Abstract:
A ureteral drainage stent is designed to be placed in a patient&#39;s ureter and extend into a patient&#39;s bladder. An elongated tubular segment includes a distal region for placement in the renal cavity, and a proximal region for placement in a urinary bladder. A central lumen connects at least one opening in the distal region to at least one opening in the proximal region. The elongated segment is constructed such that the wall surrounding the lumen is thinner in the proximal region than in the distal region. The thin-walled portion of the elongated segment extends along at least part of the ureter, across the ureteral vesicle junction, and from there into the bladder.

Description:
TECHNICAL FIELD  
         [0001]    This invention generally relates to medical devices for drainage of fluids, and more specifically to ureteral stents.  
         BACKGROUND INFORMATION  
         [0002]    Ureteral stents are used to assist urinary drainage from the kidney to the bladder in patients with ureteral obstruction or injury, or to protect the integrity of the ureter in a variety of surgical manipulations. Stents may be used to treat or avoid ureter obstructions (such as ureteral stones or ureteral tumors) which disrupt the flow of urine from the kidneys to the bladder. Serious obstructions may cause urine to back up into the kidneys, threatening renal function. Ureteral stents may also be used after endoscopic inspection of the ureter.  
           [0003]    Ureteral stents typically are tubular in shape, terminating in two opposing ends: a kidney distal end and a bladder proximal end. One or both of the ends may be coiled in a pigtail or J-shape to prevent the upward and/or downward migration of the stent due, for example, to physiological movements. A kidney end coil is designed to retain the stent within the renal pelvis and to prevent stent migration down the ureter. The bladder end coil sits in the bladder and is designed to prevent stent migration upward toward the kidney. The bladder coil is also used to aid in retrieval and removal of the stent.  
         SUMMARY OF THE INVENTION  
         [0004]    Ureteral stents, particularly the portion positioned in the ureter near the bladder and inside the bladder, may produce adverse effects including blood in the urine, a continual urge to urinate, strangury, and flank pain accompanying reflux of urine up the stent (e.g., when voiding) as pressure within the bladder is transmitted to the kidney. In short, stents may cause or contribute to significant patient discomfort and serious medical problems.  
           [0005]    The present invention concerns a ureteral stent that avoids patient discomfort and urine reflux upward toward the kidney. Patient discomfort induced by the use of a foreign body may be decreased with devices that are as small and flexible as possible in the lower (bladder) end of the ureter and in the bladder itself. Rather than rely on a tubular structure of a substantial set thickness for the entire length of the ureteral stent, the invention concerns a stent with a thin flexible wall at the proximal region of the stent. When the stent is placed within the urinary system of a patient, the proximal region of the stent generally is located in or near the end of the ureter at the junction of the ureter and the urinary bladder and also in the bladder itself, and the distal region generally is located in the kidney and in or near the other end of the ureter at the junction of the ureter and the kidney. In general, the thin-walled proximal region of the stent is sized and configured to extend along at least part of the ureter near the bladder, and may cross the ureteral vesicle junction, and into the bladder. The ureteral vesicle junction is a particularly sensitive region of the ureter and is the source of much of the discomfort resulting from the presence of an installed stent. It also is possible, and in some cases desirable, to use a stent with a thin wall throughout substantially all of its length, from near the kidney retention structure to the proximal region.  
           [0006]    The stent wall of the middle and distal regions may be constructed of a material of greater thickness than the proximal region in order to resist the pressure from the adjacent tissue that would collapse the ureter if not for the presence of the stent. The middle region is the elongated region of the stent between the distal region and a transition zone found near the proximal region. Towards the proximal region of the stent, the inner diameter of the wall that exists in the middle and distal regions increases, resulting in a comparatively thinner wall in the proximal region of the stent, while the outer diameter of the stent is constant or substantially constant over the entire length of the stent. The thin wall region can be positioned at or near the ureteral vesicle junction. The thin wall construction at the proximal region of the stent produces a softer and more flexible segment of the stent which decreases the irritation to the surrounding tissues while allowing for normal urine drainage and resistance to urine reflux.  
