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198
Indications/Contraindications
What are indications
to treating AVMs?
Cosmetic disfiguration, large mass, severe
pain, recurrent bleeding, ischemia, growth
disturbance, and high-output cardiac state
Why do clinicians
choose “watchful
waiting” rather than
treating extremity
AVMs early in their
discovery?
Treating AVMs may not be necessary for
asymptomatic patients since treatment
represents a long-term commitment to the
patient and family. Early therapy should
only be considered if there is evidence of
worsening symptoms, such as shunting,
and the patient is willing to undergo the
potential for multiple staged sessions.
What are the
advantages of
endovascular
therapy over
surgical repair?
Surgical resection oftentimes yields
poor results because AVMs are often
extensive, crossing normal tissue planes.
Endovascular embolization allows super-
selective catheterization of the feeding
vessel; however, cure is not always
achievable, and treatment may require
multiple procedures.
Why is it important
to evaluate for
severe pulmonary
hypertension when
embolizing PAVM?
PAVM embolization in someone with
severe pulmonary hypertension may
further worsen their pulmonary artery
pressure, leading to cor pulmonale—right-
sided heart failure secondary to increased
pulmonary vascular resistance.
Why might certain
treated vascular
malformations
worsen (i.e.,
enlarge)?
Vascular malformations are responsive
to stimuli, such as injury or incomplete
treatment of the nidus. This may be seen in
certain patients who present with a rapid
growth of their previously unperceived
AVM over a relatively short time period
following localized trauma. Therefore,
obliterating the nidus should be the
therapeutic goal, as incomplete destruction
will stimulate vascular growth and possible
enlargement of the AVM.
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How is worsening
right-to-left
shunting in PAVM
manifested?
Although initially asymptomatic,
worsening shunting will develop as arterial
hypoxemia, manifested as dyspnea, fatigue,
cyanosis, clubbing, and polycythemia.
Relevant Anatomy
Why might one
consider MRI
as an imaging
modality for
pre-procedural
workup?
MRI is the mainstay of AVM imaging,
especially if there are additional findings
that will affect treatment decision. There is
no ionizing radiation in MRI, and the high
contrast resolution of MRI is used to classify
the vascular anomaly and assess the extent
of the lesion from the involved anatomy. The
three-dimensional dynamic MR angiography
sequences provide important information
about the abnormal flow hemodynamics.
What are the
components of an
AVM?
The nidus is the central tangle of
communicating arterioles and venules with
one or more feeding arteries, and one or
more draining veins.
What is the
“nidus” in PAVM?
The PAVM nidus may be a single aneurysmal
sac or a plexiform septated connection. They
may be acquired or congenital.
How do the origin
of the pulmonary
arteries and
bronchial arteries
differ?
The pulmonary arteries receive blood from
the right ventricle. The bronchial arteries
receive blood from the thoracic aorta.
PAVMs are abnormally dilated vessels that
provide direct communication between a
pulmonary artery and pulmonary vein.
What is the
difference
between simple
PAVMs and
complex PAVMs?
Simple PAVMs have one feeding artery,
while complex PAVMs have multiple feeding
arteries.
(continued)
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In a patient with
known HHT,
what is the most
likely etiology
of a variceal
hemorrhage?
This patient most likely has a liver AVM.The
clinical presentations of liver AVMs
include high-output cardiac failure, portal
hypertension, biliary necrosis, portosystemic
encephalopathy, and intestinal ischemia/steal
syndrome.
Why is it important
to treat high-
flow mesenteric
AVMs in a staged
fashion?
Treatment of mesenteric AVMs can result in
severe portal hypertension as more blood is
now being drained through the portal system.
What is the
most common
multivessel supply
for pelvic AVMs?
Anterior branches of the internal iliac artery,
inferior mesenteric artery, and median sacral
artery
What is the target
of embolization in
AVMs?
Elimination of the nidus while preserving
flow to normal vessels. Incomplete
eradication of the nidus may stimulate
growth of the AVM.Treating too proximal
may block access to the nidus for future
interventions.
What is the most
common factor
that predisposes
women to uterine
AVM?
It is almost always preceded by an obstetric
event (postpartum, postabortion, or dilation
and curettage).
Relevant Materials
Compare the efficacy
and toxicity of absolute
ethanol versus other
embolic agents (n-butyl-
2-cyanoacrylate (NBCA)
glue and sodium
tetradecyl sulfate (STS)).
Ethanol is more effective in
obliterating vascular lumens, but
more toxic, as well. STS is a sclerosing
agent that is less toxic but less
effective compared to ethanol. STS
is a sclerosing agent that has gained
popularity in recent years. NBCA glue
has no sclerosant effect but is very
useful for vessel occlusion and can
significantly slow down the flow.
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What is the mechanism
of action of absolute
ethanol?
