Esophageal stent

Abstract: A device for fixation in a body lumen comprising a tubular stent (90) of open weave construction (98, 100) which can be compressed to facilitate delivery to a treatment site within the body lumen; and a continuous elastomeric film (92) formed axially along at least one-third of the axial length of the stent (90), a portion of the open weave construction (98, 100) of the stent (90) being substantially free of continuous film so as to provide a fixation region of the stent for fixing the stent within the body of the lumen by radial expansion into surface engagement with a tissue wall segment defining the body lumen.

Description: The present invention derives as a divisional from EP 9 390 7215.3 (EP-A-0 639 958). The present invention relates to body implantable treatment devices, and more particularly to stents and other prostheses intended for fixation in body lumens especially including the esophagus. Carcinomas in the esophagus lead to progressive dysphagia, i.e. difficulty in swallowing, and the inability to swallow liquids in the most severe cases. While surgical removal is sometimes effective, the majority of patients have tumors that can not be surgically removed. Repeated dilations of the esophagus provide only temporary relief. Difficult or refractory cases often are treated by intubation using rigid plastic prostheses, or laser therapy with an Nd:YAG laser. These techniques, while often effective, have disadvantages. Rigid plastic protheses are large, for example having a diameter of 10-12 mm and larger (25-29 mm) outer end flanges. Placement of rigid plastic stents is traumatic, and too frequently causes perforation of the esophageal wall. These protheses further are subject to migration, obstruction with food or tumor ingrowth, and late pressure necrosis. Laser therapy is expensive, typically requiring several treatment sessions. Tumor recurrence is frequent, in the range of 30-40 percent. Submucosal tumors, and certain pulmonary arid breast tumors causing dysphagia by esophageal compression, can not be treated by laser therapy. The search for a more suitable prosthesis has lead to experiments with Gianturco stents, also known as Z-stents. U.S. Patent No. 4,800,882 (Gianturco) describes such a device employed as an endovascular stent. Such stents for the esophagus have been constructed of 0.018 inch (.45 mm) stainless steel wire, and provided with a silicone cover to inhibit tumor ingrowth. It was found necessary, however, to provide a distal silicone bumper to prevent trauma to the esophageal mucosa. Self-expanding mesh stents also have been considered for use as esophageal prostheses. U.S. Patent No. 4,655,771 (Wallsten) discloses a mesh stent as a flexible tubular braided structure formed of helically wound thread elements. Mesh stents appear unlikely to lead to pressure necrosis of the esophageal wall. With its inherent pliability the mesh stent, as compared to a rigid plastic stent, is insertable with much less trauma to the patient. Further, the stent can mold itself to and firmly fix itself against the esophageal wall, to resist migration. However, the stent is subject to tumor ingrowth because of the spaces between adjacent filaments. A further difficulty with self-expanding stents, concerns their accurate placement and deployment. Typically a tube surrounds the self-expanding stent and radially compresses the stent into a reduced-radius delivery configuration. With the stent positioned at a treatment site, the outer tube is axially withdrawn, permitting the stent to radially self-expand. However, the larger size of an esophageal stent (as compared to biliary and vascular applications, for example) gives rise to substantial friction at the stent/outer tubing interface. As a result, it is difficult to precisely maintain the position of the stent during deployment, and practically impossible to retract the stent after partial deployment. Copending application EP-A-0 639 958 describes a stent delivery device including exterior tubing surrounding the stent and movable axially to release the stent for radial self-expansion without a tendency in the stent to follow the axial movement of the exterior tubing. Copending application EP-A-0 639 958 further describes a stent deployment device capable of retracting a radially self-expanding stent for repositioning of the stent, even though the stent has been partially deployed and is radially expanded over the majority of its axial length. Copending application EP-A-0 639 958 still further describes a device for delivering and deploying a prostheses to a treatment site within a body lumen, with means for dilating the body lumen at the treatment site prior to stent deployment. The object of the present invention is to provide a radially self-expanding stent including a freely radially self-expanding fixation region in combination with a barrier region to inhibit tumor ingrowth. Yet another object is to provide an esophageal prostheses deployable with reduced trauma to the patient, having more resistance to migration, and providing a barrier to tumor ingrowth as effective as conventional rigid plastic prostheses. WO 92/06734 describes a radially expandable stent that holds a passageway enlarged by placing the stent into a lumen. The stent comprises a cylindrical frame formed by a plurality of unit structures; said unit structures being formed into a