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Original Article
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Walailak Chaiyasoot, M.D., Jirawadee Yodying, M.D., anita Limsiri, M.D.
Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, ailand.
Selective Arterial Embolization of Renal
Angiomyolipoma: Efcacy, Tumor Volume
Reduction, and Complications
ABSTRACT
Objective: To evaluate the ecacy and complications of selective arterial embolization in renal angiomyolipoma
and to identify predictive factors for tumor rupture.
Materials and Methods: Twenty-one patients with 25 renal angiomyolipoma (AML) underwent selective arterial
embolization (SAE) between January 2008 and June 2019, 15 lesions involving prophylaxis embolization of a
tumor >4 cm diameter and 10 involving embolization for a ruptured tumor. Multidetector computed tomography
(MDCT) was performed pre- and post-SAE, using the 2D tumor diameter measurement in the ruptured AMLs.
ree-dimensional volumetry and density histogram were performed for determining the total tumor volume, fat,
and angiomyogenic component reduction in the unruptured AMLs. e predictive factors for tumor rupture, the
treatment outcome and complications were analyzed.
Results: e clinical success rate was 84% (21/25 lesions) and the technical success rate was 96% (24/25 lesions). e
3D volume post-SAE within 1-3 months showed a greater decrement of the enhanced angiomyogenic component
than the fat component, with median percentages of -62.2% and -18.4%, respectively (p-value = 0.333). Minor
complications were post-embolization syndrome (5 lesions, 20%) and minimal renal infarction (4 lesions, 16%).
Renal abscesses were the major complications (3 lesions, 12%). A factor associated with tumor rupture was the
presence of an intra-tumoral aneurysm (p-value < 0.05).
Conclusion: SAE is an eective treatment for renal AML with a high technical and clinical success rate and
limited complications. ree-dimensional volumetry and density histogram analysis might be better tools than
two-dimensional CT to evaluate post-SAE response. e presence of an intra-tumoral aneurysm is a signicant
predictive factor associated with tumor rupture.
Keywords: Renal angiomyolipoma; selective arterial embolization (Siriraj Med J 2021; 73: 337-343)
Corresponding author: Jirawadee Yodying
E-mail: jirawadee.yod@gmail.com
Received 15 January 2021 Revised 8 February 2021 Accepted 10 February 2021
ORCID ID: http://orcid.org/0000-0002-2369-9008
http://dx.doi.org/10.33192/Smj.2021.44
INTRODUCTION
Renal angiomyolipoma (AML), a benign neoplasm
accounting for 0.3-3% of all renal tumors
1
, composed of
dysmorphic blood vessels, fat, and smooth muscle.
2
Eighty
percent of renal AML is a sporadic group, found among
women in their 4
th
- 5
th
decade, usually presented as a
solitary AML. e remainder has a female predilection,
usually symptomatic with multiple bilateral AMLs
associated with tuberous sclerosis complex (TSC).
3-5
Renal AMLs can potentially grow substantially and cause
many complications
5,6
which the major fatal complication
is a retroperitoneal bleeding.
3,4,7
Previous studies have
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Chaiyasoot et al.
proposed predictive factors for tumor rupture, including
tumor size, aneurysm formation, associated TSC
3,8,9
, the
size of an intra-tumoral aneurysm and a proportion
of angiogenic component.
10,11
e bleeding tendency
of the tumor might be come from an irregular shape
appearance of the intra-tumoral aneurysm.
12
Computed tomography (CT) and magnetic resonance
imaging (MRI) are important tools to diagnose renal AML
based on the tumors’ fat component to be dierentiated
from a renal cell carcinoma.
13,14
e treatment modalities
for asymptomatic renal AML are surgery, selective arterial
embolization (SAE), tumor ablation, and the use of
Mamalian Target of Rapamycin (mTOR
R
) inhibitors.
5
Recently, SAE has been accepted as the rst-line treatment
of renal AML, either for prophylaxis in tumor >4 cm or
treatment in acute hemorrhage patients with hemodynamic
instability.
15,16
However, from the literature review, there
is no research concerning the ecacy of SAE in renal
angiomyolipoma in ailand.
Objectives
The primary objective of our study aimed to
evaluate the ecacy of transarterial embolization using
multidetector CT (MDCT) measurement of total tumor
volume, quantication of the fat and angiomyogenic
component reduction post-SAE. e secondary objectives
were to analyze the post-procedural complications and
to identify the predictive factors for tumor rupture.