           [0007]    In one aspect, the invention relates to a medical device for assisting the drainage of fluid from a body cavity. The medical device includes an elongated segment extending from a distal region through a transition zone to a proximal region, the segment having a substantially constant outer diameter and an inner wall. The inner wall defines a lumen having an inner diameter in the proximal region that is greater than the inner diameter in the distal region. The transition zone may extend through a middle segment of the stent or all the way from a middle segment to the proximal end. The variation of the inner diameter in the transition zone may be linear or non-linear, steep or smooth, continuous or combinations thereof. The variation of the inner diameter may be quantic resulting in a step change. In one embodiment, the medical device is a stent. In another embodiment the medical device is a ureteral stent.  
           [0008]    In some embodiments, the transition zone has no longitudinal length thus forming a step in the inner diameter between the proximal and distal regions. The step forms a surface for contacting a pusher during implantation of the medical device in the body cavity. In other embodiments, the segment includes a pliable proximal region.  
           [0009]    In yet other embodiments the medical device further includes at least one member extending through at least some of the lumen to the proximal region. The member may include a flexible material. The member may include a thread. In other embodiments the member is secured to an inner wall. The member may also include a substantially noncompressible material. In some embodiments, the member includes a loop.  
           [0010]    In yet another embodiment, the elongated segment includes a retention structure in the distal region. The retention structure may be kink resistant. The retention structure may include a coil.  
           [0011]    The device may further include a second segment including an exterior wall contacting at least a portion of the inner wall of the elongated segment, and further including an inner wall defining a lumen coaxial with the lumen of the elongated segment. The second segment may include a surface disposed at a proximal region for contacting a pusher during implantation of the medical device in the body cavity. In one embodiment, the exterior wall of the second tubular segment provides an interference fit with the inner wall of the first segment. In another embodiment, the transition zone includes varying inner diameters of the inner wall between the distal region and the proximal region.  
           [0012]    In another embodiment, the medical device includes at least one member extending from the second segment. In yet another embodiment, the member is secured to the elongated segment. In another embodiment, the member includes a flexible material. The member may also include a substantially noncompressible material. The member may include a thread. In some embodiments, the member includes a loop.  
           [0013]    In still another aspect, the invention relates to a medical device for assisting the drainage of fluid from a body cavity, the device including an elongated segment having an annular wall defining a lumen, the lumen extending from a distal opening to a proximal opening. The annular wall having a thickness near the distal opening greater than near the proximal opening, wherein the elongated segment is kink resistant near the distal opening and pliable near the proximal opening.  
           [0014]    In one embodiment, the medical device includes a stent. The medical device may also include a ureteral stent. In another embodiment, the medical device includes at least one member extending from and attached to the elongated segment. In yet another embodiment, the member includes a thread. In yet another embodiment, the medical device may further include a second segment including an exterior wall contacting at least a portion of the inner wall of the elongated segment, and further including an inner wall defining a lumen coaxial with the lumen of the elongated segment.  
           [0015]    In another aspect, the invention relates to a method for treatment of blockage of urine flow from a kidney to a urinary bladder. The method includes providing a medical device and inserting the device in a ureter for assisting the drainage of fluid from a body cavity. The medical device includes an elongated segment extending from a distal region through a transition zone to a proximal region, the segment having a constant outer diameter and an inner wall defining a lumen having an inner diameter in the proximal region that is greater than the inner diameter in the distal region. In an embodiment, the method further includes positioning the distal region of the medical device near a renal pelvis and positioning the proximal region of the medical device in a urinary bladder. In an embodiment, the method includes positioning the transition zone of the stent at least partly upstream of the ureteral junction.  
           [0016]    In another embodiment, the method further includes a second segment including an exterior wall contacting at least a portion of the inner wall of the elongated segment, and further comprising an inner wall defining a lumen coaxial with the lumen of the elongated segment.  
           [0017]    In another aspect, the invention relates to a method for treatment of blockage of urine flow from a kidney to a urinary bladder. The method includes providing a medical device and inserting the device in a ureter for assisting the drainage of fluid from a body cavity. The medical device includes an elongated segment having an annular wall defining a lumen, the lumen extending from a distal opening to a proximal opening. The annular wall includes a thickness near the distal opening greater than near the proximal opening, wherein the elongated segment is kink resistant near the distal opening and pliable near the proximal opening. In an embodiment, the method further includes positioning the distal region of the medical device near a renal pelvis and positioning the proximal region of the medical device in a urinary bladder. In an embodiment, the method includes positioning the transition zone of the stent at least partly upstream of the ureteral junction.  
