Abstract:
A novel endovascular approach useful in the treatment of aneurysms, particularly saccular aneurysms. The present endovascular prosthesis comprises a leaf portion capable of being urged against and blocking the opening of the aneurysm thereby leading to obliteration of the aneurysm. The leaf portion is attached to, and independently moveable with respect to, a body comprising at least one expandable portion. Thus, the body serves the general purpose of fixing the endovascular prosthesis in place at a target body passageway in the vicinity at which the aneurysm is located and the leaf portion serves the purpose of blocking the aneurysmal opening thereby leading to obliteration of the aneurysm. A method of delivering and implanting the endovascular prosthesis is also described.

Description:
This application claims benefit under 35 U.S.C § 119(e) of U.S. Provisional Application No. 60/074,521, filed Feb. 12, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     In one of its aspects, the present invention relates to an endovascular prosthesis. In another of its aspects, the present invention relates to a method of treating an aneurysm in a patient. 
     2. Description of the Prior Art 
     As is known in the art, an aneurysm is an abnormal bulging outward in the wall of an artery. In some cases, the bulging may be in the form of a smooth bulge outward in all directions from the artery—this is known as a “fusiform aneurysm”. In other cases, the bulging may be in the form of a sac arising from an arterial branching point or from one side of the artery—this is known as a “saccular aneurysm”. 
     While aneurysms can occur in any artery of the body, those which occur in the brain can lead to the occurrence of a stroke. Most saccular aneurysms which occur in the brain have a neck which extends from the cerebral blood vessel and broadens into a pouch which projects away from the vessel. 
     The problems caused by such aneurysms can occur in several different ways. For example, if the aneurysm ruptures, blood enters the brain or the subarachnoid space (i.e., the space closely surrounding the brain)—the latter is known as aneurysmal subarachnoid hemorrhage. This followed by one or more of the following symptoms: nausea, vomiting, double vision, neck stiffness and loss of consciousness. Aneurysmal subarachnoid hemorrhage is an emergency medical condition requiring immediate treatment. Indeed, 10-15% of patients with the condition die before reaching the hospital for treatment. More than 50% of patients with the condition will die within the first thirty days after the hemorrhage. Of those patients who survive, approximately half will suffer a permanent stroke. It is typical for such a stroke to occur one to two weeks after the hemorrhage itself from vasospasm in cerebral vessels induced by the subarachnoid hemorrhage. Aneurysms also can cause problems which are not related to bleeding although this is less common. For example, an aneurysm can form a blood clot within itself which can break away from the aneurysm and be carried downstream where it has the potential to obstruct an arterial branch causing a stroke. Further, the aneurysm can also press against nerves (this has the potential of resulting in paralysis or abnormal sensation of one eye or of the face) or the adjacent brain (this has the potential of resulting in seizures). 
     Given the potentially fatal consequences of the aneurysms, particularly brain aneurysms, the art has addressed treatment of aneurysms using various approaches. 
     Generally, aneurysms may be treated from outside the blood vessels using surgical techniques or from the inside using endovascular techniques (the latter falls under the broad heading of interventional (i.e., non-surgical) techniques). 
     Surgical techniques usually involve a craniotomy requiring creation of an opening in the skull of the patient through which the surgeon can insert instruments to operate directly on the brain. In one approach, the brain is retracted to expose the vessels from which the aneurysm arises and then the surgeon places a clip across the neck of the aneurysm thereby preventing arterial blood from entering the aneurysm. If there is a clot in the aneurysm, the clip also prevents the clot from entering the artery and obviates the occurrence of a stroke. Upon correct placement of the clip the aneurysm will be obliterated in a matter of minutes. Surgical techniques are the most common treatment for aneurysms. Unfortunately, surgical techniques for treating these conditions are regarded as major surgery involving high risk to the patient and necessitate that the patient have strength even to have a chance to survive the procedure. 
     As discussed above, endovascular techniques are non-surgical techniques and are typically performed in an angiography suite using a catheter delivery system. Specifically, known endovascular techniques involve using the catheter delivery system to pack the aneurysm with a material which prevents arterial blood from entering the aneurysm—this technique is broadly known as embolization. One example of such an approach is the Guglielmi Detachable Coil which involves intra-aneurysmal occlusion of the aneurysm via a system which utilizes a platinum coil attached to a stainless steel delivery wire and electrolytic detachment. Thus, once the platinum coil has been placed in the aneurysm, it is detached from the stainless steel delivery wire by electrolytic dissolution. Specifically, the patient&#39;s blood and the saline infusate act as the conductive solutions. The anode is the stainless steel delivery wire and the cathode is the ground needle which is placed in the patient&#39;s groin. Once current is transmitted through the stainless steel delivery wire, electrolytic dissolution will occur in the uninsulated section of the stainless steel detachment zone just proximal to the platinum coil (the platinum coil is of course unaffected by electrolysis). Other approaches involve the use of materials such as cellulose acetate polymer to fill the aneurysm sac. While these endovascular approaches are an advance in the art, they are disadvantageous. Specifically, the risks of these endovascular approaches include rupturing the aneurysm during the procedure or causing a stroke due to distal embolization of the device or clot from the aneurysm. Additionally, concern exists regarding the long term results of endovascular aneurysm obliteration using these techniques. Specifically, there is evidence of intra-aneurysmal rearrangement of the packing material and reappearance of the aneurysm on follow-up angiography. 
