Medical device and method

Abstract

The invention relates to an apparatus for the treatment of a bifurcation aneurysm. The apparatus comprises two embodiments. In the first embodiment, a first tubular stent has a first portion that sits in the major artery and a second portion that sits in the first branch artery. A second tubular stent slides within the first stent and passes through an aperture in the first stent, so a portion of the second stent sits within the second branch artery. This forms a Y-shaped flow diverter which relieves pressure on the cerebral aneurysm. In the second embodiment, a singular stent has a first portion that resides within the major artery and a second portion that resides in the first branch artery. It has an aperture that extends towards the second branch artery that occludes the aneurysm. This forms a Y- or T-shaped flow diverter which relieves pressure on the cerebral aneurysm.

Description

[0001]Medical Device and Method Background A cerebral aneurysm (also known as a brain aneurysm) is a weak or thin spot on an artery in the brain that balloons or bulges out and fills with blood. The bulging aneurysm can put pressure on the nerves or brain tissue. It may also burst or rupture, spilling blood into the surrounding tissue (called a haemorrhage). A ruptured aneurysm can cause serious health problems such as haemorrhagic stroke, brain damage, coma, and even death. Cerebral aneurysms can occur anywhere in the brain, but most form in the major arteries along the base of the skull. Broadly, three surgical treatment options for the treatment of cerebral aneurysms are clipping; endovascular therapy or coiling; and flow diversion stenting. Clipping an aneurysm involves attaching a clip to the neck of an internal carotid artery aneurysm. Aneurysm clips have evolved into hundreds of varieties, shapes and sizes. The mechanical sophistication of available clips, along with the advent of the operating microscope in the 1960s have made surgical clipping the gold standard in the treatment of both ruptured and un-ruptured cerebral aneurysms. In spite of these advances, surgical clipping remains an invasive and technically challenging procedure. In an endovascular coiling procedure, the surgeon uses a catheter typically inserted into a groin artery. The catheter is advanced into the affected brain artery where the coil is deployed. X-rays help guide the catheter into the artery. The coils are made of soft platinum metal, and are shaped like a spring. Upon depositing within the aneurysm, the coils expand and initiate a thrombotic reaction within the aneurysm. If successful, this prevents further bleeding from the aneurysm. In the case of broad- based aneurysms, a stent may be passed first into the parent artery to serve as a scaffold for the coils. Flow diversion is an endovascular technique whereby instead of placing a device inside the aneurysm sac, such as with coiling, the device is placed in the parent blood vessel to divert blood flow away from the aneurysm itself. Almost immediately the blood flow to the aneurysm is reduced, and the complete closure of the aneurysm occurs between 6 weeks to 6 months after the procedure. Cranial aneurysms may be classified as sidewall (A, B) or bifurcation (C, D) aneurysms (Fig 1). Bifurcation aneurysms are lesions originating from major bifurcations, including the anterior cerebral artery (ACA), anterior communicating artery (ACoA), posterior communicating artery (PCoA), internal carotid artery (ICA), middle cerebral artery (MCA), and top of the basilar artery (TOBA). Bifurcation aneurysms are more difficult to treat than sidewall aneurysms, and are associated with worse clinical outcomes. The methodology behind the use of prosthetic coils is to establish a hard thrombus formation within the sac as a means of isolating the aneurysm wall from the flow of blood. While this can be effective in the treatment of many types of aneurysm, it is less effective when the aneurysm occurs at a bifurcation (or trifurcation). It is also known to close off the entrance to the aneurysm sac or to divert the flow of fluid therefrom, but known devices are not always optimal and in general not always suitable for treatment of aneurysms at vascular bifurcations. Y stenting is recognized as a suitable treatment for complex wide-necked aneurysms. Y stenting comprises crossing-Y stenting, in which a stent is passed through the interstices of another stent, and kissing-Y stenting, in which two stents are arranged in parallel. Examples of devices for treating aneurysms can be found in WO-2010 / 085344, U.S. Pat. No.6,309,367, U.S. Pat. No.6,613,074, US-2006 / 0200234, US-2007 / 0088387, US-2009 / 0228029 and US-2011 / 022149. Summary of the Invention The present invention seeks to provide improved treatment of aneurysms, in particular by means of an implantable flow diverter. The present invention also seeks to provide an improved method of diverting fluid flow away from an aneurysm located at a vascular bifurcation. According to a first aspect, the invention relates to an apparatus for the treatment of a bifurcation aneurysm, comprising: a first generally tubular stent having a wire mesh sidewall defining an inner lumen, wherein the first generally tubular wire stent comprises a substantially longitudinal resiliently deformable aperture in the sidewall; a second generally tubular stent adapted to slide within and sit partially inside the inner lumen of the first generally tubular wire stent, and pass through the resiliently deformable aperture such that a portion of the second generally tubular wire stent protrudes from the first generally tubular wire stent. According to a second aspect, the invention relates to apparatus for the treatment of a bifurcation aneurysm located at the branch point of a major artery into first and second branch arteries, comprising: a generally tubular stent having the form of a wire mesh tube defining an inner lumen, the stent having a proximal portion, a distal portion, and a resiliently deformable convex projection located between the proximal and distal portions, the convex projection comprising an aperture, wherein the proximal portion of the stent is adapted to sit within the major