MATERIALS AND METHODS
Population
e study protocol was approved by the Institutional
Review Board (IRB) of Siriraj Hospital, Mahidol University
(Si 051/2020). Totally 161 patients with renal AML, we
retrospectively analyzed 54 patients (56 lesions) who had
CT diagnosis as renal AML (Fig 1) and undergone SAE
during January 2008 to June 2019. irty-three patients
were excluded due to unavailable CT studies, lost on
follow-up or expired. is le 21 patients enrolled in
the study.
Embolization procedure
Of the 21 patients with renal AMLs, 12 patients
were embolized electively and 9 patients had emergency
embolization. Most procedures were performed under
local anesthesia, only 3 cases needed general anesthesia
due to unstable vital signs. Selective renal angiogram was
performed using a 5 Fr catheter, followed by superselective
catheterization using a microcatheter to spare the normal
renal parenchyma. A coaxial system comprised of a
microcatheter; a 2.7 Fr Progreat® (Terumo, Tokyo, Japan)
were performed in 14 lesions, a 1.98 Fr tip Masters
Parkway® (Asahi Intecc USA, Inc.) in 7 lesions, and a 2.8
Fr Renegade HI-FLO® (Boston Scientic, Natick, MA,
USA) in 1 lesion. ree lesions used only 5 Fr selective
catheters because of large arterial feeders. Several embolic
materials were selected depend on each operator, including
polyvinyl alcohol, PVA (Contour®, Boston Scientic,
Ireland), absolute ethyl alcohol (Siriraj Hospital), N-butyl
cyanoacrylate (NBCA) or glue (Histoacryl®, Braun, Spain),
interlocking coil (Interlock® Boston Scientic, Ireland),
and thrombin (rombin-JMI®, Pzer, United States).
Technical success was dened as stasis of tumoral blood
ow and lack of contrast opacied renal AMLs on post-
embolization angiogram.
17
Imaging studies
A diagnostic CT scan (120 kVp; 115-500 mA; section
thickness, 1.25-3 mm; pitch, 0.992:1 and 1.375:1) was
conducted on a 64-slice and a 256-slice MDCT. Contrast-
enhanced CT was performed using non-ionic iodinate
contrast medium (320-370 mg I/ml) at a dose of 1.5-2
ml/kg.
All the patients had pre- and post-procedural MDCT.
e most recent pre-procedural CT (median, 29 days;
range, 0-219 days) and all post-procedural follow-up CT
(median, 2 months; range, 1–76 months) were reviewed
by a radiology resident and an interventional radiology
(IR) sta including maximal 2D diameter of the ruptured
tumor, the presence of an intra-tumoral aneurysm, the
aneurysm size and post-procedural complications. In
unruptured cases, we analyzed changes in the tumor
volume, enhanced angiomyogenic and fat component
of renal AMLs. e data analysis was performed using
an Advantage Workstation from Diagnostic Imaging
(ADW 4.6, GE Healthcare). e tumor volume was
calculated by drawing a region of interest (ROI) covering
the tumor on axial pre- and post-contrast (80-100 sec)
images and converting to 3D volumetry. e ROI of
the AML was then converted to a density histogram.
e enhanced angiomyogenic component volume was
calculated using the dierence between the area under the
curve of the density histogram with a density >100 HU
on pre- and post-contrast MDCT.
18
e fat component
volume was dened as the area under the curve of the
density histogram with a density <-20 HU on pre-contrast
phase (Fig 2). e percentage reduction was compared
between the pre- and post-procedural CT.
Clinical success was dened as no recurrence, no new
bleeding episode or complication related to SAE within
30 days, and no further surgery or re-embolization.
19
Complications were categorized as major and minor
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Fig 1. Typical CT and angiographic features of renal angiomyolipoma in the same patient (lesion no. 21)
(a) Pre-contrast axial phase CT showed a well-dened macroscopic fat-containing lesion at right kidney (arrow)
(b) Arterial phase CT demonstrated tortuous blood vessels (arrow) in the lesion
(d) Post-contrast phase CT revealed a heterogeneously enhanced fat-containing lesion (arrow)
(a) Right renal angiogram revealed a renal mass at interpolar region (arrow)
(b) Superselection into inferior segmental branch of right renal artery revealed a neovascularized and hypervascularized tumor
(arrow).