     One particular type of brain aneurysm which has proven to be very difficult to treat, particularly using the surgical clipping or endovascular embolization techniques discussed above occurs at the distal basilar artery. This type of aneurysm is a weak outpouching, usually located at the terminal bifurcation of the basilar artery. Successful treatment of this type of aneurysm is very difficult due, at least in part, to the imperative requirement that all the brainstem perforating vessels be spared during surgical clip placement. 
     Unfortunately, there are occasions when the size, shape and/or location of an aneurysm make both surgical clipping and endovascular embolization not possible for a particular patient. Generally, the prognosis for such patients is not good. 
     Accordingly, while the prior art has made advances in the area of treatment of aneurysms, there is still room for improvement, particularly in endovascular embolization since it is such an attractive alternative to major surgery. Specifically, it would be desirable to have an endovascular prosthesis which could be used in the embolization of aneurysms which are difficult or not possible to treat otherwise. It would be further desirable if such an endovascular prosthesis could be used to treat aneurysms currently treated endovascularly while mitigating or obviating the disadvantages associated with current endovascular embolization techniques. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel endovascular prosthesis which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art. 
     It is another object of the present invention to provide a novel method for endovascular blocking an aneurysmal opening which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art. 
     Accordingly, in one of its aspects, the present invention relates to a prosthesis for endovascular blocking of an aneurysmal opening, the prosthesis comprising: 
     a body having a promixal end, a distal end and at least one expandable portion disposed therebetween, the at least one expandable portion being expandable from a first, unexpanded state to a second, expanded state with a radially outward force thereon to urge the first expandable portion against a vascular lumen, and 
     a leaf portion attached to the body, 
     the leaf portion being independently moveable with respect to the body. 
     In another of its aspects, the present invention relates to a prosthesis for endovascular blocking of an aneurysmal, the prosthesis comprising: 
     a body having a promixal end, a distal end and at least one expandable portion disposed therebetween, the at least one expandable portion being expandable from a first, unexpanded state to a second, expanded state with a radially outward force thereon to urge the first expandable portion against a vascular lumen, and 
     a leaf portion attached to the body, 
     the body being flexible between: (i) a first position in which the proximal end, the distal end and the leaf portion are aligned along a longitudinal axis of the body, and (ii) a second position in which the leaf portion is aligned with only one of the distal end and the proximal end along the longitudinal axis. 
     In yet another of its aspects, the present invention relates to a prosthesis for endovascular blocking of an aneurysmal opening, the prosthesis comprising: 
     a body having a longitudinal axis comprising at least one expandable portion, the at least one expandable portion being expandable from a first, unexpanded state to a second, expanded state with a radially outward force thereon to urge the first expandable portion against a vascular lumen, and 
     a leaf portion attached to the body, 
     the body being flexible between: (i) a first position in which the at least one expandable portion and the leaf portion are aligned along the longitudinal axis, and (ii) a second position in which the at least one expandable portion and the leaf are unaligned along the longitudinal axis. 
     In yet another of its aspects, the present invention relates to a method for endovascular blocking of an aneurysmal opening with a prosthesis comprising: a body having a promixal end, a distal end and at least one expandable portion disposed therebetween, and a leaf portion attached to the body, the method comprising the steps of: 
     disposing the prosthesis on a catheter; 
     inserting the prosthesis and catheter within a body passageway by catheterization of the body passageway; 
     translating the prosthesis and catheter to a target body passageway at which the aneurysm opening is located; 
     exerting a radially outward expansive force on the at least one expandable portion such that the at least one expandable portion is urged against the target body passageway. 
     urging the leaf portion against the aneurysmal opening thereby blocking the aneurysmal opening. 
     Thus, the present inventors have discovered a novel endovascular approach useful in blocking of an aneurysmal opening, particularly those in saccular aneurysms, leading to obliteration of the aneurysm. The approach is truly endovascular in that, with the present endovascular prosthesis, there is no requirement to pack the aneurysmal sac with a material (e.g., such is used with the Guglielmi Detachable Coil). Rather, the present endovascular prosthesis operates on the basis that it serves to block the opening to the aneurysmal sac thereby obviating the need for packing material. Thus, a novel endovascular prosthesis has been discovered which obviates or mitigates many of the disadvantages of the prior art. The present endovascular prosthesis comprises a leaf portion capable of being urged against the opening of the aneurysm thereby closing the aneurysm. The leaf portion is attached to, and independently moveable with respect to, a body comprising at least one expandable portion. The tubular portion is expandable from a first, unexpanded state to a second, expanded stated with a radially outward force thereon to urge the first expandable portion against a vascular lumen. Thus, the body serves the general purpose of fixing the endovascular prosthesis in place at a target vascular lumen body passageway in the vicinity at which the aneurysmal opening is located and the leaf portion serves the purpose of sealing the aneurysmal opening thereby leading to obliteration of the aneurysm. Thus, as will be developed further hereinbelow, the leaf portion functions and is moveable independently of the body of the endovascular prosthesis. 