           [0018]    The positioning of a stent may include the use of a pusher. In one embodiment, the distal end of the pusher contacts a surface of the stent in the transition zone. In another embodiment, the distal end of the pusher is tapered and directly abuts the stent in the transition zone. In yet another embodiment, the pusher contacts a surface on a second segment disposed within the lumen of the stent near the transition zone.  
           [0019]    The foregoing and other aspects, embodiments, features, and advantages of the invention will become apparent from the following description, figures, and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis generally being placed upon illustrating the principles of the invention.  
         [0021]    FIGS.  1 A-B depict an embodiment of a medical device of the invention, with FIG. 1A showing the device positioned in a ureter with a distal region in a kidney and a proximal region in a ureteral vesical junction and bladder, and FIG. 1B showing the device outside of the body.  
         [0022]    FIGS.  2 A-C depict various embodiments of the proximal region of the medical device of FIG. 1 in longitudinal cross-section, with FIG. 2A showing the proximal region positioned in the ureter and urinary bladder, and FIGS. 2B and 2C showing this region outside of the body of a patient.  
         [0023]    [0023]FIG. 3 depicts another embodiment of a proximal region of a medical device of the invention in longitudinal cross-section positioned in the ureter and urinary bladder.  
         [0024]    [0024]FIG. 4 depicts yet another embodiment of a proximal region of a medical device of the invention in longitudinal cross-section positioned in the ureter and urinary bladder.  
         [0025]    [0025]FIG. 5 depicts still another embodiment of a proximal region of a medical device of the invention in longitudinal cross-section positioned in the ureter and urinary bladder.  
         [0026]    [0026]FIG. 6 depicts yet still another embodiment of a proximal region of a medical device of the invention in longitudinal cross-section positioned in the ureter and urinary bladder.  
         [0027]    FIGS.  7 A-D depict four examples of a transverse cross-sectional view of the proximal region of a medical device of the invention, without tail members.  
         [0028]    FIGS.  7 E-H depict four examples of a transverse cross-sectional view of the proximal region of a medical device of the invention, with tail members.  
         [0029]    FIGS.  8 A-F depict various embodiments of a distal end of a pusher, each contacting a landing within a transition zone of a stent according to the invention, as occurs during installation of the stent.  
     
    
     DESCRIPTION  
       [0030]    This invention generally concerns a drainage device that, when positioned within a body cavity of a mammal, significantly reduces discomfort to the patient such as a ureteral stent positioned in the ureter of a human. A ureteral stent assists in the flow of urine from the kidneys to the urinary bladder. The structure of the proximal region of the stent according to this invention provides an increase in comfort for the patient. The region known as the ureteral vesical junction is a small area of the ureter that is located immediately prior to the ureter joining the urinary bladder. The ureteral vesical junction has substantially greater sensitivity relative to other regions of the ureter wall and kidneys and is a major source of patient discomfort when in contact with indwelling ureteral stents.  
         [0031]    The wall thickness at the proximal region of a stent of the invention is reduced for the purpose of making the region more pliable, flexible, and supple to adapt or partially yield to the closing or narrowing of the ureter in the junction during constriction. A pliable wall is such that an annular wall of a stent will collapse, bend, and fold upon itself upon pressure exerted by body tissue within a cavity, peristaltic motion or sphincter contraction, for example. A suitable pliable wall may be constructed from biocompatible plastics or polymers including PTFE, silicone polyurethane, polyurethane plastics, polyethylene plastics, and thermoplastics and have a wall thickness of 0.5/1000 to 15/1000 inch, for example. A pliable, flexible, and supple proximal region will chafe and irritate the ureteral vesical junction to a lesser degree thus increasing the comfort level of the patient. The thin-walled proximal region of the stent facilitates normal drainage of urine through the stent while maintaining resistance to urine reflux upward toward the kidney. Typically, the thin-walled construction of the stent is sized and configured with a length sufficient to extend at least along the ureteral vesical junction and into the urinary bladder. However, the thin-walled construction may also be sized and configured with a length sufficient to extend the whole length of the ureter. A suitable length of the thin wall may be selected as small as 0.5 inch and as long as 10 inches.  
