Patent Publication Number: US-8529556-B2

Title: Detachable aneurysm neck bridge

Description:
RELATED APPLICATION DATA 
     This application is a continuation of U.S. patent application Ser. No. 13/194,730, filed Jul. 29, 2011, now issued U.S. Pat. No. 8,449,532, which is a continuation of U.S. patent application Ser. No. 12/768,659, filed Apr. 27, 2010, now issued U.S. Pat. No. 8,267,923, which is a continuation of U.S. patent application Ser. No. 12/178,364, filed Jul. 23, 2008, now issued U.S. Pat. No. 7,713,264, which is a continuation of U.S. patent application Ser. No. 10/319,379, filed Dec. 13, 2002, now issued U.S. Pat. No. 7,410,482, which is a continuation-in-part of U.S. patent application Ser. No. 09/548,644, filed Apr. 13, 2000, now issued U.S. Pat. No. 7,128,736, which is a continuation of U.S. patent application Ser. No. 09/148,411 filed Sep. 4, 1998, now abandoned, the disclosures of which are expressly incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The inventions disclosed herein pertain to systems, apparatus, and methods for treating aneurysms, and more specifically, to systems, apparatus, and methods for bridging a neck of an aneurysm. 
     BACKGROUND 
     Various implantable medical devices have been developed for treating a number of ailments associated with body lumens. In particular, occlusive devices have been proven useful in filling vascular aneurysms, which are formed due to a weakening in the wall of an artery. Vascular aneurysms are often the site of internal bleeding and stroke. A variety of different embolic agents are known to be, at least arguably, suitable for treatment of vascular aneurysms by filling them to prevent further vessel wall weakening or rupture. Use of these agents are commonly known as “artificial vaso-occlusion.” 
     Over the past few years, advancements in the artificial occlusion of vessels and aneurysms have included the delivery and implantation of metal coils as vaso-occlusive devices. Implantable metal coils that are useful as artificial occlusion devices in vasculature lumens or aneurysms are herein referred to as “vaso-occlusive coils.” Vaso-occlusive coils are typically constructed of a wire made of a metal or metal alloy wound into a helix. Such vaso-occlusive coils are typically manufactured to assume a certain shape upon discharge of the device from the distal end of the catheter into a treatment site. A variety of such vaso-occlusive coils are known. For instance, U.S. Pat. No. 4,994,069, issued to Ritchart et al., discloses a flexible, preferably coiled wire for use in small vessel vaso-occlusion. Unlike vaso-occlusive coils used prior to that time, Ritchart et al. discloses using a coil that is relatively soft and is delivered to the site using a pusher within a catheter lumen. Upon discharge from the delivery catheter, the coil may undertake a number of random or pre-determined configurations useful to fill the site. 
     Known vaso-occlusive coils may be used for filling relatively small vessel sites, e.g., 0.5-6.0 mm in diameter. The coils themselves are described as being between 0.254 and 0.762 mm in diameter. The length of the wire making up the vaso-occlusive coil is typically 15 to 20 times the diameter of the vessel to be occluded. The wire used to make up the coils may be, for instance, 0.051 to 0.152 mm in diameter. Tungsten, platinum, and gold threads or wires are typically preferred. These coils have a variety of benefits, including the fact that they are relatively permanent, they may be easily imaged radiographically, they may be located at a well defined vessel site, and they can be retrieved, if necessary. 
     In addition to the various types of known space filling mechanisms and geometries of vaso-occlusive coils, other particularized features of coil designs, such as mechanisms for their delivery through catheters and implanting them in a desired occlusion site, are well know in the art. Examples of known vaso-occlusive coils categorized by their delivery mechanisms include pushable coils, mechanically detachable coils, and electrolytically detachable coils. 
     One example of a “pushable coil” is disclosed in Ritchart et al., discussed above. Pushable coils are commonly provided in a cartridge and are pushed or “plunged” from the cartridge into a lumen of a delivery catheter. A pusher (e.g., a wire or a pressurized fluid) advances the pushable coil through and out of the delivery catheter lumen, into the desired occlusion site. 
     Mechanically detachable vaso-occlusive coils are typically integrated with a pusher rod and are mechanically detached from the distal end of that pusher after exiting a delivery catheter. Examples of such mechanically detachable vaso-occlusive coils are found in U.S. Pat. No. 5,261,916 to Engelson and U.S. Pat. No. 5,250,071 to Palermo. 
     Examples of electrolytically detachable vaso-occlusive coils may be found in U.S. Pat. Nos. 5,122,136 and 5,354,295 issued to Guglielmi et al. In these devices, the vaso-occlusive portion of the assembly is attached to a pusher via a small, electrolytically severable joint. The electrolytically severable joint is eroded by the placement of an appropriate voltage on the core wire. 