     Preferably, and as will be further developed hereinbelow, the at least one expandable portion is generally tubular in structure. Indeed, throughout this specification, reference will be made to an expandable portion which is generally tubular in structure. However, such reference is for illustrative purposes only and those of skill in the art will recognize that it is possible to utilize a non-tubular structure (e.g., a claw-like design which opens upon expansion) as the at least one expandable portion. 
     The body of the present endovascular prosthesis has a generally longitudinal axis and is flexible. The leaf portion is independently moveable between at least a first position and a second position with respect to the body, expanded or unexpanded. Thus, in the first position, the distal end and the proximal end of the body are aligned with the leaf portion. In the second position, while securing the distal end and the proximal end of the body, the leaf portion maintains a degree of independent movement. In this manner, the leaf portion is “independently moveable” with respect to the body. In one embodiment, it is preferred that this independent movement is achieved by disposing the leaf portion such that it may pivot with respect to the remainder of the endovascular prosthesis. It should be understood that, while the leaf portion is independently moveable with respect to the body, the final alignment of the distal end, the proximal end and leaf portion (i.e., the alignment after blockage of the aneurysmal opening) is not particularly restricted and depends on factors such as the size and location of the aneurysm and the anatomy of the particular patient. The key point is that the leaf portion is capable of being independently moved with respect to the body. 
     In one preferred embodiment, the body is in the form of a flexible tube, preferably a flexible, porous tube. In this embodiment, the leaf portion may be a cut-out along the length of the tube and at least one, preferably both, ends of the tube are expandable upon application of a radially outward force thereon to fix the tube in place in the target body passageway. The leaf portion is capable of moving out of the plane of the tube upon flexure of the tube and/or expansion of the tube in a radially outward direction to be urged against an opening of and thereby blocking the aneurysmal opening. 
     In another preferred embodiment, the body is in the form of a pair of opposed tubular or ring-like sections which are connected to one another. The leaf portion is connected to one or both of the tubular or ring-like sections. The ring-like sections are expandable upon exertion (e.g., applied by a catheter-mounted balloon or inherent in a self-expanding device) of a radially outward force thereon to urge fix the body in place in the target body passageway. As is known in the art, it is possible to confer expandability to the ring-like sections by designing these sections to have a porous surface (e.g., comprising a plurality of interconnecting struts). For materials such as stainless steel, this allows the ring-like structures to expand prior to reaching the point of plastic deformation. The leaf portion is capable of moving out of the plane of the tube upon flexure of the tube and/or expansion of the tube in a radially outward direction. 
     The present endovascular prosthesis is believed to provide a significant alternative the conventional surgical techniques described hereinabove. Additionally, it is envisaged that the present endovascular prosthesis may used in the treatment of certain aneurysms which are diagnosed as being inoperable. The present endovascular prosthesis also is believed to provide a significant advantage of current endovascular approaches such as the Guglielmi Detachable Coil described hereinabove. Specifically, since the present endovascular prosthesis does not rely on insertion into the aneurysm of a metal packing material (e.g., platinum coil), the risk of rupturing the aneurysm is mitigated as is the risk of intra-aneurysmal rearrangement of the metal packing material and subsequent reappearance of the aneurysm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will be described with reference to the accompanying drawings, wherein like reference numerals denote like elements and in which: 
     FIGS. 1-5 illustrate a perspective view, partially cut away, of the terminal bifurcation of the basilar artery into which the a first embodiment of the present endovascular prosthesis is being delivered and implanted; 
     FIG. 6 illustrates an enlarged view of a modification to the first embodiment of the present endovascular prosthesis illustrated in FIGS. 1-5; 
     FIG. 7 illustrates an enlarged view of another modification to the first embodiment of the present endovascular prosthesis illustrated in FIGS. 1-5; 
     FIGS. 8-10 illustrate various embodiments of the shape of the leaf portion of the present endovascular prosthesis; 
     FIG. 11 illustrates a perspective view of a second embodiment of the present endovascular prosthesis; 
     FIGS. 12-15 illustrate a perspective view, partially cut away, of the terminal bifurcation of the basilar artery into which the embodiment illustrated in FIG. 11 is being delivered and implanted; 
     FIG. 16 illustrates a perspective view of a third embodiment of the present endovascular prosthesis; 
     FIGS. 17-18 illustrate a perspective view, partially cut away, of the terminal bifurcation of the basilar artery into which the embodiment illustrated in FIG. 16 is being delivered and implanted; and 
     FIG. 19 illustrates an enlarged view of a modification to the embodiment of the present endovascular prosthesis illustrated in FIGS. 16-18; 
     FIGS. 20-22 illustrate a perspective view of a preferred embodiment of the present endovascular prosthesis shown in schematic; 
     FIG. 23 illustrates an enlarged two-dimensional representation of one embodiment encompassed by the endovascular prosthesis illustrated in FIGS. 20-22; and 
     FIG. 24 illustrates an enlarged two-dimensional representation of another embodiment encompassed by the endovascular prosthesis illustrated in FIGS.  20 - 22 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIGS. 1-5, a first embodiment of the present endovascular prosthesis will be described with particular reference to implantation of same at the terminal bifurcation of the basilar artery. 
