Endovascular coiling | |
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Other names | Endovascular embolization |
Specialty | Interventional neuroradiology |
Endovascular coiling is an endovascular treatment for intracranial aneurysms and bleeding throughout the body. The procedure reduces blood circulation to the aneurysm through the use of microsurgical detachable platinum wires, with the clinician inserting one or more into the aneurysm until it is determined that blood flow is no longer occurring within the space. It is one of two main treatments for cerebral aneurysms, the other being surgical clipping. Clipping is an alternative to stenting for bleeding.
Endovascular coiling is used to treat cerebral aneurysms. The main goal is prevention of rupture in unruptured aneurysms, and prevention of rebleeding in ruptured aneurysms by limiting blood circulation to the aneurysm space. Clinically, packing density is recommended to be 20-30% or more of the aneurysm's volume, typically requiring deployment of multiple wires. [1] Higher volumes may be difficult due to the delicate nature of the aneurysm; intraoperative rupture rates are as high as 7.6% for this procedure. [2] In ruptured aneurysms, coiling is performed quickly after rupture because of the high risk of rebleeding within the first few weeks after initial rupture. The patients most suitable for endovascular coiling are those with aneurysms with a small neck size (preferably <4 mm), luminal diameter <25 mm and those that are distinct from the parent vessel. [3] Larger aneurysms are subject to compaction of coils, due to both looser packing densities (more coils are needed) and increased blood flow. Coil compaction renders them unsuitable as they are incapable of stemming blood flow. [4] However, technological advances have made coiling of many other aneurysms possible as well.
A number of studies have questioned the efficacy of endovascular coiling over the more traditional surgical clipping. Most concerns involve the chance of later bleeds or other recanalization. [5] [6] [7] Due to its less invasive nature, endovascular coiling usually presents faster recovery times than surgical clipping, with one study finding a significant decrease in probability of death or dependency compared to a neurosurgical population. [8] Complication rates for coiling as well are generally found to be lower than microsurgery (11.7% and 17.6% for coiling and microsurgery, respectively). Despite this, intraoperative rupture rates for coiling have been documented as being as high as 7.6%. [2] Clinical results are found to be similar at a two-month and one year follow-up between coiling and neurosurgery. [9]
Reported recurrence rates are quite varied, with rates between 20 and 50% of aneurysms recurring within one year of coiling, and with the recurrence rate increasing with time. [2] [10] These results are similar to those previously reported by other endovascular groups. [11] Other studies have questioned whether new matrix coils work better than bare platinum coils. [12]
The International Subarachnoid Aneurysm Trial tested the efficacy of endovascular coiling against the traditional micro-surgical clipping. The study initially found very favorable results for coiling, however its results and methodology were criticized. Since the study's release in 2002, and again in 2005, some studies have found higher recurrence rates with coiling, while others have concluded that there is no clear consensus between which procedure is preferred. [13]
Risks of endovascular coiling include stroke, aneurysm rupture during the procedure and aneurysm recurrence and rupture after the procedure. [3] Additionally in some patients coiling may not be successful. In general, coiling is only performed when the risk of aneurysm rupture is higher than the risks of the procedure itself.
Similar to patients who experience neurosurgical procedures, coiling results in an increase in resting energy expenditure, albeit at a slightly reduced rate than their neurosurgery counterpart. This can lead to malnutrition if steps are not taken to compensate for the increased metabolic rate. [14]
The treatment works by promoting blood clotting (thrombosis) in the aneurysm, eventually sealing it from the blood flow. This is accomplished by decreasing the amount of blood flow going into the aneurysm, increasing the residence time of the blood (thereby lowering the velocity) in the aneurysm space and reducing the wall shear stress of the aneurysm wall. This change in the blood flow, or hemodynamics, is ultimately dependent on several factors, including:
While these factors are crucial to the success of the procedure, thrombosis ultimately is dependent on biological processes, with the coiling only providing the appropriate conditions for the process to occur, and hopefully closing the aneurysm.
Endovascular coiling is usually performed by an interventional neuroradiologist or neurosurgeon with the patient under general anaesthesia. The whole procedure is performed under fluoroscopic imaging guidance. A guiding catheter is inserted through the femoral artery and advanced to a site close to the aneurysm after which angiography is performed to localize and assess the aneurysm. After this, a microcatheter is navigated into the aneurysm.
