1
DOI: 10.5797/jnet.oa.2020-0003
Analysis of the Anatomical Factors
Affecting Ability to Navigate Penumbra
Catheter through Internal Carotid Siphon
Emi Kuriyama, Yoshikazu Matsuda, Takumi Kawaguchi, Rie Yako, and Naoyuki Nakao
Objective: The ecacy and safety of aspiration thrombectomy using Penumbra catheter with acute large vessel
occlusion in the anterior circulation have been reported in previous studies. In some cases, the carotid siphon (CS) is
elongated, and with this anatomy, especially where there is bifurcation of the ophthalmic artery (OA), navigation of
Penumbra catheters into distal internal carotid artery (ICA) is interrupted, which is known as the ‘ledge eect’. We
investigate the anatomical characteristics of CS that cause interruption of navigation of the Penumbra catheter.
Methods: Between January 2015 and March 2018, mechanical thrombectomy using Penumbra 60 was performed on
51 patients with middle cerebral artery (MCA) or intracranial ICA occlusion. Patients were divided into two groups: The
‘ledge-eect’ group those in whom the Penumbra catheter was unable to be navigated into the distal ICA through the CS,
and ‘no ledge-eect’ group those in whom this was possible. The anatomical characteristics of CS, the diameter of ICA,
diameter of OA, OA/ICA ratio and radius of the CS were evaluated using angiographical imaging.
Results: The ‘ledge-eect’ group numbered eight cases (17%). Only the value of the CS radius was signicantly smaller
in the ledge-eect group (p = 0.0019), other parameters were not signicantly dierent between the groups. The cuto
radius value was 3.62 mm.
Conclusion: The most notable anatomical factor aecting possibility of navigation of the Penumbra catheter through
the CS was the CS radius. This could be useful information when devices used in mechanical thrombectomy are selected.
Keywords▶ mechanical thrombectomy, Penumbra catheter, carotid siphon
Introduction
Recent trials and meta-analyses have proved the ecacy of
mechanical thrombectomy over other types of treatment
of large vessel occlusion in patients with acute ischemic
stroke. Although the eectiveness of stent retrievers has
been reported, Penumbra aspiration catheter (Penumbra
Inc., Alameda, CA, USA) has been suggested as a good
alternative device. Thrombectomy using Penumbra catheter
such as a direct aspiration rst pass technique (ADAPT)
enables recanalization signicantly faster than previously
reported means of thrombectomy.1) There are many recent
reports on adjunctive technique using Penumbra catheter.
For example, Solumbra/Trenumbra techniques are reportedly
useful as methods of reperfusion using a combination of
Penumbra catheter and the stent-retriever (Solitaire FR
device; Medtronic Neurovascular Irvine, CA, USA) or Trevo
(Stryker Neurovascular Fremont, CA, USA).2,3) Continu-
ous aspiration prior to intracranial vascular embolectomy
(CAPTIVE) and stent-retriever-assisted vacuum-locked
extraction (SAVE) technique which use a stent retriever
with continuous aspiration by large-bore catheter are help-
ful to get successful recanalization and have shorter reca-
nalization time.4,5) Proximal balloon occlusion together
with direct thrombus aspiration during stent-retriever
thrombectomy (PROTECT) using additional balloon guid-
ing catheter showed excellent results.6)
Although aspiration catheters with larger catheter lumen
have been developed to improve aspiration power, this also
This work is licensed under a Creative
Commons Attribution-NonCommercial-
NoDerivatives International License.
©2020 The Japanese Society for Neuroendovascular Therapy
Depart ment of Neurosurgery, Wakayama Medical University,
Wakayama, Wakayama, Japan
Received: January 17, 2020; Accepted: February 25, 2020
Corresponding author: Emi Kuriyama. Department of Neurosu r-
gery, Wakayama Medical Universit y, 811-1 Kimiidera, Wakayama,
Wakayama 641-8509, Japan
Email: emi.k@wakayama-med.ac.jp
Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020
2
Kuriy ama E, et al .
results in a larger prole and more diculty in achieving
distal navigation. Generally, larger Penumbra catheters
often require the use of a coaxial technique to navigate into
the site of the occlusion because of the ‘ledge eect’, being
held up by bifurcation of the ophthalmic artery (OA).7,8)
Even if a coaxial technique was used, in some cases, we
experienced that Penumbra catheter was unable to track to
distal internal carotid artery (ICA) because of the anatomy
of the carotid siphon (CS).
