A comparative study of intracranial aneurysm clips: closing and opening forces and physical endurance

Development and Evaluation of an MRI Artifact-Free Aneurysm Clip

BACKGROUND AND OBJECTIVES

The digital subtraction angiography is still the gold standard in the follow-up after aneurysm surgery, although it remains a repeating invasive technique with accumulating X-ray exposure. An alternative magnetic resonance angiography has the disadvantage of metal-related artifacts. A metal-free aneurysm clip could overcome this problem. Recent advances in manufacturing technologies of fiber-reinforced plastics might allow developing a prototype of a metal-free clip.

METHODS

The prototype was formed out of carbon fiber-reinforced polyetheretherketone (CF-PEEK) in accordance with the standard clip design. In vivo and in vitro studies were performed to analyze the central nervous system biocompatibility. The prototype was tested in a phantom in a 3 T MRI scanner and microtomography scanner. For in vivo assessment, the left renal artery of rats was either ligated with a suture, clipped with a regular titanium clip or with the CF-PEEK prototype clip. The animals underwent standard MRI sequences and magnetic resonance angiography and assessment by a blinded neuroradiologist.

RESULTS

Phantom studies showed no signs of artifacts. The prototype showed a reliable clamping and reopening after clip application, although the clamping force was reduced. In vivo studies showed a successful occlusion of the renal artery in all cases in the magnetic resonance angiography. Clip artifacts were statistically significant reduced in the prototype group (P < .01). CF-PEEK showed no signs of impaired biocompatibility compared with the titanium samples in vitro and in vivo.

CONCLUSION

Former attempts of metal-free aneurysm clips did not meet the criteria of the standard clip design. In this study, the practicability of this new CF-PEEK artifact-free aneurysm clip has been proven. The further fabrication developments should overcome the problem of a reduced clamping force in the future. After clinical approval, it will improve the magnetic resonance image quality and might help to reduce the amount of digital subtraction angiography in the follow-up.

Insufficient Closing Forces of Yasargil Titanium Clips in Two Small Aneurysms Detected with Intraoperative Indocyanine Green Videoangiography

Background and Study Aims Aneurysm clips must have adequate closing forces because residual blood flow in clipped aneurysms may result in aneurysm recurrence. Such flow can be intraoperatively detected by visual inspection, microvascular Doppler sonography, indocyanine green videoangiography (ICG-V), angiography, and puncture.

Patients We present two patients with ruptured very small middle cerebral artery aneurysms (3 and 2.9 mm). The necks of both aneurysms were microsurgically clipped with Yasargil aneurysm clips without any complications.

Results In both aneurysms, visual inspection suggested complete occlusion, but ICG-V showed persistent residual blood flow between the middle parts of the clip blades.

The first patient was treated with a 5.4-mm FT744T clip (closing force of 1.47 N). After the ICG-V finding, a second 3.9-mm FT714T clip (closing force of 1.08 N) was placed on the tips of the already implanted clip to increase the closing forces. Subsequent ICG-V did not show any further residual blood flow. In the second patient, the aneurysm was clipped with an 8.0-mm FE764K clip (closing force of 1.77 N). Intraoperative ICG-V showed persistent residual blood flow within the aneurysmal dome despite complete closure of the clip. The clip was repositioned closer to the parent vessel. Consecutive ICG-V did not show any residual blood flow.

Conclusion Visually undetected incomplete aneurysm occlusion can be revealed with ICG-V. In very small aneurysms, standard closing forces of clips may not be sufficient and complete closure of the clip branches should be intraoperatively validated with ICG-V.

Prevention of Back Bleeding During Carotid Endarterectomy: Analysis of Clamping Techniques

OBJECTIVE

Complete control of back bleeding during carotid endarterectomy (CEA) is important. We investigated the causes of back bleeding during CEA and techniques for the control of bleeding.

METHODS

A retrospective review was performed of 214 CEA procedures. We assessed the results of routine preoperative examinations, instruments used for arterial clamping (vessel loop and crude or bulldog clamps), and severity of carotid artery stenosis and arterial wall calcification. The study end point was incomplete control of back bleeding before arteriotomy. Factors associated with back bleeding were identified by univariate analysis. The culprit artery and intraoperative technique used in patients with back bleeding were also determined.

