Stent placement and removal system

Placement and non-surgical removal of a ureteral stent is accomplished by suspending a ferromagnetic bead from an indwelling stent The bead is suspended by a flaccid tether that reduces the likelihood of patient irritation when a shortened stent is used. The bead, tether, and stent assembly are advanced into the patient as a unit via a conventional cystoscope. A magnet-tipped catheter is employed to engage the bead in the bladder and permit removal of the connected stent as the catheter is withdrawn.

TECHNICAL FIELD
 This invention relates to placement and removal of full-length or shortened
 ureteral stents, or stents in other hollow or tubular structures, which
 stents may be removed by means of a magnet.
 BACKGROUND OF THE INVENTION
 Ureteral stents are used to provide drainage of urine from the kidneys to
 the bladder. The stent is a flexible, tubular structure that is
 constructed of relatively inert material. The stent is perforated to have
 a plurality of small drainage holes along its length. Some stents are
 shaped to define "hooks" at either end. The hooks prevent migration of the
 tube from the kidney toward the bladder or from the bladder upwards.
 Normally, indwelling stents must be periodically removed or replaced.
 Conventional stent removal procedures are complex and may be painful,
 sometimes requiring general anesthesia.
 The presence of a stent within the lower ureter and within the bladder may
 cause considerable irritation to some patients. To alleviate this
 irritation, stents can be shortened. The stent is shortened at the distal
 (bladder) end. Thus, the distal end of the shortened stent resides in the
 ureter, remote from the bladder and the ureteral orifice. The ureteral
 orifice is the junction of the ureter and the bladder. A thin thread may
 be attached to the shortened stent to extend into the bladder and provide
 a means for later removing the stent. To remove the shortened stent, the
 thread must be endoscopically visualized, grasped, and withdrawn. Although
 this is a relatively simple procedure, it requires specialized instruments
 used by an urologist in a sterile setting. Here, too, general anesthesia
 is sometimes required.
 Procedures for non-surgical removal of magnetically-attractible objects
 from a body cavity or tube have been used in the past. For example, U.S.
 Pat. No. 4,790,809 to Kuntz discloses a specially configured stent that
 carries a magnetically attractive tip. The tip is fastened to the hooked,
 distal end of the stent, which end resides in the bladder.
 To remove the Kuntz stent, a catheter having a magnetized end is introduced
 into the bladder to attract and connect to the special tip of the stent.
 Apparently, the tip of the Kuntz stent may be caught by the magnet-tipped
 catheter in a manner that permits complete removal of the stent upon
 withdrawal of the catheter. Otherwise, Kuntz notes that the catheter and
 stent combination may be withdrawn just enough for the hooked end of the
 stent to be reached with a forceps or other grasping device, then
 completely removed. Apparently, Kuntz does not contemplate shortened-stent
 placement and removal.
 SUMMARY OF THE INVENTION
 The present system provides a stent assembly, system, and method for
 placement of ureteral stents, and for non-surgical removal of the stent
 assembly.
 As one aspect of the invention, a conventional stent is modified to have
 connected to it a ferromagnetic member. The ferromagnetic member is
 biocompatible and is in the form of an elongated bead and is connected to
 the distal end of the stent by a tether. This permits the ferromagnetic
 member to be disposed in the bladder, suspended from the stent while the
 stent is positioned in the ureter. The bead is inserted at the time of
 insertion of the stent via a standard cystoscope that includes a guide
 wire and pusher.
 The stent may be shortened to a length of choice prior to insertion, or
 left full-length. The shortened stent and tethered bead are inserted as a
 unit. The bead is shaped to temporarily penetrate the ureter as the bead
 is pushed with the shortened stent into the ureter to the desired position
 of the stent. The bead is provided with a mechanism that permits only the
 bead to be withdrawn from the ureter, pulled back into the bladder under
 visual control, once the shortened stent is properly positioned.
 If a full-length stent is used, the bead does not, even temporarily,
 penetrate the ureter.
 The stent assembly is readily removed by a non-surgical procedure that
 involves blind insertion of a magnet-tipped catheter into the bladder. The
 magnet engages the ferromagnetic bead, and the overall stent/tether/bead
 assembly is easily removed as the catheter is withdrawn.
