American Journal of Neuroradiology 28:387-389, February 2007
© 2007 American Society of Neuroradiology
Technical Note
INTERVENTIONAL
Analysis of Complex Framing Coil Stability in a Wide-Necked Aneurysm Model
P.E. Schloessera,
R.S. Pakbazb,
D.I. Levyb,
S.G. Imbesic,
W.H. Wongc and
C.W. Kerberc
a Department of Radiology, Division of Neuroradiology, LDS Hospital, Salt Lake City, Utah
b Departments of Neuroradiology and Neurosurgery, Division of Neuroradiology, Kaiser Permanente Medical, Center, San Diego, Calif
c Department of Radiology, Division of Neuroradiology, University of California San Diego Medical Center, San Diego, Calif
Address correspondence to Peter E. Schloesser, MD, Department of Radiology, Division of Neuroradiology, LDS Hospital, 8th Ave and C St, Salt Lake City, UT 84143; e-mail: peter.schloesser{at}mtnmedical.com
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Abstract
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SUMMARY: Appropriately sized 0.010- and 0.018-inch complex framing
coils were placed in a wide-necked silicone aneurysm replica,
and their stability was evaluated at variable physiologic flow
rates using video recording. After detachment, the 0.010-inch
coils demonstrated instability/prolapse that was proportional
to flow rate. In contrast, 0.018-inch coils held their 3D configuration
regardless of flow rate. The findings support the use of 0.018-inch
coils (when possible) in aneurysms with unfavorable geometry,
particularly in circulations with higher flow rates.
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Introduction
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Endovascular treatment of wide-necked intracranial aneurysms
remains a therapeutic challenge because of the risk of coil
prolapse into the parent vessel.
1,2 The recent introduction
of devices (stents specifically designed for intracranial use)
and techniques (balloon remodeling) have expanded our ability
to treat aneurysms with unfavorable geometry.
3–6 However,
these measures can add to the complexity, duration, and consequent
risk of the procedure. In addition, treatment of acutely ruptured
aneurysms can be complicated by the necessity for full anticoagulation
and possible need for antiplatelet therapy when these devices/techniques
are used, increasing the risk of rehemorrhage.
7 With this concern
to avoid unnecessary patient risk, and the present increasing
variety of coils and devices available to the interventionalist,
our study sought to evaluate the effect of primary coil diameter
choice (0.010- versus 0.018-inch) upon complex framing coil
stability in a wide-necked silicone aneurysm replica at various
(physiologic) flow rates.
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Materials and Methods
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Silicone replicas of wide-necked aneurysms were created using
the lost wax technique.
8,9 Two 10-mm aneurysm models were created
(
Fig 1) with sack-to-neck ratios (SNR) of 1.3 (wide-necked geometry)
and 1.7 (favorable geometry). The silicone models were placed
in a circuit of pulsatile non-Newtonian fluid with rheologic
properties similar to those of blood.
10 A fluid pump apparatus
(Flowtek, San Diego, Calif) cycling at 1 pulse/s provided flow.
The flow rate in the device was calibrated to simulate basilar,
middle cerebral, and internal carotid artery levels (280, 360,
and 420 mL/min, respectively).
11 We placed single 10-mm 0.010-
and 0.018-inch standard GDC 3D (Boston Scientific/Target Therapeutics,
Fremont, Calif), MicroSphere (Micrus Endovascular, San Jose,
Calif), and MicroPlex (MicroVention, Aliso Viejo, Calif) coils
within 10-mm wide-necked aneurysms. A single 0.010 or 0.018-inch
coil from each of the 3 manufacturers was placed in both the
1.3 and 1.7 SNR sidewall aneurysms. Coil stability was visually
assessed and recorded with a digital video camera under increasing
flow rates (each coil was observed for approximately 60 seconds
at each flow rate). Instability was judged as mild (displacement/prolapse
of a single loop), moderate (displacement/prolapse of more than
one coil loop), or marked (displacement/prolapse of entire coil
mass) for each coil type.
