Patent Publication Number: US-6210416-B1

Title: Coaxial needle and severing snare

Description:
This is a division of application Ser. No. 09/025,499, filed Feb. 18, 1998, U.S. Pat. No. 5,961,526. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of tissue ligation, and more particularly to an improved device and method for severing lesions. 
     BACKGROUND OF THE INVENTION 
     A wide variety of lesions, including internal hemorrhoids, polyps, and mucositis, may be treated by severing snare ligation. 
     In severing snare ligation, a targeted lesion is removed from the surrounding tissue by an electrosurgical severing snare using radio frequency (R/F) electric current to sever tissue or to achieve hemostasis. A high radio frequency is used (i.e., above 100,000 Hz.) to avoid the potentially injurious stimulation of muscles and nerves which results from lower frequency R/F energy. Thus, electrosurgery is typically performed at frequencies of approximately 500,000 Hz., although frequencies as high as 4,000,000 Hz. may be used. 
     Medical diathermy is similar to electrosurgery in that radio frequency current is passed through the patient&#39;s body. The major difference between these two techniques is the density of the radio frequency electric current; the current density used in medical diathermy is kept low to reduce tissue heating and to prevent necrosis. 
     There are three surgical effects that can be achieved with electrosurgery. These include electrosurgical desiccation, which is a low power coagulation caused without sparking to the tissue; electrosurgical cutting, where electricity sparks to the targeted tissue and produces a cutting effect; and electrosurgical fulguration, where electricity sparks to the targeted tissue without causing significant cutting. 
     The above-described surgical effects can be accomplished by using either a monopolar or bipolar output. For many applications, however, bipolar outputs are preferable because the patient return electrode (necessary in monopolar procedures and a common source of accidents) is eliminated, and any desiccation performed is extremely localized because, in a true bipolar operation, only the tissue that is grasped between the two electrodes is desiccated. Bipolar output, however, is less effective for cutting and fulgurating, and thus monopolar tools remain commonplace. Severing snares, for example, are almost all monopolar instruments. 
     In addition, three types of electrical current waveforms are typically used in electrosurgery. These include a “cutting” waveform, which cuts tissue very cleanly but may cause the incised tissue to bleed excessively; a “coagulating” waveform, which desiccates and fulgurates tissue without significant cutting; and a “blended” waveform, which is a cutting waveform that has a moderate hemostatic effect. A waveform&#39;s “Crest Factor” describes the degree of hemostasis that a waveform will produce if properly applied. 
     To remove a lesion (or polyp) with an electrosurgical severing snare, the wire snare is looped around the targeted lesion and is tightened as the snare is drawn into the sheath. The lesion is then desiccated and cut through electrosurgically. It is also possible to sever a lesion in a single step by cutting with a “blended” current. This allows a snare to cut through a lesion in one pass without having to worry about bleeding. Alternately, the lesion may be cut through mechanically with a thin snare wire after the blood supply to the targeted tissue has been coagulated and the tissue has been softened by a desiccation current. 
     Saline-Assisted Polypectomy (SAP), or “strip biopsy,” has become an increasingly popular way of performing endoscopic mucosal resection (EMR) to diagnose and treat diseases of the gastrointestinal tract. When performing SAP, a surgeon passes a needle through an endoscope and inserts the needle into the submucosa layer proximate to the lesion. Next, the surgeon injects physiological saline into the submucosa to elevate the lesion on a bed of saline solution. Once elevated, the surgeon can easily remove the lesion by passing an electrosurgical severing snare over the lesion and ligating the lesion. SAP, however, typically requires the use of a large diameter double-channel endoscope, which is difficult to introduce into the patient and is hard to manipulate. In addition, grasping forceps must be used to lift the lesion off of the layer of saline solution, which may result in a tear in the mucosa. 
