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Hardware forInterventions
VishnuPrasadPulappadi, AbhinavBansal,
andS.H.Chandrashekhara
8
Key Messages
1. Interventional radiologists must be familiar with all the
hardware available in the armamentarium.
2. Choosing the correct hardware is a paramount step in the
technical success of the procedures.
3. The technical knowledge of hardware makes interventional radiology procedures less time-consuming with
reduced complications.
4. The inadvertent complications can be addressed if you
have essential hardware at our disposal.
8.1 Introduction
Interventional radiology (IR) is an ever-expanding speciality
that helps in the management of a wide range of diseases
using minimally invasive procedures. The availability of
proper hardware is crucial for performing such procedures.
Interventional radiologists must be familiar with all the
devices available in the armamentarium.
8.2 Puncture Needles
Needles may be either single piece bevel-tipped access
needles, or a coaxial system in which there is an outer cannula
with inner stylet. A single piece needle has a hollow core and
a beveled tip that allows easy access to vessels. The bevel
helps in steering the needle as it bends away from the bevel.
The needle also has a small notch on the hub that corresponds
to the position of the bevel. A trocar needle consists of a coaxial system in which there is an outer cannula that can be beveled or non-beveled, and an inner removable sharp three-sided
needle. The outer blunt cannula can be used for introducing
guide wire after removing the inner stylet. Both the outer cannula and inner stylet are beveled in the Chiba needle, which
helps in better steering as compared to the trocar needle [1].
Micropuncture needle and dilator system are used in cases
with difcult access (e.g., undilated biliary system, small vessel, antegrade femoral puncture) to decrease the rate of access
site complications. The initial puncture is performed with a
21G needle which is then exchanged with a coaxial dilator
over a 0.018-inch access guidewire. This can be further
exchanged for a larger sheath over a 0.035-inch wire.
8.3 Guidewires
Puncture needles are commonly used to gain access in to a
vessel, cavity, or ductal system. Needle diameter is conventionally measured in Gauge (G) with lower Gauge representing larger size needle. Guidewire is introduced through the
lumen of the needle upon gaining access. In general, a 0.018inch wire passes through 22G or larger needles whereas, a
0.035-inch wire requires a 19G or larger needle.
V. P. Pulappadi
Kovai Medical Center and Hospital, Coimbatore, India
A. Bansal
Department of Radiodiagnosis and Interventional Radiology, All
India Institute of Medical Sciences, Delhi, India
S. H. Chandrashekhara (
Department of Radiodiagnosis and Interventional Radiology, All
India Institute of Medical Sciences, IRCH, Delhi, India
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024
S. H. Chandrashekhara (ed.), Textbook of Interventional Radiology, https://doi.org/10.1007/978-981-97-9601-4_8
*)
Guidewires are used to gain access into the vascular, biliary,
or pelvicalyceal system and also for subsequent guidance.
They also allow the exchange of various devices and catheters. There are numerous types of wires based on properties
such as diameter (measured in inches), stiffness, length, and
hydrophilicity. Guidewires are available in sizes ranging
from 0.007 to 0.038inches, with 0.014, 0.018, and 0.035inch wires being the most commonly used ones. The appropriate sized wire should be tightly matched to the end hole in
the needle/catheter for smooth movement. Hydrophilic wires
are slippery when wet and sticky when dry. They are less
thrombogenic compared to non-hydrophilic wires and are
useful in uid environment when less resistance is desired.
They are easy to manipulate especially with the help of a
torque device.
67
68
V. P. Pulappadi et al.
There are various kinds of wires used for specic
indications:
• Access wires: These are short wires with atraumatic
oppy tips used for vascular access. These are then
quickly exchanged once the access is secured. An example is the Fixed Core Wire Guide (Cook Medical).
• Maneuvre wires: These are hydrophilic wires with
curved oppy tip, which helps in manipulating them into
the blood vessel of interest. This helps in selective
cannulation with catheters. Examples include Glidewire
(Terumo) and Silverway (Asahi).
• Rail wires: These are stiff wires that provide a plat-
form for the exchange of dilators, catheters, and stents.
Such stiff wires should not be steered through tortuous
structures as it can cause injury. Examples include
Amplatz (Boston Scientic) and Rosen (Cook Medical)
wires.
• Crossing wires: These are micro guidewires (0.014″ or
0.018″) that have soft tips that help in crossing chronic
total occlusions in the lower limb arteries. They have
stainless steel proximal shafts for support and are usually
300 cm long to facilitate catheter exchanges. Examples
include Gladius & Gaia PV (Asahi) and Command
(Abbott).