         [0032]    The stent wall in the distal region is sufficiently thick to be kink-resistant and maintain patency of the vessel despite constriction or removing of the vessel due to enlargement of tissue surrounding it or peristaltic motions. A kink resistant wall is such that the annular wall of the stent does not collapse upon itself upon radial or lateral pressure of the surrounding body tissue when positioned to drain a body cavity of a mammal or upon longitudinal pressure exerted during insertion of the stent into the body cavity. Kink resistant properties may be imparted to a stent by varying the thickness of the wall of the stent depending on the softness or sturdiness of the material used to manufacture the stent—for example, a wall thickness of {fraction (1/32)} to {fraction (1/16)} inch may be used with materials such as silicone, PTFE, polyurethane plastics, and polyethylene plastics.  
         [0033]    The stent of this invention may include an elongated segment that has an annular wall with a substantially constant outer diameter and an inner diameter that defines a lumen extending from a distal region, through a middle region and transition zone to a proximal region. The lumen has a proximal inner diameter greater than a distal inner diameter, and varying inner diameters in the transition zone that transition from the proximal inner diameter to the distal inner diameter. The wall near the distal region is kink resistant and the wall near the proximal region is pliable. The cross-sectional geometry of the stent may be any shape that allows the flow of liquid through the segment including round, oblong, elliptical, hexagonal, D-shaped, crescent-shaped, square, for example. The stent may be constructed from biocompatible plastics or polymers including PTFE, silicone polyurethane, polyurethane plastics, polyethylene plastics, and thermoplastics, for example. Construction of the stent may be performed by injection or extrusion molding, for example.  
         [0034]    The stent of the invention may further include one or more members, elongated thread-like structures attached at one or both ends to the stent. The members may include threads, fibers, tubes, strings, for example. Members may be of varied lengths and thickness. Members may have a thickness between 0.2 and 1.0 mm, for example. Members may be constructed from a variety of materials including, biocompatible plastic, natural fibers, glass fibers, or rubber, for example. Members assist in drainage by functioning as a fluid transport surface and by creating interstitial spaces between members and between members and the inner wall of the stent for urine to flow through. Members may be incorporated into the stent during the molding process or extrusion process. Alternatively, the member may be incorporated into the stent after the first or second segments have been constructed. Members may also be embedded in the wall of the proximal region during the molding process or extrusion process. Members embedded in the wall of the proximal region have sufficient tensile strength to allow their use as a handle to remove the stent from the body.  
         [0035]    The stent may further include an extraction thread that may be embedded in the wall of the proximal region. The extraction thread serves to reinforce and increase the resistance to tearing of the thin wall in the region. The extraction thread may or may not extend beyond the proximal end of the stent. An extraction thread that does not extend beyond the proximal end of the stent serves to strengthen the thin wall of the stent at the proximal region. An extraction thread that does extend beyond the proximal end of the stent further functions as a graspable structure of the stent for removal of the stent from the ureter.  
         [0036]    In FIG. 1A, a ureteral stent  100  includes an elongated segment  101  that has a constant or at least a substantially constant outer diameter, and that has an inner diameter that defines a lumen extending from a distal region  128  through a middle region  102  and transition zone  112  to a proximal region  104 . The kink resistant distal region  128  forms a coil or other retention structure or shape that functions as an anchor to retain the stent within the renal pelvis and calyx  130  of the kidney and to prevent migration of the stent up or down the ureter  118 . Alternatively, other geometry may be suitably be used as anchors. The stent wall in the proximal region  104  of stent  100  is substantially thinner than the stent wall of the middle region  102  or the distal region  128 . The proximal region  104  is depicted extending from upstream boundary of the ureteral vesicle junction  120  to the inside the urinary bladder  124 . The thinner wall of the proximal region  104  results from a greater inner diameter than the inner diameter present in the middle region  102 . As a result, the wall in the proximal region  104  of the stent is thinner and is soft, floppy, and pliable compared to the middle region  102 . The soft, floppy, and pliable characteristics of the proximal region  104  of the stent  100  substantially reduce the irritation of the ureteral vesical junction  120 . A thin wall at the proximal region may alternatively be formed by a lesser outer diameter at the proximal region  104  than at the middle  102  or distal region  128 . Alternatively, a combination of a lesser outer diameter and a greater inner diameter at the proximal region  104  than at the middle  102  or distal region  128  will also form a thin wall at the proximal region  104 . FIG. 1B details the boundaries of the proximal region  104 , middle region  102 , and distal region  128 . The elongated segment  101  is also shown.  