     Accordingly, an alternate procedure has been developed called endoscopic aspiration mucosectomy (EAM). As described by Torii et al. in “Endoscopic Aspiration Mucosectomy as Curative Endoscopic Surgery,”  Gastrointestinal Endoscopy , Vol. 42, No. 5 (1995), EAM can be used to lift up a targeted lesion with suction, rather than with forceps, thereby reducing the risk of injury to the mucosal surface. When performing EAM, a double-channel endoscope is introduced into the patient, the lesion is marked with a needle knife, and saline solution or Glyceol™ (e.g., a hypertonic solution of 10% glycerol, 5% fructose, and physiological saline solution; available from Chugai Pharmaceutical Co., Tokyo, Japan) is injected into the submucosal layer beneath the lesion to separate the lesion from the layer. Next, the double-channel endoscope is withdrawn from the patient and a single-channel, video endoscope equipped with a transparent aspiration cylinder is introduced into the patient and (e.g., a Teflon® tube through which suction is applied) an electrosurgical severing snare is tightened around the outer circumference of the cylinder. 
     Once the single-channel endoscope has been properly repositioned near the targeted lesion, the lesion and the surrounding mucosa are aspirated into the cylinder and the snare is pushed off the cylinder and tightened around the lesion to ligate the lesion. By first aspirating the lesion into the tube before severing it, the lesion may be severed further down on the stalk than possible with SAP. After the targeted lesion has been severed from the surrounding tissue, the severed tissue may remain aspirated into the cylinder to retrieve the sample for further study. Alternately, the severed tissue may be aspirated out of the cylinder to pass through the body naturally. 
     However, while the EAM procedure described by Torii et al. may offer certain advantages over SAP, it still has its disadvantages. To perform EAM, a surgeon must switch between a double-channel endoscope having a needle knife and an injection needle (for marking the lesion and injecting solution), and a more maneuverable single-channel endoscope having a severing snare and an aspiration cylinder(for ligating and aspirating the lesion) because the working channel of a single-channel endoscope cannot accommodate both an injection needle and a severing snare simultaneously. Alternately, as discussed by Torii et al., double-channel endoscopes are too large and are not desirable for the EAM procedure. Exchanging endoscopes, however, is time consuming-wasting surgeons&#39; time and prolonging the procedure. 
     U.S. Pat. No. 5,542,948 to Weaver et al. purports to disclose an instrument in which a severing snare and an injection needle disposed side-by-side in separate lumens of the device are prevented from being simultaneously deployed by an actuator assembly which maintains one of the instruments (e.g., the severing snare) within the lumen until the other instrument (e.g., the injection needle) has been completely withdrawn into its respective lumen. 
     This requires the use of a multi-lumen sheath including two lumens for carrying the injection needle and severing snare. However, multi-lumen sheaths take up valuable space and make the overall endoscopic apparatus large and bulky. The use of two lumens within a sheath also limits the size of the severing snare and injection needle that can be used, as the instruments are disposed through the sheath side-by-side. 
