**Preclinical Review**

**P**030004

**DATE:** 7/10/03

**Recommendation/summary comments:**

Onyx, manufactured by Micro Therapeutics, Incorporated, is a polymeric
embolization agent intended for use in the presurgical embolization of
brain arteriovenous malformations. It is similar to a recently
FDA-approved polymeric embolization agent, the Trufill n-Butyl
Cyanoacrylate (n-BCA) Liquid Embolic System manufactured by Cordis
Neurovascular, Inc. in that the material polymerizes, or in the case of
Onyx, precipitates, in situ. Its composition and chemical
characteristics are distinctly different from the n-BCA product.
Polymeric embolization agents join the family of other artificial
embolization agents that include particulate embolic agents, coils, and
balloons. Onyx is a mixture of ethylene vinyl alcohol copolymer (EVOH)
dissolved in dimethyl sulfoxide (DMSO). Micronized tantalum powder is
suspended in the liquid polymer/DMSO mixture to provide fluoroscopic
visualization. Upon contact with blood (or body fluids) the solvent
(DMSO) rapidly diffuses away causing in-situ precipitation of a soft
radiopaque polymeric embolus.

The Onyx Liquid Embolic System (LES) was initially used in clinical
feasibility studies at the University of California Los Angeles Medical
Center, in Mexico City and in Europe. The Onyx LES has received CE
marking and is commercially available in Europe, Australia, Canada, and
South America.

Onyx is compositionally similar to the embolization agent, Enteryx,
which is sold as the Enteryx Procedure Kit by Enteric Medical
Technologies, Inc. Enteryx, as approved by FDA in April, 2003, is
indicated for endoscopic injection into the region of the lower
esophageal sphincter for the treatment of gastroesophageal reflux
disease (GERD) symptoms in patients responding to and requiring daily
pharmacological therapy with proton pump inhibitors.

The sponsor has conducted an extensive array of mechanical, chemical,
biocompatibility and in vivo effectiveness preclinical evaluations of
the product. This review is focused primarily on the biocompatibility
and animal effectiveness evaluations. The sponsor has conducted the
standard biocompatibility assessments which included 1 year implantation
studies, genotoxicity evaluations and carcinogenicity determinations
using the rasH2 transgenic mouse model. In addition, the sponsor
evaluated the following:

-   the effect of injecting the material into the cerebromedullary
    cistern of the rabbit

-   the potential for the material, specifically the DMSO component, to
    cause angiotoxicity in a swine model with follow-up evaluations at
    10 and 28 days

-   the embolization effectiveness of the material in the swine rete
    mirabile model

-   the embolization effectiveness of the material in canine and swine
    surgically-created aneurysm models

The sponsor has also provided a limited histopathologic assessment of
Onyx-embolized human tissue and a report comparing the MRI/CT image
analyses of n-BCA and Onyx embolized human brain AVMs.

Dimethyl sulfoxide is considered a drug. The only approved use of DMSO
in humans is for interstitial cytstitis as a 50% solution (RIMSO^®^).
Consult review was requested from colleagues at the Center for Drug
Evaluation and Research and their review is included. As noted in the
drug review, repeat infusion animal evaluations were not conducted. This
issue will be discussed as a question to the panel. The question in
draft form is presented here:

*Preclinical animal evaluations have shown that the rate and amount of
DMSO can cause vasospasm and vascular wall damage. Patients undergoing
staged embolization procedures for Cerebral Arteriovenous Malformations
will be exposed repeatedly to the potential for DMSO-mediated vessel
damage. Do you believe additional animal evaluation should be conducted
to more completely assess for repeat-DMSO vessel wall exposure and
potential adverse effects? Do you have any recommendations regarding the
amount of DMSO a patient should be exposed to over a 24 hour period or
the length of time between embolization procedures?*

This issue will be discussed further in the second mail-out. Additional
preclinical information has been requested from the sponsor and this
will be discussed in the preclinical section of the second mail-out as
well.

In conclusion, the sponsor has conducted a thorough preclinical
assessment of their catheter-based delivery system, device
biocompatibility and device proof of concept in animal models.
Additional information regarding the repeat injection issue and the
sponsor's responses to the issues unanswered to date will be forwarded
to you within the next two weeks.

**Review:**

[Device description]{.underline}

Onyx^®^ Liquid Embolization System (LES)

Onyx^®^ 18, Model 105-7100-060

Onyx^®^ 34, Model 105-7100-060

Onyx is a mixture of ethylene vinyl alcohol copolymer (EVOH) dissolved
in dimethyl sulfoxide (DMSO). Micronized tantalum powder is suspended in
the liquid polymer/DMSO mixture to provide fluoroscopic visualization.
The Onyx material is delivered in a liquid phase through a micro
catheter to the target lesion under fluoroscopic control. Upon contact
with blood (or body fluids) the solvent (DMSO) rapidly diffuses away
causing in-situ precipitation of a soft radiopaque polymeric embolus.
The sponsor is marketing two viscosities -- Onyx 18 and Onyx 34 for use
in arteriovenous malformations in which the depth of penetration is
important. The formulations are designated 18 or 34 based upon their
respective viscosities, i.e., 18 and 34 centistokes, respectively.

**[Nomenclature]{.underline}**

MTI has licensed the Onyx LES technology to Genyx Medical, Inc. under
the trade name "Uryx" for treatment of female urinary incontinence, and
Enteric Medical, Inc. under the trade name "Enteryx" for treatment of
gastro-esophageal reflux disease. MTI, Genyx and Enteric have
participated in joint biocompatibility and safety studies for the Onyx
material.

**[Current Product Name Synonymous Name #1 Synonymous Name
#2]{.underline}**

**Onyx-18 Embolyx-6% or Onyx-6% Embolyx E-6%**

**Onyx-34 Embolyx-8% or Onyx-8% Embolyx E-8%**

**Uryx Embolyx-8% or Onyx-8% N.A.**

**Enteryx Embolyx-8% or Onyx-8% N.A.**

The Onyx LES kit contains the following:

a.  one vial (1.5 mL) of Onyx (18 or 34)

b.  one vial of DMSO (1.5 mL)

c.  3 DMSO compatible syringes (1 mL)

The Onyx material requires use of compatible delivery devices to assure
patient safety and effective performance of the embolic material. The
instructions for use provide instructions for preparation and use of
recommended syringes and delivery catheters. The following ancillary
devices are identified in the instructions for use:

a.  MTI UltraFlow™ Micro Catheter (K980104, K010004, K024118)

b.  MTI Rebar™ Micro Catheter (K993672, K001966)

c.  Onyx Syringe (K991225)

The indications for use for the devices recommended in the labeling do
not conflict with the manner in which they are used in conjunction with
the embolization agent.