         [0037]    FIGS.  2  A-C, depict cross sections of various embodiments of the transition zone at the proximal region of the ureteral stent  100 . In FIG. 2A, the transition zone  112  has no longitudinal length and forms a step that serves as a landing for a pusher. The transition zone  112  can also be a length greater than zero and still function as a landing. The transition zone  112  may also be a short region with a steep gradient in inner diameter (FIG. 2B). Alternatively, the transition zone  112  may extend into the proximal region  104  with a low rate increase in inner diameter (FIG. 2C); the rate of increase of the inner diameter may be linear as in FIG. 2B or non-linear following a curve as in FIG. 2C for example. The transition zone  112  may extend entirely along the proximal region  104 . Optionally, the stent  100  may also include an embedded extraction thread  126  in the wall of the proximal region  104 . An extraction thread  127  may also extend beyond the end of the proximal region  104 . The extraction thread  127  may function as a structure suited for grasping during the removal of the stent  100  from the body.  
         [0038]    Referring to FIG. 3, which depicts a cross-sectional view of the proximal region and a middle region of a stent of the invention. The stent  100  may further include a second segment  106  disposed near the transition zone  112 . The inner wall  108  of the second segment  106  defines a lumen which is coaxial with the lumen of the stent  100 . The second segment  106  is fixed in position in the inner of the stent  100 . The second segment  106  may be fixed in position by an interference fit with, or by gluing or bonding, onto the inner wall of the stent, for example. The proximal end  110  of the second segment  106  serves as a landing for a pusher used to insert the stent  100  into the patient. The stent  100  may also include at least one extraction thread  126  embedded either in the wall of the proximal region  104 , or at least partly in the transition zone  112  or middle region  102 . The extraction thread  126  serves to reinforce the wall of the stent in the proximal region  104  by providing an embedded structural support of greater strength than the thin wall of the proximal region  104  provides. The purpose of the extraction thread is to prevent the thin wall of the proximal region  104  from tearing during the grasping of the proximal region  104  for the purpose of removing the stent. It also may be used to grasp onto and remove the stent  100  from the patient. The extraction thread  126  should be of sufficient tensile strength to serve as the handle by which the stent  100  is grabbed and removed. An extraction thread  127  may extend beyond the end of the proximal region  104 . The extraction thread  127  may additionally serve as a graspable structure during the removal of the stent  100  from the ureter  118 .  
         [0039]    Referring to FIG. 4, which shows the proximal region of a stent according to the invention the ureteral stent  100  may further include at least one member  114  that is connected to the second segment  106 . A member  114  may comprise a thread, fiber, or filament. In this embodiment, both ends of each member  114  are connected to the proximal end  110  of second segment  106  such that the members form a loop. Alternatively, one or both ends of the members may be secured in the inner wall of the stent  100  or between the inner wall of the stent  100  and the exterior wall of the second segment  106 . Members  114  may assist in the drainage of urine through the proximal region of the ureteral stent  100  by creating interstitial spaces between the members  114  themselves, the surrounding tissue, or stent wall  104  through which urine may pass. The member  114  may form a loop extending beyond the proximal end of the stent. The stent  100  may further include an extraction loop  116  that loops around at least one looped member  114  and is used to remove the stent  100  from the patient. The extraction loop  116  should also be of sufficient tensile strength and length to serve as the handle by which the stent  100  is grabbed and removed.  