 As another aspect of this invention, the tether is flaccid, thereby
 permitting the suspended bead to move relative to the indwelling stent.
 This arrangement minimizes patient irritation that might otherwise occur
 if the tether were somewhat rigid or resilient.

DESCRIPTION OF A PREFERRED EMBODIMENT
 The preferred embodiment of the bead component 10 of the present invention
 is shown enlarged in FIG. 1. FIG. 2 depicts the bead 10 and connected
 tether 16. As will be explained, the tethered bead is connected to the
 distal end of a conventional stent (full-length, or shortened) for the
 purpose of converting that stent into one that may be non-surgically
 removed using a magnet-tipped catheter.
 The bead 10 is, primarily, a ferromagnetic member. In this regard, the term
 "ferromagnetic" is meant to include the characteristic of substances
 comprised of iron, nickel, or cobalt and various alloys that are attracted
 to a magnet. Preferably, the bead 10 is stainless steel and may be coated
 with a smooth layer of, for example, polytetrafluoroethylene, which can be
 characterized as "biocompatible" in that it prevents reaction of the bead
 10 with urine. It is contemplated that the bead 10 may be a magnet.
 In the present embodiment, the bead is an elongated member, between 6 mm
 and 12 mm in length. The preferred shape of the bead 10 features a
 large-radius, proximal end taper 14. That is, about one-third of the
 length of the bead tapers from the full outside diameter of the bead
 (between 2.25 and 4.5 mm) to a minimum outside diameter of about 1.8 mm at
 the proximal end 32 of the bead. The outside diameter of the proximal end
 32 of the bead generally matches that of the distal end of the stent 20
 (FIG. 5).
 The distal end 34 of the bead 10 has a smaller-radius taper 15. As will
 become clear, the tapered shape of both ends of the bead facilitates
 movement of the bead through a cystoscope, and, in the case of a shortened
 stent, into and out of the ureter.
 As best shown in FIGS. 1 and 5, the bead 10 includes a central (i.e.,
 through its long axis) guide lumen 12. The guide lumen 12 allows a
 commonly used guide wire 22 to be passed through the bead, thereby
 enabling the bead to be later advanced up the guide wire 22 as the stent
 and bead 10 are positioned within the patient, typically under
 fluoroscopic control.
 As noted, the bead 10 is connected to the stent 20 by the tether 16. To
 this end, the bead 10 has, located near its midpoint, a pair of
 small-diameter openings 13. The openings 13 are spaced apart and extend
 through the bead in a direction generally perpendicular to the long axis
 of the bead. Alternatively the openings may be angulated and diverging in
 the direction toward the proximal end 32 of the bead. The tether 16 is
 threaded through both openings 13 to connect the tether to the bead 10.
 Alternatively, each free end of the tether is fixed, such as by crimping,
 to one of the openings. The tether portion of the tether that extends from
 the bead defines an endless loop that is connectable to the conventional,
 perforated stent, as described below.
 It is contemplated that a single transverse opening 13 in the bead would
 suffice for connecting the tether and bead. The tether would be passed
 through the single opening before being formed into the endless loop.
 Referring, momentarily, to FIG. 6b, that figure shows a full-length stent
 20 positioned within a ureter 52. The distal end 40 of the stent has
 attached to it a tether 16 that connects the stent to the bead 10 which is
 disposed in the bladder 38. In this embodiment, the stent 20 extends
 through the ureteral orifice 44.
 The tether 16 is made of a nylon or other biocompatible, thin, flexible,
 high-break-force line. The tether is flaccid in the sense that it lacks
 any significant resilience, and it readily yields to all but tensile
 force. As a result, the bead--once disposed in the bladder 38--is
 suspended from the distal end 40 of a stent and is not forced or urged
 against the wall of the bladder 38. This suspension of the bead,
 therefore, minimizes irritation of the bladder, which might otherwise be
 present if the bead were in some way urged into contact with the wall of
 the bladder.
 Even though FIG. 6b illustrates an indwelling stent 20 having a hook-shaped
 distal end 40 (The hook is intended to halt migration of the stent toward
 the kidney.), it is contemplated that no such hooked end is required. For
 instance, the stent 20 could be terminated with a straight end, such that
 the portion of the stent illustrated below the dashed line 46 in FIG. 6b
 would not be present. The bead 10, therefore, would be suspended by the
 tether from near that location 46 of the distal end of the stent. In this
 arrangement, the possibility of irritation attributable to a relatively
 large, hooked end of the stent would be eliminated.