     Thus there is illustrated a basilar artery  10  which terminates at a junction  15  which bifurcates into pair of secondary arteries  20 , 25 . Located at junction  15  is an aneurysm  30 . Aneurysm  30  has an opening  35  (shown enlarged for illustrative purposes only) through blood enters and sustains aneurysm  30 . 
     An endovascular prosthesis  100  is mounted on a catheter  50 . 
     Catheter  50  comprises an inflatable balloon  55  and a guidewire  60 . Catheter  50 , inflatable balloon  55  and guidewire  60  are conventional. As is known in the art, inflatable balloon  55  is moveable along guidewire  60 . 
     Endovascular prosthesis  100  is constructed of a body  105 . Body  105  comprises a proximal end  110  and a distal end  115 . Endovascular prosthesis  100  further comprises a leaf portion  120  attached to body  105 . As illustrated, leaf portion comprises a neck  125  and a head  130 . Head  130  is wider than neck  125 . In the illustrated embodiment, head  130  of leaf portion  120  points away from distal end  115  (i.e., head  130  of leaf portion  120  points toward proximal end  110 ). 
     Body  105  is a generally tubular element and should be constructed to be sufficiently flexible such that it can be navigated to the target body passageway yet be sufficiently expandable such that it can be fixed at the proper location in target body passageway. 
     One approach to achieve this is to construct endovascular prosthesis  100  from a structure resembling a stent. As is known in the art, a stent is an expandable prosthesis which is generally used to obtain and maintain the patency of a body passageway (e.g., blood vessels, respiratory ducts, gastrointestinal ducts and the like). The two general design requirements of a stent are: (i) it must be sufficiently flexible in the unexpanded state such that it may be navigated to the target body passageway intact, and (ii) it must be sufficiently radially rigid in the expanded state to avoid the occurrence of restenosis and/or stent recoil. The present endovascular prosthesis is not a stent, per se, since design requirement (ii) need not be met—i.e., the aim of the present endovascular prosthesis is not to maintain patency of blocked body passageway. Rather, the present endovascular prosthesis comprises one or more expandable elements for the purposes of securing the prosthesis in the correct position. 
     Thus, in this approach body  105  may be a porous tube having a porosity defined by a plurality of intersecting members (for clarity, the porosity of body  105  is not illustrated in FIGS  1 - 5 ). The precise pattern of the intersecting members is not particularly restricted and should be chosen to achieve sufficient flexibility of the porous tube in the unexpanded state while having the potential to achieve at least some degree of expansion with radially outward forces on the tube. Typically, the plurality of intersecting members will be arranged to define a regular repeating pattern. See, for example, the various repeating patterns disclosed in the following copending patent applications: 
     Canadian patent application number 2,134,997 (filed Nov. 3, 1994); 
     Canadian patent application number 2,171,047 (filed Mar. 5, 1996); 
     Canadian patent application number 2,175,722 (filed May 3, 1996); 
     Canadian patent application number 2,185,740 (filed Sep. 17, 1996); 
     Canadian patent application number 2,192,520 (Dec. 10, 1996); 
     International patent application PCT/CA97/00151 (filed Mar. 5, 1997); 
     International patent application PCT/CA97/00152 (filed Mar. 5, 1997); and 
     International patent application PCT/CA97/00294 (filed May 2, 1997); 
     the contents of each of which are hereby incorporated by reference (hereinafter collectively referred to as the “Divysio patent applications”) and the various references cited therein. While the repeating patterns disclosed in the in the Divysio patent applications are suited for use in stent designs, they may be modified to increase the flexibility of the tubular structure (e.g., by altering the polygonal design taught in the Divysio patent application applications) to be useful in the present endovascular prosthesis notwithstanding that the resultant tube may not be useful as a stent. 
     Body  105  may be constructed of any suitable material. In one preferred embodiment, body  105  is constructed of a plastically deformable material such as a metal, alloy or polymer. Non-limiting examples of suitable metals and alloys may be selected from the group comprising stainless steel, titanium, tantalum and the like. In this embodiment, the radially outward force used to expand body  105  may be applied by expansion of a catheter-mounted balloon, as will be discussed in more detail hereinbelow. In another preferred embodiment, body  105  is constructed of “shape memory” metal alloy (e.g., nitinol) capable of self-expansion at a temperature of at least about 30° C., preferably in the range of from about 30° to about 40° C. In this embodiment, it will be appreciated that an inherent radially outward force causes expansion of body  105  when it is exposed to an environment at the programmed self-expansion temperature. In yet another preferred embodiment, body  105  may be construct of a biodegradable material. As is known in the art, a biodegradable material will degrade upon prolonged contact with body fluids and would be useful in the present endovascular prosthesis since aneurysm obliteration may occur within minutes after closing of the aneurysmal opening. 