     In addition, the depth at which a surgeon using the apparatus disclosed by Weaver et al. may sever a lesion is limited because the device is designed to be used when performing SAP and does not, therefore, provide for an aspirating device. This prevents the use of the device of Weaver et al. in performing EAM. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a device for treating a lesion within a living body, comprising a sheath extending from a proximal end which, in an operative position, is located outside the body, to a distal end which, in the operative position is located within the body. A needle extending through the sheath defines a tissue piercing distal tip and a central lumen extends through the needle from a proximal port to a distal opening formed in the distal tip. A needle actuator is provided for moving the needle between a retracted position in which the distal tip is received within the sheath to an injection position in which the distal tip extends distally beyond a distal end of the sheath and a snare extends within the lumen to a loop formed in a distal end of the snare. A snare actuator is provided for moving the snare between a covered position in which the loop is received within the lumen and an extended position in which the loop extends distally from the lumen beyond the distal tip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more readily understood through the following detailed description, with reference to the accompanying drawings, in which: 
     FIG. 1A shows an apparatus according to a first embodiment of the present invention; 
     FIG. 1B illustrates an aspiration cylinder and a distal end of an endoscope; 
     FIG. 2 shows the apparatus according to the first embodiment with both a needle handle and a snare handle fully-deployed; 
     FIG. 3 shows the apparatus according to the first embodiment with both the needle handle and the snare handle partially-deployed; 
     FIG. 4 shows the apparatus according to the first embodiment with the needle handle fully-deployed and the snare handle fully-retracted; 
     FIG. 5 shows the apparatus according to the first embodiment, arranged as seen in FIG. 4, passing through an endoscope to which an aspiration cylinder has been coupled; 
     FIG. 6 shows the apparatus according to the first embodiment, arranged as seen in FIG. 5, with the needle retracted and the snare extended and pressing against a lesion; 
     FIG. 7 shows an apparatus according to a second embodiment of the invention, wherein the needle and the snare are located external to the working channel of the endoscope, and the sheath is attached to the aspiration cylinder; 
     FIG. 8 shows the apparatus according to the first embodiment located adjacent to a targeted lesion; 
     FIG. 9 shows the apparatus according to the first embodiment with the needle injecting a sclerotherapy agent between the mucosa and the muscularis propria; 
     FIG. 10 shows the apparatus according to the first embodiment with the snare being maneuvered over the targeted lesion while the lesion and the surrounding mucosa are aspirated through the inner diameter of the snare into the aspiration cylinder; 
     FIG. 11 shows the apparatus according to the first embodiment with the snare being pulled tightly around the targeted lesion; 
     FIG. 12 shows the apparatus according to the first embodiment with the targeted lesion being ligating by the severing snare; 
     FIG. 13 shows the apparatus according to the first embodiment with the now-severed lesion aspirated into the aspiration cylinder; 
     FIG. 14 shows a cross section of the apparatus of FIG. 1; 
     FIG. 15 shows the apparatus of FIG. 1A with the needle and the snare in fully retracted positions; 
     FIG. 16 shows a cross-section of an additional embodiment of the invention including a stop for limiting the movement of the snare and needle; and 
     FIG. 17 shows a cross-section of a further embodiment including a mechanism for latching the snare and needle together so that they may be retracted in unison. 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1A, an apparatus according to a first embodiment of the invention comprises a sheath  1 , having a proximal end  5  and a distal end  10 . A lumen  15  extends between the proximal and distal ends  5  and  10 , and may preferably have a substantially circular cross-section. A distal aperture  20  is defined at the point where the lumen  15  exits the distal end  10  of the sheath  1 . 
     The sheath  1  is designed to pass through the working channel  30  of an endoscope  25  as can be seen in FIG.  1 B. The working channel  30  extends within the endoscope  25  from an accessible end (not shown) to a working end  35  of the endoscope  25 . The working channel  30  is sized to allow the free passage of instruments therethrough from an opening formed in the accessible end into the working channel  30  to the working end  35 . Of course those skilled in the art will understand that different scopes have working channels  30  of various diameters and that it is necessary only to size the sheath  1  so that a sufficient clearance is preserved within the channel so that the sheath  1  may freely is pass through the working channel  30 . Of course, when the sheath  1  extends outside the endoscope  25 , the size of the working channel  30  is not a factor in determining the size of the sheath  1 . 
     To configure the endoscope  35  for use with the apparatus according to the invention, aspiration cylinder  40  is coupled to the working end  35  of the endoscope  25 . The aspiration cylinder  40 , which may preferably be constructed of a transparent bio-compatible plastic such as, for example, polycarbonate or lexan, includes a distal end  45 , which defines a distal aperture  50  and an aspirating chamber  55 . The aspirating chamber  55  is in communication with the working channel  30  of the endoscope  25  so that an instrument, such as that according to the first embodiment of the present invention, may be passed through the working channel  30 , through the aspirating chamber  55 , and through the distal aperture  50  of the aspiration cylinder  40 . 