Good control is required to prevent guidewire dislodge-
ment while exchanging equipment over the guidewire. The
length of the exchange guidewire should be longer than the
sum of the length of the catheter and the distance from the
puncture site to the target structure. For simplicity of calculation, the wire length should be at least twice the length of the
catheter to be exchanged [1].
8.4 Sheath System
Sheaths are devices used to maintain access into a vessel and
prevent access site injury from multiple exchanges during a
procedure. The size of the sheath represents the inner diameter in French (F), unlike catheter size which is the outer
diameter. Therefore, a 6F sheath allows the passage of a 6F
catheter or dilator through it. The outer diameter of the
sheath is 1–2F larger than the sheath size. Sheaths are color
coded according to their inner diameters (Table 8.1). The
size of the sheath for a particular procedure should be chosen
according to the size of the catheters and stents that are
required to be introduced through the sheath. A sheath is usually introduced into a vessel over a dilator that is stiff and has
a tapered edge that helps in seamless entry into a vessel. The
dilator is subsequently removed upon entry into the target
structure. Sheaths also have a hemostatic valve on the trailing end to prevent any bleeding or air embolism through the
Table 8.1 Color coding for vascular access sheaths according to their
inner diameters
Color Inner diameter (F)
Pink/red 4
Gray 5
Green 6
Orange 7
Blue 8
Black 9
Magenta 10
sheath while exchanging devices. The sheath has a side port
for contrast injection and regular ushing of the sheath to
prevent thrombus formation during a procedure [1].
There are various kinds of sheaths depending on their
lengths and shapes:
• Short sheaths: These are the most commonly used ones
for vascular access and are 10–15cm long. Short sheaths
are used for initial access prior to insertion of other specialty long sheaths. They are made of Teon and are
non-braided.
• Long sheaths: Their lengths vary from 20 to 90cm and
have stainless steel braiding to provide support and prevent kinking. These sheaths are advanced up to the major
branches of the aorta for maintaining access, for support
while advancing devices into the target vessel, and for
check angiograms during the procedure. Dedicated softtipped sheaths, such as the Flexor Ansel sheath (Cook),
help to prevent vessel injury.
• Cross over sheaths: These are 40–45cm braided long
sheaths that are used for peripheral artery interventions
via contralateral femoral access. They have curved tips
that t into the curve at the aortic bifurcation, e.g., Flexor
Balkin sheath (Cook).
• Long sheaths for neuro intervention: Conventional
long sheaths are not ideal for advancement into the internal carotid artery due to their stiff ends. Dedicated sheaths
with atraumatic oppy tips and stiff proximal end are
therefore required for neurointerventions. A few examples are Cerebase (Cerenovus), Neuron Max (Penumbra),
AXS Innity (Stryker), and Ballast (Balt).
• Radial access sheaths: These sheaths have a low prole
that facilitates easy advancement into the relatively small
caliber radial artery. They are longer than the conventional short sheath, usually 23cm in length, e.g., Prelude
Radial Sheath (Merit Medical). The long length helps to
reduce the occurrence of vasospasm in the radial artery
during catheter exchanges.
• Pedal access sheaths: These are low prole short sheaths
used for securing access in below knee run-off arteries,
e.g., Glidesheath Slender (Terumo). They are used with
micropuncture access needle and 0.018″ guidewire.
8 Hardware forInter ventions
69
• Peel away sheath: It is a modication of the regular
sheath and has two plastic wings at the extravascular end
that help in peeling apart the sheath without the need for
exchanging it over the guidewire. It is used for insertion
of mediports and tunneled lines that have bulky hubs.
8.5 Catheters
The catheter is a exible hollow tube that can be inserted into
a vessel, duct, or cavity. It consists of a tubular shaft with a
hub at the rear end and a tapered or non-tapered tip. Various
kinds of catheters are available for performing interventions
in different blood vessels. The distal tip of the catheter can be
straight or curved (with primary, secondary, and tertiary
curves). Catheters are introduced through the arterial sheath
and manipulated over guidewires to reach the target site.
Subsequently, they can be used for angiograms or administration of drugs.