RESULTS

Transient back bleeding occurred in 19 CEA procedures (8.9%). Back bleeding was from the ascending pharyngeal artery in 9 cases, common carotid artery in 8 cases, and external carotid artery in 2 cases. Univariate analysis identified the following factors as being related to incomplete control of back bleeding: moderate carotid artery stenosis (20 mm thick) and use of bulldog clamps.

CONCLUSIONS

Transient back bleeding during CEA was uncommon, with the risk factors being severe carotid calcification and moderate carotid stenosis. Transient back bleeding was managed by clamping an undetected ascending pharyngeal artery or by additional clamping of the common carotid or external carotid artery. The vessel loop and crude were superior to the bulldog clamp for clamping the carotid artery.

An Investigation Into the Challenges of Using Metal Additive Manufacturing for the Production of Patient-Specific Aneurysm Clips

Cerebral aneurysm clips are biomedical implants applied by neurosurgeons to re-approximate arterial vessel walls and prevent catastrophic aneurysmal hemorrhages in patients. Current methods of aneurysm clip production are labor intensive and time-consuming, leading to high costs per implant and limited variability in clip morphology. Metal additive manufacturing is investigated as an alternative to traditional manufacturing methods that may enable production of patient-specific aneurysm clips to account for variations in individual vascular anatomy and possibly reduce surgical complication risks. Relevant challenges to metal additive manufacturing are investigated for biomedical implants, including material choice, design limitations, postprocessing, printed material properties, and combined production methods. Initial experiments with additive manufacturing of 316 L stainless steel aneurysm clips are carried out on a selective laser melting (SLM) system. The dimensions of the printed clips were found to be within 0.5% of the dimensions of the designed clips. Hardness and density of the printed clips (213 ± 7 HV1 and 7.9 g/cc, respectively) were very close to reported values for 316 L stainless steel, as expected. No ferrite and minimal porosity is observed in a cross section of a printed clip, with some anisotropy in the grain orientation. A clamping force of approximately 1 N is measured with a clip separation of 1.5 mm. Metal additive manufacturing shows promise for use in the creation of custom aneurysm clips, but some of the challenges discussed will need to be addressed before clinical use is possible.

Effects of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor on glial scar formation after spinal cord injury in rats

OBJECT

This study investigated the effects of granulocyte colony-stimulating factor (G-CSF) on glial scar formation after spinal cord injury (SCI) in rats and compared the therapeutic effects between G-CSF and granulocytemacrophage colony-stimulating factor (GM-CSF) to evaluate G-CSF as a potential substitute for GM-CSF in clinical application.

METHODS

Rats were randomly assigned to 1 of 4 groups: a sham-operated group (Group 1), an SCI group without treatment (Group 2), an SCI group treated with G-CSF (Group 3), and an SCI group treated with GM-CSF (Group 4). G-CSF and GM-CSF were administered via intraperitoneal injection immediately after SCI. The effects of G-CSF and GM-CSF on functional recovery, glial scar formation, and axonal regeneration were evaluated and compared.

RESULTS

The rats in Groups 3 and 4 showed better functional recovery and more decreased cavity sizes than those in Group 2 (p < 0.05). Both G-CSF and GM-CSF suppressed intensive expression of glial fibrillary acidic protein around the cavity at 4 weeks and reduced the expression of chondroitin sulfate proteoglycans (p < 0.05). Also, early administration of G-CSF and GM-CSF protected axon fibers from destructive injury and facilitated axonal regeneration. There were no significant differences in comparisons of functional recovery, glial scar formation, and axonal regeneration between G-CSF and GM-CSF.

CONCLUSIONS

G-CSF suppressed glial scar formation after SCI in rats, possibly by restricting the expression of glial fibrillary acidic protein and chondroitin sulfate proteoglycans, which might facilitate functional recovery from SCI. GM-CSF and G-CSF had similar effects on glial scar formation and functional recovery after SCI, suggesting that G-CSF can potentially be substituted for GM-CSF in the treatment of SCI.