[Device components]{.underline}

The Onyx material is manufactured from 3 components:

-   Dimethyl Sulfoxide

-   Ethylene vinyl alcohol copolymer

-   Tantalum

The DMSO is used to dissolve the EVOH pellets and the tantalum is used
for achieving radiopacity of the final product. The material mix ratio
will determine the performance attributes of the Onyx solution; i.e.,
the viscosity/flow properties and degree of visualization when implanted
in the vasculature. Two configurations of Onyx are proposed within this
application: Onxy 34 has a greater amount of EVOH in solution producing
a higher viscosity liquid than the Onyx 18. The "18" and "34"
designations represent the approximate viscosity of the liquid material.
Onyx-18 (6% EVOH) has an approximate viscosity of 18 cSt whereas Onyx-34
(8% EVOH) has an approximate viscosity of 34 cSt at 40˚ C.

Onyx manufacturing is a batch process (vol. 2, pg. vi)

[Part DMSO EVOH Tantalum Mixed batch size]{.underline}

Onyx-18 (6%) 880.8 g 48 g 264 g 450 vials

Onxy-34 (8%) 880.8 g 64 g 264 g 450 vials

**[Preclinical test evaluations]{.underline}**

**[Mechanical and Chemical testing]{.underline}**

The sponsor uses a number of names to represent the same formulations.
The nomenclature is repeated here for reference:

**[Current Product Name Synonymous Name #1 Synonymous Name
#2]{.underline}**

**Onyx-18 Embolyx-6% or Onyx-6% Embolyx E-6%**

**Onyx-34 Embolyx-8% or Onyx-8% Embolyx E-8%**

**Uryx Embolyx-8% or Onyx-8% N.A.**

**Enteryx Embolyx-8% or Onyx-8% N.A.**

Many of the experiments were done with the material identified as
Embolyx 8%. The Embolyx 8% formulation is Onyx 8% and is the formulation
of the highest viscosity used in the clinical study. Both formulations
of Onyx under review for the treatment of arteriovenous malformations
contain 0.33% tantalum. The approved, Cordis Neurovascular cyanoacrylate
product (also indicated for the treatment of arteriovenous
malformations) is recommended to contain tantalum at a 0.5:1 ratio
(w/v), tantalum to cyanoacrylate.

[Tests]{.underline}

[The sponsor conducted the following investigations:]{.underline}

-   Minimum mixing time for Embolyx/Onyx vials using the Vortex Genie 2
    Mixer (volume 5)

-   Onyx vial mixer study

-   Onyx solidification test

-   Embolyx 8% mechanical properties post precipitation

-   Embolyx 8% solidification time

-   Onyx HD 2500 tantalum concentration increase -- feasibility

-   Design verification 1.5F en-route micro-catheter

-   Design verification 1.5F en-route micro-catheter min/max extended
    testing test protocol

-   Design verification, 1.5F UltraFlow micro-catheter Onyx plug and
    push testing

-   Comprehensive Onyx testing summary for the Rebar Series Catheters

-   Design verification 1.5F UltraFlow w/optimized distal tubing (P/N
    30542A) and optimized coating

-   1.5F UltraFlow HPC and AVM embolic agents compatibility test report

-   UltraFlow 1.5F and Flowrider Plus 1.5F comparative comprehensive
    Onyx testing

-   Rebar-10 Micro catheter design verification

-   0.0165" ID Rebar micro catheter design verification

-   Titan micro catheter design verification test protocol (hub and
    introducer luer)

-   Design verification 1 mL long stroke syringe

The studies established the correct time to mix the solution and
established product physical chemistry specifications. In addition,
empiric evidence regarding the influence of tantalum concentration was
obtained. Testing of the catheters included many mechanically-based
determinations and also investigated the chemical compatibility of the
catheters with DMSO. The catheters were assessed in standard
biocompatibility tests and their performance was assessed in animal
models.

[Embolyx compatibility with aneurysm metal coils]{.underline}

The purpose of the study was to determine if the Onyx material was
compatible with metal aneurysm coils that might be used in conjunction
for embolization of aneurysms but also in cases of high flow AVMs. The
sponsor asserts the following:

-   The platinum, platinum alloy-based coils do not form soluble metal
    cations in the human body's aqueous setting (physiologic saline).
    Stable cations would be necessary to interact with the ethylene
    vinyl alcohol polymer.

-   DMSO has no ionizing capability in aqueous solutions (human
    physiologic aqueous system) -- ionization is necessary to dissolve
    metal and form metal cations.

-   The tantalum metal and metal oxides are stable to most conditions
    and solutions. Freshly prepared tantalum metal oxide is chemically
    reactive to hydrofluoric acid. The tantalum used is not a fresh
    precipitate and hydrofluoric acid will not be encountered in the
    human physiologic system.

I confirmed the inert chemical character of tantalum by reviewing the
text, *Basic Inorganic Chemistry by Cotton and Wilkinson*. Tantalum
oxides are only successfully chemically attacked and altered by
hydrofluoric acid.

[Onyx in vitro coil compatibility study test protocol]{.underline}

The purpose of the study was to determine how the two Onyx formulations
(18 and 34) may interact, chemically, with standard metal occlusion
coils. Various coils were used to embolize a simulated vessel in
conjunction with Onyx. The coils were soaked in DMSO for periods of time
up to 60 minutes and the extracts were analyzed for leachates via HPLC.

Results: The two Onyx formulations occluded the vessels as assisted by
the occlusion coils without distal migration of the Onyx material. The
sponsor states that examination of the DMSO extract from several coils
using HPLC demonstrated an "insignificant" amount of substance was
leached from the coil. **[The chromatograms were not provided and these
are necessary for an independent determination of what insignificant
means. In addition, the use of Onyx with coils that may have surface
coatings which could be dissolved by DMSO should be discussed in the
labeling. This information was requested and is currently under
review.]{.underline}**

[DMSO and Histocryl compatibility study test protocol PR99-084, Rev.
A]{.underline}

The purpose of the study was to ascertain Onyx compatibility with
solidified Histocryl/Lipiodol mixture. The compatibility was evaluated
for chemical as well as functional interactions. The Histocryl/Lipiodol
mixture was allowed to solidify and then the mixture was exposed to
DMSO. Control samples of DMSO alone or unsolidified Histocryl/Lipiodol
were included in the test paradigm.

Protocol deviation: The HPLC testing was performed on a pure Histoacryl
mixtue and not one mixed with 50% Lipiodol oil.

Results: HPLC analyses did not reveal any differences in peaks or areas
under the chromatograms with respect to control. **[However, no
chromatograms were provided for an independent assessment -- these will
be requested from the sponsor. This information has been requested and
is currently under review.]{.underline}** Functionally, no migration of
the histoacryl polymerized cast was observed and no Onyx material was
observed to "ooze" through the Histoacryl cast. As a result of these
findings the sponsor intends to remove the contraindication statement
regarding use of Onyx with cyanoacrylate-based polymeric embolic agents.