     As noted above, aneurysms present a particularly acute medical risk due to the dangers of potential rupture of the thin vascular wall inherent in such aneurysms. Occlusion of aneurysms by use of vaso-occlusive coils without occluding the adjacent artery is a special challenge and is a desirable method of reducing such risk of rupture. Vaso-occlusive devices may be placed in an aneurysm in a manner described in U.S. Pat. No. 4,739,768 issued to Engelson. In particular, a microcatheter is initially steered into or adjacent to the entrance of an aneurysm, typically aided by the use of a steerable guidewire. The wire is then withdrawn from the microcatheter lumen and replaced by one or more vaso-occlusive coils, which are then advanced through and out of the microcatheter, and into the aneurysm. 
     However, after, or perhaps during delivery of a coil into the aneurysm, there is a risk that a portion of the coil might migrate out of the aneurysm entrance zone and into the feeding vessel. The presence of the coil in that feeding vessel may cause a highly undesirable occlusion there. Also, there is a risk that the blood flow in the vessel and aneurysm may induce movement of the coil farther out of the aneurysm, resulting in a more developed embolus in the feeding vessel. 
     One type of aneurysm, commonly known as a “wide neck” aneurysm, is known to present particular difficulty in the placement and retention of vaso-occlusive coils, because vaso-occlusive coils lacking substantial secondary shape strength may be difficult to maintain in position within an aneurysm no matter how skillfully they are placed. Wide neck aneurysms are herein referred to as aneurysms of vessel walls having a neck or “entrance zone” from the adjacent vessel, wherein the entrance zone has a diameter that either: (1) is at least 80% of the largest diameter of the aneurysm; or (2) is clinically observed to be too wide effectively to retain commercially available vaso-occlusive coils that are deployed using the techniques discussed above. 
     Certain techniques have been developed in order to deal with the disadvantages associated with embolic material migration into the parent vessel. One such technique, commonly referred to as flow arrest, involves temporarily occluding the parent vessel proximal of the aneurysm, so that no blood flow occurs through the parent vessel until a thrombotic mass has formed in the sac of the aneurysm. While this technique helps reduce the tendency of the embolic material to migrate out of the aneurysm sac, a thrombotic mass can still dissolve through normal lysis of blood. Also, occluding the parent vessel may not prevent all embolic material migration into the parent vessel. Further, in certain cases, it is highly undesirable to occlude the parent vessel even temporarily. Thus, a flow arrest technique is, at times, not effective or even not available as a treatment option. 
     Another approach to occlude a wide neck aneurysm is described in U.S. Pat. No. 6,168,622 (“the &#39;622 patent”), which describes a vaso-occlusive device with a secondary shape having a bulbous body portion and an anchor. The bulbous body portion is deployed within the aneurysm while the anchor is set just outside of the aneurysm, covering the aneurysm&#39;s neck or entrance zone. As described in the &#39;622 patent, the device may be integrally formed from a tube—clamped at both ends—of braided Nickel-Titanium (NiTi) wires. The bulbous body functions to occlude the aneurysm, while the anchor covers the entrance zone. In some cases, it may still be desirable to deploy vaso-occlusive coils with such a device, but the bulbous body of the vaso-occlusive device may not provide much space within the aneurysm to allow for insertion and deployment of coils. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a device for bridging a neck of an aneurysm is described. The device comprises a junction region, one or more radially extending array elements secured to the junction region, each array element having an unfolded shape and a delivery shape, and a cover attached to the junction region, and extending over the delivery shape of the array elements, wherein each array element is attached at one end to the junction region and the array elements are constructed and arranged to unfold the cover when assuming their unfolded shape, and wherein the device further comprises a tip, and each array element is attached at another end to the tip, the tip comprising an opening through which a vaso-occlusive device or occlusion fluid may be delivered. 
     By way of non-limiting examples, the junction region may further comprise a tubular section defining a lumen in communication with the tip opening. The device may further comprise a radio-opaque marker carried on the tip. The cover comprises an elastic material, and may be angiogenic, and/or may comprise an anti-thrombotic agent. Additionally, the cover may comprise a plurality of loops, where each loop comprises a fiber having first and second ends attached to the junction region. The one or more radially extending array elements of the device may comprise a wire having a curvilinear shape. Further, the one or more radially extending array elements of the device may comprise a resilient, substantially elastic material, and/or a radio-opaque material. 
     In accordance with another aspect of the present invention, a device for bridging a neck of an aneurysm is described. The device comprises a junction region, a plurality of radially extending, curvlinear array elements secured to the junction region, each array element having an unfolded shape and a delivery shape, and a cover attached to the junction region, and extending over the delivery shape of the array elements, wherein each array element is attached at one end to the junction region and the array elements are constructed and arranged to unfold the cover when assuming their unfolded shape, and wherein the device further comprises a tip, and each array element is attached at another end to the tip, the tip comprising an opening through which a vaso-occlusive device or occlusion fluid may be delivered. 
