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Liquid embolic agents are also classified in the category of flow-directed
agents, although this can be somewhat variable based on the agent and the
amount of dilution used during administration. Sclerosants such as ethanol
have been used successfully as an embolic agent for certain tumors and
vascular malformations, whereas more mild agents such as sodium tetradecyl
sulfate have been used for venous applications such as varicose veins,
varicoceles, and pelvic congestion syndrome. Other sclerosants include
hypertonic glucose, doxycycline, and OK-432. Agents such as N-butyl
cyanoacrylate and Onyx (Fig. 1.7) are playing a growing role in the treatment
of cerebral and peripheral arteriovenous malformations.
In conclusion, embolotherapy has gone through significant changes
since its development in the late 1960s and early 1970s. The indications for
these procedures have greatly expanded, as have the agents available for us.
Although classifying these agents does not necessarily change the way they
are used, it is important to understand how they work and when they should
potentially be used. As new agents are introduced and new indications are
established, modern interventional radiology will continue to evolve,
resulting in the reorganization of the classification schemes used for
embolization.
REFERENCES
1. Vaidya S, Tozer KR, Chen J. An overview of embolic agents. Semin
Intervent Radiol. 2008;25:204–215.
2. Vitek JJ, Smith MJ. The myth of the Brooks method of embolization: a
brief history of the endovascular treatment of carotid-cavernous sinus
fistula. J Neurointerv Surg. 2009;1:108–111.
3. Doppman JL, Di Chiro G, Ommaya A. Obliteration of spinal-cord
arteriovenous malformation by percutaneous embolization. Lancet.
1968;1:477.
4. Newton TH, Adams JE. Angiographic demonstration and nonsurgical
embolization of spinal cord angioma. Radiology. 1968;91:873–876.
5. Rosch J, Dotter CT, Brown MJ. Selective arterial embolization. A new
method for control of acute gastrointestinal bleeding. Radiology.
1972;102:303–306.
6. Rosch J, Keller FS. Historical account: cardiovascular interventional
radiology. In: Lanzer P, ed. Catheter-Based Cardiovascular
Interventions: A Knowledge-Based Approach. Berlin, Germany:
Springer-Verlag; 2013:15–26.
7. Speakman TJ. Internal occlusion of a carotid-cavernous fistula. J
Neurosurg. 1964;21:303–315.
8. Tadavarthy SM, Knight L, Ovitt TW, et al. Therapeutic transcatheter
arterial embolization. Radiology. 1974;111:13–16.
9. Serbinenko FA. Balloon catheterization and occlusion of major cerebral
vessels. J Neurosurg. 1974; 41:125–145.
10. Gianturco C, Anderson JH, Wallace S. Mechanical devices for arterial
occlusion. Am J Roentgenol Radium Ther Nucl Med. 1975;124:428–438.
11. Rose SC. Mechanical devices for arterial occlusion and therapeutic
vascular occlusion utilizing steel coil technique: clinical applications.
AJR Am J Roentgenol. 2009;192:321–324.
12. Guglielmi G. History of the genesis of detachable coils. J Neurosurg.
2009;111:1–8.
13. Wang W, Li H, Tam MD, et al. The Amplatzer Vascular Plug: a review
of the device and its clinical applications. Cardiovasc Intervent Radiol.
2012;35:725–740.
14. Guimaraes M, Wooster M. Onyx (ethylene-vinyl alcohol copolymer) in
peripheral applications. Semin Intervent Radiol. 2011;28:350–356.
15. Laurent A, Beaujeux R, Wassef M, et al. Trisacryl gelatin microspheres
for therapeutic embolization, I: development and in vitro evaluation.
AJNR Am J Neuroradiol. 1996;17:533–540.
16. Lewis AL, Gonzalez MV, Lloyd AW, et al. DC Bead: in-vitro
characterization of a drug-delivery device for transarterial
chemoembolization. J Vasc Interv Radiol. 2006;17:335–342.
17. Yan ZP, Lin G, Zhao HY, et al. An experimental study and clinical pilot
trials on yttrium-90 glass microspheres through the hepatic artery for
treatment of primary liver cancer. Cancer. 1993;72:3210–3215.
18. Weng L, Rostambeigi N, Zantek ND, et al. An in situ forming
biodegradable hydrogel-based embolic agent for interventional
therapies. Acta Biomater. 2013;9:8182–8191.