Catheters are generally made of polytetrauoroethylene
(PTFE), polyethylene, nylon, silicone, polyvinyl chloride,
or a combination of these materials. Catheters intended for
different purposes may vary with respect to the material
used, diameter, length, tip shape, and side hole conguration. Selective catheters have different tip shapes and single-end hole to seek branches of the main vessel. They have
tapered tips to advance smoothly into a vessel with singleor double- wire braiding for extra torquability. The size of
the catheter is denoted using its outer diameter. It is measured in F (1F = 1/3 mm). A catheter is wider at the hub
than at the tip, and the diameter at the tip represents the
maximum diameter of the guidewire it can accommodate.
Most angiographic catheters are 4 or 5 F in size and are
passed over a 0.035 or 0.038-inch guidewire. The torsional
strength of a catheter refers to the ability to steer the catheter tip in various directions by rotating its hub. It depends
on catheter size and material and is proportional to the difference between the fourth powers of the outer and inner
diameter.
Catheter tips can have various shapes. There are straight
catheters with no curve, pigtail catheters with multiple
side holes near the catheter tip for ush aortograms, single-curve catheters, e.g., multipurpose angiographic catheters (MPAs), and complex curve catheters. Complex
curve catheters have secondary, and in some cases, tertiary
curves in addition to the primary curves and can be subdivided into double curve catheters (e.g., renal double curve
catheter, cobra catheter) and reverse curve catheters (e.g.,
Simmons, Roberts Uterine catheter). Both pigtail and
straight catheters have multiple side holes, which help in
injecting a large volume of contrast at a high rate.
Commonly used angiographic catheters and their uses are
listed in Table8.2 [1, 2].
Catheters have various technical properties:
Table 8.2 Various angiographic catheter shapes and their common
uses
Catheter shape Common indications Representative image
Pigtail –Flush aortogram
Marker pigtail –Measurement of
required length of stent
during transjugular
intrahepatic
portosystemic shunt
(TIPS) creation
Angled pigtail –Pulmonary angiogram;
the shallow angle helps
in maneuvering the
catheter through the
right atrium and right
ventricle into the
pulmonary artery
(continued)
70
V. P. Pulappadi et al.
Table 8.2 (continued)
Catheter shape Common indications Representative image
Multipurpose –Catheterization of
Berenstein/
Picard
hepatic vein from
jugular approach
–Catheterization of
superior mesenteric
artery from radial artery
access
–Catheterization of
branches of the aortic
arch
–Selective
catheterization of
branches of mediumsized vessels such as the
renal artery and superior
mesenteric artery
–Crossing over the
aortic bifurcation
Table 8.2 (continued)
Catheter shape Common indications Representative image
Cobra –Catheterization of
visceral arteries and side
branches of the aorta
such as the bronchial,
intercostal, and lumbar
arteries
Head hunter –Catheterization of
aortic arch branches
Rosch Celiac –Catheterization of
visceral branches of
aorta, i.e., celiac axis
and superior and inferior
mesenteric artery
(continued)
Vertebral –Catheterization of
aortic arch branches
(continued)
8 Hardware forInter ventions
71
Table 8.2 (continued)
Catheter shape Common indications Representative image
Renal double
curve
Simmons –Catheterization of the
–Catheterization of renal
arteries and side
branches of aorta
renal artery, superior
mesenteric artery, and
celiac axis with steep
downward course
–Catheterization of
aortic arch branches
through radial access
Table 8.2 (continued)
Catheter shape Common indications Representative image
Shepherd hook –Catheterization of side
Roberts uterine
artery
branches of the aorta
such as the bronchial,
intercostal, and lumbar
arteries
–A long secondary curve
that enables cannulation
of bilateral internal iliac
arteries and their
branches through single
femoral artery access
Sos –Catheterization of
internal iliac artery from
ipsilateral femoral
access
(continued)
Judkin’s –Judkin’s right and
Judkin’s left catheters
are used for cannulation
of right and left coronary
arteries, respectively
(continued)
72
V. P. Pulappadi et al.
Table 8.2 (continued)
Catheter shape Common indications Representative image
Yashiro –It has a 3D curve that
helps in the cannulation
of the celiac axis and its
branches
• Trackability is the ability of the catheter to follow the
guidewire over which it is advanced.
• Pushability is the forward push transmitted at the tip of
the catheter due to the force applied by the operator at the
hub.
• Crossability is dened as the ability of a catheter to navigate across a tortuous segment of the artery.