     By way of non-limiting examples, the cover may comprise a plurality of loops, each loop having first and second ends attached to the junction region. The radially extending array elements comprise a resilient, substantially elastic material, and/or are constructed of a radio-opaque material. 
     Other embodiments of the neck bridge in accordance with further aspects of the invention are also described. By way of non-limiting examples, the neck bridge may optionally be detachably coupled to a distal end of a delivery member, a core wire, or similar structures via an electrolytically severable joint or a mechanical joint. 
     Other aspects, features, and embodiments of the invention are described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate the design and utility of preferred embodiments of the present invention, in which similar elements are referred to by common reference numerals. It should be understood that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. 
         FIG. 1  is a cross sectional plan view of an aneurysm treatment system including a neck bridge comprising an array of elements in accordance with a preferred embodiment of the invention; 
         FIG. 2  is a partial cross sectional view of a distal end of the system of  FIG. 1 ; 
         FIG. 3  is a partial cross sectional view of a variation of the distal end of the system of  FIG. 1 , particularly showing a junction region of the neck bridge coupling to a distal tip of an inner tubular member; 
         FIG. 4  is a partial cross sectional view of the distal end of the inner tubular member shown in  FIG. 3 , particularly showing the neck bridge assuming a delivery shape; 
         FIG. 5  is a top view of the neck bridge of  FIG. 1 ; 
         FIG. 6  is a top view of a variation of the neck bridge, particularly showing a cover having a plurality of loops; 
         FIGS. 7A-7C  are side views of further variations of the neck bridge; 
         FIG. 8  is a top view of a still further variation of the neck bridge, particularly showing the array elements having substantially rectilinear shapes; 
         FIGS. 9A and 9B  show another variation of the neck bridge, particularly showing the array elements having different unfolded configurations; 
         FIGS. 10A and 10B  show yet another variation of the neck bridge, particularly showing the array elements having upright loop shapes; 
         FIG. 11  is a side view of a still another variation of the neck bridge, particularly showing the neck bridge having a pair of collars coupled to control wires; 
         FIG. 12  is a top view of the neck bridge of  FIG. 11  in a deployed (i.e., non-constrained) configuration; 
         FIG. 13  is a top view of yet another variation of the neck bridge, particularly showing the neck bridge having a braided structure; 
         FIGS. 14A and 14B  show a delivery shape and an unfolded configuration, respectively, of the neck bridge of  FIG. 13 ; 
         FIGS. 15A and 15B  show a variation of the delivery shape and the unfolded configuration, respectively, of the neck bridge of  FIG. 13 ; 
         FIG. 16  is a further variation of the neck bridge, particularly showing the junction region of the neck bridge coupled to a wall section of the inner tubular member; 
         FIG. 17  is a still further variation of the neck bridge, particularly showing the junction region of the neck bridge coupled to a core wire by a severable joint; 
         FIGS. 18A-18E  show a procedure for introducing an embodiment of the neck bridge, along with a vaso-occlusive device, into an aneurysm; 
         FIG. 19A  shows a side view of an embodiment of a neck bridge in combination with an “anchor” adapted to be placed within an aneurysm; 
         FIG. 19B  is a top view of the neck bridge of  FIG. 19A ; and 
         FIG. 19C  shows a placement of the neck bridge depicted in  FIG. 19A  within an aneurysm. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The disclosed invention relates to devices and procedures for stabilizing the position and, in some instances, the structure of vaso-occlusive devices placed in a target occlusion site, usually an aneurysm. Use of the retaining devices and neck bridges disclosed herein reduce the potential migration of vaso-occlusive devices (e.g., helically wound coils) from target occlusion sites, by forming at least a partial barrier at the entrance zone to the aneurysm, i.e., where the aneurysm meets a feeding vessel. 
       FIG. 1  shows an aneurysm treatment system  100 , which includes an aneurysm neck bridge  106  constructed in accordance with a preferred embodiment. The aneurysm treatment system  100  also includes a tubular delivery catheter  102 , and an inner elongated tubular member  104  slidable within the tubular delivery catheter  102 . The aneurysm neck bridge  106  is removably coupled to a distal end  107  of the elongated tubular member  104  via an electrolytically severable joint  122 , and is configured to be placed within an aneurysm sac or directly across a neck (i.e., in between the tissue defining the neck) of an aneurysm. The system  100  further includes a vaso-occlusive device  108  that is deliverable via the inner tubular member  104 . The vaso-occlusive device  108  is coupled to a core wire  110  via another electrolytically severable joint  130 . The severable joints  122  and  130  are of a scale that cannot easily be seen in  FIG. 1  and are depicted in greater clarity in  FIG. 2 . 