closed zig-zag configuration including an endless series of straight sections joined by bends and arranged face-to-face into a shape, together with a mesh which is wrapped around the frame. The mesh may be coated with silicon rubber. GB-A-1 205 743 describes a surgical dilator as specified in the preamble of claim 1 comprising a hollow tubular member, the wall of which is provided by a tubular metal core of lattice form and a continuous layer of resilient material, the elements making up the lattice defining diamond shapes in the unstressed condition of the dilator, the dilator being such that when the dilator is subjected to an axial tensile force, the wall will be caused to contract diametrically and extent axially and will return substantially to its normal shape of its own accord when the force is removed. The dilator may be coated with a resilient layer. EP-A-0 667 132 (published after the priority date of the present application) describes a graft for use in a body passage way. The graft comprises an elongate tube formed of tubular members alined with each other. The tubular members are embedded within a layer of a deformable and expandable plastic material. The present invention provides a device for fixation in a body lumen as specified in claim 1. The device includes a tubular stent of open weave construction having a predetermined normal configuration. The stent is radially compressible to a reduced-radius configuration to facilitate an axial insertion of the stent into a body lumen for delivery to a treatment site within the body lumen. A continuous film is formed axially along the stent and circumscribes the stent over a barrier region of the stent. The continuous film substantially prevents growth of tissue through the stent along the barrier region. A portion of the stent is substantially free of the continuous film to provide a fixation region of the stent for positively fixing the stent within the body lumen at the treatment site. Fixation is achieved by radial expansion of the stent into a surface engagement with a tissue wall segment defining the body lumen. The stent comprises a mesh formed of braided helical strands. The fixation region comprises a proximal cuff and a distal cuff, with the barrier region being a medial sleeve of the stent positioned between the cuffs. Also, the barrier region has a diameter less than the fixation region diameter when the stent is in its normal or relaxed configuration. A preferred material for the film is silicone. When properly controlled as to thickness, the silicone film provides a gradual self-expansion. More particularly, while the fixation region self-expands virtually instantaneously upon release of the stent, the medial barrier region, upon encountering a tumor or other striction, can take up to 24 hours to achieve a substantially complete radial self-expansion against the tumor. This feature is particularly advantageous in connection with treating esophageal strictures, where tissue at the stricture may be severely weakened, and where normal convulsions of the esophagus tend to cause stent migration. More particularly, the rapidly expanding fixation regions contact normal esophageal tissue on either side of a stricture, and are sufficiently pliable to adjust to esophageal convulsions. Meanwhile, the barrier region of the stent experiences a gradual radial expansion, thus causing minimal disruption to tissue along the stricture. IN THE DRAWINGS For a further appreciation of the above and other features and advantages, reference is made to the following detailed description and to the drawings, in which: Figure 1 is a side elevation of a simple stent in a relaxed configuration not covered by the present invention but representing the basic stent structure of the device of the present invention. Figure 2 is a schematic view of an esophageal prosthesis constructed in accordance with the present invention; Figures 3 and 4 illustrate alternative braid angle configurations for self-expanding prostheses; Figure 5 is a side elevational showing a mandrel used in forming the prosthesis of Figure 11; Figure 6 schematically illustrates the prostheses of Figure 2 in an esophagus, a short time after its deployment; Figure 7 schematically illustrates the prosthesis one day after its deployment; and Figure 8 illustrates an alternative prostheses constructed according to the present invention, and deployed in an esophagus, with a distal end of the prostheses protruding into the stomach. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Stent 66 in a normal or relaxed configuration is shown schematically in Figure 1. More particularly, a medial region 70 of the stent assumes a diameter of about 20 mm, and opposite end regions 72 and 74 of the stent assume a diameter of about 30 mm. Deployment of stent 66 within the esophagus is considered appropriate when a tumor, lesion or other stricture has constricted the esophageal passageway to a diameter less than about 15 mm. This represents a severe constriction in light of the normal passageway diameter of about 22 mm. While stent 66 of figure 1 is satisfactory in many respects, it is unsuitable for treatment of certain cancerous tissue in the esophagus. Such tissue is not as strong as healthy esophageal tissue, and thus is subject to rupture or other damage from an excessively rapid and forceful expansion of a conventional open weave stent. The