• Steerability/torquability refers to the steering movement of the catheter tip in response to handling maneuvers performed at the hub.
neuromicrocatheters used for specic indications are enumerated as follows:
• Flow-directed microcatheters: As opposed to other
microcatheters, these microcatheters have non-braided
tapered tips. They are used for super-selective distal catheterization of arterial feeders in high ow arteriovenous
malformations (AVMs). Examples include Marathon
(Medtronic), Apollo (Medtronic), Magic (Balt), and Sonic
(Balt).
• Dimethyl sulfoxide (DMSO) compatible: DMSO is the
solvent used during embolization using ethylene vinyl
alcohol copolymer (EVOH). As it is a highly potent solvent, microcatheters made of DMSO resistant material
must be used during for injection of EVOH.Examples
include Headway Duo (Microvention), Echelon
(Medtronic), Marathon (Medtronic), Apollo (Medtronic),
and Sonic (Balt).
• Detachable tip microcatheters: These catheters have a
detachable distal tip and are used during embolization
using liquid embolic agents. The detachable tip helps in
retrieving the microcatheter even if the tip gets stuck
within the EVOH cast [3, 4]. Examples are Apollo
(Medtronic), and Sonic (Balt).
8.7 Embolizing Agents
8.6 Microcatheters
Microcatheters are small caliber catheters with an outer
diameter ≤3F.They are used along with microguidewires for
super-selective cannulation of small vessels that cannot be
cannulated using an angiographic catheter. Like angiographic catheters, microcatheters are braided to enhance
their pushability. They have a specialized PTFE inner lining,
which is hydrophobic and allows smooth passage of the
microcatheter over hydrophilic guidewires.
The outer diameter of microcatheters ranges from 1.2 to
2.7F and lengths range from 130 to 167cm. The choice of
microcatheter depends upon the size of target vessel and the
planned procedure. Microcatheters of the range 2–2.7F are
used for peripheral and visceral artery interventions, and
commonly used ones are Progreat (Terumo) and Master
Parkway Soft (Asahi). Dedicated microcatheters are available for neuro-interventions. While microcatheters with an
inner diameter of 0.017″ are used for aneurysm coiling, those
with an inner diameter of 0.021″ or 0.027″ are used for the
deployment of stent retrievers and ow diverters. Special
A variety of embolizing agents are used in interventional
radiology practice. The type of agent to be used depends
upon the indication—whether it is for attaining tissue necrosis or to control active bleeding, the size of the vessel to be
occluded, and whether the target organ has collateral supply
from other arteries. Embolizing agents are broadly classied
as permanent or temporary (Table8.3). Various commonly
used embolizing agents are described below.
Table 8.3 Classication of embolizing agents
Temporary agents Permanent agents
Gelatin foam
Autologous blood clot
Thrombin
Coils
Vascular plugs
Particulate agents
–polyvinyl alcohol
–tris-acryl gelatin microspheres
Liquid embolic agents
–n-butyl cyanoacrylate
–ethylene vinyl alcohol copolymer
Detachable balloons
8 Hardware forInter ventions
73
8.7.1 Gelatin Foam
Gelatin foam is the most commonly used temporary embolizing agent. It is derived from porcine skin and is commonly
available as sheets. These sheets are cut into smaller pieces
and used for embolization. When proximal embolization is
desirable, it is cut into large pieces called torpedoes, which
mechanically occlude the blood vessel. Alternatively, gelfoam pledgets, which are made by cutting the sheet into
smaller pieces and agitating them in diluted contrast medium,
can be used for proximal embolization. Slurry made of gelfoam scrapings is used when distal embolization is required.
It is commonly used for cases of active bleeding. Gelfoam
being a temporary agent, the embolized blood vessel is
recanalized in 4–6 weeks. Its major advantages are cost
effectiveness and ease of use [5]. However, the occurrence of
infection is a potential concern with its use because the air
trapped within it may contain infectious bacteria [6].
8.7.2 Autologous Blood Clot
It is one of the rst agents to be used as an embolizing agent.
In current practice, it is used during percutaneous needle biopsies to seal off the puncture tract. Once the biopsy is completed, the clot formed from a small quantity of blood taken
from the patient’s peripheral vein is injected through the coaxial needle. Alternatively, the clot may be allowed to form
within the lumen of the coaxial needle once the biopsy needle
is taken out, and it is then pushed into the biopsy tract using a
blunt needle while withdrawing the coaxial needle. The advantage is that there is no added cost or additional hardware
requirement. The disadvantage is that the clot gets lysed within
a short period of time by the circulating plasmin.