     Schematically, the electrolytically severable joints  122  and  130  are configured to electrically couple to first and second power supplies  112  and  114 , respectively, which are used to deliver current to severe the respective joints in a well known manner. The severance of the severable joints  122  and  130  releases the aneurysm neck bridge  106  and the vaso-occlusive device  108 , respectively, at the site. Alternatively, a single power supply may be used to supply current for detachment of the vaso-occlusive device  108  and the aneurysm neck bridge  106 . 
       FIG. 2  is a partial cross section of a distal end of the system  100 . The distal end  103  of delivery catheter  102  carries a radio-opaque marker  116  to assist navigating the distal end  103  through a vasculature. The inner tubular member  104  also carries a radio-opaque marker  118 . In alternate embodiments, the inner tubular member  104  may have a shape other than that shown in  FIG. 2 . For example, the inner tubular member  104  may have an angle or a curvilinear shape. Preferably, the inner tubular member  104  is malleable or heat settable so that a physician or operator can create a desired shape at the time the system  100  is used. 
     A conductor wire  120  is provided for conducting current from the first power supply  112  to the electrolytically detachable joint  122 . The aneurysm neck bridge  106  includes a junction region  124 , which is detachably coupled to a distal end  107  of the inner delivery member  104 . The junction region  124  may include an opening  128  (shown in  FIG. 5 ), and may have a shape of a tubular member or a ring. The junction region  124  preferably fits around the inner tubular member  104  in a loose manner, and is maintained in position only by the electrolytic joint  122 . In alternate embodiments, the exterior profile of the junction region  124  can vary from the circular shape shown in the illustrated embodiment. Examples of variations in the shape of the junction region  124  are shown and described herein. 
     The severable joint  122  is preferably created by insulating a portion of the conductor wire  120 . For example, a portion of the conductor wire  120  may be insulated with an electrical insulator which is not susceptible to dissolution via electrolysis in blood or other ionic media, leaving the un-insulated portion of the conductor wire  120  susceptible to electrolytic dissolution. The electrical insulator may be the wall of the tubular member  104 , as shown in  FIG. 2 , or alternatively, it may be a coating placed over the conductor wire  120 . Suitable coatings include insulating materials, such as polyfluorocarbons (e.g., Teflon), polyurethane, polyethylene, polypropylene, polyimides, and other suitable polymeric materials. It will also be apparent that the sacrificial joint  122  is more susceptible to electrolysis than any other element of the device located near that joint  122 . In use, current supplied by the first power supply  112  passes to the electrolytically severable joint  122 , typically with the cooperation of an external return electrode pad (not shown) placed on a skin of a patient to complete the circuit. Passage of current through the electrolytically severable joint  122  causes the joint  122  to sever, thereby de-coupling the neck bridge  106  from the tubular member  104 . Further information regarding the construction, placement, and other physical details of electrolytically severable joints used may be found in U.S. Pat. Nos. 5,234,437, 5,250,071, 5,261,916, 5,304,195, 5,312,415, and 5,350,397, the disclosures of which are expressly incorporated by reference herein. It will be appreciated that mechanical joints, and other types of detachable joints known in the art for placing occlusive devices in aneurysms may alternatively be used to couple the neck bridge  106  to the tubular member  104 . Examples of such mechanical joints may be found in U.S. Pat. No. 5,234,437, to Sepetka, U.S. Pat. No. 5,250,071 to Palermo, U.S. Pat. No. 5,261,916, to Engelson, U.S. Pat. No. 5,304,195, to Twyford et al., U.S. Pat. No. 5,312,415, to Palermo, and U.S. Pat. No. 5,350,397, to Palermo et al, the disclosures of which are expressly incorporated herein by reference. 
     As shown in  FIG. 2 , because the neck bridge  106  is coupled to the tubular member  104  in a way that does not obstruct the distal opening  131  of the tubular member  104 , the vaso-occlusive device  108  may be delivered via the inner tubular member  104 . In the illustrated embodiment, the vaso-occlusive device  108  is detachably coupled to a distal end of the core wire  110  by the electrolytically severable joint  130 , which is formed by insulating a proximal portion of the core wire  110  by an insulating layer  125 . As noted above, delivery of vaso-occlusive devices using an electrolytically severable joint is well known in the art. Alternatively, the vaso-occlusive device  108  may be delivered by using a pusher or plunger, the distal advancement of which within the inner tubular member  104  pushes the vaso-occlusive device  108  out from the distal end of the inner tubular member  104 . Other methods of delivering the vaso-occlusive device  108  known in the art may also be used. 