We investigated the anatomical characteristics of the
ICA that render navigation of Penumbra catheters into the
distal ICA through the CS challenging.
Materials and Methods
Patient selection
We retrospectively reviewed clinical characteristics and
radiographic imaging of patients with acute ischemic
stroke who underwent mechanical thrombectomy using
Penumbra system at our institution between January 2015
and March 2018. This study was approved by the
Wakayama Medical University Ethics Committee.
Patients with basilar/vertebral artery occlusion were
excluded from this study. The inclusion criteria at our institu-
tion was as follows: (1) Symptoms were either moderate or
severe, an admission National Institutes of Health Stroke
Scale (NIHSS) score was at least 6. (2) Patients had a small
territorial infarction by non-contrast CT, dened as an Alberta
Stroke Program Early CT Score (ASPECTS) >6. (3) A mod-
ied Rankin Scale (mRS) prior to stroke onset score was 0, 1,
or 2. (4) Patients with ICA and/or middle cerebral artery
(MCA) occlusion identified by radiographic imaging
underwent mechanical thrombectomy using Penumbra 60
(Almeda, CA, USA). (5) Clinical-diusion mismatch existed.
(6) The time from onset to puncture was within 6 hours. If the
patients met the adaptation criteria of intravenous tissue plas-
minogen activator (IV-tPA), they underwent IV-tPA rst.
We divided these patients into two groups, ‘ledge-eect
group’ in whom a Penumbra 60 could not be navigated into
the distal ICA over the CS, and ‘no ledge-eect group’, those
in whom a catheter was able to be navigated over the CS.
In these groups, the patients whose OA could not be identied
on angiography was excluded from radiographic analysis.
The case details were reviewed, including demographic
data, medical history (atrial brillation, hypertension, diabetes
mellitus, hyperlipidemia), history of smoking, comorbidity
(cardiac artery disease, previous cerebral infarction, periph-
eral artery disease), NIHSS and CT-ASPECTs.
Means of conrming diagnoses
Less than 2 on the mRS was considered to be a favorable
outcome. Thrombolysis in Cerebral Infarction (TICI) 2b-3
classication was used for evaluation of successful reca-
nalization. The rst pass eect (FPE) was dened as
achieving a complete recanalization with the rst pass.
Radiographic analysis
We evaluated the anatomical characteristics of CS by
reviewing lateral angiography as follows: diameter of ICA,
diameter of OA, OA/ICA ratio, and radius of CS between
two groups. CS radius was dened as the diameter of the
circle passing the centerline of the CS through three points,
the midpoint of the diameter in the ICA at bifurcation of
the OA, the vertex of the ICA genu, and the proximal C3
(Fig. 1). Smaller CS radius means greater elongation of
the CS. These parameters were measured twice each by
E.K. and Y.M.
Endovascular procedure
All endovascular therapies were performed on the angio-
suite under local anesthesia. Generally, a 9F balloon-guiding
catheter (Optimo, Tokai Medical products, Japan) was
placed in the cervical portion of the ICA. Systematic hepa-
rin was intravenously injected during the procedure to keep
the activating clot time between 250 and 350s. In case with
IV-tPA, only 3000 units of heparin were injected after
sheath insertion. The guiding catheter was continuously
ushed with heparinized saline.
Fig. 1 Lateral angiography shows representative CS. Radius of
the CS was dened as the diameter (white arrow) of the cir-
cle (white circle) passing the centerline of the CS through
three points: (A) midpoint of the diameter in ICA at bifurca-
tion of OA, (B) the vertex of ICA genu, and (C) the proximal
C3 (white dots). CS: carotid siphon; ICA: internal carotid
artery; OA: ophthalmic artery
Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020
3
Abili ty to Na viga te Penum br a Cat heter thro ugh Int erna l CS
Cuto value of the CS radius was calculated by receiver
operating characteristic curve.