     Endoscope  25  is preferably a single-channel endoscope. Alternately, the surgeon may use a multiple-channel endoscope and use one or more of the other working channels for advancing an instrument, such as a forceps  200  (shown in FIG.  7 ), basket, needle, or other device, through the endoscope  25 , or for accommodating a fiber optical system (not shown). The length of the endoscope  25  should be sufficient to allow the surgeon to use the endoscope  25  and the attached aspiration cylinder  40  to reach the targeted lesions within the patient&#39;s body. 
     An injection needle  60  is disposed through the lumen  15  of the sheath  1 . The injection needle  60  defines a lumen  70 , which terminates in a distal aperture  67 , and has a proximal end (not shown) and a distal tip  65 . The cross-sections of the injection needle  60  and the lumen  70  are preferably generally circular, and the cross-sectional diameter of the injection needle  60  is less than the diameter of the lumen  15  of the sheath  1 , through which the injection needle  60  passes. As the cross-sectional diameter of the injection needle  60  is less than the diameter of the lumen  15  of the sheath  1 , the injection needle  60  is free to move longitudinally through the lumen  15 . 
     The proximal end of the injection needle  60  is connected to an injection needle handle  75 , which slidably engages a handle body  100 . The injection needle handle  75 , which includes an injection port  77 , may be moved longitudinally along the handle body  100  from a fully-deployed position (shown in FIG.  4 ), wherein the injection needle handle  75  has been moved away from the distal end  105  (formed as a thumb handle  106 ) of the handle body  100 , to a fully-retracted position (shown in FIG.  6 ), wherein the injection needle handle  75  has been moved proximate to the distal end  105  of the handle body  100  relative to the fully-deployed position. However, if the snare handle  90  is moved further proximally, the needle handle  75  may also be moved further proximally to further retract the needle  75 . In the preferred embodiment of the invention, it is also contemplated that the injection needle handle  75  may be positioned in any number of positions between the fully-deployed and fully-retracted positions. 
     Movement of the injection needle handle  75  controls and limits the movement of the injection needle  60  through the lumen  15  of the sheath  1 . When the injection needle handle  75  is in the fully-deployed position, the distal tip  65  of the injection needle  60  extends through and beyond the distal aperture  20  of the sheath  1  (as seen in FIGS.  2  and  3 ). When the present invention is used with an endoscope  25  and a aspiration cylinder  40 , the distal tip  65  of the injection needle  60  will extend beyond the distal aperture  50  of the aspiration cylinder  40  when the injection needle handle  75  is in the fully-deployed position and the sheath  1  is properly positioned, either within the endoscope  25  (as seen in FIG. 5) or outside the endoscope  25  (as seen in FIG.  7 ), for carrying out the desired procedure. When the injection needle handle  75  is in a mid-range (as seen in FIG. 3) or a fully-retracted position (as seen in FIG.  6 ), the distal tip  65  of the injection needle  60  is completely withdrawn within the lumen  15  of the sheath  1 . By completely retracting the injection needle  60  within the sheath  1  when the injection needle  60  is not in use, a surgeon can substantially reduce the risk of accidental perforation or entanglement. 
     An electrosurgical severing snare  80  is disposed within the lumen  70  of the injection needle  60 . The severing snare  80  has a proximal end (not shown) and a distal loop  85 , which is flexible and made of light-gauge wire such as nitinol or stainless steel. The severing snare  80  is preferably not surrounded by any insulating material so that, when r/f energy is supplied to the severing snare  80 , the injection needle  60  is also “hot.” However, the sheath  1  is preferably formed as an insulator to guard against short circuiting with an interior surface of the working channel  30  and to protect tissue surrounding the lesion from damage prior to locating a final position and deploying a desired one of the needle  60  and the snare  80 . Thus, the needle  60  may be used to cauterize bleeding vessels, or may serve as a point electrical surgery knife. 