If after review of the original chromatograms I find that the sponsor's
interpretation is accurate, I will agree that the contraindication
statement can be removed.

[In vitro evaluation of the effect of radiosurgery on Embolyx
E]{.underline}

The purpose of the study was to determine the effect of stereotactic
radiation on the biocompatibility and physical integrity of the
material.

Radiation is known to create free radicals in the irradiated polymer
materials. These free radicals generally cause either ran increase in
cross-linking or chain cleavage of polymers. Additionally, chemical by
products may be released as a result of the interaction of the radiation
energy and the polymer. The sponsor identified 3 questions regarding the
potential effect radiation might have on the material:

-   Has there been a change in the material, so that the material no
    longer is biocompatible?

-   Is there a degradation of the embolic material so that material may
    fail or fragment? Has the molecular weight distribution of the
    polymer changed?

-   Is there a degradation of the embolic material after irradiation
    with time at body temperature?

To address biocompatibility, the sponsor conducted cytotoxicity,
hemolysis, pyrogenicity and acute systemic toxicity evaluations. To
determine the effect of radiation on the chemistry or physical chemistry
of the polymer, the sponsor conducted gel permeation chromatography and
infrared absorption spectroscopy analyses. The material was exposed to
30 Gray of radiation at a distance of 94 cm. Acute, 1 year and 2 year
determinations were conducted.

Results: The sponsor asserts that there was no evidence of cellular or
systemic toxicity. No additional peaks were found and the size/breadth
of the peaks were similar, and therefore deemed identical, using IR
spectral analysis. Changes in molecular weight determinations as
detected by gel permeation chromatography were within the prescribed
acceptance criterion of less than a 20% change. **[However, no spectra
or chromatograms were provided for an independent assessment. This
information has been requested and is currently under
review.]{.underline}**

Conclusions: the sponsor notes that a radiation dose of 30 Gray is a
high dose relative to any in vivo clinical usage and therefore the lack
of an effect on the material indicates that concerns regarding
radiation-induced damage to the polymer, and subsequent untoward
clinical effects, should be allayed.

**[Biocompatibility Studies]{.underline}**

The sponsor has provided biocompatibility studies using Onyx as it is
implanted in the patient. The sponsor conducted the following tests
which had passing results (unless noted):

-   [Cytotoxicity]{.underline} --Embolyx, 8% Tantalum

-   [Cytotoxicity]{.underline} -- DMSO (tested at 92%)

-   [Sensitization]{.underline} --Embolyx, 8% with Tantalum

-   [Intracutaneous reactivity]{.underline} - Embolyx, 8% with Tantalum

-   [Acute systemic toxicity]{.underline} -- Uryx Embolyx, 8% with
    Tantalum Pass, with comment

The mice showed a staggering gait and were lethargic immediately
post-injection, followed by a staggering gait out to 15 minutes. The
animals recovered and gained weight and so passed the USP requirement of
the test. The sponsor believes that the DMSO may have contributed to the
animals' responses.

-   [Subacute toxicity (14 day, I.V.)]{.underline} - Embolyx, 8% with
    Tantalum Pass with comment

The animals receiving injections of the test material had tremors,
twitches, spasms and/or a staggering gait during or immediately after
dosing for a few seconds on most or all of the 14 days of dosing.
Piloerection was also observed. At AM/PM observations, all animals
appeared normal. The sponsor believes that this indicates that the
reactions observed during and immediately after dosing were transient
and were most probably due to the DMSO component of the extract being
administered I.V. and not due to a toxicity related to the polymer. Mean
white blood cell counts for the test animals were significantly lower
than the control but the sponsor indicated that in 2 of the test
animals' samples, blood clots were noticed and believed to be
responsible for the abnormally low value. Looking at the other blood
cell and blood parameter determinations, I believe the sponsor's
interpretation. Volume 6

-   [Implantation (7 day, muscle)]{.underline} - Embolyx, 8% with
    Tantalum

-   [Implantation (1 year, rabbit)]{.underline} - Embolyx, 8% with and
    w/o Tantalum

Intramuscular injection sites were examined microscopically and other
tissues were examined microscopically to look for the possibility of
systemic migration of test article. Severity grading of histopathologic
diagnoses was done on a scale of 1-4.

30 days: There were histopathologic differences in the appearance of the
injection sites containing material with and without tantalum,
microscopically. The inflammatory response observed due to material
containing tantalum was less severe than that seen due to material
lacking tantalum. The implantation sites contained phagocytic cells,
occasional infiltrates of lymphocytes, heterophils and also contained
spotty fibrosis. Multinucleated giant cells were observed in both
implantation sites and were observed to be degenerating in the sites
containing material without tantalum. The control implantation sites
were unremarkable.

90 days: The inflammatory response seen in areas of test article
administration consisted of a mild (+2) localized foreign body reaction
that was of similar type whether the material contained tantalum or not.
The inflammatory reaction was characterized by a predominance of
macrophages and multinucleate giant cells with fewer numbers of
lymphocytes and plasma cells. Occasional multinucleate giant cells were
observed and patchy fibrosis and mineralization of skeletal muscle
bundles was observed.

Conclusion at 90 days: The investigator asserts that the lack of
histomorphologic differences in the nature and severity of the
inflammatory response observed with material containing or not
containing tantalum indicates that there is "little meaningful
difference in tissues response under the conditions of the study".

181 days: The inflammatory response seen in areas of test article
administration was frequently minimal (+1) and occasionally mild (+2) in
severity (only material with tantalum was assessed at this time point).
Rarely, severity of this reaction was judged to be moderate (+). The
inflammatory response was typical of a localized foreign body reaction
and was characterized by macrophages and multinucleate giant cells with
fewer number s of lymphocytes and plasma cells.

216 days: The inflammatory response seen in areas of test article
administration was frequently minimal (+1) and occasionally mild (+2) in
severity (only material with tantalum was assessed at this time point).
Unlike the samples evaluated at 181 days, there were no occurrences of
moderate (+3) severity of the inflammatory response. The inflammatory
response was typical of a localized foreign body reaction and was
characterized by macrophages and multinucleate giant cells with fewer
number s of lymphocytes and plasma cells.

362 days: The inflammatory response seen in areas of test article
administration was frequently minimal (+1) and occasionally mild (+2) in
severity (both materials, i.e., with tantalum and without tantalum were
assessed at this time point). The inflammatory responses were typical of
a localized foreign body reaction and were characterized by macrophages
and multinucleate giant cells with fewer number s of lymphocytes and
plasma cells.

