Abstract:
Devices, systems and methods are provided for treating aneurysms, particularly cerebral aneurysms. Such treatment is achieved minimally invasively without the need for conventional filling materials and methods. Such treatments may be used for aneurysms located near blood vessel side-branches and bifurcations.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Patent Application No. 60/730,979 filed Oct. 27, 2005, incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     A cerebral aneurysm is an area where a blood vessel in the brain weakens, resulting in a bulging or ballooning out of part of the vessel wall. The disorder may result from congenital defects or from other conditions such as high blood pressure, atherosclerosis or head trauma. Every year, an estimated 30,000 people in the United States experience a ruptured cerebral aneurysm, and up to 6 percent of the population may be living with an unruptured aneurysm. Aneurysms occur in all age groups, but the incidence increases steadily for individuals age 25 and older, is most prevalent in people ages 50 to 60, and about three times more prevalent in women. The outcome for patients treated before a ruptured aneurysm is much better than for those treated after, so the need for adequate treatment of a cerebral aneurysm is very important.  
         [0003]     Current treatment options include a surgical operation to “clip” the aneurysm which is performed by doing a craniotomy, and isolating the aneurysm from the bloodstream using one or more clips, which allows it to deflate. Surgical repair of cerebral aneurysms is not possible if they are located in unreachable parts of the brain. Angiography is used to visualize closure of the aneurysm and preserve normal flow of blood in the brain.  
         [0004]     A less invasive technique which does not require surgery, called endovascular therapy, uses micro catheters to deliver coils to the site of the enlarged blood vessel that occludes the aneurysm from inside the blood vessel. In some cases, the aneurismal opening or neck is too large to retain these coils. In such cases, a stent may be used to create a bridge across the neck and prevent the coils from encroaching into the vessel lumen. Typically, such a stent comprises a small flexible cylindrical mesh tube that provides a scaffolding to assist in holding the coils in place. An example of such a stent is provided by Neuroform3™ Microdelivery Stent System (Boston Scientific, Inc.). Neuroform3 Stents employ a highly flexible, hybrid cell design for better tracking during access and greater conformability within a variety of vessel morphologies. The Neuroform3 hybrid cell design is also engineered to provide greater scaffolding for coil mass support and sufficient radial force to generate stability within the vessel. However, the Neuroform3 Stents are only used to hold the coils in place and cannot be used independently to treat aneurysms.  
         [0005]     Therefore, a stent design is desired that is useable itself for treatment of an aneurysm without the need for filling material, such as coils. Therefore, such a stent may be used to treat aneurysms which are typically unsuitable for filling with material. Such a stent design should provide high flexibility for deliverability through tortuous cerebral anatomy and for conformability within a variety of vessel morphologies while providing sufficient radial strength to hold the stent firmly in place. Such a stent design should also be useable to treat aneurysms located near blood vessel side-branches and bifurcations. At least some of these objectives will be fulfilled by the present invention.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     Devices, systems and methods are provided for treating aneurysms, particularly cerebral aneurysms. Such treatment is achieved minimally invasively without the need for conventional filling materials and methods. Such treatments may be used for aneurysms located near blood vessel side-branches and bifurcations.  
         [0007]     In a first aspect of the present invention, a stent device is provided for covering an aneurysm in a blood vessel, particularly wherein the blood vessel includes at least one side-branch near the aneurysm. In some embodiments, the stent device comprises a tubular frame having a first end and a second end, and a covering between the first and second ends of the frame. The covering substantially restricts flow of blood through the frame to the aneurysm while the stent device is positioned within the blood vessel so that the covering substantially covers the aneurysm. Also, the tubular frame has a cell geometry which allows sufficient flow of blood through the cell geometry at least between the ends and the covering so as to maintain blood flow through to the at least one side-branch. The frame typically also includes at least one anchoring portion which provides radial anchoring force.  