artery, the distal portion of the stent is adapted to sit within the first branch artery, and the resiliently deformable convex projection projects at least partially into the second branch artery. According to a third aspect, the invention relates to a first generally tubular stent as described in connection with the first aspect. According to a fourth aspect, the invention relates to a kit comprising a generally tubular stent having the features of the first or second aspect contained within the inner lumen of a delivery catheter. According to a fifth aspect, the invention relates to a kit comprising a second generally tubular stent having the features of the first or second aspect, contained within the inner lumen of a delivery catheter. According to a sixth aspect, the invention relates to a method of treatment of a cerebral aneurysm located at the bifurcation of a major artery into first and second branch arteries, comprising: i. introducing a first generally tubular stent formed having a wire mesh sidewall defining an inner lumen, wherein the first generally tubular wire stent comprises a substantially longitudinal resiliently deformable aperture in the sidewall, so that a first portion resides in the major artery and a second portion resides in the first branch artery; ii. introducing a second generally tubular stent adapted such that a first portion sits partially inside the inner lumen of the first generally tubular wire stent, passes through the resiliently deformable aperture and a second portion sits partially within the second branch artery. According to a seventh aspect, the invention relates method of treatment of a cerebral aneurysm located at the bifurcation of a major artery into first and second branch arteries, comprising: introducing into the major artery a generally tubular stent having the form of a wire mesh tube defining an inner lumen, the stent having a proximal portion, a distal portion, and a resiliently deformable convex projection located between the proximal and distal portions, the convex projection comprising an aperture, locating the proximal portion of the stent within the major artery, the distal portion of the stent within the first branch artery, and the resiliently deformable convex projection projects at least partially into the second branch artery. Brief Description of Figures Figure 1 shows types of aneurysms that may occur. Figure 2 shows a first generally tubular wire stent according to an embodiment of the two-stent apparatus of the invention. Figure 3 shows a first generally tubular wire stent, according to an embodiment of the two-stent apparatus of the invention, loaded into a delivery catheter. Figure 4 shows a first generally tubular wire stent in a delivery catheter having been guided to a location proximate a bifurcation aneurysm. Figure 5 shows a first generally tubular wire stent having been deployed proximate a bifurcation aneurysm. Figure 6 shows a second generally tubular wire stent loaded into a delivery catheter having been guided through inner lumen of first stent and through the resiliently deformable aperture. Figure 7 shows the two-stent apparatus of the invention deployed adjacent to a bifurcation aneurysm. Figure 8 is a photograph of a first generally tubular wire stent, according to an embodiment of the two-stent apparatus of the invention. Figure 9 is a photograph showing detail of a first generally tubular wire stent, according to an embodiment of the two-stent apparatus of the invention, in the region of the resiliently deformable aperture. Figure 10 is a photograph showing a second view of a first generally tubular wire stent, according to an embodiment of the two-stent apparatus of the invention. Figure 11 is a photograph a second generally tubular wire stent, according to an embodiment of the two-stent apparatus of the invention. Figure 12 is a photograph showing a deployed apparatus according to an embodiment of the two-stent apparatus of the invention. Figure 13 shows a singular generally tubular wire stent, according to an embodiment of the singular-stent apparatus of the invention, in a delivery catheter having been guided to a location proximate a bifurcation aneurysm. Figure 14 shows a singular generally tubular wire stent having been deployed proximate a bifurcation aneurysm. Figure 15 is a photograph showing a deployed apparatus according to an embodiment of the singular-stent apparatus of the invention. Figures 16 and 16a are photographs showing a deployed apparatus according to another embodiment of the singular-stent apparatus of the invention. Figure 17 is photograph showing a deployed apparatus according to an embodiment of the singular-stent apparatus of the invention within a model of a bifurcation aneurysm. Figure 18 is a further photograph showing detail of the arrangement of Figure 17. Figure 19 is an alternative perspective photograph showing the device of Figure 16. Detailed Description of the Preferred Embodiments As will be understood, the two-stent apparatus of the invention comprises two stents, referred to as the “first generally tubular stent” and the “second generally tubular stent.” The first tubular stent is formed from a wire mesh, in any one of a number of configurations that will be known to those familiar with the art. The first generally tubular stent has a proximal open end and a distal end. The distal end may be open, or alternatively may be closed, such as in the form of a hemisphere, taper or point. The first generally tubular stent is preferably radially collapsible, so that it can be contained within a catheter or other delivery device. The second generally tubular stent has a proximal open end and a distal end. The distal end may be open, or alternatively may be closed, such as in the form of a hemisphere, taper or point. The first generally tubular stent is preferably radially collapsible, so that it can be contained within a catheter or other delivery device. The first generally tubular stent comprises a substantially longitudinal resiliently deformable aperture in its sidewall. This is dimensioned to be significantly larger than the mesh apertures in the sidewall and is preferably dimensioned such that the second generally tubular