In summary, the observations indicate that the presence of tantalum in
the material did not alter the inflammatory response observed to the
embolic material. The histophotomicrographs indicate that the material
(with or without tantalum) elicits a similar inflammatory response and
that over the course of the study i.e., out to 1 year, the response
gradually lessens in both cases. The test articles were not observed to
migrate from the site of implantation.

-   [Genotoxicity (Ames mutagenicity)]{.underline} --Embolyx, 8% with
    Tantalum

-   [Genotoxicity (*In vitro* mammalian cell)]{.underline} - Embolyx, 8%
    with Tantalum

-   [Genotoxicity (Micronucleus)]{.underline} - Embolyx, 8% with
    Tantalum

-   [Carcinogenicity (rasH2 Transgenic mouse)]{.underline} - Embolyx, 8%
    with Tantalum Pass with comment

Previously reviewed during the investigational phase of the study, this
protocol evaluated the liquid embolic material (ethylene vinyl alcohol)
with and without tantalum. The device tested contained 8% EVOH dissolved
in DMSO containing tantalum (30% w/v)/Volume 7. The test articles were
administered as a single subcutaneous injection into the interscapular
region of the dorsal surface of the animal.

[Animal Studies]{.underline}

[Effect of Onyx within the Cerebromedullary Cistern]{.underline}

The purpose of the study was to evaluate the effect of Onyx in direct
contact with neurological tissue in the subarachnoid space as might
occur during embolization of vascular malformations and/or the rupture
of vascular embolizations during treatment with Onyx.

The cerebello-medullary cistern is formed by the arachnoid bridging the
interval between the medulla oblongata and the inferior surface of the
cerebellum and is triangular on sagittal section. Here the arachnoid is
separated form the pia mater by wide intervals, which communicate freely
with each other and are named subarachnoid cisterns. The space is filled
with cerebrospinal fluid and blood vessels of the brain.

In this experiment, rabbits were given cisterna magna injections of 6%
Onyx, 25% Onyx, saline or autologous blood as controls. Each animal
underwent digital subtraction angiography of the vertebrobasilar system
using a microcatheter system. Nonsubtracted images documented placement
of the polymer in the cisterna magna. Animal evaluations were conducted
at 2, 4, or 90 days via angiography, and gross and microscopic
histopathology. At least 3 sections were trimmed, to include
representative sections of the medulla oblongata and cerebellum and were
examined by a board-certified veterinary pathologist.

[Results]{.underline}

The results and raw data (day 90) of the study were provided. The
reviewing pathologist states, "there was a minimal to mild focal or
multifocal vasculitis in the meninges adjacent to injected Onyx polymer
on sacrifice days 2 and 4 which was characterized by necrosis of the
wall of meningeal veins with slight infiltration of the wall by
granulocytes." The vasculitis was observed exclusively in the Onyx
treated animals and reached its highest incidence in the 6% Onyx group
and was of lower incidence in the 25% Onyx group. Onyx polymer was
observed in the meninges overlying the medulla oblongata or cerebellum,
less frequently observed in the cistern and occasionally found in the
cerebellum parenchyma. Another finding unique to Onyx treated animals
was a proteinaceous exudates observed on days 2 and 4. Also, there was
an increase in the incidence and severity of subacute inflammation in
the meninges in Onyx treated animals. The incidence and severity of
proteinaceous exudates and subacute inflammation were comparable between
the 6 and 25% groups. On day 90 vasculitis and proteinaceous exudates
were not observed in the meninges. Onyx was present in the meninges of
most brains and was associated with minimal to moderate accumulation of
foreign body giant cells and occasional mineralization and/or osseous
metaplasia.

"Degeneration/necrosis was observed in the medulla oblongata and the
cerebellum and assumed two distinct patterns. Subarachnoidal
distribution consisted of superficial neuropile and neuronal damage
characterized by spheroids, neuronal necrosis, and gliosis. Parenchymal
distribution was patchy and not associated with the surface and
consisted of localized liquefaction necrosis with reactive gliosis.
Parenchymal degeneration/necrosis was of comparable incidence and
severity in all groups on day 2 and was considered to be due to
mechanical trauma." "On day 90, only subarachnoidal changes were
observed and consisted of degeneration/necrosis in the medulla in two
Onyx treated animals and subarachnoidal gliosis often with neuropile
mineralization in 3 Onyx treated rabbits. The distribution of this
change in the cerebellum and medulla oblongata as well as the occurrence
of similar changes in the Saline and Blood groups (days 2 and 4 only)
strongly suggest that acute pressure against the bone of the skull is
involved in the pathogenesis of this change in the rabbit and that
direct toxicity of the Onyx is not a factor. Increased intracranial
pressure would most likely result from the combined effects of Onyx
material and associated proteinaceous fluid accumulation and to the fact
that Onyx is not resorbed or redistributed like saline or blood would
be."

The raw data/observations from day 90 indicate that the vasculitis and
proteinaceous exudates were of short duration, i.e., seen at 2 and 4
days but not reported out to 90 days. The inflammatory response observed
early, i.e., 2 and 4 days, was severe (3) in 2 of 4 animals and either
slight or moderate in the other 2 animals at 90 days. I believe the
reviewing pathologist's interpretation that the necrosis and
subarachnoid gliosis observed can be explained by increased intracranial
pressure due to the unresorbed EVOH polymer is reasonable. I think the
study indicates that the risk of adverse events or complications due to
the material escaping the vascular site into brain parenchyma is slight.
However, the information could be used for constitution of a warning or
precaution on the product label.

[Proposed Warning or precaution]{.underline}

Animal experimentation has shown that when Onyx escapes outside the
vascular space, as might occur if the vessel wall is compromised, a
subacute inflammatory response to the material may occur. Increased
intracranial pressure due to unresorbed Onyx material in this space may
cause tissue damage.

[Study of angiotoxicity of DMSO utilizing the rete mirabile in the swine
model test protocol]{.underline}

The purpose of the study was to determine the injection rates and
volumes of DMSO that could be safely used for delivery of the
embolization agent in humans. The sponsor chose the swine rete mirabile
animal model for the evaluation. Previous work by other investigators
had shown that infusion of DMSO could cause "severe, rapidly progressive
vasospasm in the distal ascending pharyngeal artery and retial
arteries." "Histological results showed hemorrhage, angionecrosis and
thrombosis." Further evaluation of DMSO associated vascular toxicity
indicated that slower infusion rates minimized angiotoxicity.

The experiment was conducted to address the time of injection of DMSO at
two volumes. The amount of the DMSO used to prime the catheter was
assumed to be 0.3 mL. Twenty-six swine were infused and sacrificed at 10
and 28 days. Times of injection were 30, 60 or 90 seconds for 0.5 and
0.8 mL volumes. Saline was used as the control vehicle injected into the
other rete. Vasospasm was monitored via contrast visualized angiography.
A five point grading system was used to quantify the severity of
vasospasm. The grading system was developed for the Thrombolysis in
Myocardial Infarction (TIMI) Clinical Trials.