         [0008]     The covering partially occludes, blocks or covers the frame so as to restrict the flow therethrough, i.e. in a lateral direction through the wall of the stent. The covering may cover any suitable portion of the frame, such as approximately 10-90 percent of the frame or more particularly approximately 30-40 percent of the frame. Such percentages may be in length of the frame covered or in area of the frame covered. In some embodiments, the covering is positioned approximately equidistant from the ends. In other embodiments, the covering is positioned at one of the first end or the second end.  
         [0009]     The covering may have a variety of shapes, sizes, materials and configurations as will be described in more detail herein. For example, the covering may comprise an expandable polymer material. Or the covering may be woven through the cell geometry of the frame, such as in a spiral configuration. In some embodiments, the covering comprises a tubular sleeve positionable around the frame. In these embodiments in particular, the device may also include at least one security ring configured to assist in holding the covering on the frame.  
         [0010]     In another embodiment, the stent device comprises a tubular frame having a first end, a second end, an occlusional cell geometry and an open cell geometry. The occlusional cell geometry is configured to be positioned so as to cover the aneurysm and substantially prevent flow of blood therethrough to the aneurysm while the stent device is positioned within the blood vessel. The open cell geometry is configured to be positioned so as to maintain blood flow through to the at least one side-branch while the stent device is positioned within the blood vessel. Typically, the occlusional cell geometry has smaller cells than the open cell geometry. In some embodiments, the occlusional cell geometry comprises approximately 10-90 percent of the frame, particularly approximately 30-40 percent of the frame.  
         [0011]     In some instances, the occlusional cell geometry is disposed approximately equidistant from the ends. The frame may also include at least one anchoring portion which provide radial anchoring force.  
         [0012]     In another aspect of the present invention, a method is provided for covering an aneurysm in a blood vessel, particularly wherein the blood vessel includes at least one side-branch near the aneurysm. In one embodiment, the method includes advancing a stent through the blood vessel, wherein the stent comprises a tubular frame having a first end, a second end, an open cell geometry and a covering. The method also includes positioning the stent within the blood vessel so that the covering substantially covers the aneurysm restricting blood flow to the aneurysm and the open cell geometry substantially covers the at least one side-branch allowing blood flow to the at least one side-branch.  
         [0013]     When the covering is disposed approximately equidistant from the ends, positioning may comprise positioning the ends on opposite sides of the aneurysm. When the stent includes an anchoring portion near the first end and the covering near the second end and when the blood vessel includes a bifurcation near the aneurysm, positioning may comprise positioning the anchoring portion within the blood vessel so as to anchor the stent while the second end is disposed near the bifurcation.  
         [0014]     In addition, positioning the stent typically comprises expanding the stent within the blood vessel. Such methods are often performed when the blood vessel comprises a cerebral blood vessel but are not so limited. Other objects and advantages of the present invention will become apparent from the detailed description to follow, together with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  illustrates a perspective view of an embodiment of a stent of the present invention.  
         [0016]      FIG. 2  illustrates the stent of  FIG. 1  positioned within a blood vessel having an aneurysm.  
         [0017]      FIG. 3  illustrates an embodiment of a frame.  
         [0018]      FIG. 4  illustrates a covering asymmetrically positioned over a frame.  
         [0019]      FIG. 5  illustrates the stent of  FIG. 4  positioned within blood vessel having an aneurysm near a bifurcation.  
         [0020]      FIGS. 6A-6D  illustrate an embodiment of the stent of the present invention.  
         [0021]      FIGS. 7A-7C  illustrate embodiment of the stent of the present invention wherein the frame has a variable density.  
         [0022]      FIG. 8  illustrates another embodiment of a stent wherein the frame has a higher density toward the ends and a lower density therebetween.  
         [0023]      FIGS. 9A-9B  illustrate an embodiment of a stent wherein the frame has circular belts near the ends comprised of a plurality of elongate struts in a zig-zag arrangement.  
         [0024]      FIG. 10A-10C  illustrate an embodiment of a stent having a covering that is woven through the frame so that the covering wrapped on itself.  
