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Abstract
Introduction Endovascular embolization of intracranial vascular malformations with N-butyl cyanoacrylate (nBCA) using a detachable tip microcatheter allows prolonged injection and decreases the risk of catheter retention.
Methods Between March and December 2013, the Apollo 1.5 cm detachable tip microcatheter was used in five patients after being approved by both the Food and Drug Administration and the institutional review board as a compassionate use device. Nine pedicles were embolized and the follow-up ranged from 1 to 3 months.
Results Five of the nine catheter tips detached. The length of reflux was not directly associated with the detachment of the distal tip. There were no cases of premature microcatheter detachment during navigation, manipulation with multiple microguidewire reintroduction and guidance. There was no leak of embolic agent at the detachment zone. Follow-up showed the detached tip to be stable without migration.
Conclusions A detachable tip microcatheter offers an advance in the safety and effectiveness of nBCA embolization. Catheter retrieval becomes more controlled and less traumatic. Our initial experience is encouraging, and more experience is needed to categorically ascertain its safety and efficacy.
- Arteriovenous Malformation
- Catheter
- Liquid Embolic Material
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Introduction
Endovascular embolization has become an indispensable arm in the multimodal treatment of intracranial vascular malformations in children and adults. It may be used alone to achieve cure or as an adjunct to surgical or radiosurgical treatment. Two agents commonly used for embolization are N-butyl cyanoacrylate1 (nBCA) (Tru-Fill; Cordis Microvascular, Miami Lakes, Florida, USA and Histoacryl B; Braun, Germany) and ethylene vinyl alcohol2 (Onyx; ev3, Irvine, California, USA). nBCA, a liquid adhesive approved for use by the US Food and Drug Administration (FDA) in 2000, is a rapidly polymerizing agent with a long history and support in the literature for use in arteriovenous malformation (AVM) embolization.3–6 Due to its rapid polymerization, there is a risk of retention of the delivery microcatheter within the artery. A detachable tip catheter should allow for decreased risk of retention and longer injection times. We present our initial experience using the Apollo detachable tip microcatheter (Covidien, Mansfield, Massachusetts, USA) for nBCA vascular malformation embolization.
Materials and methods
From March to December 2013, the Apollo detachable tip microcatheter was used in five patients ranging in age from 4.5 months to 37 years for injection of nBCA. Currently, the Apollo detachable tip microcatheter is not FDA approved. Compassionate use approval was obtained for the microcatheter use from the FDA and the institutional review board on a case-by-case basis. In total, nine pedicles were catheterized and an equal number of injections were made. In all cases MRI, MR angiography and catheter angiography were used as a diagnostic tool in planning for treatment. All cases were discussed in multidisciplinary conference and agreement was reached to undergo staged embolization procedures, either as the primary treatment or as preparation for microsurgical resection or radiosurgery. The follow-up ranged from 1 to 3 months. In all the presented cases nBCA was used over Onyx, based on the hemodynamic nature of the catheterized pedicle of the malformation and past experience.
The Apollo detachable tip microcatheter is a single-lumen end-hole catheter that has a semi-rigid proximal shaft and a highly flexible distal shaft to facilitate the advancement of the catheter. It has been designed to be used as an over the guidewire microcatheter, but has some flow-guided properties due to its very supple distal segment. It is designed to facilitate catheter retrieval in the event that the catheter tip becomes entrapped within the embolization cast when using it with Onyx. The distal section of the catheter incorporates a detachment zone that allows detachment of the distal tip when the force required to extract the catheter exceeds the force required to detach the tip. The catheter has two radiopaque marker bands to visualize the position of the catheter and the detachment zone (figures 1 and 2). It comes in 1.5 and 3 cm detachment tip lengths.
Apollo Onyx delivery detachable tip microcatheter.
Apollo Onyx delivery detachable tip microcatheter after detachment.
All procedures were done in a biplane angiographic suite under general anesthesia with neurophysiologic monitoring (somatosensory and motor evoked potentials). Transfemoral access was obtained in each case with ultrasound guidance when needed. Depending on the age and size of the patient, a 4 Fr or 5 Fr guide sheath was placed with a 4 Fr or 5 Fr guide catheter. An Apollo detachable tip microcatheter with 1.5 cm distal detachment zone was used during all nine injections to gain access to each arterial feeder, placed at or close to the nidus and/or fistula site. The microcatheter was advanced with the support of 0.008 or 0.010 microguidewires. In all attempts, the catheter tracked well and was successfully placed at the desired location.