[Results]{.underline}

The results indicate that a slow and controlled infusion of DMSO
(anhydrous) has no severe or permanent vascular effect in the swine
model. The dose rate of 0.5 mL/90 sec. (0.33 mL/min.) resulted in low
vasospasm scores, low vasospasm duration times and no permanent vascular
damage. Vasospasm did occur in all animals injected. In 21 of 24 cases
the vasospasm showed complete resolution and in the remaining 3 cases
minimal residual vasospasm was noted. At fast injections, i.e., above
0.5 mL/min. or greater, gross and microscopic histopathology revealed
inflammatory reactions and intimal hyperplasia.

The investigators note that for some types of clinical applications it
actually may be desirable to use an embolic agent that elicits a more
intense inflammatory reaction, since the affected vessels in such cased
are less likely to develop recanalization. This potential enhancement in
durability, however, may be counterbalanced by potential increased
peritherapeutic morbidity related to innocent bystander histotoxicity of
adjacent normal organ tissue.

As noted by the sponsor, repeat injections of DMSO and potential
vascular injury was not evaluated in this study. This is a safety
concern that should be addressed, as pointed out by CDER consultant
reviewers, by panel discussion.

Because the potential for vasospasm and vascular injury is a significant
concern, the product label and instructions for use must provide
sufficient information for individuals to use the product safely.

[Proposed Warning]{.underline}

The infusion rate of Onyx/DMSO (polymer solvent) must be carefully
controlled. More rapid infusion of DMSO in animal studies was shown to
cause vasospasm and vascular wall damage.

[Proposed Panel Question]{.underline}

Preclinical animal evaluations have shown that the rate and amount of
DMSO can cause vasospasm and vascular wall damage. These experiments
were conducted with a one-time injection of DMSO and short (10 day) and
chronic (28 day) follow-up. Patients undergoing staged embolization
procedures for Cerebral Arteriovenous Malformations will be exposed
repeatedly to the potential for DMSO-mediated vessel damage. Do you
believe additional animal evaluation should be conducted to more
completely assess for repeat-DMSO vessel wall exposure and potential
adverse effects?

[Evaluation of Embolyx E8 for Embolization of AVMs Using the Rete
Mirabile in the Swine Model]{.underline}

The purpose of the study was to evaluate the use of the device as an
embolization agent in the swine rete mirabile. This study was one of the
earlier safety and efficacy evaluations of the product.

A total of 20 swine were used in the study: the left rete was embolized
with the embolic agent whereas the right rete was embolized with
contrast reagent as a control. Animals were sacrificed at 3, 6 and 12
months. Prior to sacrifice an angiographic assessment of the retia was
performed.

Embolization protocol: DMSO delivery was maintained at 0.3 mL over 5-10
seconds for catheter priming. Delivery of the material ranged from
0.1-0.6 mL with delivery rates of 5-14 µL/second. The mean Embolyx/Onyx
volume and delivery rate was **[0.25 mL and 10 µL/second]{.underline}**.

Results: There were no reported incidences of vasospasm during the
procedures and all swine recovered without evidence of neurological
deterioration or behavior change. There was no reported abnormality or
deterioration in swine behavior following embolization or through
chronic maintenance periods. There were no embolization related
technical problems associated with using the catheters -- no reported
incidents of catheter occlusion, rupture or adhesion to the embolic
mass.

[Histology/gross and microscopic]{.underline}

-   Gross examination of harvested rete was reported as spongy and
    easily resected and no significant abnormality, rupture, or
    hemorrhage was observed.

-   Control rete specimens were unremarkable with normal vasculature in
    all respects

-   Acute specimens of retes were grossly unremarkable with no
    significant abnormalities. The acute specimens showed occlusion of
    the arteries with embolic material without evidence of endothelial
    denudation or arterial wall angionecrosis. There was no evidence of
    an acute cellular inflammatory response or hemorrhage in the
    perivascular spaces. Mild focal disruption of the lumen wall with
    embolic material and a mild inflammatory response was observed in
    1/7 specimens.

-   In the 3 and 6 month chronic specimen groups retes were occluded by
    dense aggregates of black particulate material, **[and a robust
    intraluminal foreign body giant cell reaction with massive
    multinucleated cells totally occluding most of the
    lumina.]{.underline}** Surrounding the foreign body giant cells were
    abundant lymphoplasmacytoid cells. Thrombi, although occlusive and
    sometimes organizing, did not appear to extend through the vessel
    walls, i.e., the foreign body giant cell and lymphoplasmacytoid
    reaction was largely superficial to the internal elastica lamina,
    although they prominently indented into the elastica in a few areas.
    **[No histological evidence of arterial wall angionecrosis was
    identified in these chronic rete specimens.]{.underline}** Focal
    elastica disruption without angionecrosis was identified in most
    specimens.

-   At 12 months, the rete specimens had histological findings
    substantially equivalent to the 3 and 6 month chronic embolization
    groups, but exhibited a substantial **[decrease]{.underline}** in
    chronic inflammation in 4/5 specimens. Disruption of the elastica
    was observed in 4/5 sepcimens with focal intimal hyperplasia
    occurring in 2/5 specimens. Non-material thrombi, generally well
    organized, were present in 4/5 specimens with indications of early
    calcification in 1/5. Negligible recanalization was observed in 1/5
    specimens. Overall, there was no observed eosinophilic activity or
    hemosiderin/.hematoidan present. [**The foreign body giant cell
    response was moderate to heavy in 4/5 specimens**. **No arterial
    wall angionecrosis or extravasation of emboic material was observed
    in any specimen.**]{.underline}

[Conclusions/comments]{.underline}

The authors note that the DMSO and Embolyx/Onyx delivery volumes and
injection rates were well tolerated with no reported vasospasm,
neurological deterioration, or behavioral modification post-procedure or
during chronic maintenance periods. The delivery catheters functioned as
anticipated with no occlusion, rupture or adhesion type technical
problems reported. Histopathological results indicated hyperplasia,
inflammatory reaction, foreign body giant cells and focal disruption of
elastica due to the foreign material. No significant recanalization,
hemorrhage or angionecrosis was reported.