         [0025]      FIG. 11  illustrates an embodiment of a stent having a covering that is woven through the frame so that the covering is wrapped in a spiral configuration.  
         [0026]      FIG. 12  illustrates an embodiment of stent for use without a separate covering. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]      FIG. 1  illustrates an embodiment of a stent  10  of the present invention. In this embodiment, the stent  10  comprises a frame  12 , a graft or covering  14 , and a pair of security rings  16 . The frame  12  has a tubular shape and extends from a first end  18  to a second end  20 . The covering  14  is sized to cover a portion of the frame  12 , typically approximately ⅓ of the length of the frame  12 . In this embodiment, the covering  14  is positioned over the exterior of the frame  12  and secured in place by the security rings  16  which are positioned thereon. Additional description and embodiments are provided in later sections.  
         [0028]      FIG. 2  illustrates the stent  10  of  FIG. 1  positioned within a blood vessel V having an aneurysm A. As shown, the stent  10  is positioned so that the covering  14  covers the opening of neck of the aneurysm A, restricting blood flow into the aneurysm A. Thus, the aneurysm A is excluded from the circulation without the need for filing the aneurysm A, such as with coils. In this example, the blood vessel V also has side-branches S which are located relatively close to the aneurysm A. The covering  14  is positioned so as to substantially avoid covering the side-branches S and allow continued blood flow into the side-branches S, as illustrated by arrows. In this embodiment, the ends  18 ,  20  of the frame  12  are positioned on opposite sides of the aneurysm A and side-branches S. Thus, the frame  12  extends over the side-branches, however, the frame  12  has an open cell geometry which allows adequate flow into the side-branches through the frame  12 . In this embodiment, the frame  12  also includes anchoring portions  22  near each end  18 ,  20  wherein the cell geometry is provides a higher radial strength. This assists in anchoring the stent  10  within the blood vessel V.  
         [0029]     The frame  12  may have a variety of configurations. Example embodiments of frames  12  are provided in U.S. Pat. Nos. 6,371,980; 6,451,050; 6,520,984 and PCT/US2006/031059, each of which are incorporated herein by reference for all purposes. The frame  12  is expandable from a contracted, small-diameter condition to a radially expanded condition under the influence of an expanding force, typically an expandable balloon catheter used in delivering and placing the device in a blood vessel, according to conventional stent placement methods. Alternatively, the stent may be self-expanding. In some embodiments, the frame  12  has a length in the range of approximately 5-30 mm, particularly in the range of approximately 8-20 mm. Likewise, in some embodiments, the frame  12  has an outer diameter in the range of approximately 1-10 mm, particularly in the range of approximately 2.5-6 mm.  
         [0030]     An example of such a frame  12  is illustrated in  FIG. 3 . As shown, the frame  12  has a plurality of axially spaced-apart circular belts  21  which are interconnected by interconnectors  24 . Each belt  21  is comprised of a plurality of circumferentially spaced-apart elongate struts  26 . The interconnectors  24  adjoin the ends of the struts  26  and form in conjunction therewith the circular belts  21 . The interconnectors  24  are disposed at circumferentially spaced-apart positions to provide circumferential support when the stent is expanded while at the same time being axially flexible. In preferred embodiments, the interconnectors  42  are sinusoidal or serpentined shaped which assist in allowing expansion.  
         [0031]     The frame  12  may be formed from any suitable method. For example, the frame  12  may be comprised of a tube having a desired pattern formed or cut therefrom, such as by laser cutting or chemical etching. Alternatively, the desired pattern may be formed out of a flat sheet, e.g. by laser cutting or chemical etching, and then rolling that flat sheet into a tube and joining the edges, e.g. by welding. Further, the frame  12  may be formed by etching a pattern into a material or mold and depositing stent material in the pattern, such as by chemical vapor deposition or the like. Or the frame  12  may be formed from a weave or braid. Any other suitable manufacturing method known in the art may be employed for manufacturing a frame in accordance with the invention.  