19. Owen RJ, Nation PN, Polakowski R, et al. A preclinical study of the
safety and efficacy of Occlusin™ 500 artificial embolization device in
sheep. Cardiovasc Intervent Radiol. 2012;35:636–644.
20. Davidson GS, Terbrugge KG. Histopathologic long-term follow-up after
embolization with polyvinyl alcohol particles. Am J Neuroradiol.
1995;16:843–846.
21. 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. 1992;76:607–614.
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follow-up of bronchial arteries after therapeutic embolization with
polyvinyl alcohol (Ivalon) in patients with cystic fibrosis. Hum Pathol.
1988;19:555–561.
23. 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. 1996;7:897–905.
24. Siskin GP, Englander M, Stainken BF, et al. Embolic agents used for
uterine fibroid embolization. AJR Am J Roentgenol. 2000;175:767–773.
25. Abada HT, Golzarian J. Gelatin sponge particles: handling
characteristics for endovascular use. Tech Vasc Interv Radiol.
2007;10:257–260.
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derived from gelatin for use in hemostasis. J Neurosurg. 1945;2:435–
455.
27. Barth KH, Strandberg JD, White RI. Long-term follow-up of
transcatheter embolization with autologous clot, oxycel, and gelfoam in
domestic swine. Invest Radiol. 1977;12:273–280.
28. Gold RE, Grace DM. Gelfoam embolization of the left gastric artery for
bleeding ulcer: experimental considerations. Radiology. 1975;116:575–
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abdominal, retroperitoneal, and pelvic hemorrhage. Radiology.
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interferon. Pharm Res. 1989;6:422–427.
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gelatin sponge particles in a porcine kidney model. J Vasc Interv Radiol.
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should be used when? Part 1: large-vessel embolization. Semin Intervent
Radiol. 2009;26:352–357.
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should be used when? Part 2: small-vessel embolization. Semin Intervent
Radiol. 2010;27:99–194.
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Tech Vasc Interv Radiol. 2007;10:248–256.
35. Weng L, Rusten M, Talaie R, et al. Calibrated bioresorbable
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P
Section B Coils and Plugs
2
Pushable Coils
Keigo Osuga
ushable coils have been widely used for mechanical occlusion of
peripheral and visceral vessels because they are relatively inexpensive,
easily available, and simple to handle. Since the original stainless steel
coils were developed in the mid-1970s,1 refinements have been made in the
materials and designs used for pushable coils, including the recent addition of
hydrogel coating technology.2 Similarly, detachable microcoils, although
they are expensive, have been also increasingly indicated in peripheral
vessels because they can be repositioned and offer more precise coil
deployment. However, pushable coils still remain the standard tool for
indications requiring mechanical embolic agents and can save both cost and
procedure time.
DEVICE DESCRIPTION
Pushable fibered coils are composed of metallic springs with inert synthetic
fibers, such as polyester or nylon, attached to the spring to induce thrombosis
around the coil. Pushable coils are supplied in a straight cartridge and are
typically loaded into the catheter using a guidewire or the provided mandrel.
The loop sizes, lengths, thickness, and configurations vary among pushable
coil designs (Fig. 2.1). Two major options are 0.035-in coils for delivery
through 4-Fr to 5-Fr catheters and 0.018-in microcoils for delivery through
microcatheters for more selective embolization.3 Platinum coils are softer and
more radiopaque than stainless steel or Inconel alloy coils. Because stainless
steel is responsible for severe local artifacts on magnetic resonance (MR)
imaging, MR conditional coils made of platinum and Inconel alloy are
currently preferred. Long pushable platinum coils or microcoils with an
extended lengths are pliable and pack easily into a dense coil mass.4 Most
recently, hydrogel-coated pushable coils (AZUR Pushable 35 and 18;
Terumo Medical Corporation, Somerset, New Jersey) have become available,
and they have the advantage of greater filling volume, independent of
thrombus formation.