stent can pass through the deformable aperture during deployment within the patient’s vasculature. In order to do so, it may be necessary to inwardly collapse or compress the second generally tubular stent. Preferably, when the second generally tubular stent is in its uncompressed (relaxed) state, it fits snugly within the deformable aperture, and lateral movement is prevented. In one embodiment, the invention relates to a device having a single stent. This embodiment of the invention is referred to as the “single stent device.” The single stent device is preferably formed from a wire mesh, in any one of a number of configurations that will be known to those familiar with the art. The single stent device has a proximal portion terminating in a proximal end, and a distal portion terminating in a distal end. The distal end may be open, or alternatively may be closed, such as in the form of a hemisphere, taper or point. The single stent device is preferably radially collapsible, so that it can be contained within a catheter or other delivery device. The single stent device in some embodiments includes a resiliently deformable convex projection that, in unconstrained form, projects from the radius of the wire mesh tube. In other words, it forms a bulge. This deformable convex projection is also radially collapsible so as to be dimensioned to fit within a catheter, and upon release, relaxes to protrude beyond the perimeter of the wire mesh tube. In some embodiments, the aperture is substantially longitudinal. The aperture is preferably configured to open when the deformable convex projection is released from the delivery device. Optionally, the aperture closes when the single stent device is restrained within the delivery device (e.g. catheter). This aperture is dimensioned to be significantly larger than the mesh apertures in the sidewall. In embodiments where it is present, the resiliently deformable convex projection comprises an aperture. In a preferred embodiment, the single stent device is formed such that the longitudinal axis of the proximal portion and the longitudinal axis of the distal portion form an angle of less than 180°, such as less than 150°, preferably between 100 and 80°, such as about 90°. In other words, the wire mesh tube has a bend between the proximal portion and the distal portion. In preferred embodiments, the aperture is in the region of the bend, preferably on the outside of the bend. This has been found to greatly assist location of the device in the region of a bifurcation aneurysm. When located in the vasculature in the region of the bifurcation aneurysm, the proximal portion of the stent sits within the major artery, the distal portion of the stent sits within the first branch artery, and the aperture is oriented towards the second branch artery. In this way, that blood flowing through the major artery is diverted away from the aneurysm along the first and second branch arteries. Furthermore, the neck of the aneurysm is substantially occluded (blocked) by a portion of the mesh sidewall of the distal portion, preventing or reducing blood flow into the aneurysm and hence relieving pressure within it. In a particularly preferred embodiment of the single stent device, the proximal portion and distal portion of the device are substantially tubular in configuration, having a proximal portion longitudinal axis, and a distal portion longitudinal axis. The axes meet at an angle of less than 180° as described in the previous paragraph. The distal portion and the aperture are substantially diametrically opposed to one another about the proximal portion longitudinal axis, and together form an open passage. An occluding portion of the distal portion sidewall is disposed across the proximal portion longitudinal axis. In use, the occluding portion sits across the neck of the aneurysm, and reduces or prevents ingress of blood flow into the aneurysm. The first generally tubular stent and the single stent device are preferably formed from a resilient metal fabric wherein one, or a plurality of resilient strands or wires are provided, with the metal fabric being formed by braiding the resilient strands to create a resilient material mesh. Preferably, the mesh defines a pattern of interlocked diamonds or squares of wire over the surface of the first generally tubular stent or the single stent device, respectively. When formed from shaped memory metal wires, such as nitinol or Elgiloy®, the wires will have a relatively small diameter, typically in the range from 25 µm to 500 µm, usually from 50 µm to 250 µm, where the braid will include from as few as 2 to as many as 200 wires, more commonly being from 20 wires to 100 wires. In exemplary cases, the wires will be round having diameters in the range from 75 µm to 200 µm with a total of from 24 to 60 wires. The wires are braided into a tubular geometry by conventional techniques, and the tubular geometry will be heat-treated to impart the desired shape memory. Usually, the braided tube will be formed into the desired final (deployed) state. The wires could also be of non-circular cross-section, such as of square or rectangular cross-section, in which case it is preferred that they have a circumference of 40-200 µm. It is also possible to use combination of diameters and wire materials in one device to achieve structural stability and / or desired radio- opacity characteristics. The filaments of the exemplary braided embodiment can be made of any suitable material which are bio-compatible and which can be worked into a braid. Bio- compatible herein includes any material that can be safely introduced and implanted in human or animal bodies for indefinite periods of time without causing any significant physiological damage. Preferably, the filaments are made of a material selected from among the 316L stainless steel, tantalum, and super elastic Nitinol, cobalt base alloy, polymer or any other suitable metal or metal combination. The filament can be coated with bio-compatible coatings [Ufrich Sigwart, "Endoluminal Stenting", W. B. Saunders Company Ltd., London, 1996]. It is possible to use a combination of several filament materials in one device and combinations of several materials in one