Scissoring of a Cobalt Alloy Aneurysm Clip causing Slippage during Cerebral Aneurysm Surgery: Case report and review of literature

Clip slippage is a rare occurrence, and the scissoring or torsional failure of aneurysm clips is rarer still. Titanium clips have been implicated in a few such reported cases. The authors report its occurrence while using a fenestrated cobalt alloy clip for an internal carotid artery aneurysm which was identified by intraoperative angiography and rectified by re-applying a non-fenestrated cobalt alloy clip. The possible mechanism of this complication, and measures that may prevent its occurrence, including meticulous dissection, decompression when possible, proper clip selection, and intraoperative angiogram are described.

Benchtop testing and comparisons among three types of through-the-scope endoscopic clipping devices

BACKGROUND

Through-the-scope (TTS) endoscopic clipping devices are widely used. No benchtop testing or direct comparisons of these endoclips have been performed to show their rotational ability and inherent mechanical strengths during closure and after deployment. This study aimed to provide benchtop data that can be used to guide clinical applications and to promote future device research and development.

METHODS

Benchtop testing and comparisons were performed for three groups of TTS clips: QuickClip2 long, resolution, and instinct clips. The main outcome measurements were device-in-endoscope retroflection angles (DIERA), opening strength, "snapping" force of acute clip closure, and neoprene pulling strength.

RESULTS

The achievable gastroscope DIERA was 10° for QuickClip2, 3° for the resolution clip, and 10° for the instinct clip. The QuickClip and the Instinct clip rotated almost equally well under all endoscope configurations, including endoscopic retrograde cholangiopancreatography (ERCP). With or without a sheath, the resolution clip lacked the ability to rotate. During clip opening force testing (the amount of force required to force open the jaws of a deployed clip by 3.2 mm; 3.2 mm was chosen due to the standard dimension of the gauge used for the measurement), the Instinct clips were the strongest. For the Instinct clips, an opening force of 404 ± 124 g was needed to open the closed clip, and an additional 386 ± 133 g was required to open the clip jaws to 3.2 mm. In terms of snapping force during acute closure and neoprene pulling strength, the instinct and resolution clips performed almost equally. The limitations of the study were the benchtop testing and the finite sample size for closing and pulling strength comparisons.

CONCLUSIONS

The QuickClip2 and the Instinct clip rotate equally well under different endoscope configurations. The resolution clips lack rotational ability. The instinct clips are stronger mechanically than the other two TTS clips. Stronger clips are perhaps associated with higher therapeutic efficacy and retention rates.

Inappropriate application of Yaşargil aneurysm clips: a new observation and technical remark

OBJECTIVE

Recurrences after complete surgical clipping of an aneurysm base are rare. We describe a potential reason for such recurrences: the inappropriate application of a popular aneurysm clip.

CLINICAL PRESENTATION

We present 3 cases in which intraoperative indocyanine green video angiography after clipping clearly demonstrates filling of the aneurysm.

INTERVENTION

During surgery, the necks of the aneurysms were clipped with Yaşargil aneurysm clips (Aesculap AG & Co., Tuttlingen, Germany) without any problems; however, indocyanine green video angiography after clipping showed filling of the aneurysms through the point located at the junction of the blade and spring portions of the clips. In the first patient, the aneurysm sac was further coagulated, and a second, smaller clip was applied to completely occlude the untreated part. In the second patient, the clip was replaced with a different clip that had longer blades. In the third patient, 2 additional clips were applied, and the aneurysm sac was also coagulated. The postoperative computed tomographic angiographic examinations showed total occlusion of the aneurysms and patency of the parent arteries. All patients achieved full recovery after the operations.

CONCLUSION

We present here, for the first time, evidence that the small orifice located at the junction of the blade and spring portions of Yaşargil aneurysm clips can lead to failure of initial surgery and/or recurrence. This can be avoided by using clips with slightly longer blades to keep the orifice away from the aneurysm or by applying a second clip to occlude the untreated part.