       FIG. 3  shows another variation of the neck bridge  106 . Unlike the previously shown embodiment, in which the junction region  124  of the neck bridge  106  is configured to fit around the distal end  107  of the inner tubular member  104 , the junction region  124  of the neck bridge  106  of  FIG. 3  is distal to the distal end  107  of the tubular member  104 , and is configured to couple to a distal end  107  of the inner tubular member  104  via the severable joint  122 . In this variation, the cross sectional dimension of the junction region  124  is substantially the same as the cross sectional dimension of the inner delivery member  104  to form a substantially continuous outer surface. Vaso-occlusive devices  108  exiting the distal end  107  of the tubular member  104  can be delivered to an aneurysm by passing through the opening  128  of the junction region  124 , as discussed previously. The distal end  107  of the inner tubular member  104  may further include a Teflon liner or an extension (not shown) coupled to the interior surface of the inner tubular member  104 , such that fluid (e.g., an embolic agent) can be delivered through the opening  128  of the junction region  124  without escaping into the gap between the tip of the inner tubular member  104  and the junction region  124 . 
     The neck bridge  106  includes one or more radially expanding array elements or wires  126  attached to the junction region  124 , and a cover  127  attached to the junction region  124 . In alternate embodiments, the cover  127  may also be secured to the array elements  126 . In further alternate embodiments, the cover  127  may be attached to both the array elements  126  and the junction region  124 . Upon placement in an aneurysm, the array elements  126  together with the cover  127  spread to the general shape shown in  FIG. 2 . In the illustrated embodiment, each of the array elements  126  is a wire loop or ribbon rim. The number of array elements  126  may vary between embodiments, depending on factors such as the size of an aneurysm, the width of the tubular delivery catheter  102 , and the thickness of the wire making up the array elements  126 . Before the neck bridge  106  is deployed to a target site, the neck bridge  106  resides within a lumen  132  of the delivery catheter  102 , and it is generally stretched to assume and maintain the shape of the lumen  132  as shown in  FIG. 4 . The cover  127  is folded into a low profile when positioned in the lumen  132 . When the neck bridge  106  is pushed from the distal end of the delivery catheter  102 , the array elements  126  assume their so-called “unfolded” shapes or configurations, thereby unfolding the cover  127 . 
     The array elements  126  may be required to undertake relatively significant changes in shape during deployment of the neck bridge  106 . To undertake such stress, it is usually preferable that the array elements  126  be produced of a material such as a super-elastic alloy. Super-elastic or pseudoelastic shape recovery alloys are well known in this art. For instance, U.S. Pat. Nos. 3,174,851; 3,351,463; and 3,753,700 each describe one of the more well known super-elastic alloys, known as Nitinol. These alloys are characterized by their ability to be transformed from an austenitic crystal structure to a stress-induced martensitic (SIM) structure at certain temperatures and then to return elastically to the austenitic shape when the stress is removed. These alternating crystal structures provide the alloy with its super-elastic properties. 
     The above described alloys are especially suitable because of their capacity to recover elastically, and almost completely to an unfolded configuration once a bending stress is removed. Typically during use, these alloys suffer little permanent plastic deformation, even at relatively high strains. This ability allows the neck bridge  106  to undertake substantial bends while residing within the lumen  132  of the tubular delivery catheter  102  and while passing through a vasculature. In spite of this bending, the neck bridge  106  returns to its original shape, i.e., unfolded configuration, without retaining any substantial permanent kinks or bends once deployed from the lumen  132 . 
     Of the super-elastic alloys currently available, the preferred material is 50.6.+−0.2% nickel with most of the remainder being titanium. Up to about 5% of the alloy may be a member of the iron group of metals, particularly chromium and iron. The alloy is preferred to not contain more than about 500 parts per million of oxygen, carbon, or nitrogen. The transition temperature of this material is not particularly important, but it should be reasonably below the typical temperature of the human body so as to allow it to be in its austenitic phase during use. The wires or ribbons making up the various array elements  126  preferably have a diameter less than about 0.010 inches. These super-elastic alloys are not always sufficiently visible under fluoroscopy as it is used in the human body. Consequently it may be desirable to add a radio-opacity covering to the array elements  126 . Radio-opaque metals such as gold and platinum are well known. Radio-opaque metals may be added to the array elements  126  by plating or by wrapping the array element  126  in a radio-opaque wire or ribbon, as is known in the art. Alternatively, one or more radio-opaque markers may be secured to the array elements  126 , for example at a perimeter of the neck bridge defined by the array elements  126 . 
     Other metals may also be appropriate for construction of the array elements  126 . Such metals include stainless steels and other highly elastic, if not super-elastic, alloys. Polymeric materials which are somewhat easier to work with in forming a device may also be used for construction of the array elements  126 . Polymeric materials are somewhat easier to work with in forming a device. Such polymeric materials may include members from the group of polyethylene, polypropylene, polytetraflouroethylene, various Nylons, and the like. Suitable polymers may also include most biocompatible materials, which may be made into fibers, including thermoplastics, e.g., polyesters such as polyethyleneterephthalate (PET) especially Dacron; polyamides including Nylons; polyolefins such as polyethylene, polypropylene, polybuylene, their mixtures, alloys, block and random copolymers; polyglycolic acid; polylactic acid; fluoropolymers (polytetrafluoro-ethylene), or even silk or collagen. 