     The manner by which body  105  is manufactured is not particularly restricted. Preferably, the body  105  is produced by laser cutting techniques applied to a tubular starting material. Thus, the starting material could be a thin tube of a metal, alloy or polymer as described above which would then have sections thereof cut out to leave the desired repeating pattern discussed above. By using such a technique, it is then possible to produce leaf portion  120  simply by laser machining a cut in the outline of neck  125  and head  130  of leaf portion  120 . 
     Alternatively, it is possible to construct body  105  having the desired porous repeating pattern from one or more pre-formed wires. In another alternate embodiment, it is possible to construct body  105  having the desired porous repeating pattern using a flat bed laser cutting technique, optionally combined was a welding technique. 
     Since endovascular prosthesis  100  functions by blocking opening  35  to aneurysm  30 , it is important that leaf portion  120  be designed accordingly. Specifically, leaf portion  120  should be design such that it may occlude opening  35  to aneurysm  30 . This may be achieved in a number of ways. In one embodiment, head  130  of leaf portion  120  is designed to be non-porous. In another embodiment, head  130  of leaf portion  120  is designed to be porous (e.g., for ease of manufacture of body  105 ) and thereafter covered with a suitable non-porous coating material. The non-porous coating material may be active (e.g., a pharmaceutical, an adhesive and the like to a non-porous surface and an additional benefit) or inactive (e.g., an inert coating material which serves the sole purpose of providing a non-porous surface). In yet another embodiment, the entire surface of leaf portion  120  (i.e., the combination of neck  125  and head  130 ) may be non-porous by original design or originally porous and subsequently covered with a non-porous coating. 
     Endovascular prosthesis  100  may further comprise a coating material thereon. The coating material may be disposed continuously or discontinuously on the surface of the prosthesis. Further, the coating may be disposed on the interior and/or the exterior surface(s) of the prosthesis. The coating material can be one or more of a biologically inert material (e.g., to reduce the thrombogenicity of the prosthesis), a medicinal composition which leaches into the wall of the body passageway after implantation (e.g., to provide anticoagulant action, to deliver a pharmaceutical to the body passageway and the like) and the like. 
     Endovascular prosthesis  100  is preferably provided with a biocompatible coating in order to minimize adverse interaction with the walls of the body vessel and/or with the liquid, usually blood, flowing through the vessel. The coating is preferably a polymeric material, which is generally provided by applying to the prosthesis a solution or dispersion of preformed polymer in a solvent and removing the solvent. Non-polymeric coating material may alternatively be used. Suitable coating materials, for instance polymers, may be polytetraflouroethylene or silicone rubbers, or polyurethanes which are known to be biocompatible. Preferably, however, the polymer has zwitterionic pendant groups, generally ammonium phosphate ester groups, for instance phosphoryl choline groups or analogues thereof. Examples of suitable polymers are described in International application numbers WO-A-93/16479 and WO-A-93/15775. Polymers described in those specifications are hemo-compatible as well as generally biocompatible and, in addition, are lubricious. It is important to ensure that the surfaces of the prosthesis are completely coated in order to minimize unfavourable interactions, for instance with blood, which might lead to thrombosis in the parent vessel. 
     This good coating can be achieved by suitable selection of coating conditions, such as coating solution viscosity, coating technique and/or solvent removal step. 
     With further reference to FIG. 1, once it is desired to implant endovascular prosthesis  100 , it is mounted on balloon  55  of catheter  50 . Catheter  50  is then translated through basilar artery  10  in the direction of arrow A. 
     With reference to FIG. 2, endovascular prosthesis  100  mounted on balloon  55  of catheter  50  is navigated to the location of aneurysm  30  using conventional guidewire and fluoroscopy techniques. In the illustrated embodiment, distal end  115  of body  105  enters secondary artery  20 . In practice, the secondary arteries at the bifurcation of the basilar artery are asymmetric and distal end  115  of body  105  is navigated into the larger of the two secondary arteries. Further, in the illustrated embodiment, as body  105  is flexed on navigation into secondary artery  20 , leaf portion  120  lifts or moves out of alignment with respect to the tubular plane of body  105  to define an opening  135 . 
     With reference to FIGS. 3 and 4, once endovascular prosthesis  100  is in the correct position, balloon  55  is expanded thereby exerting radially outward forces on body  105 . Initially, this results in expansion of body  105  such that a portion of it is urged against the walls of both of basilar artery  10  and secondary artery  20 . With reference to FIG. 4, as expansion of balloon  55  continues, a portion of balloon  55  urges against neck  125  and head  130  of leaf portion  120  resulting in urging of leaf portion  120  against the walls of secondary arteries  20 , 25  in a manner which results in blocking of opening  35  of aneurysm  30 . 