2
TECHNIQUE
As a rule, the coil delivery process should be carefully monitored under
fluoroscopy. The coil should be appropriately sized according to the vessel
size and anatomy. The first coil should be approximately 20% larger in size
than the vessel diameter to minimize the risk of coil migration. The delivery
catheter should be accurately positioned within the target vessel. The coaxial
technique, using a guide catheter and a coaxial delivery catheter, gives
stability and control for coil deployment. A standard catheter can also serve
as a guide catheter to deploy microcoils through a microcatheter. There are
two methods for delivery of pushable coils. The first method is the “push”
technique, in which the coil is pushed by a floppy guidewire or designated
pusher wire. The other method is the “flush” technique, in which the coil is
forced out of the catheter by saline flush. Although this technique can speed
up the delivery process, it should be avoided when precise coil placement is
critical and when coil dislodgement is a concern, especially for the first or
last coil.
Clinical Application
Pushable coils are mechanical embolic agents used both in arteries and veins
for various indications: to control bleeding; to occlude vascular lesions such
as aneurysms, varices, and arteriovenous fistulas (AVFs); and to redistribute
blood flow to protect nontarget vessels. The details for each indication will be
described in later chapters. In general, to occlude a terminal artery that is
unlikely to have associated collateral circulation, coils are simply pushed out
at, or just before, the site to be occluded. In a larger vessel, proximal coil
occlusion may allow persistent flow distal to the site of occlusion via
collaterals but at a lower pressure than before embolization. For example,
proximal splenic artery embolization is an accepted technique in the setting
of traumatic splenic injury to control bleeding. If significant retrograde filling
of an embolized vessel(s) is likely via collaterals, the sandwich technique is
effective; that is, coils should be placed both proximal and distal to arterial
pathology such as a wide-necked aneurysm or pseudoaneurysm (Fig. 2.2).
Proximal coil embolization is not effective for arteriovenous malformations
(AVMs), as it not only results in persistent flow to the nidus of the AVM via
collaterals but also sacrifices the main arterial access for subsequent
interventions. For pulmonary AVMs, pushable coils are often used to occlude
the distal feeding artery as close to the venous sac as possible.5 Finally, for
the purpose of protective embolization, the right gastric and gastroduodenal
arteries are often occluded with coils before liver-directed therapy such as
arterial infusion chemotherapy or radioembolization for liver tumors.
2
Potential Complications
Technical failures and complications can occur during or after coil
embolization, although few are specific to pushable coils. First, the coil
thickness, lumen of the delivery catheter, and size of the pusher wire should
be properly matched, or else the coil can become stuck inside the catheter.
Catheters with a side hole should not be used for delivery because the coil
can get caught in the side hole. Sizing coils is important because
inappropriately sized coils may migrate distally into nontarget vessels if too
small or deployed in a straight, poorly controlled manner if too large. Coils
can potentially migrate upon catheter removal if the proximal end of the coil
remains inside the catheter. Reversal of blood flow can also cause migration
of a short straight coil placed in an arterial arcade. Retrieval devices such as a
loop snare and basket should be always available to retrieve migrated coils.
Rarely, coils can cause vessel wall rupture when the coil is oversized or if the
vessel wall is very fragile due to severe inflammation near a
pseudoaneurysm. Late recanalization can occur through the coils when the
target vessel is inadequately packed or if the patient is coagulopathic.
Clinically, ischemic adverse events can occur as a result of intended or
nontarget embolization. When adequate perfusion distal to the site of
occlusion does not remain via collaterals, organ infarction may occur in the
corresponding territory, such as the kidney and lower intestinal tracts.
6
TIPS AND TRICKS
• It is critical to find suitable anatomy and adequate vessel length for
safe coil deployment.
• The catheter chosen for coil delivery is as important as the coils
selected for embolization. A coaxial technique helps to control coil
delivery and prevent coil elongation.
• Adjunctive techniques may be necessary to prevent coil migration,
especially in a large high-flow vessel. If there is a side branch close to
the target vessel, the initial part of the first coil can be anchored into
the side branch and then deployed in the target vessel as the delivery
catheter is withdrawn7 (Fig. 2.3). When there is no suitable anchor
branch, oversized high-radial force coils can be initially deployed to
provide a scaffold for subsequent softer platinum coils (scaffold
technique).
7
• Proximal balloon occlusion is useful for temporary blood flow arrest
that will reduce the risk of coil migration.
• In suitable vessels, Amplatzer Vascular Plugs (St. Jude Medical, Inc.,
St. Paul, Minnesota) can be deployed initially with coils added
proximally to the plug. In this case, the plug will help prevent coil
migration.
8