stent is subject to tumor ingrowth due to its open weave construction. Further, points or edges at the opposite ends of the stent may perforate the esophageal wall. A prostheses or stent 90, shown in Figure 2, is constructed to address all of these concerns. Like stent 66, stent 90 is of mesh or open weave construction, comprised of multiple braided and helically wound strands. Stent 90 has a medial sleeve or region 92, a distal cuff 94 and proximal cuff 96. The proximal and distal ends of the stent are directed radially inward, as indicated at 98 and 100. When stent 90 is in its relaxed or normal configuration as shown in the figure, medial region 92 has a diameter of about 20 mm, and the cuffs have a diameter of about 30 mm. The filaments forming the stent, preferably of a body compatible stainless steel, are about 0.22 mm or less in diameter. While cuffs 94 and 96 are open, medial region 92 is circumscribed, i.e. completely covered, with a continuous polymeric film, preferably silicone. The silicone film is applied by dip coating of stent 90, in which event the film initially covers one of the cuffs, and is removed from that cuff prior to using the stent. The preferred thickness of the silicone film is in the range of 0.003 - 0.01 inches (0.075 - 0.25 mm), and is controlled primarily by the number of dip coating applications. More specifically, from three to five dip coatings result in a thickness within the preferred range. The silicone film is elastic, and thus is radially self-expanding like the remainder of stent 90. However, the silicone reinforces the medial region such that it has a much greater restoring force than the open weave portions of the stent. In particular, while cuffs 94 and 96 tend to recover virtually instantaneously from a radially compressed configuration, a tumor would inhibit their recovery. Medial region 92 recovers against a tumor, although it has been observed to take.24 hours for recovery. It has been found that the recovery rate of the medial region 92 can be controlled by controlling the thickness of the silicone film. The gradual recovery rate of the medial region against tumors affords several advantages which make stent 90 particularly well suited for treating esophageal strictures. Certain advantages arise from the coated medial region itself, and other advantages arise from the combination of the medial region with cuffs 94 and 96. Considered alone, medial region 92 provides an effective barrier to tissue ingrowth, because of the continuous silicone film. The gradual recovery of medial sleeve 92, from the radially compressed state when the stent is deployed, substantially reduces the chance that weakened cancerous tissue will be harmed during stent radial self-expansion. While a recovery rate of about one hour would significantly reduce most of the risk, the observed recovery rate of 24 hours is highly preferred. A further advantage arises from the fact that the residual force along the medial region is greater than the residual force along the more rapidly expanding cuffs. As a result, the maximum radial dilating force is provided along that portion of stent 90 aligned with the esophageal stricture. As mentioned above, cuffs 94 and 96 radially expand rapidly upon their release from a stent confining means such as exterior catheter 18. Thus, the cuffs rapidly contact and reach equilibrium with healthy tissue of the esophageal wall. Residual force in the cuffs at equilibrium is much less than the residual force along medial region 92. As a result, cuffs 94 and 96 readily conform to changes in the esophageal wall during swallowing and other convulsions of the esophagus. Thus, the cuffs are particularly effective in resisting either proximal or distal migration the stent. The open weave construction of the cuffs does not give rise to the problem of tumor ingrowth, since medial region 92 is aligned with the stricture, while the cuffs engage healthy tissue. Yet another advantage of the silicone film is that it provides reinforcement along medial region 92, enabling the stent to be constructed with a reduced braid angle. The braid angle is defined as the angle between two intersecting helical strands and encompasssing a longitudinal axis of the stent in its normal or relaxed configuration. Figures 3 and 4 illustrate a high braid angle and a low braid angle, respectively. In each case, the stent is oriented with its axial length in the horizontal direction. Heretofore, 90 degrees has been considered a lower practical limit for the braid angle of a mesh or open weave stent. Employing the silicone film, however, enables a reduction of the braid angle to as low as 70 degrees, as illustrated in Figure 4. The advantage of a lower braid angle resides in the fact that the braid angle determines the ratio of stent axial shortening to radial increase, as the stent self-expands. With a reduced braid angle, there is less axial shortening for a given radial expansion. Due to the reduced axial "drift", the stent can be more accurately positioned within body lumens during its deployment. Figure 5 illustrates a mandrel 102 particularly well suited for forming stent 90. Mandrel 102 includes a central shank 104, enlargements 106 and 108 on opposite sides of the shank, and end portions 110 and 112. To form the stent, the individual filaments or strands are wound in helical fashion to form an open weave cylinder. The