     With reference to FIG. 5, balloon  55  is deflated and, together with guidewire  60 , withdrawn from endovascular prosthesis  100  in the direction of arrow B. In the illustrated embodiment, endovascular prosthesis  100  is secured in position by body  105  being urged against the walls of basilar artery  10  and secondary artery  20 . Further, in the illustrated embodiment, leaf portion  120  is secured in position by a combination forces against it by the flow of the blood in the direction of arrow C and the inherent forces open flexure of body  105  to navigate distal end  115  into secondary artery  20 . Once leaf portion  120  blocks opening  35 , aneurysm  30  is obliterated thereafter. 
     With reference to FIG. 6, there is illustrated an enlarged view of a modification to the endovascular prosthesis illustrated in FIGS. 1-5. In FIG. 6, like numerals are used to designate like elements in FIGS. 1-5 and modified or new elements in FIG. 6 are denoted with the suffix “a”. Specifically, leaf portion  120   a  has been modified such that neck  125   a  is made of an electrically non-conductive material whereas head  130   a  is made of an electrically conductive material. Additionally, a pharmaceutically acceptable adhesive  132   a  is disposed on the aneurysmal side of head  130   a  and a positioning wire  140   a  is secured to head  130   a  at a connection point  145   a . In use, positioning wire  140   a  may be utilized to orient leaf portion  120   a  such that head  130   a  correctly closes opening  35  of aneurysm  30 . Once leaf portion  120   a  is in the correct position, an electric current is passed through positioning wire  140   a  thereby resulting in detachment thereof from head  130   a  at connection point  145   a . Additionally, depending on the nature of adhesive  132   a , the electric current which is passed through positioning wire  140   a  may serve the additional purpose of activating adhesive  132   a . Of course, it is possible to modify the specific embodiment illustrated in FIG. 6, for example, to: (i) omit adhesive  132   a  so that the electric current serves to seal head  130   a  to the periphery of opening  35 ; (ii) omit positioning wire  140   a  so that the seal of head  130   a  to the periphery of opening is achieved via adhesive  132   a ; or (iii) to construct head  130   a  from the same material (electrically conductive or non-conductive) so that the principal purpose of positioning wire  140   a  is alignment of leaf portion  120   a.    
     A preferred modification to the embodiments illustrated in FIGS. 1-6 involves modifying positioning wire  140   a  to a supplementary (or second) guidewire to guidewire  60  illustrated in FIGS. 1-5. Specifically, whereas guidewire  60  is navigated in secondary artery  20 , the supplementary guidewire would pass through an aperture in the leaf portion (e.g., near the location of connection point  145   a  in FIG. 6) and be navigated into secondary artery  25  during implantation of the endovascular prosthesis. By passing the supplementary guidewire through the leaf portion in this fashion, delivery of the prosthesis is greatly facilitated and, importantly, enhanced control is achieved of the orientation of the leaf portion to seal the aneurysmal opening. 
     With reference to FIG. 7, there is illustrated yet another modification to the endovascular prosthesis illustrated in FIGS. 1-5. In FIG. 7, like numerals are used to designate like elements in FIGS. 1-5 and modified or new elements in FIG. 7 are denoted with the suffix “b”. Specifically, leaf portion  120   b  has been modified such that head  130   b  is coated on the aneurysmal side thereof with a pharmaceutically acceptable expandable compound  132   b . In use, once leaf portion  120   b  is orientated such that head  130   b  correctly closes opening  35  of aneurysm  30 , expandable compound  132   b  chemically reacts with bodily fluids expands to fill aneurysm  30  as an expanded compound  134   b . Alternatively, expandable compound  132   b  may be electrically activated using a positioning wire such as illustrated in FIG.  6 . 
     With reference to FIGS. 8-10, there are illustrated various modifications to the shape of the head of the leaf portion. In FIGS. 8-10, like numerals are used to designate like elements in FIGS. 1-5 and modified elements in FIGS. 8-10 are denoted with the suffix “c”, “d” and “e”, respectively. It will be clear to those of skill in the art that head  130   c ,  130   d  or  130   e  illustrated in FIGS. 8-10, respectively, may be cut out of or overlap with respect to body  105 . 
     With reference to FIG. 11 there is illustrated a second embodiment of the present invention in the form of endovascular prosthesis  200 . Endovascular prosthesis  200  is constructed of a body  205 . Body  205  comprises a proximal end  210  and a distal end  215 . Endovascular prosthesis  200  further comprises a leaf portion  220  attached to body  205 . As illustrated, leaf portion  220  comprises a neck  225  and a head  230 . Head  230  is wider than neck  225 . In the illustrated embodiment, head  230  of leaf portion  220  points away from distal end  215  (i.e., head  230  of leaf portion  220  points toward proximal end  210 ). 