Absolute ethanol causes direct tissue
toxicity, causing endothelial damage
and rapid thrombosis resulting in
permanent occlusion. It has a poor
safety profile due to its direct intrinsic
toxicity and higher likelihood of skin
necrosis and neuropathy.
What is the purpose of
mixing ethiodized oil
(Ethiodol) with NBCA
glue?
NBCA is an adhesive that rapidly
polymerizes upon contact with any
ionic solution. Ethiodol is an oil used
to provide radiopacity to the glue,
as well as slow the polymerization
time. Higher ethiodol to NBCA
ratio leads to longer polymerization
time. Therefore, different ratios of
Ethiodol to glue will result in different
viscosities and polymerization times,
necessitating user experience and
careful manipulation of technique
depending on the mixture.
What is typically used to
flush the catheter when
using NBCA?
Nonionic, 5% dextrose in water is
used to flush the catheter prior to
administering NBCA to completely
remove ionic substances and allow
distribution of the NBCA glue. NBCA
polymerizes after coming into contact
with ionic substances.
How does occluding
the dominant venous
outflow facilitate NBCA
embolization?
Dominant venous outflow occlusion
will slow the flow through the
lesion and allow the NBCA glue to
concentrate at the nidus.
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General Step by Step
What are the
available access
routes to treat
AVMs?
AVMs may be accessed via transvenous,
direct puncture, or transarterial routes.
Transarterial access to embolize the nidus
has been conventionally preferred. If there
is no reasonable transarterial access, such
as multiple arterioles shunting into a single
venous component, or if the remaining
feeding arterioles are too small or tortuous
to catheterize, then direct puncture of the
nidus may allow for effective embolization.
In addition to requiring a safe access window
for percutaneous direct puncture, there
are inherent risks, such as air embolization
introduced by the access needle and
pneumothorax as a result of transthoracic
access.
Why should
embolization
of the proximal
portion of the
feeding artery be
avoided?
Embolization of the proximal portion of the
feeding artery without obliterating the nidus
will prevent future access to the viable nidus
and will promote collateral resupply over
time.
Is there an ideal
embolic agent for
all AVMs?
No. There is no ideal embolic agent that
encompasses both safety and efficacy.
There are a wide range of agents available,
including absolute ethanol, liquid-casting
agents (NBCA glue), sclerosant (STS),
embolization coils, vascular plugs, and
ethylene vinyl alcohol copolymers (Onyx).
Onyx has weak sclerosant properties and acts
through polymerization. Occluding devices
(coils, vascular plugs, or microvascular
plugs) will benefit fistula-like connections.
It is better to embolize the nidus for
complex malformations by taking advantage
of the blood flow mechanics and using
flow dependent embolic agents, such as
microspheres, NBCA glue, Onyx, or absolute
ethanol.
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Why may
embolization of
the vein in AVMs
not be preferred?
The passage of embolic materials into the
draining outflow vein can cause nontarget
embolization. A situation in which
embolization of the draining vein is preferred
is when there are multiple inflow arterioles
draining into an aneurysmal venous sac. The
mechanical occlusion of the venous drainage
can then be combined with retrograde
injection of the nidus with a liquid embolic
or sclerosant.
Why do some
operators use
Swan-Ganz
monitoring when
using absolute
ethanol?
Absolute ethanol is toxic, and escape of the
agent into the central circulation has been
associated with cardiac arrhythmias, acute
pulmonary vasoconstriction, and pulmonary
embolization. Due to these risks, some
operators prefer careful monitoring using a
Swan-Ganz. Additionally, nerve monitoring
may be beneficial if the treatment area is
within close proximity of a major nerve.
Why should
treatment be
limited to only a
few vessels when
treating AVMs in
the extremity?
Embolizing multiple feeding arteries may
lead to peripheral ischemia. Therefore, in
addition to eradicating the nidus of the AVM,
limited treatment of a few involved vessels
will decrease the occurrence of ischemic
complications. This may require multiple
sessions to accomplish.
Where is the ideal
site of occlusion
for PAVMs?
The goal is to occlude all the feeding
arteries, as distal as possible and beyond any
significant supply to normal lung.
What is an ideal
embolic agent for
PAVMs?
Mechanical agents, such as coils, are typically
recommended.
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Complications
What is an initial
treatment consideration
for skin ulcers that
develop following
treatment?
Topical antiseptic cream, such as 1%
silver sulfadiazine (Silvadene) and
non-steroidal anti-inflammatory drugs.
What should one
consider if a patient
develops shortness of
breath and chest pain
following embolization
of high-flow
malformations?
Embolization of the embolic agent or
iatrogenic introduction of air into the
pulmonary circulation
What is a differential
consideration in
someone with chest
pain and fever following
PAVM embolization?