     The diameter of the severing snare  80 , the cross-section of which is preferably generally circular, is less than the diameter of the lumen  70  of the injection needle  60 , through which the severing snare  80  passes. Those skilled in the art will understand that, because two strands of the wire of the distal loop  85  or the severing snare  80  are received within the distal end of the lumen  70 , it is preferable to select a light-gauge wire which is less than half the diameter of the lumen  70 . As the cross-sectional diameter of the severing snare  80  is less than the diameter of the lumen  70 , the severing snare  80  is free to move longitudinally through the lumen  70 . The proximal end of the severing snare  80  is connected to a snare handle  90 , which slidably engages the handle body  100 , and is in electrical communication with an R/F snare plug  95 . Snare handle  90  may be moved longitudinally along the handle body  100  between a fully-deployed position, (shown in FIGS. 2 and 3) in which the distal loop  85  extends from the distal end of the lumen  70 , wherein the snare handle  90  is close to the distal end  105  of the handle body  100 , and a fully-retracted position (shown in FIG.  4 ), in which the distal loop  85  is completely retracted into the lumen  70 , wherein the snare handle  90  is located adjacent to the thumb ring  106  of the handle body  100 . In the preferred embodiment of the invention, it is also contemplated that the snare handle  90  may be positioned in any number of positions between the fully-deployed and fully-retracted positions. 
     Movement of the snare handle  90  controls and limits the movement of the severing snare  80  through the lumen  70  of the injection needle  60 . When the snare handle  90  is in the fully-deployed position, the distal loop  85  of the severing snare  80  extends through and beyond the distal aperture  67  of the injection needle  60 . When the present invention is used with an endoscope  25  and a aspiration cylinder  40 , the distal loop  85  of the severing snare  80  will extend beyond the distal aperture  50  of the aspiration cylinder  40  when the snare handle  90  is in the fully-deployed position, and the injection needle  60  and sheath  1  are properly positioned, either within the endoscope  25  (as seen in FIG. 6) or outside the endoscope  25  (as seen in FIG.  6 ), for carrying out the desired procedure. 
     When the snare handle  90  is in the fully-retracted position, the distal loop  85  of the severing snare  80  is completely withdrawn and collapsed within the lumen  70  of the injection needle  60 . Of course, the loop  85  will initially be compressed when it is drawn into the sheath  1  and, by drawing the needle  60  proximally along with the snare loop  85 , a user can ensure that the snare loop  85  is collapsed by the sheath  1  before being retracted into the lumen  70 . By completely retracting the distal loop  85  and the severing snare  80  within the lumen  70 , a surgeon can substantially reduce the risk of accidentally having another instrument, such as a forceps  200  (shown in FIG. 7) become entangled in the distal loop  85 . The distal loop  85  of the severing snare  80  is also protected from being accidentally perforated by the injection needle  60  by the fact that the distal loop  85  is located distal to the injection needle  60 . 
     For each of the above-described embodiments, when fully-extended and not deformed by another object, the distal loop  85  defines a generally elliptical area, which can be referred to as having a length  1  and a width w. When the distal loop  85  is retracted into the lumen  70  of the injection needle  60  (i.e., “collapsed”), width w is reduced to approximately the diameter of the lumen  70 . Accordingly, the area defined by the distal loop  85  is substantially smaller after the distal loop  85  has been collapsed than before it has been collapsed. Distal loop  85  is able to be collapsed upon being retracted because the wire that comprises the distal loop  85  is flexible. The distal loop  85  is preferably biased so that, when the distal loop  85  is redeployed it will return to its precollapsed state and define roughly the same area as it did before it was collapsed within the lumen  70 . In addition as shown in FIGS. 11 and 12, the snare loop  85  may be biased so that, when outside the lumen  70 , the loop  85  extends in a plane disposed at an angle, e.g., 90°, relative to the longitudinal axis of the needle  60 . That is, the loop  85  may be biased so that, when deployed, it extends across an opening of the aspiration cylinder  40 . This facilitates placement of the loop  85  over a lesion aspirated into the aspiration cylinder  40 . 