filament. The above embodiments have been described in relation to a braid mesh tube, however this is not meant to be limiting in any way. Other mesh-like structures, such as woven or knitted tubes exhibiting similar porosity and flexibility can be used without exceeding the scope of the invention. Such foreshortened-memory configurations will allow the first generally tubular stent or the single stent device to be delivered in a constrained configuration (either radially or axially elongated) and thereafter released from constraint so that the body assumes the correct configuration at the target site. The time and temperature of the heat treatment is selected to substantially set the braided fabric in its deformed state. After the heat treatment, the fabric is removed from contact with the moulding element and will substantially retain its shape in the deformed state. The braided fabric so treated defines a relaxed state of a medical device which can be stretched or expanded and deployed through a catheter into a channel in a patient's body. Those skilled in the art will appreciate that the cavities of the moulds must mirror the desired shape of the device. Additionally, the mould may include cores and / or cams to adequately form the desired shape and passages there through. In some embodiments, both the first generally tubular wire stent frame and the single stent device preferably include a wire having a wire first portion and a wire second portion; wherein the wire first portion is configured into a first elongated tubular body having a first helical pattern; wherein the wire second portion is configured into a second elongated tubular body having a second helical pattern having a pitch about opposite a pitch of the first helical pattern; wherein the wire first portion and the wire second portion are braided together forming a stent wall having an elongated tubular braided helical pattern; wherein at least a portion of the stent wall comprises an aperture significantly larger that the holes defined by the braid. It is possible that the deformable aperture is formed simply by cutting a number of wires which define the sidewall of the first generally tubular stent and the single stent device. However, this is not preferred, as the cut ends tend to snag on either the vasculature or the second generally tubular stent, and the first generally tubular stent becomes prone to fraying or unravelling. In a preferred embodiment, the aperture is formed from a series of apexes in the wire, which are arranged in two rows substantially opposite to one another along the length of the aperture. The rows of apexes together define the edges of the aperture. The rows of apexes run substantially longitudinally with respect to the first generally tubular stent and single stent device, respectively. The apexes may be formed as part of the wire mesh, wherein, instead of overlapping or interlocking as in the remainder of the sidewall, the wires are not interlocked, but instead are bent so as to define an apex. The apexes may form an angle and thus define a sharp point. However, this is not preferred. Preferably, the apexes are radiused. Having a radius prevents the apexes from snagging or catching on the vasculature or the second generally tubular stent (in the two-stent apparatus). The radius will depend on the dimensions of the wires and the either the first generally tubular stent (in the two-stent apparatus) or the generally tubular stent (in the single stent device), but will usually be between 10 and 1000 µm, such as 40-200 µm. In one embodiment, the aperture is positioned along a portion of the sidewall that defines a bulge or protuberance. The protuberance serves a number of advantageous functions. Firstly, it assists the surgeon in correctly positioning the first generally tubular wire stent at the junction of the vasculature proximate to the aneurysm. Secondly, in the two-stent apparatus, it helps to guide the second generally tubular wire stent through the deformable aperture and so correctly form the Y-shaped flow diverter within the vasculature of the patient. In some embodiments of the two-stent apparatus, the first and second generally tubular wire stent frames comprise a wire first portion having a first helical pattern along a first portion of its length, and a second helical pattern along a second portion of its length; and a second helical pattern having a pitch about opposite a pitch of the first helical pattern. Where the first helical pattern and second helical pattern meet, they define an apex in the first wire portion. Similarly, the wire second portion has a first helical pattern along a first portion of its length, and a second helical pattern along a second portion of its length; the second helical pattern having a pitch about opposite a pitch of the first helical pattern. Where the first helical pattern and second helical pattern meet, they define an apex in the second wire portion. Preferably, both the first generally tubular wire stent frame (in the two-stent apparatus) and the singular generally tubular wire stent frame (in the single stent device) comprise at least one apex in the wire first portion and at least one apex in the wire second portion, wherein the apexes are arranged to define the periphery of the aperture in the wall of the first generally tubular wire stent frame. According to the present invention, the constituent elements making up the mesh-like tube are of a sufficiently small size in cross-section and define windows of a size such that the mesh-like tube, when in its contracted condition, is sufficiently flexible so as to be easily manoeuvrable through the blood vessel to be implanted at the bifurcation; and when in its implanted condition anchoring itself to both the source blood vessel and at least one of the branch vessels thereby skewing flow of blood away from the aneurysm sufficiently to decrease the possibility of rupture of the aneurysm. The skewing is caused by the flow of blood through the walls of the mesh-like tube, and the amount of skew is a function of the pre-determined implanted porosity index. In an exemplary embodiment, in which the mesh-like tube is constituted of braided filaments, the windows defined