The clinical utility of the Kopitnik arteriovenous malformation microclip during STA-MCA bypass surgery

Purpose

Yasagil temporary clips have been widely used in extracranial-intracranial (EC-IC) arterial bypass surgery. However, the extremely delicate vessels involved often require the application of finer clips. We report on the use of the Kopitnik arteriovenous malformation (AVM) microclip system for superficial temporal artery-middle cerebral artery (STA-MCA) bypass.

Methods

Kopitnik AVM microclips are new mechanical devices that are used during AVM surgery. They exert a pre-defined closing force of 50–70 g, and also feature a special, pyramid-shaped structure stamped on inner surfaces of the blades. These characteristics avoid vascular intimal injury and provide a secure grip. We prospectively studied their use in 15 patients requiring STA-MCA anastomosis.

Results

Clinical results were excellent and there were no new ischemic events during 6-months’ follow-up.

Conclusions

Kopitnik AVM microclips have several advantages; they have small and variously sized clip blades (2, 3, 4 and 5 mm), and the small clip head allows the operator an excellent view of the pathology and clip status. The Kopitnik AVM microclip appears to be clinically effective and safe for EC-IC bypass surgery, especially when smaller vessels are involved.

Standardizing optic nerve crushes with an aneurysm clip

OBJECTIVES

Despite the widespread use of optic nerve injury models to simulate central nervous system injury, model protocols vary from laboratory to laboratory, making it difficult to directly compare findings between studies.

METHODS

To standardize the optic nerve crush injury model, the commercially available Yasargil aneurysm clip, which provides a consistent clamping force, was used to produce a crush injury to the rat optic nerve. Histology was verified with hematoxylin-eosin. The number of retinal ganglion cells (RGCs) was counted by fluorescent gold dye labeling.

RESULTS

Following nerve crush injury, the density of RGCs was substantially reduced in the aneurysm clip-operated group relative to the normal and sham-operated groups, and no discernable difference was noted between the latter two control groups.

DISCUSSION

The present findings suggest that Yasargil aneurysm clip effectively produces permanent injury to the optic nerve with evidence from retrograde tracing of RGCs and may provide a standard technique for optic nerve crush studies.

Fenestrated aneurysm clips in the surgical management of anterior communicating artery aneurysms: operative techniques and strategy

Object

Aneurysms of the anterior communicating artery (ACoA) can be a considerable challenge to treat surgically based on variations in the anatomy and morphological features of the ACoA complex. The fenestrated aneurysm clip can be a simple and practical tool in the operative management of ACoA aneurysms. The goal in this study was to characterize the particular surgical situations in which the use of a fenestrated clip facilitates the clip ligation of ACoA aneurysms.

Methods

The authors present their operative strategy and techniques for the use of fenestrated clips in the treatment of ACoA aneurysms.

Results

One hundred ninety-nine patients underwent surgical clipping of an ACoA aneurysm at the authors' institution between the years 1991 and 2008. Of these patients, fenestrated aneurysm clips were used in 20 cases (10%). The following structures were enclosed in the clip aperture: ipsilateral A2 artery, 12 patients (60%); ipsilateral A1 artery, 4 patients (20%); ipsilateral A1 artery plus recurrent artery of Heubner, 1 patient (5%); ACoA, 1 patient (5%); frontopolar artery, 1 patient (5%); and no structures, 1 patient (5%). Aneurysms approached from the left side more frequently required fenestrated clips than did right-sided aneurysms (80 vs 20%, p = 0.0073). In all cases, patency of the A2 vessels was confirmed on postoperative angiography. In 2 patients, small remnant aneurysm necks were identified on postoperative angiography.

Conclusions

The use of fenestrated aneurysm clips can minimize tedious and potentially dangerous dissection of adherent branch vessels, while maintaining the integrity of structures placed within the clip aperture. The ACoA aneurysms pointing in a superior direction are more likely to require clip fenestration around the A2 vessel, whereas those pointing in an inferior direction are more likely to require clip fenestration around the A1 vessel. The parallel approximation of the fenestrated clip blades makes them especially useful in the treatment of large or giant aneurysms.