For nBCA injections, the catheter was flushed with 5% dextrose in water. For each nBCA injection, different ratios of nBCA, tantalum powder and ethiodized oil were used, depending on the flow and territory to be occluded. We used nBCA in concentrations ranging form 40% to 80% mixed with ethiodized oil and tantalum. Controlled injections of nBCA were performed with the proximal reflux limit guided by the proximal marker and arterial anatomy. The rate of injection was varied based on the infiltration of nBCA and reflux along the catheter. We were able to reflux minimally and pause the injection before resuming an additional injection of nBCA to achieve good penetration into the vascular malformation. In one case (patient no 3) with a multi-hole pial fistula in the posterior fossa, during the fourth injection, after initial occlusion of the desired fistula, we achieved controlled reflux along the catheter to achieve occlusion of additional fistulas supplied by the proximal segment of the feeding artery. The quantity of nBCA injected per pedicle ranged from 0.4 to 1.4 mL. Following injection, the nBCA cast was allowed to polymerize and the microcatheter was pulled in a controlled fashion under fluoroscopic guidance with a graduated increase in traction pressure allowing for controlled tip detachment.
Results
In five patients after nine successful nBCA injections using the Apollo detachable tip microcatheter with desired occlusion of the feeder to the malformation, the tip detached four times (45%). The length of reflux was around 1 cm (range 0.8–1.25 cm) during seven injections (table 1). Although these data are limited, the detachment of the distal tip was not directly associated with the length of reflux. There were no cases of premature microcatheter detachment while navigating normal vessels despite tortuosity and distal cortical vessel catheterization requiring significant manipulation with multiple microguidewire reintroduction, change, and guidance. There were no leaks of embolic agent at the detachment zone. Follow-up in two of the microcatheter detachments at 1 month and the other at 3 months showed that the detached tip was stable without migration.
Details of the use of the Apollo detachable tip microcatheter for the injection of nBCA
Case example
A patient diagnosed in utero with a posterior fossa vascular malformation was delivered by C-section without complication. The child was tested and documented positive for capillary malformation-arteriovenous malformation (CM-AVM) syndrome, an autosomal dominant disorder caused by mutations in the RASA1 gene, as the family history was positive as suggested by a sibling having the same mutation along with multiple pial fistulous malformation in the parietal region. The cardiac condition deteriorated at 3 months and the patient was taken up for endovascular embolization. High-flow multiple pial fistulas in the posterior fossa were detected and the patient underwent endovascular embolization (figure 3). Three embolizations were performed during the first session of treatment using a 1.5 cm Apollo detachable tip microcatheter and 80% nBCA. During the first and third embolizations the tip did not detach in spite of reflux while, during the second embolization, using the same concentration of nBCA, the tip detached (figure 3). The cardiac status stabilized and the patient was brought for second stage embolization 3 months later. The detached tip remained stable in the nBCA cast without migration. Further, one embolization was done using the same catheter and the same concentration of nBCA. This time the tip detached. The child is developing normally with stable cardiac status and has residual malformation that will need further treatment.
A child with capillary malformation-arteriovenous malformation syndrome was diagnosed in utero to have posterior fossa vascular malformation. At 3 months of age the child underwent embolization due to his deteriorating cardiac condition. The MRI and angiogram in anteroposterior and lateral views show a posterior fossa high-flow pial arteriovenous fistulous malformation (A–C). During the first session, three embolizations were done with N-butyl cyanoacrylate (nBCA) using an Apollo detachable tip microcatheter. Following the first and third embolizations, the microcatheter was retrieved without detachment (arrow in D, E, K and L). (F, G) During the second catheterization and following nBCA embolization, the tip detached and was retained during retrieval (arrowhead in H and I). The third catheterization is shown (J). The glue cast at the end of the first embolization session with one catheter tip retained (M, N). The angiogram in anteroposterior view at the end of the first embolization session (O) shows significant reduction in flow and residual malformation.
Discussion
nBCA, commonly referred to as glue, is a monomer that is a clear free-flowing liquid which polymerizes rapidly by an anionic reaction. Its properties allow penetration of vascular beds in a flow-directed fashion. Rapid embolization and a low rate of recanalization have made it a suitable agent for embolization of a wide variety of vascular malformations, including high-flow arteriovenous fistulas requiring a rapid polymerizing agent. In most cases it is used during preoperative embolization.1 ,3–6 It is mixed in varying concentrations with ethiodized oil, an iodinated poppy seed oil used for radiopacity and as a polymerization retardant. Based on concentration, rate of injection and the flow characteristics of the vascular malformation it results in permanent occlusion of embolized vessels.7 1–3 μm ground metal tantalum powder is mixed with nBCA to improve radiopacity, mostly in high-flow fistulas, where lower concentration of ethiodized oil is used in the range of 10–30%.