Results
Flowchart for exclusion and inclusion of the patients
underwent thrombectomy in our study is shown in Fig. 2.
No ledge-eect group comprised 43 of 51 cases (83%),
and the ledge-eect group comprised eight of 51 cases
(17%). Patient characteristics are shown in Table 1. In all,
24 male patients (56%) were in the no ledge-eect group,
six (76%) were in the ledge-eect group. Mean ages were
75.7 in the no ledge-eect group and 78.6 in the ledge-
eect group. Risk factors and comorbidity were not signi-
cantly dierent between the two groups. Mean NIHSS
scores were 17 and 15, respectively. Acute stroke severity
assessed by the NIHSS and ASPECTs at presentation was
not signicantly dierent between the two groups.
The site of occlusion of the intracranial ICA was 18.6%
(8/43) in the no ledge-eect group and 25% (2/8) in the
ledge-eect group. The occlusion of the rst segment of
MCA (M1) was 76.7% (33/43) in the no ledge-eect group
Penumbra 60 was navigated just proximal to the throm-
bus over intermediate catheter, Penumbra 3Max (Alameda,
CA, USA) or Marksman catheter (Covidien, Irvine, CA,
USA) and a Chikai 0.014 inch microguidewire (Asahi
Intecc, Aichi, Japan). After positioning, the catheters and
microguidewires were withdrawn. After no retrograde
blood was identied, pump aspiration was performed. Pen-
umbra 60 was gently withdrawn under continuous aspira-
tion. If this procedure was unsuccessful, the same procedure
was tried once more. In unsuccessful aspiration proce-
dures, use of a stent retriever was considered. In case, the
Penumbra 60 was unable to be navigated over the CS,
another method, such as using a stent retriever, was also
considered.
Statistical analysis
ImageJ software (National Institutes of Health, USA) was
used for anatomical measurements. JMP pro13 software
(SAS Institute Inc., Cary, NC, USA) was used for statistical
analysis. The chi-square homogeneity test and Student’s
t-test were used to compare categorical variables. P value
of <0.05 was considered to be statistically signicant.
Fig. 2 Flowchart for exclusion and inclusion of the patients underwent thrombectomy in our study
Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020
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Kuriy ama E, et al .
Trevo and/or Revive [Codman, Raynham, Massachusetts,
USA]) to achieve recanalization because of the diculty
for navigation of Penumbra 60. The ADAPT method using
3MAX was performed in the latter one case. IV-tPA was
conducted 18.6% (8/43, no ledge-eect group) and 12.5%
(1/8, ledge-eect group), respectively. The dierence of
inner intermediate catheters of Penumbra 3MAX and
Marksman demonstrates no signicant dierence in track-
ability of Penumbra 60. Mean pass times to recanalization
were 2.0 in both groups. FPE was achieved in 34.5%
(15/43) and 37.5% (3/8), respectively (p = 0.33). Results
are shown in Table 2.