Note contrast excretion into dilated right renal pelvis, indicating hydronephrosis (arrowhead)
(c) Post-embolization angiogram showed arterial occlusion supplying the tumor (arrow) with preservation of normal renal
parenchymal blood supply
Fig 2. ree-dimensional (3D) volumetry and density
histogram comparing between pre- (a, c, d, g) and
1-month post-procedural CT (b, d, f, h)
(a-b) Axial post-contrast CT showed a right
renal AML (arrows) containing macroscopic
fat. e region of interest (ROI) was drawn
encircling the mass
(c-d) 3D volumetry of a total tumor volume
measured 169.0 and 148.2 cc, respectively
(12.3% reduction)
(e-f) Density histogram of the fat component
volume (attenuation <- 20 HU) measured
126.1 cc and 113.7 cc, respectively (9.8%
reduction)
(g-h) Density histogram of the enhanced
angiomyogenic component volume (attenuation
>100 HU) measured 4.48 cc and 1.34 cc,
respectively (69.8% reduction)
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Chaiyasoot et al.
complications according to the Society of Interventional
Radiology Clinical Practice Guidelines.
20
e patients’
medical records and MDCT ndings were reviewed for
the predictive factors associated with tumor rupture.
Statistical analysis
Data were analyzed using PASW Statistics 21.0 (SPSS
Inc., Chicago IL USA). Patients’ demographic data and
the lesions’ characteristics were recorded as the mean±SD
(range) and median (P
25
, P
75
) for the quantitative variables,
while numbers and percentages were summarized for the
qualitative variables. Comparisons between the percentage
reduction of fat and enhanced angiomyogenic component
were calculated using the Wilcoxon Signed Rank test.
Fisher’s exact test, 2-sample T-test, and Mann-Whitney
test were used to identify predictive factors associated
with tumor rupture. A p-value of <0.05 was considered
as a statistically signicant dierence.
RESULTS
Patients’ demographic data
A total of 21 patients (16 female, 5 male) and 25
lesions were analyzed. e mean patient’s age at the
diagnosis was 47 years old (range, 9-68 years) and during
the treatment was 50 years old (range, 22-68 years). Four
patients (19%) had underlying tuberous sclerosis complex.
Nine asymptomatic lesions were incidentally found
renal AMLs from prior check-up ultrasound. Fourteen
lesions presented with abdominal pain, 5 with anemia,
and 1 with hematuria. Single renal AML was found in
12 patients (57.1%), and multiple AMLs in 9 patients
(42.9%). Bilateral and unilateral lesions were found in
13 cases (61.9%) and 8 cases (38.1%), respectively. e
mean renal AML diameter before SAE was 8.93.3 cm
(range, 3.8-18.4 cm). Among 25 lesions, 10 were ruptured
AMLs (40%) and 15 were unruptured AMLs (60%).
Embolization and outcome
e embolic materials and outcomes of SAE are
shown in Table 1. e most common embolic material
was PVA particles (13 lesions, 54%) and the second
common was combined materials (4 lesions, 17%).
e technical success rate of SAE was 96% (24/25)
and a clinical success rate of 84% (21/25) including 9
lesions in asymptomatic patients, who had no complication
within 30 days post SAE and no re-intervention. Four
lesions had clinical failure and one lesion had technical
failure. Fieen unruptured AML patients had imaging
follow-up intervals. Almost 19/21 patients had long-
term clinical follow-up period (range 14-128 months,
mean 63 months) and all were well without requiring
re-intervention. Two patients died from the other non-
related diseases.
Post-embolization syndrome found in 5 lesions
characterized by fever, nausea, and abdominal pain.
Four lesions had a minimal renal infarction which did
not contribute to renal impairment during the follow-
up period (mean, 41.3 months; range, 16-70 months).
Two lesions with renal abscesses post-SAE required
percutaneous drainage and conservative treatment.
Another lesion with infected hematoma underwent
percutaneous drainage.
Imaging comparison between pre- and post-SAE
ree-dimensional (3D) volumetry and the density
histogram showed the total tumor volume, fat, and
angiomyogenic component reduction aer SAE during
the follow-up period (1 to >12 months) (Table 2). e
median percentage of fat reduction was -18.4% while
the median percentage of enhanced angiomyogenic
reduction was -62.2% at 1-3 months follow-up, with a
p-value of 0.333.
e analysis of predictive factors for tumor rupture
showed that the presence of an intra-tumoral aneurysm
was statistically signicantly associated with tumor rupture
(p-value = 0.015). e tumor size and aneurysm size
were also associated with tumor rupture but did not
show a signicant dierence (p-value = 0.071 and 0.154,
respectively) (Table 3).