 The bead 10 is generally free to rotate relative to the tether 16 to which
 it is connected. The tether is attached to the bead at a location
 generally aligned with the center of mass of the bead, but offset somewhat
 from the long axis of the bead. As a result, the bead tends to hang from
 the tether with its long axis oriented generally perpendicular to the
 length of the ureter, as shown in FIGS. 6b and 7c, thereby preventing the
 suspended bead from migrating into the ureteral orifice. Also, and
 irrespective of the orientation of the bead, the suspended bead 10 is
 sized so that it will not migrate into the ureter in the absence of a
 pushing force with the bead properly aligned with the ureter. Moreover, if
 the tether is made short enough, the bead thus prevents upward (toward the
 kidney) migration of the stent.
 In instances where a shortened stent 23 is employed (that is, a stent
 having a distal end 42 that resides in the ureter 52, away from the
 ureteral orifice 44--see FIG. 7c), the thin, flaccid tether 16 extends
 between the distal end 42 of the shortened stent 23, through the ureteral
 orifice 44, to the bead 10 that is within the bladder 38. Thus, the very
 thin, flaccid tether prevents irritation that would occur as a result of
 the presence of an indwelling stent passing through the ureteral orifice.
 Returning to FIGS. 1, 2, and 5, the bead 10 is also provided with a larger
 diameter passage 11 which allows a flexible line 17 to be threaded through
 the bead. Such a line 17 would be employed for withdrawing the bead from
 the ureter to locate the bead in the bladder after a shortened stent is in
 position. This is explained more below.
 As noted above, the system of the present invention may be used with any
 conventional ureteral stent, such as those designated "Bander Ureteral
 Diversion Stents" and manufactured by Cook Urological Incorporated, of
 Spencer, Ind. Such stents are flexible, tubular members that, in addition
 to a central lumen, include spaced apart perforations 21 (FIG. 5) that
 serve as drain holes. Described next is an elegantly simple technique for
 attaching the looped tether to a selected portion on the distal end of the
 stent.
 FIG. 3 shows an elongated instrument or needle 31 for attaching the tether
 16 and stent 20. The needle 31 is pointed but not sharp at its proximal
 end 27. The needle 31 also has a slot 28 near its proximal end, thus
 defining a hook at that end of the needle. The distal end of the needle is
 fastened to a handle 29.
 The needle is sized to pass its hooked end through a perforation 21 from
 outside the stent to inside of the central lumen of the stent, without
 damaging the stent. The end 27 of the needle is then protruded from the
 distal end of the stent. The tether 16 is moved into the slot 28, and the
 needle, while engaging the tether is retracted through the lumen and
 perforation so that a portion of the tether loop is exposed outside of the
 stent, emerging from the perforation. The proximal end of the stent is
 moved through this loop portion, which will now provide an assured
 connection of the bead 10 and tether 16 to a stent, as best seen in FIG.
 5.
 FIG. 5 shows an assemblage including a guide wire 22, a hollow pusher 19,
 the bead 10, and the stent 20 all being advanced as a unit through and
 from a cystoscope 50. FIG. 5 also shows a positioning line 17 threaded
 through the passage 11 in the bead 10 and then through the inner lumen of
 the pusher 19. This positioning line 17 extends from the bead to the
 outside of the cystoscope, exposed for grasping by the user. The bead 10
 is fastened to the stent 20 by the tether 16, which, as described above,
 has been threaded through the central lumen of the stent 20 and through
 the perforation 21 of the stent 20 then looped around the stent 20 at the
 level of the selected perforation 21 of the stent 20.
 FIG. 6a shows the initial stage of inserting a full-length stent 20 which
 has a bead 10 connected to its distal end. This stage positions the distal
 end of the stent 20 in the bladder 38 with the bead 10 well away from the
 ureteral orifice 44. Once the distal end of the stent 20 is in the bladder
 and the proximal end of the stent is in the kidney (not shown), the guide
 wire 22 and pusher 19 are removed. This allows the stent 20 to assume its
 hooked-end position, said to help prevent migration of the stent into the
 ureter (FIG. 6b). As noted, in this position, the bead 10 is suspended
 from the stent 20 by the tether 16.