by the filaments of the braided tube are such as to reduce the flow of blood therethrough to the aneurysm to decrease the possibility of rupturing it, but not to unduly reduce the blood flow to the branch vessels to the degree likely to cause damage to tissues supplied with blood by such vessels. Experimental evidence indicates that patency can be maintained, and ischemia and infarction can be prevented, if less than 50% of the ostial diameter of the branch vessel is occluded. The ostial diameter of intercranial branch vessels are typically on the order of 80-800µm, thus to ensure patency of the intercranial branch vessels, filaments of the braided tube must be less than 50 µm in diameter for round filaments, and preferably less than or equal to 40 µm. For non-round filaments, a similar dimensional limitation is necessary. Stents illustrated and equivalents thereto may be delivered to a body lumen using various techniques. Generally, under the aid of endoscopic and / or fluoroscopic visualization a delivery device containing the stent is advanced into the vicinity of the target anatomy. The targeted lumen may be predilated with a balloon catheter or other dilation device, if necessary or desired. Preferably, the stent is delivered in a compressed state in a low-profile delivery device. This approach may reduce the risk of tissue perforations during delivery. Once the delivery device is in place, the stent may be released from the retaining sheath or the like. In one preferred embodiment, a stent may be delivered with a controlled release system (e.g., EVOLUTION® Controlled-Release Stent, Cook Endoscopy Inc., Winston-Salem, N.C.). A controlled release device permits the physician to slowly release the stent from the retaining sheath and in some instances, recapture the stent to allow for repositioning. After implantation, the delivery device and any other devices (e.g., wire guides, catheters, etc.) may be removed. Stents illustrated and equivalents thereto may include one or more components configured to aid in visualization and / or adjustment of the stent during implantation, repositioning, or retrieval. For example, a stent may include one or more radiopaque markers configured to provide for fluoroscopic visualization for accurate deployment and positioning. Radiopaque markers may be affixed (e.g., by welding, gluing, suturing, or the like) at or near the ends of the stent at a cross point of wire first portion and wire second portion. In some embodiments, a stent may include four radiopaque markers with two markers affixed to a first flange and two to a second flange. Optionally, radiopacity can be added to a stent through covering (also referred to as coating) processes such as sputtering, plating, or co-drawing gold orsimilar heavy metals onto the stent. Radiopacity can also be included by alloy addition. Radiopaque materials and markers may be comprised of any suitable biocompatible materials, such as tungsten, tantalum, molybdenum, platinum, gold, zirconium oxide, barium salt, bismuth salt, hafnium, and / or bismuth subcarbonate. Additional methods are contemplated, including but not limited to, use of a nitinol wire with a platinum core, such as the DFT® wire available from FortWayne Metals, Fort Wayne, Ind. The stents may be self-expanding, mechanically expandable, or a combination thereof. Self-expanding stents may be self-expanding under their inherent resilience or may be heat activated wherein the stent self-expands upon reaching a predetermined temperature or range of temperatures. One advantage of self- expanding stents is that traumas from external sources or natural changes in the shape of a body lumen do not permanently deform the stent. Thus, self-expanding stents may be preferred for use in vessels that are subject to changes in shape and / or changes in position, such as those of the peripheral and gastrointestinal systems. One common procedure for implanting a self-expanding stent involves a two-step process. First, if necessary, the vessel may be dilated with a balloon or other device. The stent may be loaded within a sheath that retains the stent in a compressed state for delivery to the targeted vessel. The stent may then be guided to the target anatomy via a delivery catheter and thereafter released by retracting or removing the retaining sheath. Once released from the sheath, the stent may radially expand until it contacts and presses against the vessel wall. In some procedures, self-expanding stents may be delivered with the assistance of an endoscope and / or a fluoroscope. An endoscope provides visualization as well as working channels through which devices and instruments may be delivered to the site of implantation. A fluoroscope also provides visualization of the patient anatomy to aid in placement of an implantable device, particularly in the gastrointestinal system. Additionally, the stent may be post-dilated with a balloon or other means. In the two-stent apparatus of the invention, the first generally tubular stent is positioned near the location of the aneurysm with the distal end located within the first branch artery. The substantially longitudinal resiliently deformable aperture is located at or near the location of the arterial junction at the entrance to second branch artery. The proximal portion of the stent resides in the major cerebral artery. Due to the self-expanding nature of the first generally tubular stent, the inner lumen is dimensioned to approximately the same diameter as the arteries, with the sidewall in close contact with the arterial wall. The second generally tubular stent is compressed and loaded into a delivery cannula in the manner described above. The tip of the cannula is manoeuvred through the vasculature by the surgeon under non-invasive visualisation, and into the proximal end of the first stent. The cannula is passed along the inner lumen of the first stent, and the tip is guided through the resiliently deformable aperture into the second branch artery. The cannula is advanced to such an extent that the second stent projects partially from the aperture and into the second branch artery. The remainder of the second stent is contained within the inner lumen of the first stent. When