DISCUSSION
Recently, SAE has become widely accepted as a rst-
line treatment for symptomatic renal AMLs or an AML
sized >4 cm.
15,16
Planché et al
18
also suggested that SAE is
eective, especially on the angiomyogenic component.
Our study showed a high technical success (96%) and
clinical success rate (84%) of SAE, agreed with Bardin
et al
10
who reported a 95.6% technical success rate of
SAE in 34 cases of symptomatic and asymptomatic renal
AMLs over a mean follow-up period of 20.5 months.
Ramon et al
8
found a clinical success rate of 91% in 48
symptomatic renal AMLs or renal AML >4 cm. over a
mean follow-up period of 58 months.
e total tumor size reduction in our study measured
by 3D volumetry at 1-3 months, 6-12 months, and >12
months follow-up were -7.1%, -48.9%, and -65.3%,
respectively, corresponding with the study by Planché
et al
18
, which showed a mean total volume reduction of
-54% and -81% during 1-12 months and >12 months
follow-up period, respectively.
Previous studies reported that the size of the intra-
tumoral aneurysm and a proportion of the angiogenic
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TABLE 1. Embolic materials and outcomes.
Embolic material used (n=24 lesions*)
Particles (PVA
†
) 13 (54%)
Alcohol 3 (13%)
Glue 2 (8%)
Coil 1 (4%)
Thrombin 1 (4%)
Combined 4
‡
(17%)
Treatment success (n=25 lesions)
Technical success 24/25 (96%)
Clinical Success 21/25 (84%)
Complication
§
(n=25 lesions)
Minor complications
Post-embolization syndrome 5/25 (20%)
Non-target Embolization 4/25 (16%)
Major complications 3/25 (12%)
Renal abscess Conservative
Renal abscess Percutaneous drainage
Infected hematoma Percutaneous drainage
* Twenty-four lesions were embolized and one lesion was not embolized due to failure selection into arterial pedicle
†
PVA = Polyvinyl alcohol
‡
Combined particles and glue (3 lesions) and combined coil and glue (1 lesion)
§
Categorized followed Society of Interventional Radiology Guidelines
TABLE 2. Total tumor volume, fat component volume and angiomyogenic component volume in pre-treatment,
post-treatment and %reduction during follow-up.
Follow-up period
1-3 months 6-12 months >12 months
Total tumor volume (ml): median (P
25
, P
75
)
Lesion (n)* 10 4 6
Pre-treatment 146.9 (52.3, 177.2) 140.2 (76.7, 315.7) 65.2 (61.5, 76.7)
Post-treatment 142.2 (40.5, 154.8) 67.2 (37.5, 298.3) 27.8 (9.3, 64.3)
% Reduction -7.1 (-26.6, +0.6) -48.9 (-58.9, -8.1) -65.3 (-85.7, -11.4)
Fat component volume (ml): median (P
25
, P
75
)
Lesion (n)* 10 4 6
Pre-treatment 127.1 (46.0, 164.0) 115.0 (73.5, 274.0) 63.4 (53.3, 73.5)
Post-treatment 107.0 (34.8, 129.5) 59.0 (34.5, 274.6) 24.8 (8.8, 58.0)
% Reduction -18.4 (-32.3, -3.8) -48.2 (-56.7, -5.6) -66.2 (-86.0, -10.0)
Angiomyogenic component volume (ml): median (P
25
, P
75
)
Lesion (n)* 10 3
†
3
†
Pre-treatment 1.4 (0.4, 4.0) 1.5 (0.4, 3.9) 0.5 (0.4, 1.8)
Post-treatment 0.7 (0.2, 1.4) 0.4 (0.2, -) 1.5 (0.3, -)
% Reduction -62.2 (-72.8, +13.5) -82.8 (-85.5, -) -13.1 (-49.0, -)
*Number of lesions are depended on post-treatment MDCT availability during follow-up period
†
Only 3/4 lesions and 3/6 lesions had post-contrast MDCT for angiomyogenic component volume analysis in 6-12 months and >12 months
follow-up period, respectively
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TABLE 3. Predictive factors associated with tumor rupture.