The investigators state that **["additional safety issues relative to
the cumulative histotoxicity on local and pervisvascular tissue may need
to be addressed for outcome optimization."]{.underline}**

With respect to the histopathological changes observed, the authors
noted that PVA particles and N-butyl cyanoacrylate glue both have been
reported to elicit similar effects. References identified by the sponsor
support the assertion that the histologic response observed in this
study is not unlike what has been observed previously with other embolic
agents. In a study by Germano et al (J Neurosurgery, 1992, 76:607-614)
surgical specimens of 66 human cerebral arteriovenous malformations were
analyzed to determine the sequence of histopathological events after
embolization with poly vinyl alcohol particles. "Poly vinyl alcohol
particles indented the endothelium in 69% of cases but were rarely found
subendothelially. Clotted blood and fibroblasts were present among the
particles and abundant intraluminal mononuclear and polymorphonuclear
inflammatory cells were found in all vessels containing PVA particles.
Foreign body giant cells appeared 2-14 days after embolization in most
cases. Patchy mural angionecrosis and necrotizing vasculitis was found
in 39% of the cases. Recanalized lumina were seen in 18% of
PVA-embolized vessels." Vinters et al (N Engl J Med 1986; 314:477-483)
examined 17 intracranial arteriovenous malformations that were resected
after treatment by embolization using isobutyl-2-cyanoacrylate. "In 9
specimens removed 5 days to 16 months after embolization therapy, a
series of pathologic changes was seen, including patchy mural
angionecrosis (adjacent to the isobutyl cyanoacrylate fragment) up to 6
weeks after embolization, the presence of isobutyl cyanoacrylate in
vessel walls and fibromuscular intimal cushions, and the occurrence
(after several months) of entirely extravascular isobutyl cyanoacrylate.
Occasional parts of recanalized vascular malformations were identified.
Isobutyl cyanoacrylate was present within arteriovenous malformations as
late as 16 months after embolization although the amount appeared to be
diminished. These findings suggest a specific sequence of events in the
interaction between isobutyl cyanoacrylate and mural components within
the malformations and may explain some important complications of
embolization therapy." The authors also noted that foreign body giant
cells, perivascular cuffing by mononuclear inflammatory cells, and
widespread necrosis was observed. "Angionecrosis was not observed later
than 41 days after embolization but \[they\] did not have the
opportunity to examine a specimen in the critical follow-up period from
41 days to 3.5 months. In addition to necrosis of the channel walls
(which was identified by the presence of karyorrhexis of mural nuclei,
intense eosinophilia, and polymorphonuclear infiltration throughout the
full thickness of the wall layers) necrosis of parenchyma adjacent to
embolized channels (with or without an inflammatory response) was
observed."

Commentary by reviewing contributors of the paper regarding the animal
study results published in Neurosurgery (1998) by Murayama et al raised
2 concerns:

-   DMSO compatible catheters must be used due to the ability of the
    solvent to chemically degrade some polymers. The sponsor
    acknowledged this concern in their development of DMSO compatible
    catheters designed for use with the embolic agent.

-   The use of this embolic agent may have limitation in cases of AVMs
    with high-flow arteriovenous fistulae because of the danger of
    migration of the embolic agent into the venous drainage system. The
    reviewer notes that the issue is not resolved by the animal study
    because the swine rete mirabile is close to a plexiform AVM but does
    not mimic the common clinical scenario of an AVM with a high-flow
    arteriovenous fistula. Another reviewer states that "because of its
    lack of adhesiveness, \[the embolic agent\] may migrate into the
    venous site in high-flow fistulae, and it may be necessary to
    combine this agent with other agents, such as coils, buffers, or
    acrylics, to close the high-flow fistulae and reserve this embolic
    agent for a nidus type architecture.

[Study: Onyx aneurysm system: embolization of experimental
aneurysms]{.underline}

The purpose of the study was to evaluate the feasibility of treating
intracranial aneurysm by embolization with the subject device. The
information obtained in these evaluation, although more directly
applicable to treatment of aneurysms, can be extrapolated to the
treatment of AVMs and the histopathologic assessment for tissue
responses to the material.

Methods: The study series included both swine and canine animal models
with experimental aneurysms surgically created on the common carotid
arteries using carotid vein graft techniques. A total of 37 aneurysms in
31 animals were evaluated. Post-embolization evaluates include aneurysm
occlusion, parent artery patency, procedural complications, and overall
system performance. Sixteen animals in a pivotal series were assessed at
3, 6, or 12 months after treatment. Angiographic assessment of aneurysm
fill and arterial patency was obtained prior to animal sacrifice.
Fourteen additional aneurysms were treated with GDC coils and used for
histopathological control comparison to Onyx treated animals at the 3
and 6 month chronic follow-up evaluations.

Aneurysm embolization was performed using a "flow arrest" technique in
which a balloon occlusion catheter placed in the parent artery with the
balloon bridging the aneurysm neck effectively isolates the aneurysm
from the parent artery flow dynamics. The temporary interruption of
blood flow and stasis within the aneurysm sac permits delivery and
precipitation of the Onyx material from a pre-positioned delivery
catheter. **[Delivery of Onyx was staged with alternating periods of
balloon deflation to re-establish blood flow through the parent
vessel.]{.underline}** Angiographic assessment of aneurysm occlusion was
performed at the completion of the embolization procedure and again
immediately prior to animal sacrifice at designated implant periods.
Observations were recorded relative to aneurysm fill, neck remnant,
protrusion or migration of embolic material, and vasospasm or thrombotic
events associated with the treatment. Animals were closely monitored
daily for up to 12 weeks after treatment for indications of physical
impairment or abnormal behavior. At the conclusion of each study period,
aneurysms were excised and preserved for gross and microscopic
histologic analysis. Aneurysm morphology was characterized with detailed
observations of aneurysm fill, tissue remodeling at neck, protrusion or
migration of embolic material, and inflammatory response to the embolic
materials. The brain and rete mirabile of 3 swine were removed and
submitted for analysis of the effect of DMSO, and signs of brain
infarct, hemorrhage or softening of brain tissue.

Results: In the sponsor's narrative they state that, "overall physician
assessment rated the Onyx system performance as "acceptable" to
"excellent" when compared to GDC experience and performance." "Delivery
of Onyx within the aneurysm sac was controllable and well tolerated by
the animals with no significant technical or procedural incidents that
would suggest a compromise of safety in a clinical setting.
Pre-sacrifice angiography at 3, 6, and 12 months following embolization
confirmed parent artery patency and sustained angiographic obliteration
of the aneurysm with no incidence of recanalization. Aneurysm
histopathology specimens at 3, 6, and 12 month time periods showed
complete healing of the aneurysm neck with acceptable tissue response
comparable to GDC treated aneurysms with inflammation diminishing to
mild focal collections of lymphocytes and giant cells in 12 month
chronic specimens. There was no evidence of aneurysm rupture or wall
erosion seen in any specimen. Healthy neointimal tissue remodeling with
variably mature endothelial cell growth was observed across the aneurysm
neck in continuity with the parent artery lumen in all Onyx treated
aneurysms of the pivotal study group."