         [0040]    Referring to FIG. 5, which shows a cross sectional view of the proximal region of a stent according to the invention, the ureteral stent  100  may also further include at least one member  114  that is connected to the inner wall of the middle region  102 . Alternatively, at least one member  114  may connect to the distal region  128  (not shown). The attachment of the member  114  may require that the member pass through the lumen of the middle region  102  and/or distal region  128  of the stent  100 . The member  114  or members may assist in maintaining interstitial spaces within the lumen and maintain drainage should the stent  100  be compressed by peristaltic motion, for example. Attachment of the members  114  to the middle  102  or distal region of the stent  100  prevents the direct interference of the members  114  with the step  112  that serves as the landing for the pusher during insertion of the stent. The stent  100  may further include an extraction loop  116  that loops around the member  114 .  
         [0041]    Referring to FIG. 6, which shows a cross-sectional view of the proximal region of a stent according to the invention, the stent  100  includes a member  114  that is attached to the transition zone  112 . The transition zone  112  is depicted having essentially no longitudinal length, thus forming a step in the inner diameter between the proximal region  104  and the middle region  102 . The position of attachment of the member  114  to the landing should be configured such that, when inserting for positioning the stent in the ureter using a pusher, the pusher does not damage the member by compressing or bending the member  114  at its attachment site on the landing. Alternatively, the member may extend from the outside wall of the proximal region  104  or transition zone  112 .  
         [0042]    With cross-sectional views of the proximal region  104  of the stent, FIGS.  7 A-H depict four examples of the many configurations that the wall of the proximal region  104  can fold into while the stent  100  is positioned in the body with (FIG. 7E-H) and without (FIG. 7A-D) members  114 . FIGS.  7 E-H illustrate how the members  114  assist in forming interstitial spaces  136  when the stent wall  104  becomes compressed. With members  114  (FIGS.  7 E-H), the lumen is less susceptible to being compressed and collapsed to a point that hinders or blocks the flow of urine.  
         [0043]    The stent of the invention may be used to treat a blockage of fluid flow between body cavities, for example from a kidney to the urinary bladder. The treatment of urine blockage within the kidney or ureter may be provided by inserting a ureteral stent according to the invention over a guide wire with a pusher through the urethra and urinary bladder to the final position in the ureter. The guide wire or a cannula may be used to temporarily straighten the retention structure in the distal region. The distal region is constructed from material that reforms its structure after having its shape distorted. This property of the material comprising the distal region allows for the retention structure at the distal region to be straightened during insertion of the stent into the body and still allowing the retention structure to reform into its original shape. The stent can also be inserted into position by use of an endoscope, ureteroscope, and a cytoscope, for example. Once the stent is located in the ureter it must be positioned so that the distal region is properly seated in the renal pelvis and the proximal end is located in the urinary bladder. Proper placement of the stent should also position the proximal thin-wall region over the ureteral vesical junction thus relieving irritation to this region and increasing patient comfort.  
         [0044]    FIGS.  8 A-F depict various embodiments of the proximal region of a stent according to the invention and the distal region of a pusher  132  contacting either the landing of the stent located at the transition zone  112  (FIGS.  8 A-D) or the proximal end  110  of the second segment  106  (FIGS.  8  E-F) as occurs during installation of the stent  100 . The pusher  132  abuts and applies a force against the landing on the stent  100  to push the stent into the body of the patient during the installation of the stent  100 . The distal end of the pusher  132  is adapted to the structure of the landing so that the force applied to the pusher  132  can be effectively transferred to the stent  100  so that installation can occur. In some instance the distal end  134  of the pusher may also extend slightly within the narrower lumen of the stent beyond the transition zone (FIGS. 8B and C) or the lumen of the second segment (FIG. 8F).  
         [0045]    A guidewire  136  (FIGS. 8A and E) may function to assist in the installation of the stent. The guidewire  136  is inserted into the body, travelling through the urinary bladder and ureter until reaching the renal pelvis. Once the guidewire  136  is in the body, the stent  100  (FIGS. 8A and E) is inserted into the body by inserting the proximal end of the guidewire  136  into the lumen of the distal end of the stent  100  and by moving the stent  100  along the length of the guidewire  136 , by the use of a pusher  132  (FIGS. 8A and E). The pusher  132  includes a lumen that is configured to accept a guidewire  136 .  
         [0046]    Having thus described certain embodiments of the present invention, various alterations, modifications, and improvements will be apparent to those of ordinary skill. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description of embodiments of the invention is not intended to be limiting.