     Body  205  further comprises a pair of rings  235 , 240  which are interconnected by a pair of wires  245 , 250 . In the illustrated embodiment leaf portion  220  is connected to ring  235 . Wires  245 , 250  preferably are dimensioned to confer to prosthesis  200  sufficient integrity while maximizing flexibility to provide enhanced navigation. The purpose of wires  245 , 250  is to interconnect rings  235 , 240  while allowing prosthesis  200  to be sufficiently flexible such that it can be navigated to the target body passageway yet be sufficiently expandable such that it can be fixed at the proper location in target body passageway. Wires  245 , 250  are not particularly important during expansion of prosthesis  200  (i.e., after the point in time at which prosthesis  200  is correctly positioned). Further, as will be apparent to those of skill in the art, leaf portion  220  is independently moveable with respect to proximal end  210  and distal end  215  of prosthesis  200  (in the illustrated embodiment, leaf portion  220  is independently moveable with respect to rings  235 , 240 ). 
     With reference to FIGS. 12-15, prosthesis  200  is mounted on a catheter  50  and delivered and implanted in the manner described above with reference to FIGS. 1-5. In this embodiment, it is preferred to implant prosthesis  200  in a manner such that wires  245 , 250  are adjacent basilar artery  10  and secondary artery  20  (in the illustrated embodiment). 
     This embodiment of the invention is useful in illustrating the difference between the present endovascular prosthesis and a conventional stent. Specifically, in this embodiment of the present prosthesis, the expansible elements are rings  235 , 240 . Rings  235 , 240  comprise a porous structure of interconnecting struts which, for the purpose of clarity is not illustrated in the drawings. The precise nature of the porous structure of interconnecting struts is not particularly restricted and is within the purview of a person skilled in the art. The principal purpose of expanding rings  235 , 240  is to secure prosthesis  200  in place and not necessarily to alter the flow of blood through that portion of the artery in which the rings are expanded—i.e., this is the purpose of a stent. 
     With reference to FIG. 16 there is illustrated a third embodiment of the present invention in the form of endovascular prosthesis  300 . Endovascular prosthesis  300  is constructed of a body  305 . Body  305  comprises a proximal end  310  and a distal end  315 . Endovascular prosthesis  300  further comprises a leaf portion  320  attached to body  305 . Body  305  comprises a pair of rings  335 , 340  which are interconnected by a pair of wires  345 , 350 . Again, rings  335 , 340  comprise a porous structure of interconnecting struts which, for the purpose of clarity is not illustrated in the drawings. The precise nature of the porous structure of interconnecting struts is not particularly restricted and is within the purview of a person skilled in the art. As illustrated, leaf portion  320  is connected to rings  335 , 340  by a pair of wires  322 , 324 . Further, each of wires  345 , 350  each contains a pair of undulating sections  355 , and each of wires  322 , 324  contains a single undulating section  355 . Undulating section  355  improves flexibility and navigation of prosthesis  300 . 
     Again, wires  322 , 324 , 345 , 350  preferably are dimensioned to confer to prosthesis  300  sufficient integrity while maximizing flexibility to provide enhanced navigation. The purpose of wires  345 , 350  is to interconnect rings  335 , 340  while allowing prosthesis  300  to be sufficiently flexible such that it can be navigated to the target body passageway yet be sufficiently expandable such that it can be fixed at the proper location in target body passageway. Wires  345 , 350  are not particularly important during expansion of prosthesis  300  (i.e., after the point in time at which prosthesis  300  is correctly positioned). The purpose of wires  322 , 324  is to allow for more independent movement of leaf portion  230  with respect to proximal end  310  (in the illustrated embodiment this would in include ring  335 ) and distal end  315  (in the illustrated embodiment this would in include ring  340 ) of prosthesis  300 . With reference to FIGS. 17-18, prosthesis  300  is mounted on a catheter  50  and delivered and implanted in the manner described above with reference to FIGS. 1-5. With further reference to FIG. 18, it will be appreciated by those of skill in the art that, for optimal effect, wires  322 , 324 , 345 , 350  should be positioned on rings  335 , 340  such that wire  324  does not cross secondary artery  25  after implantation of the endovascular prosthesis. 
     With reference to FIG. 19, there is illustrated a modification to the endovascular prosthesis illustrated in FIGS. 16-18. In FIG. 19, like numerals are used to designate like elements in FIGS. 16-18 and new elements in FIG. 19 are denoted with the suffix “f”. In FIG. 19, an undulating wire  326 f has been added to interconnect leaf portion  320  and wires  345 , 350 . Additionally, there is no interconnecting wire between leaf portion  320  and ring  340 . In this embodiment, omission of an interconnecting wire between leaf portion  320  and ring  340  obviates a connecting wire crossing the lumen of secondary artery  25  after implantation of the endovascular prosthesis while addition of undulating wire  326 f improves the physical integrity of the prosthesis. 
     FIGS. 20-22 illustrate how the various elements of an endovascular prosthesis  400  may be cut out of a tubular starting material (again, for clarity, the specific porosity of prosthesis  400  and the balloon catheter delivery system are not illustrated in FIGS.  20 - 22 ). 