The goals of nBCA embolization include good penetration of the vascular malformation based on the flow characteristics of the catheterized pedicle; prevention of excess penetration to the venous side; and, most importantly, prevention of excess proximal reflux along the catheter to prevent catheter retention and non-target embolization. The variability of the ideal nBCA mixture preparation and rate of injection to achieve these goals makes it highly operator-dependent. Prolonged contact of the microcatheter with polymerized nBCA adheres it to the endothelium, leading to the risk of retained catheter or vessel injury.8 Microcatheter fracture and vessel rupture can occur if excess force is used to pull back the catheter. The frequencies of these complications are unknown. Most of the information about retained catheters is derived from reports of individual clinical experiences.9–12
The long-term course of patients with retained catheters is not well-known. The retained catheter may be fixed to the arterial wall or it may be mobile. Complications such as arterial thrombosis, embolism, microcatheter migration, and fragmentation arterial thrombosis may occur. The catheter may become partially incorporated into the wall of the blood vessel, which can result in delayed thromboembolic complications.13 We have personal experience of 16 microcatheters retained in the last 25 years without adverse effects, although it would be better to avoid this problem. Although catheter gluing is significantly reduced with the introduction of hydrophilic-coated microcatheters, rapid retrieval of the microcatheter can cause vessel injury leading to hemorrhage resulting in increased morbidity. We have had three such complications in the last 25 years.
To avoid this complication, conventionally before injection the redundant loops in the microcatheter are removed to ensure the ability for quick and controlled pullback. In addition, during the injection, reflux is either avoided or kept to a minimum and, at the end of the injection, the catheter tip is pulled back rapidly and sufficiently to free the tip before the glue polymerizes. Because of the risk of catheter retention, the endovascular surgeon is forced to stop the injection prematurely in some cases, resulting in suboptimal penetration of the vascular malformation or incomplete occlusion of the fistula.
The problem of catheter entrapment and attempts at retrieval resulting in catheter or vessel rupture also occur with Onyx, as the conventional technique of Onyx embolization involves intentional formation of a proximal plug around the distal end of the catheter.14 ,15 To circumvent this problem, a detachable tip microcatheter was developed and its use was first reported in 2008.16 There have since been two reports of its use with Onyx in adults, which show that this microcatheter can be used safely and efficaciously.17 ,18 The Sonic catheter (Balt, Montmorency, France) was the first generation of this type of catheters. This catheter has been used extensively and safely with Onyx,17 ,18 and there is one case report of it being used during nBCA embolization16 for the treatment of intracranial AVM. In the report the authors used 12.5% nBCA mixed with ethiodized oil injected alternately with 5% dextrose over a period of 16 min, achieving good penetration into the malformation and, in the end, the microcatheter was retrieved without detachment. The appeal of this type of microcatheter is that embolic agents can be used to penetrate fistulas and malformations more deeply with permissible reflux based on the length of the detachable tip and less concern for the need to retain the full microcatheter.
In our early experience, the navigability of the Apollo microcatheter is comparable to or better than other available over-the-wire microcatheters. We were able to place the microcatheter at the desired location with every attempt. We have used a high concentration of nBCA (70–80%) in most cases. In high-flow fistulas, the higher concentration of nBCA is essential to achieve precise obliteration with minimal escape into the venous side as well as prevention of reflux along the catheter. Using the detachable tip microcatheter, we can control the rate of injection of concentrated nBCA and allow reflux in a controlled fashion, as we know our proximal limit of reflux to prevent entrapment guided by the proximal marker in the catheter. During injection when there is reflux along the catheter, we pause the injection momentarily to allow the refluxed nBCA to harden before resuming the injection to achieve better penetration and obliteration of the malformation. On completion of the injection, the microcatheter is left in situ while the nBCA completely polymerizes. Withdrawal is done in a less traumatic controlled fashion with graduated pressure under fluoroscopic guidance. In our series, the tip has detached in only 45% of the injections and, with this controlled retrieval maneuver, we believe there is less chance of catheter entrapment, vessel rupture and hemorrhage. In our limited experience, the reflux length was not directly related to the tip detachment.
The possible downside to using this catheter is that it may not be possible to achieve catheterization of very small and tortuous vessels that are usually catheterized with flow-guided catheters. Inadvertent detachment of the tip during catheterization or during retrieval is a potential problem, although we have no experience of it. The proximal marker is an arbitrary marker for the limit of reflux, as one has to be aware that normal branches may arise within the 1.5 cm mark. We did not use the 3 cm detachable tip microcatheter as we believed that it may not be useful in brain parenchymal vessels as proximal vessels arise much closer to the embolized feeder in most cases.
Conclusion
A detachable tip microcatheter offers an advance in the safety and effectiveness of nBCA embolization of brain vascular malformations including high-flow fistulas. Catheter retrieval becomes more controlled and less traumatic. Our initial experience is encouraging, and more experience is needed to categorically ascertain its safety and efficacy.
References
Footnotes
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Contributors SP, DA, SO-G and JF contributed to data collection. SP prepared and revised the draft. AB conceptualized the idea.
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Competing interests None.
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Ethics approval Institutional Review Board at St Luke's Roosevelt Hospital.
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Provenance and peer review Not commissioned; externally peer reviewed.
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Data sharing statement Upon request.