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Fig 1. The wide-necked aneurysm replica. Photograph (top) and radiograph (bottom) show the wide-necked (SNR 1.34) sidewall aneurysm (far left on both images) used in the study. The model was placed in a circuit of pulsatile fluid with flow direction from right to left.
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Results
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The 0.010-inch coils held their 3D configuration in the 1.7
SNR model regardless of flow rate. In the 1.3 SNR model, the
0.010-inch coils were difficult to place, requiring 3 to 7 attempts
before a presumed stable configuration was achieved (
Fig 2).
After detachment in the 1.3 SNR model, the 0.010-inch coils
prolapsed (in different manners and to different degrees) into
the parent vessel (
Fig 3). Instability increased with increasing
flow rates
(Table 1). In contrast, the 0.018-inch coils held
their 3D configuration in the 1.3 SNR model regardless of flow
rate (
Fig 4). These findings were reproducible and independent
of coil manufacturer.
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Fig 3. A 0.010-inch coil within the replica at increasing flow rates (280, 360, and 420 mL/min, from left to right). Greater coil prolapse into the parent vessel was demonstrated with increasing flow rate.
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Fig 4. A 0.018-inch coil within the replica at increasing flow rates (280, 360, and 420 mL/min, from left to right). No significant coil prolapse was demonstrated with increasing flow rate.
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Discussion
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In vivo coil stability is influenced both by inherent features
of the aneurysm (which are nonmodifiable) and inherent characteristics
of the embolization coil (modifiable). Aneurysm features that
are known to affect coil stability include neck width and geometry,
aneurysm location (neck inflow zone characteristics), and parent
vessel flow rate.
12,13 Coil characteristics that influence stability
include filling versus framing geometry, coil stiffness, and,
in light of our results, primary coil diameter.
14,15 Our study
investigated the in vitro effect of primary coil diameter upon
stability; the results showed significantly better stability
of the larger, 0.018-inch diameter coils. These results corroborate
the findings by Marks et al,
15 who demonstrated increased coil
stability in a glass aneurysm model by increasing stiffness
of the primary coil through modifying metal type and wire diameter
used to create the coil. The approach in the current study was
to create an aneurysm model that was then placed in a circuit
of fluid with the flow dynamics matched as closely as possible
to those found in humans. The model was then calibrated for
flow velocity and pulsatility to match in vivo conditions. We
recognize that there is an inherent difference in coefficient
of friction when platinum coils are placed within silicone replicas
compared with the lowered friction coefficient of endothelium;
this difference is not accounted for in our study. However,
the nature and degree of coil prolapse observed in our model
closely matched in vivo wide-necked aneurysm coil behavior (before
coil detachment) that we have observed. Aneurysm sizes for which
both 0.010- and 0.018-inch coils are available are in the range
of 6–15 mm, with the softer, 0.010-inch coils generally
selected for smaller, ruptured aneurysms. By extrapolating our
study to in vivo aneurysm therapy, the results would support
the use of 0.018-inch coils in appropriate aneurysms of unfavorable
(wide-necked) geometry, particularly in high flow locations
(internal carotid artery versus basilar artery) or states (ie,
arteriovenous malformation pedicle aneurysms).
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Footnotes
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Paper previously presented at: Annual Meeting of the American
Society of Neuroradiology; May 11–17, 2002; Vancouver,
British Columbia, Canada.
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References
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- Cognard C, Weill A, Spelle L, et al. Long-term angiographic follow-up of 169 intracranial berry aneurysms occluded with detachable coils. Radiology 1999;212:348–56[Abstract/Free Full Text]
- Byrne JV, Sohn MJ, Molyneux AJ, et al. Five-year experience in using coil embolization for ruptured intracranial aneurysms: outcomes and incidence of late rebleeding. J Neurosurg 1999;90:656–63[Medline]
- Moret J, Cognard C, Weill A, et al. [Reconstruction technic in the treatment of wide-neck intracranial aneurysms. Long-term angiographic and clinical results. Apropos of 56 cases.] J Neuroradiol 1997;24:30–44[Medline]
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Received June 13, 2006;
accepted after revision August 23, 2006.
TOP
Abstract
Introduction