       FIG. 5  shows a top view of the neck bridge  106 . As shown in  FIG. 5 , the cover  127  is unfolded to have a substantially continuous surface when the array elements  126  assume their unfolded configurations. The cover  127  may be a fabric, a woven or non-woven mesh, or other sheeting or planar structure. Although the array elements  126  are each preferably of a form that retains a large measure of elasticity after having been bent, the cover  127  may be less elastic. The cover  127  may be made from a variety of materials such as polymers, nylons, and polyester. These materials do not provide substantial strength to the cover  127 , so as to allow the device to be readily folded into a low profile and placed into the delivery catheter lumen  132  without adding unnecessary stiffness. The sole function of the cover  127  is to remain an implanted vaso-occlusive device in an aneurysm. The function of the array elements  126  is to maintain the structural integrity of the neck bridge device as it is situated within an aneurysm. Alternatively, the cover  127  may be made to have a similar elasticity as the array elements  126 . Therefore, any of the materials discussed previously with reference to the array elements  126  may also be suitable for construction of the cover  127 . Other materials suitable for construction of the cover  127  include Dacron (polyethyleneterephthalate), collageneous materials, polyluorocarbons, combinations thereof, and other vascular graft materials. Fibrous materials, such as polyglycolic acid, wool, or cotton, may also be used. 
       FIG. 6  shows a variation of the cover  127 , which has a braided or mesh-like structure. In the illustrated embodiment, the neck bridge  106  includes six array elements  126  attached to the cover  127 . The cover  127  includes a plurality of loops  210 , each of which formed by securing ends of a fiber to the junction region  124 . The loops  210  may overlap one another, or alternatively, be inter-woven with each other, to form the cover  127 . It should be noted that the shape of the loop  210  is not limited to that shown in the illustrated embodiment. Furthermore, the cover  127  may have different braided patterns than those shown herein. 
     In each of the above-described embodiments of the neck bridge, the cover  127  may be placed at a top side of the array elements  126  ( FIG. 7A ), a bottom side of the array elements  126  ( FIG. 7B ), or it may cover both sides of the array elements  126  ( FIG. 7C ). In the embodiment shown in  FIG. 7C , the neck bridge may further include a disk (not shown) placed between the bottom and top surfaces of the cover  127  for reducing the porosity of the neck bridge. 
     Notably, the shape of the cover  127  is not limited to the circular shape shown in the previously discussed embodiments. The cover  127  can have other shapes, such as an elliptical or rectangular shape ( FIG. 8 ). 
     Generally, as with the embodiments shown in  FIGS. 7A and 7C , the cover  127  is not required to be directly secured to any of the array elements  126 . Rather, the array elements  126  exert a bearing and/or frictional force on the cover  127  when they assume an unfolded configuration. However, the cover  127  may optionally be secured to the array elements  126  at one or more various points. The securing may be accomplished using a glue, epoxy, heat bond, or other suitable adhesives, depending upon the materials from which the respective cover  127  and array elements  126  are made. By way of further example, the cover  127  may also be secured to the array elements  126  by sewing them together using a thread. Securing the cover  127  to the array elements  126  may assist the array elements  126  in unfolding the cover  127  into a desired shape as the array elements  126  assume their unfolded configurations. Alternatively, the array elements  126  may be embedded within the cover  127 , or inter-woven with the cover  127 . 
     It should be noted that the shape of the individual array element is not limited to the loop shape shown in the previous embodiments, and that the array element  126  may have other shapes as well.  FIG. 8  shows a variation of the array element  126  that has a substantially rectilinear profile. As shown in the illustrated embodiment, the array elements may optionally have blunted tips to avoid trauma to the arteries in which they are placed. The array elements  126  may also have other shapes as well. In the embodiment of  FIG. 8 , the cover  127  has a rectangular shape, as previously noted. 
     The manner in which the array elements fold or bend when positioned within the lumen of a tubular delivery member is not limited. By way of illustration,  FIGS. 9A and 9B  show another variation of the neck bridge, wherein the array elements  126  are folded in a manner that is different from that shown in  FIG. 4 . In the embodiment of  FIGS. 9A and 9B , each of the array elements  126  has an end  211  coupled to a tip  212 . The tip  212  includes a radio-opaque marker  216 . The tip  212  also includes an opening  217  through which a vaso-occlusive device or occlusion fluid may be delivered. The array element  126  has a mid portion that flares outward while maintaining the end  211  of the array element  126  in close proximity to an axis  214  of the junction region  124 . The array elements  126  are stretched to the delivery shapes shown in  FIG. 9A  when positioned within the lumen  132  of the delivery catheter  102 , and assume the unfolded configurations shown in  FIG. 9B  when unconfined outside the delivery catheter  102 . The array elements  126  can also have curvilinear shapes or other unfolded configurations, so long as the array elements  126  unfold the cover  127  once deployed outside the lumen  132  of the delivery catheter  102 . 
