in mind, we prepared the following review in an attempt to answer these and other questions regarding the historical and current use of polyvinyl alcohol and Gelfoam throughout the body and specifically in the pelvis for uterine fibroid embolization and other applications.
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TopIntroductionPolyvinyl AlcoholThe Role of Polyvinyl...GelfoamThe Role of Gelfoam...ConclusionReferences |
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The preparation of polyvinyl alcohol for use as an embolic agent first involves its conversion into a foam that can absorb water and become readily compressible [14]. Once the compressed foam is dried, it retains its compressed shape but when placed into solution, resumes its original shape [14]. Particles are prepared by rasping or blending a compressed block of polyvinyl alcohol or punching out polyvinyl alcohol plugs [14,15,16]. The resulting shavings or particles are passed through sieves with sequentially smaller holes to separate them into various sizes (Mangin S, personal communication). One potential problem with this method is that the irregular shape of the polyvinyl alcohol particles may allow large particles to pass through small holes depending on the orientation of a particular particle as it passes through the holes [15]. This problem was responsible for the variability in size and shape that was seen in early particle preparations, before changes were made in the manufacturing process to ensure size uniformity [17].
The first successful use of polyvinyl alcohol as an embolic agent was reported by Tadavarthy et al. [13, 14] in two studies of patients with cervical carcinoma, hemangiosarcoma of the liver, hemangioendothelioma of the neck and forehead, and an arteriovenous malformation of the spine. Since then, polyvinyl alcohol has been successfully used to embolize vessels in patients with a variety of disorders including head and neck arteriovenous malformations and tumors [18], lower gastrointestinal bleeding [19], hepatic neoplasms [20], bone metastases from renal cell carcinoma [21], and hemoptysis caused by cystic fibrosis [22].
Before its use in uterine fibroid embolization procedures, polyvinyl alcohol was not routinely used during pelvic embolization procedures. In men, polyvinyl alcohol has been successfully used in the treatment of both high-flow and low-flow priapism [23]. In women, Pisco et al. [24] reported the use of polyvinyl alcohol in the treatment of hemorrhage caused by pelvic neoplasms; the researchers found that when compared with Gelfoam, polyvinyl alcohol particles resulted in better control of bleeding and fewer recurrences. Poppe et al. [25] reported the successful use of polyvinyl alcohol particles to control bleeding associated with a uterine arteriovenous malformation and preservation of a patient's ability to conceive and carry a pregnancy to term.
Depending on the disease process and the involved organ, the desired level of occlusion (i.e., proximal or distal) will determine the particle size selected for a given embolization procedure. Generally, the use of small particles will result in a more distal occlusion, increasing the risk for end-organ infarction. However, the tendency of polyvinyl alcohol particles to clump together often makes the effective size of this agent larger than that of the individual particles, which may account for a proximal occlusion during embolization [26]. Reducing the tendency for particulate aggregation, with dilution and slow infusion, may lead to a more distal embolization [26]. The optimum particle size for uterine fibroid embolization has not been established, but most centers are using particles measuring 350-500 or 500-710 µ in diameter [2,3,4,5,6].
The histologic effects of polyvinyl alcohol on embolized blood vessels have been revealed in several studies. Initially, polyvinyl alcohol particles adhere to the vessel wall, leading to slow flow in the vessel [27]. Ultimately, this leads to thrombosis and inflammatory reactions, foreign body reactions, and focal angionecrosis of the vessel wall [17, 28,29,30,31,32,33]. Angionecrosis tends to be localized to where particles are in contact with the vessel wall and can potentially lead to perivascular extravasation of polyvinyl alcohol particles [22, 30]; however, this finding has not been consistently observed [17]. The foreign body reaction induced by polyvinyl alcohol has been reported to persist as long as 28 months after embolization [22].
Polyvinyl alcohol is considered by many to be a permanent embolic agent because it is not biodegradable. The long-term appearance of intravascular polyvinyl alcohol particles was studied by Davidson and Terbrugge [31] in a patient with a facial vascular malformation that was resected 8 years after embolization. In this patient, no evidence of particle fragmentation was found, and the only change in particle morphology was slight calcification. However, polyvinyl alcohol particles are not consistently found in specimens obtained after embolization [32]. Some reports have theorized that this may be caused by the distal migration of particles [17, 29]. Other researchers have said that conflicting findings may be caused by the use of H and E staining during the preparation of pathologic slides; polyvinyl alcohol particles are best seen with the Verhoeff-van Gieson stain [33].