The treatment uses detachable coils made of platinum that are inserted into the aneurysm using the microcatheter. A variety of coils are available, including Guglielmi Detachable Coils (GDC) which are platinum, Matrix coils which are coated with a biopolymer, and hydrogel coated coils. Coils are also available in a variety of diameters, lengths, and cross sections. [16] A coil is first inserted along the aneurysm wall to create a frame, with the core then being filled with more coils. [17] A series of progressively smaller coils may also be used. Success is determined by injecting a contrast dye into parent artery and qualitatively determining if dye is flowing into the aneurysm space during fluoroscopy. If no flow is observed, the procedure is considered completed. [2] In the case of wide-necked aneurysms a stent may be used. [18]
Endovascular coiling was a developed through the synthesis of a number of innovations that took place between 1970 and 1990 in the field of electronics, neurosurgery, and interventional radiology. [4] While the procedure itself has been and continues to be compared to surgical clipping, the development of the concept and procedure has resulted in it becoming the gold standard at many centers. [4]
The first documented technique of using metal coils to induce thrombosis was accomplished by Mullan in 1974. Copper coils were inserted into a giant aneurysm through externally puncturing the aneurysm wall via craniotomy. Five patients died, with ten having satisfactory process. [19] It did not gain popularity due to the specialized equipment required, in addition to the technique being unsuitable for many types of aneurysms. [4] Later, in 1980, similar techniques were developed by Alksne and Smith using iron suspended in methyl methacrylate in a limited set of patients. There were no deaths in 22 consecutive cases with low morbidity. [20] This technique also did not gain traction due to advances in clipping. [4]
As a means of avoiding invasive methods, early endovascular interventions involved the usage of detachable and nondetachable balloon catheters to occlude the aneurysm while preserving the parent artery. [21] Despite the innovative approach, the aneurysms were often found to adapt to the shape of the balloon itself resulting in higher incidents of aneurysm rupture. This procedure was deemed "uncontrollable" due to its high morbidity and mortality rate, but it demonstrated that the endovascular approach was feasible for many aneurysms. [4] Endovascular coils would later be used in 1989 by Hilal et al., but these were short, stiff coils that offered no control, preventing dense packing of the aneurysm. [22] Controllable microguidewire systems were later used. [4]
In 1983 the use of electrically induced thrombosis for intracranial aneurysms was described for the first time. [23] A stainless steel electrode supplied a positive current to the aneurysm to stimulate electrothrombosis. Minimal occlusion was achieved, but the researchers discovered that the erosion of the electrode due to electrolysis would be useful as a detachment system. [4] Detachable coils were constructed from a platinum coil soldered to a stainless steel delivery wire, first described in 1991 by Guglielmi et al. [3] When combined with a controllable microguide wire system, multiple coils could be inserted to fully pack an aneurysm. [4]
Given the complexity of modeling the vasculature, much research has been devoted towards modeling the hemodynamics of an aneurysm before and after an intervention. Techniques such as particle image velocimetry (PIV) and computational fluid dynamics/finite element analysis (CFD/FEA) have yielded results that have influenced the direction of research, but no model to date has been able to account for all factors present. [2] [24] [25] Advantages of the in-silico research method include flexibility of selecting variables, but one comparative study has found that simulations tend to over-emphasis results compared to PIV, and are more beneficial for trends than exact values. [25]
Medical images, particularly CT angiography, can be used to generate 3D reconstructions of patient specific anatomy. When combined with CFD/FEA, hemodynamics can be estimated in patient specific simulations, giving the clinician greater predictive tools for surgical planning and outcome evaluation to best promote thrombus formation. [26] [27] However, most computer models use many assumptions for simplicity, including rigid walls (non-elastic) for vasculature, substituting a porous medium in place of physical coil representations, and navier-stokes for fluid behavior. However, new predictive models are being developed as computational power increases, including algorithms for simulations of coil behavior in-vivo. [16]
A cerebral arteriovenous malformation is an abnormal connection between the arteries and veins in the brain—specifically, an arteriovenous malformation in the cerebrum.
An intracranial aneurysm, also known as a cerebral aneurysm, is a cerebrovascular disorder in which weakness in the wall of a cerebral artery or vein causes a localized dilation or ballooning of the blood vessel.
An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus for clot formation (thrombosis) and embolization. As an aneurysm increases in size, the risk of rupture, which leads to uncontrolled bleeding, increases. Although they may occur in any blood vessel, particularly lethal examples include aneurysms of the circle of Willis in the brain, aortic aneurysms affecting the thoracic aorta, and abdominal aortic aneurysms. Aneurysms can arise in the heart itself following a heart attack, including both ventricular and atrial septal aneurysms. There are congenital atrial septal aneurysms, a rare heart defect.
Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. Symptoms may include a severe headache of rapid onset, vomiting, decreased level of consciousness, fever, weakness, numbness, and sometimes seizures. Neck stiffness or neck pain are also relatively common. In about a quarter of people a small bleed with resolving symptoms occurs within a month of a larger bleed.
A subdural hematoma (SDH) is a type of bleeding in which a collection of blood—usually but not always associated with a traumatic brain injury—gathers between the inner layer of the dura mater and the arachnoid mater of the meninges surrounding the brain. It usually results from tears in bridging veins that cross the subdural space.
Intracranial hemorrhage (ICH), also known as intracranial bleed, is bleeding within the skull. Subtypes are intracerebral bleeds, subarachnoid bleeds, epidural bleeds, and subdural bleeds.