GM-CSF inhibits glial scar formation and shows long-term protective effect after spinal cord injury

OBJECT

This study investigated the effects of granulocyte macrophage-colony stimulating factor (GM-CSF) on the scar formation and repair of spinal cord tissues in rat spinal cord injury (SCI) model.

METHODS

Sprague-Dawley male rats (8 weeks old) were randomly divided into the sham-operated group, spinal cord injury group, and injury with GM-CSF treated group. A spinal cord injury was induced at T9/10 levels of rat spinal cord using a vascular clip. GM-CSF was administrated via intraperitoneal (IP) injection or on the dural surface using Gelfoam at the time of SCI. The morphological changes, tissue integrity, and scar formation were evaluated until 4 weeks after SCI using histological and immunohistochemical analyses.

RESULTS

The administration of GM-CSF either via IP injection or local treatment significantly reduced the cavity size and glial scar formation at 3-4 weeks after SCI. GM-CSF also reduced the expression of core proteins of chondroitin sulfate proteoglycans (CSPGs) such as neurocan and NG2 but not phosphacan. In particular, an intensive expression of glial fibriallary acidic protein (GFAP) and neurocan found around the cavity at 4 weeks was obviously suppressed by GM-CSF. Immunostaining for neurofilament (NF) and Luxol fast blue (LFB) showed that GM-CSF preserved well the axonal arrangement and myelin structure after SCI. The expression of GAP-43, a marker of regenerating axons, also apparently increased in the rostral grey matter by GM-CSF.

CONCLUSION

These results suggest that GM-CSF could enhance long-term recovery from SCI by suppressing the glial scar formation and enhancing the integrity of axonal structure.

Prototypical metal/polymer hybrid cerebral aneurysm clip: in vitro testing for closing force, slippage, and computed tomography artifact

Object

The aim of this study was to explore the possibility that a hybrid aneurysm clip with polymeric jaws bonded to a metal spring could provide mechanical properties comparable to those of an all-metal clip as well as diminished artifacts on computed tomography (CT) scanning.

Methods

Three clips were created, and Clips 1 and 2 were tested for mechanical properties. Clip 1 consisted of an Elgiloy spring (a cobalt-chromium-nickel alloy) bonded to carbon fiber limbs; Clip 2 consisted of an Elgiloy spring with polymethylmethacrylate (PMMA) jaws; and Clip 3 consisted of PMMA limbs identical to those in Clip 2 but bonded to a titanium spring. Custom testing equipment was set up to measure the aneurysm clip clamping forces and slippage. Clips 2 and 3 were visualized in vivo using a 64-slice CT unit, and the slices were reformatted into 3D images.

Results

According to the testing apparatus, Clip 2 had a similar closing force but less slippage than three similar commercial aneurysm clips. The artifact from the cobalt alloy spring on CT scanning largely offset the advantage of the nonmetal PMMA limbs, which created no artifact. The hybrid titanium/PMMA clip (Clip 3) created very little artifact on CT and allowed visualization of the phantom through the limbs.

Conclusions

It is feasible to build a potentially biocompatible hybrid cerebral aneurysm clip with mechanical properties that closely resemble those of conventional metallic clips. Further testing should be directed toward establishing the reliability and biocompatibility of such a clip and optimizing the contour and surface treatments of the polymer limbs.

The effect of temporary aneurysm clip on the common carotid artery of atherosclerotic rabbits

BACKGROUND

We compared the effect of temporary aneurysm clips on atherosclerotic and nonatherosclerotic CCA of rabbits by morphometric and ultrastructural methods.

METHODS

The rabbits (N = 12) were divided into 2 groups: the first group was fed a 2% cholesterol diet, and the second group, a normal diet for 4 weeks. Atherosclerotic lesions developed after 4 weeks. Temporary aneurysm clips were placed on the left CCA of both groups; the right CCA of both groups served as control. Thus, a total of 4 groups were used: atherosclerotic (A), atherosclerotic/clip (AC), nonatherosclerotic (NA), and nonatherosclerotic/clip (NAC). Temporary aneurysm clips were applied for 1, 5, and 10 minutes in the AC and NAC groups. No temporary clip was placed on the right CCA (A and NA groups). The affected parts of the CCA via clips were examined under light microscope and SEM.