The rates of successful recanalization (TICI grade ≥2b)
were 86.0% (37/43, no ledge-eect group) and 100% (8/8,
and 50% (4/8) in the ledge-eect group, the occlusions of
the second segment of MCA (M2) were 4.7% (2/43) and
25% (2/8), respectively. The tandem occlusion was 9.3%
(4/43) in the no ledge-eect group and 12.5% (1/8) in the
ledge-eect group. There was one case (12.5%) with
embolism from carotid artery occlusion requiring carotid
artery stenting (CAS) in the ledge-eect group. There were
four cases (9.3%) with embolism due to carotid artery ste-
nosis or occlusion requiring CAS or percutaneous translu-
minal angioplasty (PTA) in the no ledge-eect group. The
simple aspiration method was used in 23.3% (10/43) of the
no ledge-eect group and 12.5% (1/8) in the ledge-eect
group. In the former group, other ve5 cases with M1 dis-
tal occlusion required additional stent retrievers (Solitaire,
Table 1 Characteristics of patients
No ledge-effect group Ledge-effect group p
No. of patients (%) 43 (83) 8 (17) 0.3
Age (years) (SD) 75.7 ± 1.8 78.6 ± 4.4 0.94
Sex, male (%) 24 (56) 6 (75) 0.43
Af/pAf (%) 28 (65) 3 (38) 0.27
Risk factors (%) Hypertension 26 (60) 6 (75) 0.69
Hyperlipidemia 7 (16) 3 (38) 0.18
Diabetes mellitus 8 (19) 4 (50) 0.08
(Ex-)smoker 5 (31) 1 (13) 1
Comorbidity (%) CAD 9 (19) 2 (20) 0.62
Previous CI 12 (28) 2 (20) 1
CKD 2 (4) 0 (0) 1
PAD 1 (2) 0 (0) 1
NIHSS (mean) 17 15 0.29
CT-ASPECTs (mean) 9 9 0.85
Af: atrial fibrillation; ASPECTs: Alberta Stroke Program Early CT Score; CAD: cardiac artery disease; CI: cerebral infarction;
PAD: peripheral artery disease; pAf: paroxysmal atrial fibrillation; NIHSS: National Institutes of Health Stroke Scale
Table 2 Sites of occlusion and methods for mechanical thrombectomy
No ledge-effect group Ledge-effect group p
ICA occlusion 8 2 0.25
MCA occlusion M1 33 4 0.25
M2 2 2
Tandem occlusion 4 1 1
Side Left 26 2 0.06
IV-tPA 8 1 1
Inner catheter 3MaxACE 6 2 0.76
Marksman 35 6
Others 2 0
Other system Solitare 14 4 0.04
(Stent) Trevo 7 4
Revive 10 0
None 10 1
Number of passes 2 2 0.79
Number of FPE 15 3 0.33
FPE: first pass effect; ICA: internal carotid artery; IV-tPA: intravenous tissue plasminogen activator; MCA: middle
cerebral artery
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Abili ty to Na viga te Penum br a Cat heter thro ugh Int erna l CS
distal ICA. Generally, ledge eect is reported to render
navigation of the catheter into the distal ICA both chal-
lenging and time-consuming.7) Therefore, we evaluated
CS anatomy inuencing the ledge eect and focused on
the diameter of ICA, OA, OA/ICA ratio, and radius of
CS for the following reasons.
Diameter of ICA
The average diameter of the cavernous part of the ICA was
reported to be 3.68 mm on the right, 3.85 mm on the left.9)
In the no ledge eect and ledge-eect group, these aver-
ages were 4.53 mm and 4.06 mm, respectively. It was
slightly larger than that previously reported. Small diame-
ter of ICA was assumed to make navigation of the Penum-
bra catheter challenging, but in this study, the average ICA
diameter was not signicantly small.
Diameter of OA
A larger diameter of the OA would create a larger ledge
eect to advance the Penumbra catheter through the CS.
OA is the rst branch of the ICA immediately after it arises
from the cavernous sinus and enters the cranial cavity. Its
diameter ranges between 0.7 and 1.8 mm.10,11) The average
OA diameter in this study was not signicantly dierent
between groups: 1.08 and 1.11 mm, reference value range.
OA could be measured except in four cases and be located
in supraclinoid segment of the ICA. Recanalization was
not necessary in one of the cases. OA was not detected in
the other three cases with successful recanalization.
ledge-eect group), respectively. (p = 0.22). Puncture to
recanalization times were 61.0 and 73.5 minutes in each
group (p = 0.34). Favorable outcome was 39.5% and 37.5%
(17/43 and 3/8), considered to be without signicant dier-
ence (Table 3).
The radius of CS in ledge-eect group was signicantly
smaller than that in the no ledge-eect group (p = 0.0019).
The other parameters, diameter of ICA, OA, and OA/ICA
ratio, between the two groups showed no signicant dier-
ence (Table 4). Cuto value of the radius was 3.62 mm.