cylinder is placed upon mandrel 102 and heated to a temperature in the range of from about 800-1,000 degrees F (420 - 538°C). The filaments, when cooled, retain the shape of the mandrel. Portions of the stent formed along the outer ends of the mandrel are trimmed, leaving the inwardly directed ends 98 and 100. Figures 6 and 7 schematically illustrate stent 90 after its deployment in the esophagus. An esophageal wall 114 includes a tumor 116. Using a device such as device 16, stent 90 is deployed as above explained. Medial region 92 of the stent is aligned with the tumor, and cuffs 94 and 96 are aligned with healthy portions of the esophageal wall 114 proximally and distally of tumor 116. The cuffs expand into engagement and equilibrium with esophageal wall 114 substantially immediately after deployment. Medial region 92, while it may engage tumor 116, remains radially reduced. Figure 7 illustrates stent 90 one day after deployment. Medial region 92 has recovered, and presses against tumor 116 to maintain the esophageal passage along the stricture. The diameter of medial region 92 at equilibrium is likely to be greater than two-thirds of the cuff diameter at equilibrium, because of the greater residual force due to the silicone film. Figure 8 illustrates another alternative stent 120 particularly suited for esophageal placement near the stomach, more particularly when a flared distal end or lower end 122 of the stent is near or protruding into the stomach, e.g. to treat a stricture near the stomach. Accordingly, stent 120 includes a distal region 124 circumscribed with a continuous silicone film, and a proximal cuff 126 of mesh or open weave construction. The proximal end 128 of the stent is inclined inward, to avoid the chance for esophageal perforation. Stent 120 can be deployed with a tool as described in copending application EP-A-0 639 958. Thus, in accordance with the present invention, a radially self-expanding stent includes a barrier region circumscribed by a silicone film to reduce tumor ingrowth, in combination with a fixation region of open weave construction. The stent is resistent to migration and to tumor ingrowth, and can be configured to recover gradually along its barrier region after deployment, to minimize harm to weakened, cancerous tissue.

Claims: A device for fixation in a body lumen, including; a tubular stent (90) of open weave construction having an axial length and a predetermined normal configuration and being radially compressible to a reduced-radius configuration to facilitate an axial insertion of the stent into a body lumen for delivery to a treatment site within the body lumen; a continuous elastomeric film formed axially along the stent (90) and having an axial length, said continuous film circumscribing the stent (90) to define a barrier region (92) of the stent to substantially prevent growth of tissue through the stent (90) along the barrier region (92), said axial length of said film being at least about one-third the axial length of the stent; a portion of the open weave construction of the stent (90) being substantially free of the continuous film to provide a fixation region comprised of a proximal cuff (94) and a distal cuff (96) for positively fixing the stent (90) within the body lumen at the treatment site by radial expansion of the stent (90) into a surface engagement with a tissue wall segment defining the body lumen; the barrier region being comprised of a medial sleeve (92) of the stent between the proximal and distal cuffs characterised in that said barrier region has a diameter less than the diameter of the fixation region when the stent is in the normal or relaxed configuration and in that the braid angle defined as the angle between two intersecting helical strands and encompassing a longitudinal axis of the stent is greater than 70° in the normal or relaxed configuration of the stent. A device according to Claim 1 characterised in that the stent is elastic, tending to assume the reduced-radius configuration in response to the application of an external force, and tending to assume the normal configuration in the absence of the external force. A device according to Claim 2 or Claim 3 characterised in that the film reinforces the stent along the barrier region. A device according to any preceding claim characterised in that the film is formed of silicone. A device according to any preceding claim characterised in that the film comprises a polymeric film. A device according to any preceding claim characterised in that the fixation region of the stent tends to exert lower restoring force in its return toward the normal configuration, as compared to the barrier region of the stent, upon removal of the external force. A device according to any preceding claim characterised in that the stent comprises a mesh formed of braided helical strands. A device according to any preceding claim characterised in that the braid angle is approximately 70°. A device according to any preceding claim characterised in that the stent is formed of braided helical strands, with opposite ends of the strands at proximal and distal ends of the stent bent radially inward.

Inventors: JOHNSON LIANN M, SCHOLL JOHN A, THOMPSON RICHARD J, JOHNSON, LIANN M., SCHOLL, JOHN A., THOMPSON, RICHARD J.
Applicants: SCHNEIDER USA INC, SCHNEIDER (USA) INC.
Application year: 1993
Main classification: A61F2
IPC codes: A61F2