         [0032]     The frame  12  may be comprised of plastic, metal or other materials and may exhibit a multitude of configurations. Example plastics include polyurethanes and polycarbonates. Example metals include 316LVM, L605 Cobalt Chromium, stainless steel, titanium, Nitinol, and tantalum among others. The frame  12  may also be treated to improve biocompatibility, such as by electropolishing or polymer coating.  
         [0033]     It may be appreciated that the frame  12  may have a variety of other forms, including conventional stents, coils, wireframes, etc.  
         [0034]     Typically, the covering  14  has a tubular shape configured to fit over the frame  12 . However, the covering  14  may alternatively be disposed under the frame  12  and attached thereto. Thus, the covering  14  is also expandable from a contracted, small-diameter condition to a radially expanded condition. This may be achieved by constructing the covering  14  from a flexible material, such as a polymer. Example materials include expandable polymer material, e.g., a porous or non-porous polytetrafluoroethylene (PTFE) material. Alternatively, this may be achieved by movement of the covering  14  as the frame  12  expands, such as by reducing overlap of the covering  14 .  
         [0035]     An exemplary covering  14  is described in U.S. Pat. No. 6,371,980, issued Apr. 16, 2002, and in PCT/US2006/031059, each of which are incorporated by reference herein in their entirety. It may be appreciated that the covering  14  may have a variety of other forms, including conventional sleeves, spirals or helixes. Also, the covering  14  may cover a side of the frame  12 , rather than extending around the frame  12 .  
         [0036]     In the present invention, the covering  14  covers only a portion of the frame  12 , preferably approximately 10-90% of the frame  12 , more preferably approximately 30-40% of the frame  12 . The covering  14  may be symmetrically positioned over the frame  12 , such as equidistant from the ends  18 ,  20 , as illustrated in  FIG. 2 . Or, the covering  14  may be asymmetrically positioned, such as covering at least part of end  18  or end  20  but not both, as illustrated in  FIG. 4 . Such asymmetrical positioning may be useful when treating aneurysms located near a bifurcation in a blood vessel V, such as illustrated in  FIG. 5 . Here, the covering  14  covers the aneurysm A and end  18  of the frame  12  is secured within the blood vessel. However, the bifurcation on the opposite side of the aneurysm A is not conducive to anchoring therein so the stent  10  is primarily secured in place by end  18 .  
         [0037]     In some embodiments, the stent  10  includes one or more clips or security rings  16  which are used to secure the covering  14  to the frame  12 , such as illustrated in  FIGS. 1-2 . Exemplary security rings  16  are described in U.S. patent application Ser. No. 10/255,199, filed Sep. 26, 2002, and PCT/US2006/031059, each of which are incorporated by reference herein in their entirety. In order to ensure that the covering  14  remains in the desired position on the frame  12 , security rings  16  are positioned over the covering  14 , such as over the outer ends of the covering  14 . Alternatively, the rings  16  may be positioned inside or within the frame  12 , such as when the covering is within the frame  12 . The security rings  16  may be formed of a metal and preferably the same metal which is used for the frame  12 , or the rings  16  may be comprised of other suitable material, such as a polymer. By way of example, the security rings  16  can be formed from laser cut tubing in the same manner as some embodiments of the frame  12  having a suitable wall thickness of 0.003″ to 0.006″. The inner surfaces of the security rings  16  can be left unpolished so that they have a rougher inner surface finish to enhance gripping to the outer surface of the covering  14 . Alternatively, a texture can be applied to the inner surface to enhance the gripping capabilities of the security ring  16 .  
         [0038]     The rings  16  may have a variety of shapes, including sinusoidal-shaped convolutions so that they can be expanded with the frame  12  and covering  14 . The security rings  16  can be placed at any location along the covering  14  including partially over the covering  14  and partially over the frame  12  itself. Optionally, the rings  16  may also include at least one radiopaque marker. In addition, spun FEP or polymer may be used to hold the rings  16  in place or create a smooth transition between the rings and the frame or covering.  