A representative case, a 72-year-old female, with occlu-
sion of ICA top had small CS radius and was in the ledge-
eect group (Fig. 3). Small radius indicates that the vertex
of CS is severe. First, Penumbra 60 with Penumbra 3MAX
intermediate catheter into 9F balloon guide catheter was
applied. It failed to be passed through CS because of the
ledge eect. Marksman microcatheter was navigated to the
distal thrombus through Penumbra and stent retriever
(Trevo 4 × 20 mm) was deployed across the thrombus and
the microcatheter was removed completely. After waiting
for 5 minutes, continuous aspiration was started and the
stent was retrieved into the aspiration catheter. After two
passes of same the procedure, full recanalization was
shown on nal angiography.
Discussion
In our study, the CS radius was independent factor in
unsuccessful navigation of Penumbra catheter into the
Table 3 Outcome of procedure
No ledge-effect group Ledge-effect group p
TICI 3 19 6 0.22
2b 18 2
2a 4 0
10 0
02 0
TICI 2b–3 (%) 37(86) 8(100) 1
Puncture to recanalization (min) 61 73.5 0.34
mRS 0–2 at 30 days (%) 17(39.5) 3(37.5) 1
mRS: modified Rankin Scale; TICI: Thrombolysis in Cerebral Infarction
Table 4 Anatomical results
No ledge-effect group Ledge-effect group p
Diameter of ICA (mm) 4.53 4.06 0.11
Diameter of OA (mm) 1.08 1.11 0.78
OA/ICA ratio 0.22 0.23 0.11
Radius (mm) 4.19 2.92 0.0019
ICA: internal carotid artery; OA: ophthalmic artery
Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020
6
Kuriy ama E, et al .
ICA at bifurcation of OA, vertex of the genu of ICA, and
midpoint of the proximal C3. Radius of the CS means rel-
atively the tortuosity. Smaller radius shows severe elonga-
tion of the vessel which can make advancement of a
catheter challenging. In our study, only this parameter had
signicant dierence between the two groups. It proved
the bending of the CS in the ledge-eect group aected
feasibility to navigate Penumbra over CS.
Greater dierence in diameters between inner diameter
of Penumbra 60 and outer diameter of intermediate cath-
eter (Penumbra 3MAX or Marksman microcatheter)
causes greater ledge eect. The coaxial advancement
technique was reported previously. If a microguidewire is
just used for advancing the Penumbra 60, the gap between
the two devices is expected to be large and this could
OA/ICA ratio
If the OA/ICA ratio is smaller, it means a relatively smaller
diameter of OA. Smaller ratio is expected to facilitate the
navigation of Penumbra catheter into distal ICA through
CS. In our study, however, there was no dierence between
the two groups.
Radius of CS
Previous reports on radius of ICA reported that bending of
the CS resembles the circle. Chi Zhang et al. (2013)
reported geometric classication of the CS and dened the
osculating circle (OC) as the curvature radius tting to the
bend of centerline of CS.12–14) We dened radius of the CS
as the diameter of the circle passing the centerline of CS
through three points including midpoint of the diameter in
Fig. 3 (A) Representative case, a 72-year-old female, with small radius of CS (3.54 mm) and ledge-eect group is shown.
Small radius indicates severe bending of the CS. Diameter of ICA is 5.46 mm, diameter of OA is 0.94 mm, and OA/
ICA ratio is 0.17. (B) Diagnostic angiography shows the occlusion of ICA top. (C) Stent retriever Trevo 4 × 20 mm was
deployed across the thrombus. Penumbra catheter was navigated just proximal of Trevo. Trenumbra was conducted.
(D) Two passes of the same procedure showed full recanalization on nal angiography. CS: carotid siphon; ICA:
internal carotid artery; OA: ophthalmic artery
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Abili ty to Na viga te Penum br a Cat heter thro ugh Int erna l CS
result in diculty controlling the catheter. The coaxial
advancement technique was used to reduce the gap
between the inner diameter of Penumbra 60 and the outer
diameter of intermediate catheter so to allow navigation
of the Penumbra 60 into distal portion over CS.15) How-
ever, in our study, the dierence of intermediate catheter
was not signicant. The outer diameter of Penumbra
3MAX is 0.050 inch. On the other hand, that of Marks-
man microcatheter is 0.037 inch. This difference of
0.013 inch was negligible for navigation of Penumbra 60
through CS. When comparing the Penumbra 60 with the
intermediate catheter, the ledge eect (inner diameter of
Penumbra 60 [0.060 inch] – outer diameter of intermedi-
ate catheter), is 0.010 inch for Penumbra 3Max and 0.023
inch for Marksman microcatheter. This dierence could
be negligible from our result.