8.7.3 Thrombin
for embolization, different types of coils have been developed
for use in specic situations. Coils are usually made of platinum and are available in various diameters, lengths, and
stiffness. They can be classied on the basis of their properties as follows:
• Deployment mechanism.
1. Pushable: These coils are deployed by pushing out of
the catheter using a pusher wire. They cannot be
retrieved back into the catheter once deployed. They
are used for embolization in blood vessels other than
in the intracranial circulation.
2. Detachable: These coils stay attached to the pusher
wire till they are deployed electrolytically or mechanically. This allows the coil to be retracted and repositioned until the intended coil position is attained. They
are used predominantly for coiling of intracranial
aneurysms where precise placement of the coils is of
utmost importance. They are costlier than pushable
coils.
• Presence of bers.
1. Fibered: Coils with bers made of nylon and polyester
promote thrombus formation adjacent to the coil mass.
These coils are used for embolization in the peripheral
circulation.
2. Non-bered: These are used in intracranial circulation
where bered coils may promote thrombus propagation into the parent artery and distal embolism.
• Shape.
1. Framing coils: These are three dimensional coils that
are used to create the initial frame within an aneurysm.
Once the rst framing coil is deployed, further space
within the aneurysm is lled with packing coils that
are helical in shape.
2. Helical coils: They are general-purpose coils used for
embolization of blood vessels and for packing inside
an aneurysm after placing a framing coil.
Thrombin is a component of the coagulation cascade and is
involved in the conversion of brinogen into brin, which is
necessary for clot formation. Human thrombin is widely used
as a hemostatic agent during various surgeries. In interventional radiology practice, the use of thrombin is limited to the
treatment of supercial narrow neck pseudoaneurysms, such as
those that develop at the femoral artery puncture site. Thrombin
is rst mixed with calcium chloride for its activation and then
injected into the pseudoaneurysm under USG guidance.
8.7.4 Coils
Coils are the most commonly used agents when proximal
embolization is desired. After its introduction by Gianturco
The diameter of the coil to be used depends upon the tar-
get vessel diameter. The coil has to be oversized by 20%
more than the target vessel diameter for effective occlusion.
Use of larger coils will prevent the coil from forming its
shape while smaller coils may embolize distally [5].
8.7.5 Vascular Plugs
Vascular plugs are large embolization devices used for proximal occlusion when the vessel diameter is too large for coil
placement. Amplatzer plugs (Abbott) are the most commonly used vascular plugs. It is a nitinol mesh that is
detached from the delivery wire by screw-release mechanism. This detachment mechanism allows for resheathing
74
Amplatzer plugs, of which Amplatzer II and IV are the most
commonly used ones. Amplatzer II is a trilobed device with
a diameter range of 3–22 mm and a sheath compatibility
range of 4–7 F. Amplatzer IV is a smaller prole bilobed
device that can be deployed through any diagnostic catheter
and has a diameter range of 4–8mm. The most common uses
of plugs are embolization of pulmonary AVMs, plug-assisted
transvenous retrograde obliteration of varices (PARTO), and
embolization of visceral arteries to prevent endoleak after
endovascular aneurysm repair. Plugs are oversized by
30–50% greater than the target vessel diameter to ensure
complete occlusion [5].
8.7.6 Particulate Agents
These are used for distal embolization of small vessels.
Commonly used particulate agents are polyvinyl alcohol
(PVA) particles and trisacryl gelatin microspheres (TAGM)
(Embospheres, Merit Medical). They block vessels by physically occluding them, inducing slow ow, thrombus formation, and inammation in the vessel wall.
PVA particle size ranges from 100 to 1100μm, and particles of various sizes are separated from each other by passing the particles through appropriately sized lters. The rst
generation PVA particles are made by scraping PVA foam
sheets and are irregular in shape with non-uniform sizes.
These non-spherical PVA particles have a tendency to clump
together, resulting in more proximal embolization. Despite
this drawback, they are commonly used due to their low cost.
To overcome the issue of clumping of particles, secondgeneration spherical PVA particles were developed (Contour,
Boston Scientic). Hydrogel microspheres are newer thirdgeneration PVA particle agents that are made of hydrophilic
or amphiphilic polymers (Bead Block, Boston Scientic).