     The R/F snare plug  95  is provided to transmit energy from an external source (not shown) to the distal loop  85  of the severing snare  80 . 
     In the preferred embodiment of the invention, the sheath  1  is designed to pass through the working channel  30  of the endoscope  25 . By using the device in this manner, the overall cross-sectional area of the endoscope is not increased due to the presence of the sheath  1 , injection needle  60 , and severing snare  85 , although the aspiration cylinder  40  may slightly increase the profile of the endoscope  25 . Furthermore, because the severing snare  80  is coaxial with the injection needle  60 , the combination of the two instruments takes up approximately the same amount of room within the working channel  30  that a standard injection needle would. 
     If, however, the injection needle  60  and the severing snare  80  were positioned side-by-side and electrically isolated from one another by separate sheaths, the combination of the two instruments would require more room within the working channel  30 , thereby necessitating the use by the surgeon of a large endoscope or the elimination of the advantages of having both instruments simultaneously present at the site of the lesion and, instead, having to perform several “exchanges” as discussed in the prior art. 
     Thus, a surgeon using the present device may use an endoscope with a relatively small working channel  30  while still enjoying the benefits of locating both an injection needle  60  and a severing snare  80  simultaneously at the site of a lesion. Alternately, the surgeon may use any “free space” within an larger diameter endoscope (such as the diameter that would be needed if the two instruments were positioned side-by-side) for passing other instruments, such as a forceps  200 , through the working channel  30 . Also, the surgeon could select an injection needle  60  and a severing snare  80  having slightly larger diameters, thereby allowing for more injection flow through the injection needle  60  and for a stronger severing snare  80 . 
     In an alternate embodiment as shown in FIG. 7, the sheath  1  may be located external to the working channel  30  of a relatively small diameter endoscope  25 . In such a configuration, a portion of the sheath  1  is attached to the aspiration cylinder  40  by tape, cable ties, or mesh means (not shown). While this configuration enlarges the overall profile of the endoscope  25  and aspiration cylinder  40  assembly, the surgeon is then free to use another instrument, such as a forceps  200 , basket, needle, or cautery device, through the working channel  30  of the endoscope  25 , without having to first remove the injection needle  60  and the severing snare  80  from the patient. The open working channel  30  of the endoscope  25  also allows for multiple combinations of instruments to be used within the working channel  30  without having to remove the endoscope  25  from the body of the patient. 
     A novel method for ligating a lesion will now be described with reference to FIGS. 8-13. 
     First, a surgeon administers a local pharyngeal anesthesia or general anesthesia to the patient and introduces into the patient an endoscope  25  having an aspiration cylinder  40  coupled thereto. The surgeon then passes the sheath  1  through the working channel  30  of the endoscope  25  with the sheath  1  protecting the endoscope from being scraped or damaged by the needle as it is passed through the working channel  30 . A needle  60  is passed through the lumen  15  of the sheath  1  with a severing snare  80  disposed within the lumen  70  of the needle  60 . Alternately, the surgeon may forgo use of a aspiration cylinder  40  and may attach the sheath  1  to the outside of the endoscope  25 . 
     As shown in FIG. 8, the surgeon positions the distal end of the aspiration cylinder  40  adjacent to the lesion  205  that the surgeon wishes to remove. The lesion  205  as shown in FIGS. 8-13 is illustrative of a lesion found in the gastrointestinal tract and may, for example, be associated with early gastric cancer or adenoma. The lesion  205  is part of the mucosa  210 , and is positioned over a submucosa layer  215  (the muscularis propria). 
     Next, the surgeon passes an injection needle  60  (shown in FIG. 9) through the mucosa  210 , and injects a sclerotherapy agent L or saline solution between the mucosa  210  and the muscularis propria  215 , thereby separating the mucosa  210  from the muscularis propria  215 . It is preferable that a sclerotherapy agent L, such as Glyceol™, be used rather than saline solution because the bulge formed between the mucosa  210  and muscularis propria  215  lasts longer when a sclerotherapy agent is used. 