       FIGS. 10A and 10B , respectively show side and top views of another variation of the neck bridge  106 , wherein the array elements  126  have upright loop shapes. Although the array elements  126  are shown attaching to an interior surface of the junction joint  124 , the array elements  126  may also be secured to the ends or the side of the junction joint  124 . In the illustrated embodiment, the array elements  126  wrap around a perimeter of the cover  127  such that the cover  127  is between the ends of the wires defining the loop shape array elements  126 . Alternatively, as shown by the dashed-lines, the cover  127  may also be placed at a bottom side of the array elements  126 . 
     The array elements  126  may also be deployed using mechanical methods.  FIG. 11  shows another variation of the neck bridge  220  that is delivered on the exterior of a delivery member  221 . This variation includes a number of radially extending array elements  222  which are joined at their outer ends. The radially extending array elements  222  are joined by a cover  224  which also may be scrim-like. The array elements  222  are joined to a pair of collars  226  that slide on the delivery member  221  and are controlled by one or more control wires  228 . Each of the control wires  228  may have a releasable joint  229 , desirably an electrolytically severable joint, as discussed previously. During delivery of the neck bridge  220 , the array elements  222  lie generally against the delivery member  221 . During deployment, the control wires  228  are axially manipulated to extend the radially extending array elements  222  into the deployed shape depicted in  FIG. 12 . 
     In the previously discussed embodiments, the neck bridge includes one or more array elements attached to the cover. However, the array elements may not be required.  FIG. 13  shows a variation of the neck bridge which includes a junction region  202  and a braided or mesh-like structure  230  secured to the junction region  202 . The braided structure  230  may carry a radio-opaque marker (not shown), or be plated or coated with a radio-opaque material. The braided structure  230  is preferably made from an elastic material, such as Nitinol. However, any of the materials discussed previously with reference to the array element  216  may also be suitable for construction of the braided structure  230 . The advantage of making the braided structure  230  using elastic material is that the braided structure  230  can assume an unfolded shape without the help of the array elements. The braided structure  230  may also be made from a radio-opaque material. In the illustrated embodiment, the braided structure  230  includes a number of loops  232 , each of which formed by securing ends of a fiber to the junction region  202 . However, the braided structure  230  can have other woven or non-woven patterns as well.  FIGS. 14A and 14B  show that the braided structure  230  can assume a delivery shape by bending the loops  232  such that the portions of the loops  232  defining the periphery of the braided structure  230  are distal to both ends of the fibers making up the loops  232 . 
       FIGS. 15A and 15B  show a variation of the neck bridge of  FIG. 13 . As shown in the embodiment, a first end of the fiber making up each of the loops  232  is secured to a first portion  202   a  of the junction region  202 , and a second end of the fiber making up each of the loops  232  is secured to a second portion  202   b  of the junction region  202 . When residing within the delivery catheter  102 , the braided structure  230  is stretched or bent into a delivery shape such as that shown in  FIG. 15A . When the neck bridge is deployed outside the delivery catheter  102 , the first portion  202   a  and the second portion  202   b  of the junction region move closer to each other, and the portion of the loop  232  near the mid-section  234  of the loop  232  becomes the periphery of the braided structure  230 . It should be noted that the manner in which the braided structure  230  is folded or deployed should not be limited to the examples described previously, and that other methods of folding or deploying the braided structure  230  can also be used. 
     In all of the previously described embodiments, the junction region includes the opening  128  through which a vaso-occlusive device  108  may be delivered. However, the opening  128  is optional.  FIG. 16  shows a cross sectional view of a variation of the junction region  124  that does not have the opening  128 . In the illustrated embodiment, the junction region  124  is detachably secured to a wall section of the inner tubular member  104  by an electrolytically severable joint  240 . The vaso-occlusive device  108  may also be delivered via the inner tubular member  104 , as discussed previously. 
     The neck bridge  126  may be detachably coupled to other structures instead of the inner tubular member  104  described previously.  FIG. 17  shows a cross sectional view of a neck bridge  126  that is detachably coupled to a core wire  250  by an electrolytically severable joint  252 . A proximal portion of the core wire  250  is insulated by an insulating layer  254  to form the severable joint  252 . In this case, the delivery catheter  102  is used to deliver both the neck bridge  106  and the vaso-occlusive device  108 . 