TAGMs are particles that are calibrated to a more uniform
size than PVA particles and are available in size ranges varying from 40 to 1200μm. They do not get clumped due to
their uniform spherical shape. This property, in addition to
their ability to get compressed, facilitates more distal
embolization as compared to PVA particles. Therefore, if
TAGMs were to be used instead of PVA particles for a specic indication, the size of TAGMs has to be larger than that
of PVA particles to avoid organ ischemia due to distal embolization [5].
Further advancements in technology have enabled the
development of even more tightly calibrated microspheres.
An example is Embozene (Boston Scientic), which has
95% of the particles calibrated to a specic diameter instead
of a size range. It has a core made of polymethyl methacrylate and a coating made of Polyzene-F. Particles that are
capable of carrying chemotherapeutic agents are used for
trans-arterial chemoembolization (DC beads, Boston
V. P. Pulappadi et al.
Scientic). Biodegradable hydrogel microspheres are available that resorb over a period of time and act as temporary
embolizing agents. Gel-bead (Teleex) is a bioresorbable
microsphere made of gelatin and can be used in place of
gelatin foam as a temporary embolizing agent.
Embolization of bronchial, uterine, prostate and geniculate arteries, tumor embolization, and embolization for epistaxis are the most common indications for the use of
particulate agents.
8.7.7 Liquid Embolic Agents
N-butyl cyanoacrylate (NBCA) and ethylene vinyl alcohol
copolymer (EVOH) are the two commonly used liquid
embolic agents.
NBCA (Histoacryl, Braun; Trull, Cordis) polymerizes
instantly upon coming in contact with an anionic medium
such as blood. Solidied NBCA glue cast causes mechanical
occlusion of the blood vessel. Unlike other embolizing agents
such as coils, NBCA is not dependent on additional thrombus
formation for complete occlusion of the vessel. Due to this
reason, it is the preferred agent in patients with coagulopathy.
It is used in combination with ethiodized oil (Lipiodol,
Guerbet) in various concentrations ranging from 1:5 (~16%
NBCA) to 3:1 (75% NBCA). Highly concentrated NBCA is
used in high-ow lesions such as AVMs and arteriovenous
stulas, where NBCA has to polymerize instantly without
distal embolization into the pulmonary circulation. A more
dilute NBCA mixture is used during embolization of AVM
nidus or vascular tumors where it has to penetrate deep into
the lesion. In addition to delaying the polymerization of
NBCA, ethiodized oil, being radio- opaque, facilitates visualization of the mixture during injection. Prior to injection, the
catheter and the vascular bed are primed with dextrose, which
is a non-ionic solvent. Advantages of NBCA are that it is
cheap, causes instant occlusion of the blood vessel, and can
be used as a proximal or distal embolizing agent by varying
its concentration. The disadvantages include the need for
expertise for its injection, risk of catheter occlusion during
injection, and catheter getting stuck within the NBCA glue
cast. Common uses of NBCA are embolization of high-ow
AVMs, tumor embolization, and portal vein embolization. It
is also used for embolization of pseudoaneurysms by transarterial route, if the microcatheter cannot be advanced till the
pseudoaneurysm for coil placement, or by percutaneous route
under USG guidance.
EVOH (Onyx, Medtronic; Menox, Meril) takes longer
time to polymerize than NBCA, enabling slow and more
controlled embolization. EVOH comes pre-mixed with tantalum powder, which is radio-opaque. EVOH vial is placed
in a shaker for at least 20min prior to using it to ensure uniform mixing of EVOH with tantalum powder. Prior to injecting EVOH, the catheter is primed with DMSO to prevent
8 Hardware forInter ventions
75
polymerization within the catheter. Because DMSO is a
potent solvent, specialized DMSO-compatible microcatheters are to be used for embolization using EVOH.It is commonly used for embolization of intracranial AVMs. Although
it can also be used in peripheral AVMs as well, there is a risk
of skin pigmentation secondary to tantalum deposition when
used in supercial lesions. Onyx (Medtronic) is an EVOH
agent that comes in two different preparations of varying viscosities: 18 and 34centiStokes (cSt). While the low viscosity
preparation is used for embolization of the nidus as it has
deep penetration, the high viscosity one is used for embolization of high ow stulous components. Squid (Balt) is
another EVOH agent that is available in 12 and 18cSt preparations. The major disadvantage of EVOH is its high cost.
8.8 Detachable Balloons
These were once popular for embolization of caroticocavernous stulas. These balloons are made of latex or silicon and are deployed across the stula through transarterial
access. They are not popular nowadays due to the high incidence of balloon deation and migration [5].
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