the surgeon withdraws the delivery cannula, the second stent radially expands. The whole apparatus defines a Y-shaped arrangement along which blood can flow and diverts blood flow away from the neck of the aneurysm. In the single stent device of the invention, the generally tubular stent is positioned near the location of the aneurysm with the distal end located within the first branch artery. The aperture is located at or near the location of the arterial junction and in some embodiments projects partially into the second branch artery by virtue of its location on the resiliently deformable convex projection; in all cases, the aperture is directed towards the first branch artery. The proximal portion of the stent resides in the major cerebral artery. Due to the self-expanding nature of the singular generally tubular stent, the inner lumen is dimensioned to be approximately the same diameter as the arteries, with the sidewall in close contact with the arterial wall. The whole apparatus defines a Y- or T- shaped arrangement along which blood can flow, and diverts blood flow away from the neck of the aneurysm. Description of an embodiment with reference to the figures. Figure 3 shows first generally tubular wire stent (301) contained within flexible delivery catheter (302). The first generally tubular wire stent (301) is radially compressed to fit slidably within the inner lumen of the catheter (302). Delivery catheter (302) is suitably provided with a plunger (303) or other ejection mechanism that serves to urge first generally tubular wire stent (301) out of distal end (304) of delivery catheter (302) when at the appropriate location within the vasculature. The substantially longitudinal resiliently deformable aperture (305) is flush with the remainder of the sidewall of the first generally tubular wire stent (301). Figure 4 shows an aneurysm (401) present at the bifurcation of a major cerebral artery (402) into first (403) and second (404) branch arteries. Catheter (302) is guided by the surgeon via a suitable vascular access point to the approximate location of aneurysm (401), with distal end (304) located within the first branch artery (403). The substantially longitudinal resiliently deformable aperture (305) is located at or near the location of the arterial junction. The catheter may be guided using an appropriate non-invasive visualisation technique. If appropriate, a guidewire may first be manoeuvred through the vasculature and the catheter (302) subsequently slid along it to reach the desired location. Figure 5 shows first generally tubular wire stent (301) in situ near the aneurysm (401). The catheter (302) has been withdrawn through the vascular access point, allowing the first generally tubular wire stent (301) to expand. The sidewall of the first generally tubular wire stent (301) along a first portion of its length abuts the wall of the major cerebral artery (402), where it exerts a radially outward force to maintain patency of the artery, whilst along a second portion of its length abuts the wall of the first branch artery (403). Substantially longitudinal resiliently deformable aperture (305) is positioned opposite the entrance to the second branch artery (404). The bulge or protuberance (501) along which the resiliently deformable aperture (305) is located serves to correctly position the first generally tubular wire stent (301), and to correctly orient the resiliently deformable aperture (305) for the subsequent step of the procedure. Figure 6 shows the second generally tubular wire stent (601) contained within a further delivery catheter (602). For clarity, a portion near the distal end (603) of the catheter (602) is shown cut away. The further delivery catheter (602) is guided by the surgeon via a suitable vascular access point to within the inner lumen of first generally tubular wire stent (301), and out of the substantially longitudinal resiliently deformable aperture (305) so that it emerges into second branch artery (404). Figure 7 shows the final configuration of the device deployed within the vasculature. Second generally tubular wire stent (601) has been unsheathed from further delivery catheter (602) and radially expanded due to the absence of the constraining force of the further delivery catheter (602). A first portion (701) sits coaxially within the first generally tubular wire stent (301) allowing blood to flow freely through the inner lumen thereof. A second portion (702) of the second generally tubular wire stent (601) emerges from the resiliently deformable aperture (305) and protrudes some length along the second branch artery (404). Together, the first (301) and second (601) generally tubular wire stents defines a Y-shaped structure, which diverts blood along the arms and away from aneurysm (301). This in turn serves to relieve pressure within aneurysm (301), whereupon it naturally shrinks and the risk of thrombosis disappears. Figure 8 is a photograph of the first generally tubular wire stent (301) according to an embodiment of the invention it its relaxed (uncompressed) state. First generally tubular wire stent (301) comprises a sidewall (801) formed of a diamond pattern mesh of interwoven wire filaments. The stent (301) has an open distal end (802) and an open proximal end (803), interconnected by the inner lumen. Resiliently deformable aperture (305) is shown along protuberance or bulge (501). Figure 9 is a photograph showing the detail of first generally tubular wire stent (301) along the region of the resiliently deformable aperture (305). First (901) and second (902) rows of apexes in the wire mesh are shown defining the periphery of the resiliently deformable aperture (305). Figure 10 is a second view of the first generally tubular wire stent (301) shown in Figures 9 and 10. Resiliently deformable aperture (305) can be clearly seen. In the relaxed (uncompressed) state shown, the resiliently deformable aperture (305) forms a substantially elliptical shape, defined along its periphery by first (901) and second (902) rows of apexes in the wire mesh. Figure 11 is a photograph of the second generally tubular wire stent (601). As may be seen, the stent (601) is formed from a plurality of helical wires which