The reported duration of vascular occlusion induced by polyvinyl alcohol has been variable. Some investigators reported occlusions lasting for at least several months [14, 22, 28]. A persistent occlusion will occur with the organization of thrombus, disappearance of inflammatory infiltrate, and ingrowth of connective tissue into the particles, resulting in fibrosis [22, 28, 29]. Luminal recanalization after embolization with polyvinyl alcohol has been reported as well [17, 22, 31]. Proposed mechanisms for recanalization have included angioneogenesis and capillary regrowth caused by vascular proliferation inside the organized thrombus [17, 22] and resorption of the thrombus found between clumps of polyvinyl alcohol in the lumen of an embolized vessel after the resolution of inflammation [17, 30, 34]. Recanalization does seem to occur in the portion of the vessel lumen previously containing thrombus and not in the portion containing polyvinyl alcohol particles [30].
Complications relating to the use of polyvinyl alcohol particles as an embolic agent have been reported. The inclusion of small particles in early preparations of polyvinyl alcohol increased the risk for inadvertent end-organ injury. Specific complications have included facial nerve palsy after external carotid artery embolization [35], paralysis after bronchial artery embolization [36], bladder or muscle necrosis and paralysis after pelvic embolization [37, 38], and two infant deaths after the embolization of hepatic arteriovenous malformations [39]. Both of the deaths were attributed to pulmonary hypertension, presumably caused by particles passing through the malformation and into the pulmonary artery circulation. In response to these reports, manufacturing techniques were modified to minimize the number of particles smaller than the sizes specified for a given preparation of polyvinyl alcohol [15, 39].
The Role of Polyvinyl Alcohol in Uterine Fibroid Embolization
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TopIntroductionPolyvinyl AlcoholThe Role of Polyvinyl...GelfoamThe Role of Gelfoam...ConclusionReferences |
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Since 1997, published reports [3,4,5,6] have confirmed the initial findings of Ravina et al. [2]. The most common indication for uterine fibroid embolization is abnormal or heavy menstrual bleeding [3,4,5,6]. Improvement of symptoms has been reported in 80-96% of patients undergoing uterine fibroid embolization with polyvinyl alcohol particles [3,4,5]. This procedure has also been associated with uterine volume reductions of 40-48% and fibroid volume reductions of 46-78% [3,4,5] (Fig. 1A,1B,1C,1D,1E). Recently, midterm results have revealed the continued success of this procedure, with 81% of patients reporting improvement of their symptoms at a mean follow-up of 16 months after embolization [6]. Complications resulting in significant patient morbidity or requiring additional therapeutic procedures are rare, with an estimated rate of occurrence of less than 2% [5].
Siskin et al. [32], Aziz et al. [34], and McLucas et al. [40] specifically studied the histologic effects observed after uterine artery embolization with polyvinyl alcohol particles. Both Aziz et al. and McLucas et al. noted that the particles did not occupy the entire lumen of the embolized vessel. Instead, a foreign body reaction initiates platelet aggregation and thrombus formation in the intraluminal lattice of polyvinyl alcohol particles. It is the thrombus formation that results in arterial occlusion and ultimately leads to interstitial edema within the fibroid followed by ischemic necrosis and hyalinization [32, 40]. The myometrium adjacent to a fibroid embolized with polyvinyl alcohol particles has been noted to be viable but edematous and chronically inflamed [40].
Luminal recanalization may represent one of the possible causes of treatment failure after uterine artery embolization [6]. Because the particles do not occupy the entire vessel lumen, partial recanalization of the thrombus is possible and has been reported [6, 34]. Treatment failure, which has been reported in 4-19% of patients, may be attributed to other factors including incomplete or unilateral embolization [6], adenomyosis [6, 41], large fibroids (McLucas B et al., Society for Minimally Invasive Therapy meeting, September 1999), persistent collateral supply to the uterus and fibroids [42], and sarcomatous degeneration (Pron G et al., presented at the SMIT meeting, September 1999).
Aziz et al. [34] also noted that after uterine artery embolization particles can be found in the arteries of the parametrium and outer myometrium, which would likely permit continued endometrial function after the recanalization of larger vessels. However, inadvertent end-organ damage, in this case involving the uterus, can possibly result in uterine ischemia [4] or endometrial infection [3], both of which may potentially require a hysterectomy for treatment. A single case of infection resulting in sepsis and death has been reported after uterine fibroid embolization [43].