         [0039]     It may be appreciated that other structures may be employed in the stent  10  for anchoring the covering  14  on the frame  12 . For example, the covering  14  could be sewn on the frame  12  or bonded to the frame  12  by polymer welds, urethane, spun fiber or the like.  
         [0040]      FIGS. 6A-6D  illustrate an embodiment of the stent  10  of the present invention. As shown, the stent  10  comprises a frame  12  ( FIG. 6A ), a covering  14  ( FIG. 6B ), and at least one security ring  16  ( FIG. 6C ).  FIG. 6D  illustrates the assembled stent  10  wherein the covering  14  is positioned over the frame  12  symmetrically between the ends  18 ,  20 . Also, the security rings  16  are placed over the covering  14  to hold the covering in place.  
         [0041]      FIGS. 7A-7C  illustrate another embodiment of the stent  10  of the present invention. Here the stent  10  comprises a frame  12  ( FIG. 7A ) that has a variable density. The density of the frame  12  toward the ends  18 ,  20  increases so as to provide higher radial strength. Thus, these areas may be considered anchoring portions  22 . The density of the frame  12  decreases toward the center so as to provide sufficient support the covering  14  yet allow adequate flexibility and flow therethrough so as to avoid occluding side-branches of a blood vessel. A lower density portion of the frame  12  may have a more open cell geometry wherein the cells are larger. Or, the percentage of open space may be larger.  FIG. 7A  shows the lower density portion of the frame  12  to have longitudinal struts extending between the ends  18 ,  20 .  FIG. 7C   6 D illustrates the assembled stent  10  wherein the covering  14  is positioned over the frame  12  symmetrically between the ends  18 ,  20 .  
         [0042]      FIG. 8  illustrates another embodiment of a stent  10  wherein the frame  12  has a higher density toward the ends  18 ,  20  and a lower density therebetween. In this embodiment, the frame  12  has a plurality of axially spaced-apart circular belts  30  which are interconnected by interconnectors  32 . Each belt  30  is comprised of a plurality of elongate struts  34  in a “zig-zag” arrangement. The interconnectors  32  adjoin the ends of the struts  34 . In this embodiment, belts  30  near the ends  18 ,  20  have a shorter strut length (e.g. 0.020-0.100 inches, preferably 0.070-0.090 inches) than belts  30  therebetween having a longer strut length (e.g. 0.070-0.200 inches, preferably 0.100-0.120 inches). Thus, the belts  30  near the ends  18 ,  20  have a higher density and therefore higher radial strength while the belts  30  therebetween have a lower density and therefore lower stiffness (higher flexibility).  
         [0043]      FIGS. 9A-9B  illustrate another embodiment of a stent  10  wherein the frame  12  has a higher density toward the ends  18 ,  20  and a lower density therebetween. In this embodiment, the frame  12  has circular belts  30  near the ends  18 ,  20  comprised of a plurality of elongate struts  34  in a zig-zag arrangement. The belts  30  are joined by longitudinal struts  34 ′ that extend between the ends  18 ,  20 . The longitudinal struts  34 ′ have a zig-zag or accordion shape. The circular belts  30  near the ends  18 ,  20  provide sufficient radial strength for anchoring of the stent  10  within a blood vessel. And, the longitudinal struts  34 ′ provide sufficient support for a covering yet a low enough density to allow passage therethrough of blood flow into side-branches of the blood vessel. In addition, the accordion shape of the longitudinal struts  34 ′ allows for higher bending and flexibility through tortuous anatomy. For example,  FIG. 9B  shows the stent  10  of  FIG. 9A  positioned in a curved or bent configuration as may occur when passing through the vasculature, particularly the cerebral vasculature. The accordion shape of the longitudinal struts  34 ′ allows for some struts  34 ′ to extend while other struts  34 ′ contract. Thus, the struts  34 ′ resist fatigue and allow higher flexibility of the stent  10 .  
         [0044]     It may be appreciated that the embodiments of stents  10  illustrated in  FIG. 8  and  FIGS. 9A-9B  typically include a covering positioned over a portion of the stent  10 . In preferred embodiments, the covering is positioned between the ends  18 ,  20  and is supported by the lower density portion of the frame  12 . Optionally, the covering is held in place by security rings.  