     Endovascular prosthesis  400  is constructed of a body  405 . Body  405  comprises a proximal end  410  and a distal end  415 . Endovascular prosthesis  400  further comprises a leaf portion  420  attached to body  405 . As illustrated, leaf portion  420  comprises a blocking portion  425  for blocking aneursymal opening  35 . In the illustrated embodiment, the free end of leaf portion  420  points away from distal end  415  (i.e., the free end of leaf portion  420  points toward proximal end  410 ). 
     Body  405  further comprises a pair of expandable tubular sections  435 , 440  which are interconnected by a spine  450 . In the illustrated embodiment leaf portion  420  is connected to tubular section  435 . Spine  450  is preferably dimensioned to confer to prosthesis  400  sufficient integrity while maximizing flexibility to provide enhanced navigation. The purpose of spine  450  is to interconnect tubular sections  435 , 440  while allowing prosthesis  400  to be sufficiently flexible such that it can be navigated to the target body passageway. As will be apparent to those of skill in the art, leaf portion  420  is independently moveable with respect to proximal end  410  and distal end  415  of prosthesis  400  (in the illustrated embodiment, leaf portion  420  is independently moveable with respect to tubular sections  435 , 440 ). 
     FIG. 23 illustrates a two-dimensional representation of one embodiment of expandible prosthesis  400 . In the illustrated embodiment, blocking portion  425  comprises a series of generally longitudinal, meandering struts  426 , 427 , 428  independently connecting to tubular section  435  at one end and interconnected at the opposite end via a transverse strut  429 . 
     The porous structure created by struts  426 , 427 , 428 , 429  is covered with a material suitable to: (i) withstand expansion of prosthesis  400 , and (ii) block the opening  35  of aneurysm  30  after deployment. The nature of the material used for this purpose is not particularly restricted. Preferably, the material comprises Cardiothane 51™ (Kontron Instruments, Inc., Everett, Mass.), a medical grade polyurethane/silcone polymer which is known to be useful in intravascular devices (e.g., as a balloon material for intraaortic cardiac assist devices). Thus, a “bare” blocking portion  425  may be initially coated with a 5.7% weight:volume (w:v) solution of Cardiothane 51™ dissolved in an organic solvent (e.g., 2:1 tetrahydrofuran:1,4-dioxane). The initially coated blocking portion  425  may then be further covered with an 11.7% w:v solution of Cardiothane 51™ dissolved in the same solvent. When the polymer is dry, the struts of blocking portion are substantially embedded within the polyurethane-silicone cover. The covered blocking portion  425  may then be sterilized with ethylene-oxide. For more information about this approach, see “In Vivo Evaluation of Porous Versus Skinned Polyurethane-Polydimethylsiloxane Small Diameter Vascular Grafts” by Okoshi et al.,  ASAIO Transactions  1991; 37: M480-M481, the contents of which are hereby incorporated by reference. 
     FIG. 24 illustrates a two-dimensional representation of one embodiment of expandible prosthesis  400 . In the illustrated embodiment, blocking portion  425  comprises a tab  470  connected to tubular section  435  at a connection point  475 . As illustrated, a portion of tab  470  contains a series of tightly spaced microcuts  480 . The selection of dimension, number and disposition of microcuts  480  is within the purview of a person skilled in the art and is chosen to optimize flexibility of tab  470  while limiting porosity therethrough of bodily fluids. 
     Other variations and modifications of the specific embodiments described hereinabove which do not depart from the scope and spirit of the invention will be immediately apparent to those of skill in the art having this specification in hand. For example, while in various of the illustrated embodiments, the leaf portion is shown pointing toward the proximal end of the prosthesis during delivery, this is not essential and, in some cases, a reverse orientation may be preferred. Further, while in various of the illustrated embodiments, the leaf portion comprises a head and a neck, the presence of the neck is not essential in all cases. Still further, while in various of the illustrated embodiments, a pair of expandable, annular rings is shown, it is possible to construct the prothesis using a single expandable anchoring means (e.g., annular ring, etc.) or 3 or more expandable anchoring means (e.g., annular rings, etc.). Still further, while in various of the illustrated embodiments, the leaf portion is substantially elongate and disposed parallel to the longitudinal axis of the prosthesis, it is possible to dispose the leaf portion such that it is orthogonal to the longitudinal axis of the prosthesis. Still further, while in various of the illustrated embodiments, the expansible portion of the body comprises a pair of rings having a porous structure, it is possible to use rings having a non-porous structure by folding down the rings and maintaining them in this state using a removable mechanical restraint which, when removed, allows the rings to unfold into a deployed state (in this embodiments, the rings would be dimensioned to their final implanted diameter and then folded down—see for example, WO-A-95/26695, the contents of which are hereby incorporated by reference). Other modifications which do not deviated from the spirit and scope of the invention will be immediately apparent to those of skill in the art having the present specification in hand.