[Developmental Study Series Results -- detailed]{.underline}

A number of complications were observed in the developmental research
series, i.e., those animals embolized using various modifications of the
delivery system and embolization protocol. Physician assessment of the
procedure and treatment outcome rated 16/21 as "acceptable" to
"excellent" when compared to embolization with GDC coils. Three of 21
were rated "terrible" due to procedure or device related complications.
Summary embolization results are provided in the table below:

[Acute angiographic aneurysm assessment]{.underline}

Occlusion ≥ 95% 11

Occlusion ≥ 90-95% 3

Incomplete fill \< 90% 4

Not recorded 3

Three animal deaths occurred in the developmental series; 2 in recovery
and 1 during treatment. Two animals had transient visual impairment. One
animal, with a 3 day visual impairment following treatment, had
migration of Onyx reported and external carotid artery occlusion at 14
day follow-up angiography. Brain pathology showed significant fibrin
emboli consistent with the thrombotic arterial occlusion observed during
treatment. No Onyx material was detected. A second animal, with a 2 day
visual impairment following treatment, had vasospasm reported during the
treatment and transient parent artery occlusion at completion.
Histopathology showed the parent artery attenuated with marked
denudation and loss of smooth muscle cells attributed to a balloon
dilatation procedure to resolve the vasospasm. Parent artery stenosis or
complete occlusion occurred in 8 animals. Restriction of the parent
artery with Onyx and thrombus occurred in 4 animals. Complete thrombotic
occlusion occurred in 3 animals and a transient arterial occlusion in 1
animal. Thirteen occurrences of Onyx protrusion were observed and 4
incidents of Onyx migration in the parent artery. Nine of the 13
protrusions were unremarkable. Resistance to detachment of the delivery
catheter from the aneurysm at completion of embolization occurred in 4
procedures and adhesion of the Onyx to the delivery catheter in 3
procedures. A modified version of the FlowRider micro catheter
incorporation of a low profile marker band and siliconized distal tip
coating minimized further incidents.

[Pivotal Study Series -- detailed]{.underline}

Complications again were observed, if at a lower incidence than was
observed in the developmental series animals. Physician assessment of
the procedure and treatment outcome rated 15 of 16 embolizations as
"acceptable" to "excellent" when compared to GDC treatment experience.
Physician assessment of GDC treatment rated 14 of 14 as "good". The
percent of aneurysm fill with Onyx and GDC is provided:

Summary Embolization results

[Aneurysm occlusion Onyx GDC]{.underline}

100% 8 8

≥ 95% 5\* 0

90-95% 2 0

Incomplete 0 2

Not available - 4

\* one aneurysm is counted twice since it was 95%

The incidence of Onyx leakage into the parent vessel was significantly
reduced in the pivotal series following implementation of device and
procedure refinements. Two incidents were reported. Four of 14 aneurysms
treated with GDC coils had coil protrusion angiographically observed in
the parent artery at completion of treatment. Arterial vasospasm and
clot formation were observed in both Onyx and GDC treated animals. The
rate of occurrence in the Onyx group exceeded that reported for the GDC
treated group. One animal death in the Onyx group occurred although
necropsy attributed death to respiratory distress caused by
regurgitation and intubation trauma. One Onyx treated animal experienced
a seizure in recovery that resolved with no additional complications.
Two Onyx treated animals had transient parent artery occlusion
angiographically observed at completion of treatment. One of the 2 had
some arterial vasospasm associated with catheter detachment from the
aneurysm following embolization and one had experienced intra-procedure
vasospasm and post-procedure clot formation. Both occlusions resolved
with no further sequelae.

[Histopathologic observations]{.underline}

Histopathologic examination of aneurysms in the pivotal series was
performed to correlate angiographic assessment with actual morphologic
presentation of the aneurysm, i.e., to verify isolation of the aneurysm
from the parent artery flow dynamics and to evaluate the acute and
chronic tissue response to the Onyx material. In addition, the brains
and rete mirabile of 3 swine were studied to observe for tissue reaction
or significant sequelae distal to the aneurysm site.

The Onyx precipitate within the aneurysm sac was generally a conformal
mass characterized by cohesive peripheral laminations and a central
homogenous core. The precipitated masses remained non-adherent within
the aneurysm site. Chronic time point specimens were characterized by
active and sometimes obliterative fibrosis at 6 and 12 months. The
aneurysm sac and inner surfaces were characterized by mild to moderate
and occasionally severe, inflammation with palisading histiocytes
rimming the polymer cast. At 12 months, 2 of 3 specimens had a mild
inflammatory reaction limited to focal collections of lymphocytes in the
aneurysm wall with occasional giant cells lining the Onyx mass. One of
the 12 month specimens had marked chronic lympho-histiocytic
inflammatory response and numerous giant cells in the aneurysm wall.
Masses of necrotic acute inflammatory cells were observed in hollow
spaces and invaginations of the Onyx mass. The inflammatory response was
suggestive of delayed healing possibly due to compromise of sterility at
the time of treatment. Inflammation was frequently associated with
sutures in most specimens (i.e., sutures were used to help surgically
create the aneurysm), but rarely extended to the parent vessel or
neointimal growth across the aneurysm neck. The aneurysm necks were
typically filled with Onyx precipitate and either covered with fresh
thrombus in acute specimens or a variably organized thrombus and
fibro-muscular neointimal tissue isolating the sac from the parent
artery in chronic specimens. Progressive to complete development of
endothelial tissue over the fibro-muscular membrane was observed in
chronic specimens at 21 through 88 days. Neointimal tissue remodeling
readily developed over the surface of the Onyx in the aneurysm neck of
all specimens examined at 3, 6 and 12 month chronic periods. Neointimal
tissue thickness reported for 3 specimens at 3 months was 0.7-1.08 mm --
a thickness comparable to the parent artery wall thickness. The mean
neointimal tissue thickness for 3, 6 and 12 month specimens combined was
1.1 mm and ranges from 0.48 to 1.93 mm thick.