Factors Unruptured (n=15) Ruptured (n=10) p-value
TSC
Related 3 (60%) 2 (40%) 1.000*
Not related 12 (60%) 8 (40%)
Lesion size (cm)
Mean±SD 7.9±2.7 10.3±3.7 0.071
†
Aneurysm
Present 4 (33.3%) 8 (66.7%) 0.015*
Not present 11 (84.6%) 2 (15.4%)
Aneurysm size (mm)
Median (P
25
, P
75
) 5.3 (3.2, 8.0) 15.7 (4.8, 29.0) 0.154
‡
*Fisher’s Exact Test
†
2-Sample T-Test
‡
Mann-Whitney Test
component were the main causes of tumor rupture.
9,10-12,21
erefore, a reduction of the total tumor size might not
represent the treatment endpoint of SAE. Planché et
al
18
and Han et al
21
suggested that the angiomyogenic
component disappeared faster with a higher percentage
of decrement than the fat component. Correspond to
our study that a median percentage of fat reduction
was -18.4% while the median percentage of enhanced
angiomyogenic reduction was - 62.2% within 1-3 months
follow-up post-SAE.
ere were 4/25 lesions (16%) of clinical failure. e
rst lesion was a ruptured AML with an increased tumoral
size containing hemolyzed blood on 2 months follow-
up CT. is patient underwent surgical nephrectomy 9
months later. e second was also a ruptured AML with
30% decreased tumoral size plus resolving hematoma on
CT 3 months follow-up post-SAE. Six-month later, this
patient received surgical tumor removal. In these two
lesions, the associated perirenal hematoma might limit
the accuracy of the tumor measurement, resulting in an
unnecessary surgery. e third lesion was an unruptured
AML locating at renal collecting system (lesion no. 21)
(Fig 1) which showed decreased total tumor size, fat,
and enhanced angiomyogenic components on follow-up
CT at 1 and 29 months. However, the tumor gradually
increased causing obstructive le hydronephrosis on
follow-up CT at 75 months, then it was surgically removed
6 years later.
e last clinical failure lesion was the same as a
technical failure lesion (1/25, 4%). is was a 7.5 cm
unruptured AML receiving a 2
nd
SAE due to an inadequate
decreased size (38.7%) on follow-up CT at 6 months
aer the 1
st
SAE. e 2
nd
SAE was unsuccessful due to
the inability to catheterize into the arterial feeder, this
patient subsequently received surgery. However, our
retrospectively 3D-volumetry and density histogram
showed a signicant reduction of the total tumor volume
(41%), fat component (44%), and enhanced angiomyogenic
component (53%) on follow-up CT at 6 months aer
the 1
st
SAE. is could imply that 3D measurement
and density histogram might be more precise than 2D
measurement to evaluate post-treatment response, thus
avoiding further unnecessary treatment.
Post-embolization syndrome, a common minor
complication of SAE
10
found in 5/25 lesions (20%), all
were improved aer conservative treatment. Four lesions
(16 %) had limited renal infarction without impact on
renal function. ere were only 3 lesions (12%) of major
complications, consisting of renal abscesses. ese results
suggested that SAE had low rate of major complication,
in agreement with other studies.
10,15,18
We used several embolic materials depend on the
operator and the lesions. For devascularization distally, we
usually used particles. But for an intra-tumoral aneurysm,
we preferred glue injection or microcoil placing at the
proximal arteries feeding the aneurysm.
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Many prior studies have reported predictive factors
associated with ruptured renal AMLs, including the
tumor size, aneurysm formation, and the presence of
TSC.
3,8,9
Similar to our study that found statistically
signicantly of an intra-tumoral aneurysm associated
with tumor rupture. e tumor size and aneurysm size
were also associated with tumor rupture but TSC failed
to show the association.
Our study had some limitations. First, only symptomatic
or large renal AMLs are indicated for SAE, leading to a
small sample size. Second, the retrospective study design
could make the selection bias. ird, we did not have
a standard protocol of MDCT aer SAE, resulting in
dierent interval and imaging follow-up.
CONCLUSION
SAE is an eective treatment for renal AML with
a high technical and clinical success rate and limited
major complications. ree-dimensional volumetry
and density histogram analysis might be better tools
than 2D CT measurement for evaluation of post-SAE
response. e presence of an intra-tumoral aneurysm
is a signicant predictive factor associated with tumor
rupture.
ACKNOWLEDGEMENTS
e authors would like to express our gratitude to
all IR stas at Siriraj Center of Interventional Radiology
for their suggestion and sincerely thanks Asst. Prof.
Chulaluk Komoltri for the statistical analysis.
Conict of interest: No potential conicts of interest
relevant to this article are reported.
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