Pleurisy is the most common side
effect after PAVM embolization, which
may develop in 3%–16% of patients
several days after the procedure. In
patients with delayed pleurisy, a chest
radiograph will show infiltrates, which
are usually self-limiting.
Describe the Spetzler-
Martin grading scale for
intracranial AVMs.
The Spetzler-Martin grading scale
estimates the risk of surgery on the
basis of size, neurological eloquence
of adjacent brain, and pattern of
venous drainage. The grade is based
on the total score, with higher grades
correlating with increased surgical
morbidity and mortality
(See Table 23.2).
T . Spetzler-Martin grading scale for intracranial AVMs
Score
Size
< 3cm 1
3–6cm 2
> 6cm 3
(continued)
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What is
a serious
complication
when treating
PAVMs?
An air embolism passing into a PAVM is a
serious risk because it can pass directly into the
left-sided circulation and into the brain.
What is a
common
side effect
following the
use of Onyx?
The garlic-like smell that follows Onyx
administration is due to DMSO, and it usually
dissipates within 2days. DMSO is slowly injected
inside the microcatheter to fill its dead space
and prevent direct contact with the bloodstream,
thereby preventing its solidification prematurely.
Landmark Research
Pollak JS, White RI Jr. Distal cross-sectional occlusion is the
“key” to treating pulmonary arteriovenous malformations. J
Vasc Interv Radiol. 2012;23(12):1578–1580.
Score
Location
Non-eloquent brain area (anterior frontal or temporal
lobes, or cerebellar cortex)
0
Eloquent brain area (sensorimotor, language, visual
cortex, hypothalamus, thalamus, internal capsule, brain
stem, cerebellar peduncles, and deep cerebellar nuclei)
1
Deep venous drainage
Absent 0
Present 1
T . (continued)
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What are the four ways
persistence or reperfusion
of an apparently successfully
embolized PAVM may
occur?
Recanalization of the vessel
Growth of a missed or previously
small accessory artery
Bronchial artery or other systemic
artery collateral flow into the
pulmonary artery beyond the level
of the embolization
Pulmonary artery-to-pulmonary
artery collateral flow about the
occlusion
Ratnani R, Sutphin PD, Koshti V, Park H, Chamarthy M,
Battaile J, Kalva SP.Retrospective Comparison of Pulmonary
Arteriovenous Malformation Embolization with the
Polytetrafluoroethylene-Covered Nitinol Microvascular Plug,
AMPLATZER Plug, and Coils in Patients with Hereditary
Hemorrhagic Telangiectasia. J Vasc Interv Radiol. 20 19
Jul;30(7):1089–1097.
What are the persistence
rates associated with the
coils, AMPLATZER vascular
plugs, and microvascular
plugs when treating PAVM?
The persistence rates for PAVM
with coil embolization are
47%, compared with 15% for
AMPLATZER vascular plug, and
2% with the microvascular plug.
Faughnan ME, Palda VA, Garcia-Tsao G, Geisthoff UW,
McDonald J, Proctor DD, Spears J, Brown DH, Buscarini E,
Chesnutt MS, Cottin V, Ganguly A, Gossage JR, Guttmacher
AE, Hyland RH, Kennedy SJ, Korzenik J, Mager JJ, Ozanne
AP, Piccirillo JF, Picus D, Plauchu H, Porteous ME, Pyeritz
RE, Ross DA, Sabba C, Swanson K, Terry P, Wallace MC,
Westermann CJ, White RI, Young LH, Zarrabeitia R; HHT
Foundation International - Guidelines Working Group.
International guidelines for the diagnosis and management
of hereditary haemorrhagic telangiectasia. J Med Genet. 2011
Feb;48(2):73–87.
C. Hua
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At what
diameter feeding
artery should
embolization
of PAVM be
considered?
PAVMs with feeding artery diameter
of 3mm or greater should generally be
treated. Targeting sub-3mm feeding arteries
may also be appropriate, if technically
feasible. It has been shown that paradoxical
embolization is independent of feeding
artery diameter.
Cho SK, Do YS, Shin SW, Kim D, Kim YW, Park KB, Kim
EJ, Ahn HJ, Choo SW, Choo IW. Arteriovenous malforma-
tions of the body and extremities: analysis of therapeutic
outcomes and approaches according to a modified angio-
graphic classification. J Endovasc Ther. 2006
Aug;13(4):527–38.
Name the four main types of AVMs based on nidus
angiographic morphology.
Type of
AV M
Nidus morphologic
structure Description
Angiographic
appearance
I Arteriovenous fistula Three or less
arteries shunt
into a single
vein
Clear
communication
of the feeding
arteries and
draining vein
II Arteriolovenous/
plexiform fistula
Four or more
arterioles
shunt to a
single vein
Plexiform
IIIa Arteriolovenulous
fistula without
dilation
Multiple
arterioles
communicating
with multiple
venules
Blush or fine
striation
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