Some endothelial denudation of the parent arteries was observed in acute
specimens and occasionally in chronic specimens adjacent and/or
contralateral to the arterial anastomosis and sutures. This observation
is most likely related to the surgical trauma caused during creation of
the aneurysm. Neointimal tissue remodeling at the aneurysm neck of
chronic specimens was observed smooth and in continuity with the parent
vessel. Occasional mild to moderate parent vessel inflammation was
observed with rare fibrosis and intimal hyperplasia. Occasional
neutrophilic infiltrate of parent artery intima and internal elastic
layer adjacent to the aneurysm neck was observed originating from the
anastomoses and sutures. The rete mirabile and brains of 3 animals who
had died in recovery, or had visual impairment or parent vessel
occlusion were sectioned and processed for histopathology analyses. The
rete and brains were generally unremarkable with minimal to mild
mononuclear cell infiltrates observed. Nine aneurysms treated with GDC
coils were examined histopathologically for comparison to the Onyx
treated animals. All specimens showed complete healing of the aneurysm
neck with well-organized intimal growth consisting of smooth muscle
cells in a proteoglycan-rich matrix. Intimal growth over the necks was
essentially equal in both the 3 month and 6 month groups with a mean
thickness of 0.92 mm that ranged from 0.48 to 1.93 mm thick. Two
specimens had parent artery compromise of 50% and 95% from a thrombus.
There was moderate to extensive chronic lympho-histiocytic infiltration
of the sac and occasional multi-nucleated giant cells along the surface
of the coils. Healing and thrombus organization within the aneurysm sac
had progressed from granular tissue with chronic inflammatory
infiltration seen at 3 months to more organized, highly vascularized
fibrous tissue formation with diminished inflammation at 6 months.
Specimens showed either focal erosion of the aneurysm wall or were
extremely attenuated. An aneurysm sac from a 3 month specimen appeared
to have ruptured with coils protruding from the sac. Endothelial tissue
growth across the neck was seen in all 3 month specimens and of 3 of 4
specimens at 6 months.

Reviewer's interpretation: I believe the information supports the
sponsor's assertion that aneurysms treated with Onyx exhibited an
"acceptable tissue response" in that the response does not appear to be
worse than, or significantly different from what is observed with GDC
coils. This study, including the developmental series of experiments, I
believe, mirrors what has been seen, or would be seen histologically, in
the human clinical evaluation of the product. The material elicits an
acute inflammatory response that evolves into a chronic response which
includes the infiltration of lympho-histiocytic cells. Foreign body
giant cells are observed as usually are with implanted medical devices.
The inflammatory response does not appear to be worse than what is seen
with GDC coils which are legally marketed embolization agents. Although
the study reported here was presented by the sponsor in support of an
aneurysm indication for use, the information is relevant to the use of
the product on arteriovenous malformations, and especially arteriovenous
malformations that do not undergo surgical excision. I also believe this
study somewhat addresses the "repeat" DMSO vasculature exposure concern.
The material was layered on as would be done during embolization of an
AVM or an aneurysm, and so, vascular necrosis or vasospasm due to repeat
instillation of DMSO has been assessed in this model. What has not been
answered by this study is whether patients undergoing staged
embolization procedures in which the procedures are separated in time
are at greater risk for vascular complications due to repeat exposure to
DMSO.

[Histopathology study: evaluations of cerebral arteriovenous
malformations embolized with Embolyx liquid embolic]{.underline}

To assess Onyx for potential chronic histotoxic effects, 7 BAVMs
embolized with Onyx were surgically excised and submitted for evaluation
to a board certified histopathologist. The time from treatment with Onyx
to surgical excision ranged from 3 to 19 months. Histopathological
findings generally indicated successful embolization of AVM feeders and
reduction of AVM size without ischemic or hemorrhagic complications.
There were no indications of vascular necrosis, rupture or extravasation
of the Onyx material. Numerous vessels were observed with disruption of
the internal elastic lamina, but there did not appear to be any serious
adverse effect on the vessel wall. There were frequent indications of
small diameter reformed vascular lumens characterized by
endothelialization over well organized masses of Onyx material, but no
evidence of actual recanalization. BAVM embolization with Onyx did not
appear to be definitively associated with any morphologic changes that
would be expected to produce adverse clinical sequelae.

The tissue evaluated was obtained from patients in either the Mexico
City Embolyx Pilot Study or the International Brain Arteriovenous
Malformation Clinical study.

Results: BAVM (brain AVM) sizes ranged form 2.3 to 93.65 cm^3^ (mean
size 35 cm^3^). Prior to surgery, 1 of 7 patients received a single
embolization treatment, 2 of 7 received 2 treatments, 1 of 7 received 3
treatments and 3 of 7 received 4 treatments. The timing between
embolization and surgery ranged from 1 week to 19 months while all
patient had pre-surgical embolization periods of at least 3 months,
i.e., no one had one embolization procedure and then within 1 week went
to surgery whereas some patients may have had multiple embolization
procedures with the last one being 1 week prior to surgery.

**With specific note to the concern regarding repeat exposure to DMSO**

Two patients had 4 and 5 feeder vessels respectively embolized during
their initial embolization treatment. The volume of DMSO delivered was
recorded at 1.2 and 1.05 cc, and the volume of Embolyx was 0.25 and 2.77
cc, respectively. These patients continued with additional treatments,
receiving a total of 2.05 and 1.90 cc of DMSO and 1.35 and 4.08 cc of
Embolyx respectively prior to surgical excision of their AVMs. **["The
volume (and exposure) of DMSO and Embolyx seemed to be well tolerated by
the vasculature and the histopathology for these specimens appears
unremarkable."]{.underline}** The report shows favorable results (albeit
limited), with no indication of vascular necrosis, rupture or
extravasation of the Embolyx material. In 5 of 6 AVMs receiving multiple
embolization treatments, progressive reduction of AVM size was reported
with each embolization and there were no reported ischemic or
hemorrhagic complications resulting from untoward migration or abrupt
occlusion of an AVM nidus.

[MRI/CT Evaluation of brain AVMs treated with Onyx or n-BCA]{.underline}

A review of CT, MRI and flat film skull x-rays obtained from patients
whose BAVMs were treated with Onyx or n-BCA was performed for MTI by a
central reader to determine if any direct neurotoxicity due to Onyx can
be detected in the grain post-embolization. A total of 54 patients were
studied in the Onyx group and 19 in the n-BCA group (total = 73). The
central reader was blinded as to treatment. All MRI and CT studies were
evaluated for the presence of absence of gliosis, encephalomalacia,
edema, leptomeningeal or parenchymal enhancement and hemorrhage. These
parameters were pre-defined based on specific imaging characteristics.

Results: The average time post-embolization for all imaging studies was
23 months, with a range of 9 to 50 months. Forty-one patients of the 73
had imaging findings that required an assessment as to whether the
finding was due to the device. Twelve of the 19 n-BCA patients had
imaging changes that were due to: concurrent neurosurgical resection of
the AVM, changes in the brain related to neurosurgery, or due to the
natural history of the AVM. Twenty-nine of 54 patients in the Onyx
groups demonstrated imaging findings post-embolization that were not
present pre-embolization. The reader (Director, Clinical Image
Processing Service for UCLA Department of Radiological Sciences) asserts
that "in all cases the etiology of the post-embolization findings was
found to be due to events unrelated to the presence of Onyx." The
findings were believed to be due to radiosurgery, surgical resection of
the AVM and the natural history of the AVM. The images were not provided
in the report found in amendment 3 to MAF1071. An FDA radiologist
reviewed the images and their review of the images did not disagree with
the sponsor's interpretation.

This review is not finalized. Additional information has been requested
and review comments will be provided in the second mail-out.