RESULTS

Comparison of atherosclerotic and nonatherosclerotic CCA of rabbits under light microscope indicated that the wall of atherosclerotic CCA was thicker than that of nonatherosclerotic CCA. The difference between the thickness of atherosclerotic and nonatherosclerotic CCAs was significant. SEM analyses showed that in nonatherosclerotic CCAs, the effect of temporary aneurysm clips was seen after 10 minutes, but in atherosclerotic CCAs, the effect was seen within the 1st minute of clipping and continued in the 5th and 10th minutes.

CONCLUSION

The duration of temporary clipping should be decreased for the neurovascular surgery of atherosclerotic patients.

Clampage vasculaire temporaire

In many situations, temporary artery occlusion is an integral component of aneurysm surgery. The use of temporary clip may allow safer and easier aneurysmal dissection and clipping. Several points, concerning the duration and overall risks of temporary occlusion and the method of choice for cerebral function monitoring have to be discussed.

MATERIAL AND METHODS

Non exhaustive review of neurosurgical literature.

DISCUSSION

Temporary clip application decreases the risk of intraoperative aneurysmal rupture. The analysis of data published in the literature showed that several questions remain open concerning the optimal method of neuroprotection and cerebral function monitoring, as well as the limit of occlusion duration. Other clinical trials are needed to assess the efficacy and safety of this technique.

Endurance of aneurysm clips: mechanical endurance of Yaşargil and Spetzler titanium aneurysm clips

OBJECTIVE

To determine whether repeated use weakens titanium aneurysm clips, making them unsafe for clinical use.

METHODS

Nine Yaşargil (titanium alloy) and five Spetzler (pure titanium) clips were subjected to clinically relevant maneuvers, and the effects on the closing force were assessed. Clips were considered unsafe if 1) the blades crossed, 2) the clips failed to close completely, or 3) the blood pressure could open them.

RESULTS

Yaşargil and Spetzler clips significantly (P < 0.01 for both) weakened, by 18.9% and 26.1%, respectively, after 10 minutes of sustained maximal opening. After 100 open-close cycles, Spetzler clips showed no change in closing force, but the closing force of Yaşargil clips decreased significantly (P < 0.01), by a further 12.0%.

CONCLUSION

Repeated use weakens Spetzler and Yaşargil clips. All Spetzler and all but one Yaşargil clips were deemed safe for clinical use at the end of the experiments.

Great potentiality of neonatal facial motor neurons for neural plasticity as determined by functionally essential neuronal population

The present study was undertaken to determine the neuronal population essential for normal and minimal facial function of young adult rats that had received various degrees of crush injuries to the facial nerve in the neonatal period. Using a neuronal tracer, it was found in young adult rats receiving neonatal injuries that the minimum number of tracer-labeled facial motor neurons necessary for normal facial function corresponded to 13-14% of the neurons (2540+/-64) of the age-matched control animals, whereas the minimum number of neurons necessary for minimal facial function corresponded to 5%. On the other hand, the minimum numbers of tracer-labeled facial motor neurons necessary for normal and minimal facial function of young adult rats that received various degrees of crush injuries corresponded to 61 and 27-30%, respectively, of the neurons (2540+/-64) of the uninjured control animals. These results indicate that the facial function of animals with nerves crushed at the neonatal stage can be adequately maintained by a very small population of neurons, implying a great potential of neonatal neurons for neural plasticity.

Functionally essential neuronal population of the facial motor nucleus

Cranial nerve impairment is one of the more serious complications in neurosurgery. Nevertheless, the important question of how many neurons are required for cranial nerve functions remains unanswered. The VIIth cranial nerve (facial nerve) in mice was subjected to graded crush injuries. After assessment of the facial function, the number of uninjured, healthy facial motor neurons was quantified with a retrograde neuronal tracer. We report that normal facial function is preserved if intact neurons account for more than 56% of the control value, while complete facial paralysis occurs if intact neurons are reduced to less than 32% of the control value.