Previous reports detailed other methods of navigation of
Penumbra catheter through CS smoothly.
One method of navigating the Penumbra catheter
through the CS is by steam-shaping the tip of the Penum-
bra catheter. It allows easy navigation through the CS. In
the previous reports, there were three types of “sim-
ple-curved” steam shaping; a 45° curve, a 90° curve, and
J-shape curve. In most cases, advancement is more
smoothly achieved using a steam-shaped catheter tip with
a 45° curve. However, in some cases with extreme tortuos-
ity or severe atherosclerotic stenosis, a 90° curve or J-shape
can be occasionally used.16) Therefore, if tortuosity of CS
is severe, although in our study steam-shaping was not per-
formed, it may be better to shape the Penumbra catheter
before puncture. The disadvantage of this proposal is that it
is time-consuming and shaping might induce the malfor-
mation of tip of the Penumbra catheter.
Another means of navigating the Penumbra catheter
through the CS is by the so-called ‘buddy wire’ technique.
It means introducing a supportive microguidewire. This
can be used to support the Penumbra catheter and provide
added stability. This method is usually used for percutane-
ous coronary intervention (PCI), CAS, stenting of the ver-
tebral artery, and other endovascular therapies.17–19) Double
wires might enable reduction of the gap between microgu-
idewire and microcatheter and improve usability of the
catheter by reducing the ledge eect.
More recently, Sofia Non-wire Advancement tech-
niKE (SNAKE) is reported benefit for mechanical
thrombectomy. Because the distal end of the Sofia cath-
eter is extremely soft, it could be safely advanced into
the intracranial vessels without any microcatheter or
microguidewire. This technique may be one method to
overcome the challenging of the ledge effect.20)
Successful recanalization with TICI 2b or 3 was
achieved in 75–87% with ADAPT in other reports.21) The
reperfusion rate of TICI2b or 3 in no ledge eect and
ledge-eect group was 86% and 100%, respectively. These
results were similar to those of previous reports.22) The
mean reperfusion times were 61.0 and 73.5 minutes,
respectively (p = 0.33). There was no dierence in pass
times or in treatment for cervical lesion between both
groups. Ledge-eect group had tendency for longer reper-
fusion time. Consequently, change of devices in cases of
unsuccessful navigation of Penumbra catheter through CS
may be required, and more patients in the ledge-eect
group would result in dierence between these groups.
In this study, in unsuccessful navigation through CS,
correct selection of devices could reduce reperfusion time.
Furthermore, aspiration catheters with larger lumen that
could improve power of aspiration are under developed.
These catheters could produce greater ledge eect, how-
ever. Therefore, this study is meaningful for mechanical
thrombectomy using Penumbra catheters.
A limitation of our study is that, because of limited
resources, this was a retrospective study and it was con-
ducted in a single institution. Actually CS radius would
rely on a completely orthogonal view of the CS but lat-
eral angiograph is not completely orthogonal to the skull.
To reduce the inuence, strict lateral angiography with
the acoustic meatus at same level was obtained. The tor-
tuosity of femoral artery and arch of aortic artery might
aect navigation of Penumbra catheter to thrombus.
However, ination of balloon guiding catheter not only
stop ow of ICA but also support anchoring ability for
navigation of Penumbra catheter. As a results, this ina-
tion of balloon could minimize elongation of femoral
artery and aortic arch.
Conclusion
The main factor in ability to navigate a Penumbra catheter
through the CS was the radius of the CS. This measure-
ment could be helpful for selection of devices for mechan-
ical thrombectomy.
Disclosure Statement
There is no conict of interest for the rst author and
coauthors.
Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020
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Kuriy ama E, et al .
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Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020Journal of Neuroendovascular Therapy Advance Published Date: March 13, 2020