 Although FIG. 5 shows the assembly with positioning line 17 in place, it
 will be appreciated that for the placement of full-length stents (FIGS. 6a
 and 6b) there is no need for the line, and it may be omitted.
 FIGS. 7a, 7b, and 7c show three stages of the insertion of a shortened
 stent 23. The distal end 42 of such a stent is ultimately positioned in
 the ureter 52. To accomplish this positioning, the bead 10 and the
 proximal end of the pusher 19 are pushed into the ureter 52 as shown in
 FIG. 7a. That is, the bead 10 completely or partially penetrates
 (proximal-end first) the ureter 52. The guide wire 22 is then withdrawn.
 The second stage of the positioning of the shortened-stent system, shown in
 FIG. 7b, comprises the removal of the pusher 19, followed by the bead 10.
 Preferably, the bead is removed by pulling on the positioning line 17
 (that is, the outer ends of the line that are exposed to the user) after,
 or simultaneously with removing the pusher 19. This withdraws the bead
 from the ureter, distal-end first. In this regard, the tether 16 is of a
 length such that there is sufficient slack to allow the withdrawal of the
 bead from the ureter to the bladder without pulling the stent 23 toward
 the bladder. Once the bead is withdrawn, the line 17 is removed from (slid
 through) the bead, leaving the bead 10 suspended by the tether 16 spaced
 from the ureteral orifice 44 and disposed within the bladder 38.
 Preferably, the passage 11 through which the positioning line 17 passes is
 located near the distal end and passes diametrically through (or close to
 diametrically through) that end of the bead. This arrangement is best to
 ensure that the bead is withdrawn from the ureter along a straight path to
 avoid damage to the wall of the ureter.
 FIG. 4 depicts a component of the system that enables non-surgical removal
 (that is, no endoscopy is required) of both a full-length and shortened
 tent. The component, designated a retrieval catheter 24 comprises a
 conventional Foley catheter that is modified to serve as the retrieval
 catheter 24. Specifically, the catheter includes a magnet 26 mounted at
 its proximal tip. The magnet 26 is part of an assembly which consists of a
 grooved end 25 that is inserted into the catheter and acts as a barb to
 retain the magnet affixed to the catheter 24. The magnetic material of the
 retrieval magnet 26 may be covered with a biocompatible inert layer 30.
 The magnet-tipped end of the retrieval catheter is inserted, through the
 urethra and into the bladder, whence it magnetically engages the suspended
 ferromagnetic bead 10. Then, the withdrawal of the catheter 24 brings with
 it the bead and tether-connected stent. Preferably, the magnet 26 is
 rounded to avoid injury to the patient.
 As the magnet 26 approaches the bead 10, the magnetic flux acting on the
 bead 10 should cause the bead to rotate relative to the tether from its
 normal, suspended position, so that one of the ends of the bead swings
 about 90 degrees into contact with the magnet 26. As a result, the bead
 will be oriented generally coaxially with the end of the retrieval
 catheter 24 that carries the magnet 26. If this orientation is not
 attained in the bladder, as the retrieval catheter magnet and bead enter
 the urethra passage, the urethra will assure the axial alignment of the
 assembly. This orientation is desired for sure and comfortable removal of
 the bead through the urethra. It will be appreciated that this rotation of
 the bead will be assured where the bead is magnetized, and one of its ends
 has a polarity opposite that of the catheter magnet 26.
 While the present invention has been described in terms of a preferred
 embodiment, it will be appreciated by one of ordinary skill that the
 spirit and scope of the invention is not limited to those embodiments. For
 example, the stent system may be universal in the sense that it may be
 employed in other cavities, etc. of the human anatomy.
 Also, the indwelling bead could be made as a magnet, with the retrieval
 catheter tipped with ferromagnetic material. Although a rare-earth magnet
 is preferred, other types, including electromagnets could be employed with
 the retrieval catheter. In addition, the bead may be of a more ball shape
 rather than the described elongated bead.
 Thus the invention is considered to extend to the various modifications and
 equivalents as defined in the appended claims.