coil around the longitudinal axis, with a first portion winding in a clockwise fashion and a second portion in the opposite anticlockwise fashion, the portions being interwoven to form a mesh sidewall. Second generally tubular wire stent (601) has an open proximal end (1101) and a distal end which tapers to a point (1102). The tip (1103) is formed with the ends of the wires held together with a crimp. Tip (1103) is of a looser weave than the remainder of the stent (601), and permits fluid to flow therethrough in a relatively unimpeded fashion. Figure 12 shows an embodiment of the apparatus of the invention as would be deployed in the vasculature. A first portion (1201) of the second generally tubular wire stent (601) protrudes from resiliently deformable aperture (305), whilst a second portion (1202) sits within the inner lumen of first generally tubular wire stent (301). The whole forms a Y-shape and serves to divert blood flow down the “arms” of the device and thus relieve pressure on the aneurysm. Figure 13 shows an aneurysm (1301) present at the bifurcation of a major cerebral artery (1302) into first (1303) and second (1304) branch arteries. A catheter (1305) is guided by the surgeon via a suitable vascular access point to the approximate location of the aneurysm (1301), with distal end (1306) located within the first branch artery (1303). The substantially longitudinal resiliently deformable aperture (1307) is located at or near the location of the arterial junction. The catheter may be guided using an appropriate non-invasive visualisation technique. If appropriate, a guidewire may first be manoeuvred through the vasculature and the catheter (1305) subsequently slid along it to reach the desired location. Figure 14 shows the final configuration of the single stent device (1401) deployed within the vasculature. The catheter (1305) has been withdrawn through the vascular access point, allowing the generally tubular wire stent (1401) to expand. The wire mesh tube of the generally tubular wire stent (1401) along a first, proximal portion of its length abuts the wall of the major cerebral artery (1302), where it exerts a radially outward force to maintain patency of the artery, whilst a second, distal portion of its length abuts the wall of the first branch artery (1303). The resiliently deformable convex projection (1307) protrudes some length along the second branch artery (1304). The generally tubular wire stent defines a Y-shaped structure, which diverts blood along the first (1303) and second (1304) branch arteries and away from the aneurysm (1301). This in turn serves to relieve pressure within the aneurysm (1301), whereupon it naturally shrinks and the risk of thrombosis reduces. Figure 15 is a photograph of the single stent device (1401) according to an embodiment of the invention it its relaxed (uncompressed) state. The generally tubular wire stent (1401) comprises a sidewall (1501) formed of a diamond pattern mesh of interwoven wire filaments. The generally tubular wire stent (1401) has an open proximal end (1502) and a open distal end which tapers on the periphery to a point (1503). The tip (1504) is formed from the ends of the wires held together with a crimp. The tip (1504) is of a looser weave than the remainder of the stent (1401) and permits fluid to flow therethrough in a relatively unimpeded fashion. The resiliently deformable convex projection (1307) bearing the aperture is shown. First (1505) and second (1506) rows of apexes in the wire mesh are shown defining the periphery of the aperture. Figure 16 is a photograph of the single stent device (1601) according to an embodiment of the invention it its relaxed (uncompressed) state. The generally tubular wire stent (1601) comprises a sidewall (1501) formed of a diamond pattern mesh of interwoven wire filaments. The stent comprises proximal (1602) and distal (1603) portions, which, in the relaxed configuration shown, have their longitudinal axes substantially perpendicular to one another. The generally tubular wire stent (1601) has an open proximal end (1604) and an open distal end (1605). The resiliently deformable convex projection (1606) bearing the aperture (1607) is shown. Figure 16a also illustrates the device of Figure 16 to indicate further aspects. Proximal portion (1602) is substantially tubular in configuration, having longitudinal axis A. A section of (1707) of the sidewall of distal portion (1603) lies across axis A; in use, this section (1707) occludes the neck of the aneurysm and prevents or reduces blood inflow into the aneurysm. Figure 17 is a photograph of a model of a bifurcation aneurysm (1701) with the single stent device (1601) of Figure 16 in position. Model bifurcation aneurysm (1701) includes major artery portion (1702), first branch artery portion (1703), second branch artery portion (1704) and aneurysm portion (1705). Aneurysm portion (1705) is in fluid communication with the bifurcation of the first (1703) and second (1704) branch arteries via aneurysm neck (1706). In position as shown, the proximal portion of the sidewall (1602) sits within inner lumen of major artery (1702) and distal portion (1603) sits within first branch artery portion (1703). Resiliently deformable convex projection (1606) projects partially into second branch artery portion (1704). Aperture (1607) is oriented towards the second (1704) branch artery. The aneurysm neck (1706) is occluded by a portion (1707) of the mesh sidewall of the distal portion (1501), preventing blood from entering the aneurysm (1705). Blood flowing up the major artery (1702) is diverted along the first (1703) and second (1704) branch arteries, and away from the aneurysm neck (1706). This relieves pressure within the aneurysm (1705). Figure 18 is an alternative perspective view of the arrangement of Figure 17. The photograph is taken along the central axis of the aneurysm, and shows the the aneurysm neck (1706) occluded by a portion (1707) of the mesh sidewall of the stent (1501). Figure 19 is a side-on view of the single stent device (1601) along the axis of the distal portion (1603). It can clearly be seen that an open passage (1901) is formed between the open distal end (1605) and the aperture (1607).