Particles may also be found in the mesovarium and mesosalpinx after uterine artery embolization, which may contribute to potential ovarian and/or tubal dysfunction after uterine artery embolization by reducing blood flow to the adnexa [34]. Permanent amenorrhea, a rare event occurring in fewer than 2% of patients, has been reported after uterine artery embolization with polyvinyl alcohol particles and has been attributed to diminished ovarian perfusion or infarction [6]. However, in the absence of a documented change in follicle-stimulating hormone levels before and after embolization, the true-cause-and-effect relationship between a polyvinyl alcohol embolization and premature menopause remains unproven at this time. Other rare complications of uterine fibroid embolization with polyvinyl alcohol particles include transcervical expulsion of an embolized fibroid [6, 44], a small-bowel infection caused by necrosis of an adjacent pedunculated fibroid after embolization (Ravina JH et al., SMIT meeting, September 1998), and fatal pulmonary embolism (Lanocita R et al., SMIT meeting, September 1999).
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TopIntroductionPolyvinyl AlcoholThe Role of Polyvinyl...GelfoamThe Role of Gelfoam...ConclusionReferences |
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Gelfoam, a water-insoluble hemostatic material prepared from purified skin gelatin (a nonantigenic carbohydrate), is frequently used as a biodegradable, intravascular embolic agent [45]. Correll and Wise [46] were the first to report the hemostatic properties of Gelfoam and its use in obtaining hemostasis during surgery. It has been reported that in this setting, Gelfoam promotes hemostasis by hastening the development of and providing structural support to thrombus [47].
In 1964, Gelfoam was first used as an intravascular agent for occluding a traumatic carotid cavernous fistula [48]. Since then, Gelfoam has been successfully used as an embolic agent for a variety of indications including renal cell carcinoma before resection [49], bone cancers [50], gastrointestinal bleeding [51], hemobilia [52], and arterial injury caused by trauma [53].
In 1979, Heaston et al. [54] described the first use of Gelfoam in the pelvis for postpartum hemorrhage after bilateral hypogastric artery ligation. Since then, postpartum hemorrhage [55,56,57], postoperative hemorrhage [58], arteriovenous fistulas [59], cervical ectopic pregnancies [60], and bleeding caused by pelvic malignancies [61] have all been effectively treated with Gelfoam embolization of the uterine or internal iliac arteries.
Gelfoam is currently available in two forms: a powder containing particles ranging in diameter from 40 to 60 µ or a sheet from which sections of various sizes can be cut [45]. Gelfoam, like polyvinyl alcohol, is not radiopaque and is typically mixed with iodinated contrast material before injection. The small size of the particles in Gelfoam powder increases the risk for ischemia caused by distal artery occlusion [37]. The pledgets cut from a sheet of Gelfoam are typically larger and result in a more proximal artery occlusion [45]. An additional technique is to create a Gelfoam slurry by mixing pledgets between two syringes via a three-way stopcock. This method will decrease the size of the injected Gelfoam and allow a more distal delivery than that achieved with pledgets.
Histologically, Gelfoam initiates an acute full-thickness necrotizing arteritis of the arterial wall, with local edema and interruption of the elastic interna [49, 62]. Within 6 days after Gelfoam administration, an acute inflammatory reaction and a foreign body reaction with the appearance of giant cells have been observed [63]. These reactions induce thrombus formation, the residue of which can be found for several months [64]. However, Light and Prentice [63] noted that the cellular reaction initiated by Gelfoam abated by day 30 and no Gelfoam or thrombus was seen at day 45, which served as the basis for the premise that Gelfoam has the potential to induce a shortterm occlusion with minimum tissue reaction. Studies have revealed that the resorption time for Gelfoam typically occurs within 7-21 days of embolization [64, 65]. However, when used for surgical hemostasis, unabsorbed gelatin sponges have been found to remain in wounds 2-12 months after implantation [66].
The arterial occlusion induced by Gelfoam is often recanalized within weeks to months of the embolization procedure. In animals, the time to recanalization after a Gelfoam embolization has ranged from 3 weeks to 4 months [64, 65, 67]. Bracken et al. [49] found arterial recanalization in two patients who underwent embolization for renal cell carcinoma after 5 and 6 months. However, persistent occlusion after Gelfoam embolization has also been observed [49, 68]. Jander and Russinovich [68] found that the permanence of Gelfoam occlusion may be related to the amount of Gelfoam used, stating that if a bleeding vessel was densely packed with Gelfoam, the occlusion would be permanent.