     The method of using the previously described neck bridges will now be discussed with reference to  FIGS. 18A-18E . First, the delivery catheter  102  is inserted into the body of a patient. Typically, this would be through a femoral artery in the groin. Other entry sites sometimes chosen are found in the neck and are in general well known by physicians who practice these types of medical procedures. The delivery catheter  102 , which may be a microcatheter or a sheath, may be positioned so that the distal end of the delivery catheter  102  is appropriately situated, e.g., near the neck of an aneurysm  306  to be treated. ( FIG. 18A ) The placement of the delivery catheter  102  may be assisted by the use of guide wire and/or a radio-opaque marker, as are known in the art. 
     A neck bridge  308 , which is representative of any of the embodiments of the neck bridge discussed previously, is carried within the delivery catheter  102  before it is deployed. While positioned within the delivery catheter  102 , the neck bridge  308  is stretched into a delivery shape. If the neck bridge  308  is coupled to the inner tubular member  104 , the neck bridge  308  may be deployed by retracting the delivery catheter  102  relative to the tubular member  104 , or by advancing the tubular member  104  relative to the delivery catheter  102 . Alternatively, if the neck bridge  308  is coupled to the core wire  250 , such as that shown in  FIG. 17 , the neck bridge  308  may be deployed by retracting the delivery catheter  102  relative to the core wire  250  or by advancing the core wire  250  relative to the delivery catheter  102 . Once the neck bridge  308  is unconfined outside the delivery catheter  102 , it assumes an unfolded configuration.  FIG. 18B  shows the neck bridge  308  having been deployed and placed within the aneurysm  306 . 
     Next, one or more vaso-occlusive devices  314  may be delivered into the aneurysm using any of the conventional methods. ( FIG. 18C ) If the neck bridge  308  includes a junction region  316  that has an opening, such as the opening  128  shown in  FIG. 5 , the vaso-occlusive device  314  may be delivered via the inner tubular member  104 , through the opening  128  of the junction region  316  of the neck bridge  308 , and into the aneurysm  306 . It should be noted that instead of vaso-occlusive devices, other occlusion substance such as occlusion fluid or occlusion particles may also be delivered through the opening of the junction region  316  and into the aneurysm  306 . If the junction region  316  of the neck bridge  308  does not have an opening, such as the embodiment shown in  FIG. 16  or  17 , the vaso-occlusive device  314  may be delivered to the aneurysm  306  along a path that is exterior to the tubular member  104  or to the core wire  250  if one is used. In this case, the neck bridge  308  should be made sufficiently flexible to distend around the vaso-occlusive delivery device. Alternatively, the vaso-occlusive device  314  may be delivered into the aneurysm  306  by going through an opening in the cover, such as a pre-made opening, or an opening defined by the fibers making up the cover. The vaso-occlusive device  314  may also be delivered into the aneurysm by puncturing the cover of the neck bridge  308 . 
     After a desired number of the vaso-occlusive coils  314  have been placed in the aneurysm  306 , the electrolytically severable joint  122  (or joint  129 ,  140 , or  252 ) is then severed, thereby de-coupling the neck bridge  308  from the tubular member  104  or from the core wire  250  if one is used. ( FIGS. 18D and 18E ) The delivery catheter  102  and the inner tubular member  104  are then withdrawn, leaving the vaso-occlusive device  314  in place within the aneurysm  306 . As shown in  FIG. 18E , the neck bridge  308  stabilizes the presence of the vaso-occlusive device  314  and prevents the vaso-occlusive coil  314  from being drawn or escaping into the feed vessel. If desired, a stent or a perfusion balloon may optionally be placed in the parent vessel to help seat the neck bridge  308  within the aneurysm  306 . 
     It should be noted that the neck bridge may also be placed outside the neck of an aneurysm.  FIGS. 19A-19C  show another variation of the neck bridge  400  having a junction region  402 , a number of radially extending array elements  404 , and a cover  406 . Unlike the previously described embodiments, the neck bridge  400  also includes a cage  408  made up of a plurality of, e.g., platinum or nickel-titanium coils or wires  409 . A connector  410  connects the cage  408  to the junction region  402  or to the array elements  404 , and is situated within the neck of the aneurysm after implantation. The array elements  404  are typically joined to a releasable joint, which may be an electrolytically severable joint as discussed previously. As may be seen from  FIG. 19B , the cage  408  extends outwardly from the general center-line of the device and generally should be sized to conform to the size of, and generally to the shape of, the aneurysm.  FIG. 19C  shows the general placement of the device within an aneurysm  414 . The cage  408 , which is within the sac of the aneurysm  414 , anchors the cover  406 , which is placed outside the neck of the aneurysm  414 . The method of using the neck bridge  400  is similar to that described previously with reference to  FIGS. 18A-18E . 
     Many alterations and modifications may be made by those of ordinary skill in this art, without departing from the spirit and scope of this invention. The illustrated embodiments have been shown only for purposes of clarity and the examples should not be taken as limiting the invention as defined in the following claims, which are intended to include all equivalents, whether now or later devised.