Cerebral angiography is a form of angiography which provides images of blood vessels in and around the brain, thereby allowing detection of abnormalities such as arteriovenous malformations and aneurysms. It was pioneered in 1927 by the Portuguese neurologist Egas Moniz at the University of Lisbon, who also helped develop thorotrast for use in the procedure.
The International Subarachnoid Aneurysm Trial (ISAT) was a large multicenter, prospective randomised clinical medical trial, comparing the safety and efficacy of endovascular coil treatment and surgical clipping for the treatment of brain aneurysms. The study began in 1994. The first results were published in The Lancet in 2002, and the 10-year data were published again in The Lancet in early September 2005. A total of 2,143 study participants were mostly drawn from U.K. hospitals with the rest drawn from North American and European hospitals.
A dural arteriovenous fistula (DAVF) or malformation is an abnormal direct connection (fistula) between a meningeal artery and a meningeal vein or dural venous sinus.
The anterior clinoid process is a posterior projection of the sphenoid bone at the junction of the medial end of either lesser wing of sphenoid bone with the body of sphenoid bone. The bilateral processes flank the sella turcica anteriorly.
Neurocritical care is a medical field that treats life-threatening diseases of the nervous system and identifies, prevents, and treats secondary brain injury.
An external ventricular drain (EVD), also known as a ventriculostomy or extraventricular drain, is a device used in neurosurgery to treat hydrocephalus and relieve elevated intracranial pressure when the normal flow of cerebrospinal fluid (CSF) inside the brain is obstructed. An EVD is a flexible plastic catheter placed by a neurosurgeon or neurointensivist and managed by intensive care unit (ICU) physicians and nurses. The purpose of external ventricular drainage is to divert fluid from the ventricles of the brain and allow for monitoring of intracranial pressure. An EVD must be placed in a center with full neurosurgical capabilities, because immediate neurosurgical intervention can be needed if a complication of EVD placement, such as bleeding, is encountered.
Joshua B. Bederson is an American neurosurgeon, Leonard I. Malis, MD/Corinne and Joseph Graber Professor of Neurosurgery, and System Chair of Neurosurgery at the Mount Sinai Health System in New York City. He is a Fellow of the American College of Surgeons, and an attending neurosurgeon at The Mount Sinai Hospital.
Vein of Galen aneurysmal malformations(VGAMs) and Vein of Galen aneurysmal dilations (VGADs) are the most frequent arteriovenous malformations in infants and fetuses. A VGAM consists of a tangled mass of dilated vessels supplied by an enlarged artery. The malformation increases greatly in size with age, although the mechanism of the increase is unknown. Dilation of the great cerebral vein of Galen is a secondary result of the force of arterial blood either directly from an artery via an arteriovenous fistula or by way of a tributary vein that receives the blood directly from an artery. There is usually a venous anomaly downstream from the draining vein that, together with the high blood flow into the great cerebral vein of Galen causes its dilation. The right sided cardiac chambers and pulmonary arteries also develop mild to severe dilation.
Interventional neuroradiology (INR) also known as neurointerventional surgery (NIS), endovascular therapy (EVT), endovascular neurosurgery, and interventional neurology is a medical subspecialty of neurosurgery, neuroradiology, intervention radiology and neurology specializing in minimally invasive image-based technologies and procedures used in diagnosis and treatment of diseases of the head, neck, and spine.
An infectious intracranial aneurysm is a cerebral aneurysm that is caused by infection of the cerebral arterial wall.
A flow diverter is an endovascular prosthesis used to treat intracranial aneurysms. It is placed in the aneurysm's parent artery, covering the neck, in order to divert blood flow and determine a progressive thrombosis of the sac. Flow diverting stents consist of structural Cobalt-chrome or Nitinol alloy wires and often a set of radiopaque wires woven together in a flexible braid.
William T. Couldwell is a Canadian neurosurgeon who is professor and Chairman of the Department of Neurosurgery at the University of Utah, a position he assumed in 2001.
Alexander Coon is an American neurosurgeon who is the Director of Endovascular and Cerebrovascular Neurosurgery at the Carondelet Neurological Institute of St. Joseph's and St. Mary's Hospitals in Tucson, Arizona. He was previously the Director of Endovascular Neurosurgery at the Johns Hopkins Hospital and an assistant professor of neurosurgery, Neurology, and Radiology at the Johns Hopkins Hospital. He is known for his work in cerebrovascular and endovascular neurosurgery and his research in neuroendovascular devices and clinical outcomes in the treatment of cerebral aneurysms, subarachnoid hemorrhage, and AVMs.
Luca Paolo Eugenio Regli is a neurosurgeon and full professor and chairman of the Department of Neurosurgery of the University Hospital of Zürich since October 2012. He is the son of Franco Regli, a Swiss professor of neurology and founder of the Foundation Franco Regli for the Research in the Field of Neurodegenerative Diseases.
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