Ischemic and infectious complications have been reported when using Gelfoam as an embolic agent. Ischemic complications associated with the use of Gelfoam in the pelvis include buttock ischemia [54], lower limb paresis [37], and bladder gangrene [69]. These complications have been attributed to the small size of the embolic agent used, prompting recommendations that Gelfoam powder not be used in the nonmalignant setting [42, 70]. Infectious complications, including at least three pelvic abscesses, have been reported after pelvic embolization with Gelfoam [58, 71, 72]. In addition, hepatic infections resulting in abscess formation have been reported when using Gelfoam during hepatic arterial chemoembolization procedures [73]. These infections may be caused by the potential for Gelfoam to retain enough air bubbles to support aerobic organisms [66]. Because of this potential, early surgical articles recommended using as little Gelfoam as possible, avoiding prolonged exposure of Gelfoam to contaminated air, and thoroughly compressing the Gelfoam so that large air bubbles are eliminated and not introduced into a patient [66]. These recommendations remain important when using Gelfoam as an embolic agent.
The Role of Gelfoam in Uterine Fibroid Embolization
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TopIntroductionPolyvinyl AlcoholThe Role of Polyvinyl...GelfoamThe Role of Gelfoam...ConclusionReferences |
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It is not yet certain whether fertility and the ability of the uterus to successfully maintain an intrauterine gestation are preserved when polyvinyl alcohol is used for uterine fibroid embolization. To date, at least 14 pregnancies in 1007 patients have been reported after the use of polyvinyl alcohol during uterine fibroid embolization (Forman RG et al., SMIT meeting, September 1999). These findings imply that uterine artery embolization performed with polyvinyl alcohol does not definitively preclude future pregnancy. The problem with studying absolute numbers of pregnancies after uterine fibroid embolization is that the true number of patients wishing and actively attempting to become pregnant after this procedure is small compared with the number of patients undergoing this procedure. Patients considering treatment for symptomatic uterine fibroids are often perimenopausal and do not desire children [2,3,4,5,6]. Because of this fact and the reluctance of many centers to perform this procedure on patients desiring future children, the pregnancy rate after uterine fibroid embolization with polyvinyl alcohol is difficult to ascertain.
Recently, the potential for Gelfoam to be used as an embolic agent during uterine fibroid embolization has been explored because of its proven ability to provide effective pelvic vascular occlusion while preserving a patient's ability to maintain an intrauterine gestation. To date, the preliminary results from two studies supporting the use of Gelfoam during uterine fibroid embolization have been presented at national meetings. Katz et al. [7] presented the results of 10 patients who underwent uterine fibroid embolization: five patients received polyvinyl alcohol particles and five patients received Gelfoam. This study found similar results in both patient populations in terms of symptomatic relief and fibroid and uterine volume reduction. Mizukami et al. [8] used Gelfoam in 18 patients and reported an 89% rate of symptomatic improvement and a mean reduction in uterine volume of 45%. Given the fact that these are preliminary results from studies involving small patient populations, larger studies with defined follow-up must be performed to determine the clinical efficacy of Gelfoam in uterine fibroid embolization. In addition, even in the presence of clinical data supporting the use of Gelfoam, pathologic studies revealing the ability of Gelfoam to cause fibroid infarction, the desired effect of this procedure, would be important before the widespread use of Gelfoam can be advocated. Finally, pregnancy after uterine artery embolization with Gelfoam must be shown and reported before Gelfoam can be recommended as the embolic agent of choice in patients desiring to preserve their fertility options after uterine fibroid embolization.
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TopIntroductionPolyvinyl AlcoholThe Role of Polyvinyl...GelfoamThe Role of Gelfoam...ConclusionReferences |
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With the increasing interest to broaden the application of this procedure to younger patients wishing to preserve their childbearing options, future studies must be performed to determine the true potential for future pregnancies after embolization. At the present time, pregnancies described after uterine fibroid embolization with polyvinyl alcohol show that fertility is potentially preserved. However, if clinical efficacy and fertility preservation can be proven after the use of Gelfoam in uterine fibroid embolization, it may represent an attractive option in patients desiring future children given its resorbability and its proven success in preserving the ability of an embolized uterus to maintain intrauterine gestation. A summary of the characteristics of polyvinyl alcohol and Gelfoam can be found in Table 1.
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As uterine fibroid embolization evolves as an accepted treatment option for symptomatic uterine fibroids, the role of the interventional radiologist as a primary caregiver for this patient population is evolving as well. By developing and maintaining a comprehensive fund of knowledge regarding the technique and materials used during this procedure, interventional radiologists can play an integral role in educating referring gynecologists and in counseling individual patients regarding the treatment options and applicability of uterine fibroid embolization as a treatment for the common problem of uterine fibroids.
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TopIntroductionPolyvinyl AlcoholThe Role of Polyvinyl...GelfoamThe Role of Gelfoam...ConclusionReferences |
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