Claims

CLAIMS:

1. An apparatus for the treatment of a bifurcation aneurysm, comprising: a first generally tubular stent formed having a wire mesh sidewall defining an inner lumen, wherein the first generally tubular wire stent comprises a substantially longitudinal resiliently deformable aperture in the sidewall; a second generally tubular stent adapted to slide within and sit partially inside the inner lumen of the first generally tubular wire stent, and pass through the resiliently deformable aperture such that a portion of the second generally tubular wire stent protrudes from the first generally tubular wire stent.

2. An apparatus for the treatment of a bifurcation aneurysm located at the branch point of a major artery into first and second branch arteries, comprising: a generally tubular stent having the form of a wire mesh tube defining an inner lumen, the stent having a proximal portion with a sidewall, a distal portion with a sidewall, and a resiliently deformable aperture located between the proximal and distal portions, wherein the proximal portion of the stent is adapted to sit within the major artery, the distal portion of the stent is adapted to sit within the first branch artery, and the aperture is oriented towards the second branch artery, such that blood flowing through the major artery is diverted away from the aneurysm along the first and second branch arteries.

3. An apparatus as claimed in claim 2 wherein the proximal portion has a first longitudinal axis, and the distal portion has a second longitudinal axis, and the first and second longitudinal axes are oriented at an angle of less than 180°.

4. An apparatus as claimed in claim 2 or 3 wherein the aneurysm is in fluid communication with the vasculature via a neck, and in use the sidewall of the distal portion substantially occludes the neck.

5. An apparatus according to any preceding claim wherein the aperture is defined along at least one side by a row of wire apexes in the mesh sidewall.

6. An apparatus according to claim 5, wherein the aperture is defined along both sides by a row of wire apexes in the mesh sidewall.

7. An apparatus according to claim 6 wherein the rows of apexes are generally arcuate when the first generally tubular stent is in a relaxed or expanded configuration.

8. An apparatus according to any one of claims 5 to 7 wherein the apexes are radiused.

9. An apparatus according to claim 1 or 2 wherein the resiliently deformable aperture is arranged along a protuberance in the sidewall.

10. An apparatus according to any preceding claim wherein the wire mesh has a closed cell structure.

11. An apparatus according to any preceding claim wherein the first generally tubular stent, the second generally tubular stent or both are inwardly collapsible.

12. An apparatus according to any preceding claim wherein the first generally tubular stent, the second generally tubular stent or both are self-expanding.

13. An apparatus according to any preceding claim wherein the first generally tubular stent has an open proximal end, and / or an open distal end.

14. An apparatus according to claim 1 wherein the second generally tubular stent has an open proximal end, and / or an open distal end.

15. An apparatus according to claim 1 wherein the second generally tubular stent has an open proximal end, and a distal end forming a taper or point.

16. A first generally tubular stent having the features defined in claim 1.

17. A kit comprising a generally tubular stent having the features defined in any one of claims 1 to 16 contained within the inner lumen of a delivery catheter.

18. A kit comprising a second generally tubular stent having the features defined in claim 1 contained within the inner lumen of a delivery catheter.

19. A method of treatment of a cerebral aneurysm located at the bifurcation of a major artery into first and second branch arteries, comprising: i. introducing a first generally tubular stent formed having a wire mesh sidewall defining an inner lumen, wherein the first generally tubular wire stent comprises a substantially longitudinal resiliently deformable aperture in the sidewall, so that a first portion resides in the major artery and a second portion resides in the first branch artery; ii. introducing a second generally tubular stent adapted such that a first portion sits partially inside the inner lumen of the first generally tubular wire stent, passes through the resiliently deformable aperture and a second portion sits partially within the second branch artery.

20. A method according to claim 19 wherein the first and second generally tubular stents form a Y-shaped flow diverter which relieves pressure on the cerebral aneurysm.

21. A method according to claim 19 or 20 comprising a further step of coiling the aneurysm.

22. A method of treatment of a cerebral aneurysm located at the bifurcation of a major artery into first and second branch arteries, comprising: introducing into the major artery a generally tubular stent having the form of a wire mesh tube defining an inner lumen, the stent having a proximal portion, a distal portion, and an aperture between the proximal and distal portions, locating the proximal portion of the stent within the major artery, the distal portion of the stent within the first branch artery, and the aperture towards the second branch artery, such that the neck of the aneurysm is substantially occluded by the sidewall of the distal portion.

23. A method according to claim 22 wherein the stent forms a Y- or T- shaped flow diverter which relieves pressure on the cerebral aneurysm.

24. A method according to claim 22 or 23 comprising a further step of coiling the aneurysm.

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