         [0045]     In some embodiments, the covering  14  is woven through the frame  12  so that the covering  14  is substantially held in place by such weaving. An example of such an embodiment is illustrated in  FIG. 10A . In this embodiment, the frame  12  comprises longitudinal struts  34 ′ through which the covering  14  is woven circumferentially around the frame  12 . As shown, the covering  14  has a ribbon shape and alternates passing over and under the individual struts  34 ′. The covering  14  can also be placed in any position between the ends  18 ,  20 .  FIGS. 10B-10C  illustrate a cross-sectional view of the woven covering  14  of  FIG. 10A .  FIG. 10B  shows the stent  10  in an unexpanded position having a smaller diameter. In this position, the covering  14  is wrapped on itself, as illustrated by a free end  40  of the covering  14  extending circumferentially within the frame  12 .  FIG. 10C  shows the stent  10  in an expanded position having a larger diameter. As the stent  10  expands, the covering  14  is pulled outwardly with the expanding frame  12  and the covering at least partially unwraps, as illustrated by the free end  40  of the covering  14  extending less within the frame  12 . In some embodiments, as illustrated in  FIG. 11 , the covering  14  is woven circumferentially around the frame  12  in a spiral fashion. Thus, rather than the covering  14  wrapping on itself, the free ends  14  are pulled around the frame  12  as the frame expands.  
         [0046]     It may be appreciated that in some embodiments, a separate covering is not used; rather, portions of the frame  12  itself act as the “covering” so as to block or restrict flow into the aneurysm. Such portions may be considered to have an occlusional cell geometry. An example of such a stent  10  is illustrated in  FIG. 12 . As shown, the stent  10  is comprised of a frame  12  having a variety of densities for various purposes. For example, the frame  12  includes higher density areas near the ends  18 ,  20  for anchoring (anchoring portions  22 ), a higher density area positionable over the aneurysm A to block flow therethrough (occlusional cell geometry  50 ), and lower density areas therebetween (open cell geometry  52 ) for flexibility and passage of flow therethrough into side-branches S of the blood vessel V. Densities may be controlled by strut length, interconnector length, etc. In addition, radial strength and flexibility may be controlled by strut thickness or cross-sectional dimensions. In some embodiments, typical strut cross-sectional dimension is approximately 0.006 in. by 0.006 in. square. Some portions of the frame  12  may have thinner cross-sections, such as approximately 0.004 in. by 0.004 in. square, to provide higher flexibility. Other portions of the frame  12  may have thicker cross-sections, such as approximately 0.010 in. by 0.010 in. square, to provide higher radial force. Thus, strut cross-sectional dimension may be varied to provide differing stent characteristics.  
         [0047]     In any of the above embodiments, the cell geometry of the frame  12  may be altered in desired areas to accommodate particular anatomies. For example, to ensure adequate flow to a side-branch, the frame  12  may be altered in the area of the side-branch to increase flow therethrough. This may be achieved by widening the cell geometry in this area, typically the lower density area or open cell geometry area. To widen a desired cell, an inflatable member or balloon may be passed through the desired cell and expanded to change its dimensions (e.g. cause widening). When the frame  12  is comprised of a weave or braid, the struts move apart according to the weave. When the frame  12  is comprised of a cut tube or sheet, the struts may be deformed upon widening of the cells. Any number of cells may be widened in any location to achieve the desired result. It may be appreciated that widening in some areas may cause constriction or narrowing in other areas which may be utilized for various purposes. For example, widening in an open cell geometry area may cause narrowing in the occlusional cell geometry area which may benefit the overall stent design.  
         [0048]     Although the foregoing invention has been described in some detail by way of illustration and example, for purposes of clarity of understanding, it will be obvious that various alternatives, modifications and equivalents may be used and the above description should not be taken as limiting in scope of the invention which is defined by the appended claims.