     Once the lesion  205  has been elevated on a bed of sclerotherapy agent L, the surgeon deploys the snare  80  and positions the loop  85  around the lesion  205  and then aspirates the lesion  205  through the loop  85  into the aspirating chamber  55  of the aspiration cylinder  40  (shown in FIG. 10) and tightens the loop  85  around the tissue to sever the lesion  205  (shown in FIG.  12 ). 
     If the surgeon is using an electrosurgical severing snare, as described in the background of the invention, he would apply the appropriate R/F energy (i.e., “cutting,” “coagulating,” or “blended”) to the snare through an R/F snare plug  95  while severing the lesion  205 . As shown in FIG. 13, after the lesion  205  has been severed, it may be retained in the aspiration cylinder  40  to be removed from the body for further pathology study or aspirated out of the aspirating chamber  55  to pass through the body. If the lesion  205  is aspirated out of the aspiration cylinder  40 , the surgeon may immediately proceed to treat a subsequent lesion (not shown) without having to remove the endoscope  25  and the aspiration cylinder  40  from the body. 
     Alternately, the surgeon may pass an instrument, such as a forceps  200 , through the working channel  30  or an external or an addition lumen (not shown) of the endoscope  25  to grasp and retrieve the lesion  205 . If the sheath  1  occupies the working channel  30  and no other lumen is provided, then the surgeon could exchange sheath  1  for the desired instrument  200 , or attempt to pass the instrument  200  around the sheath  1  within the working channel  30 . This exchange would be eliminated, however, if the sheath  1  were connected to the outside of the aspiration cylinder  40  (as seen in FIG.  7 ), thereby freeing up the working channel  30  of the endoscope  25  for other instruments, such as the forceps  200 . 
     In addition, if the surgeon opts not to perform EAM and instead elects for SAP, the forceps  200 , rather than suction, would be used to separate the lesion  205  and the mucosa  210  from the muscularis propria  215 . Accordingly, it would be desirable to adapt the present invention to allow for both the coaxial needle  60 /severing snare  80  instrument and the forceps  200  to be simultaneously located at the site of the lesion  205 . In accordance with an alternate embodiment of the present invention, the sheath  1  could be located external to the endoscope  25 , thereby still allowing the surgeon to use a single-channel (rather than a double-channel) endoscope  25  to perform the SAP procedure. 
     Those skilled in the art will understand that the injection needle handle  75  is preferably coupled to the severing snare handle  90  so that, when the severing snare  80  is retracted, the injection needle  60  is also retracted at least until the distal tip  65  of the injection needle  60  is received within the sheath  1 . For example, after grasping tissue, the diameter of the distal loop  85  will be expanded to surround the tissue and, when the snare  80  is retracted while the injection needle  60  is fully or partially deployed, the expanded loop  85  will be too large to enter the injection needle  60 . Thus, the needle  60  will be pushed proximally by the proximal travel of the distal loop  85  until the severing loop  85  comes into contact with the distal end  10  of the sheath  1 . As shown in FIG. 14, as the snare  80  is drawn further into the sheath  1 , decreasing the diameter of the distal loop  85 , there is no impediment to the proximal travel of the needle  60  which is pushed further proximally into the housing  100 . FIG. 15 shows the apparatus of FIG. 14 in which no stop  110  is provided to limit the proximal travel of the needle  60 , wherein both the snare  80  and the needle  60  are completely withdrawn into the sheath  1 . 
     FIG. 16 shows a further embodiment of the apparatus according to the present invention in which a mechanism is provided to control the motion of the needle  60  and the snare  80 . Specifically, the apparatus of FIG. 16 includes a stop  110  formed as a rod extending across the interior lumen of the handle body  100  preferably substantially perpendicular to a longitudinal axis of the handle body  100 . The stop  110  contacts the snare handle  90  to define the distal-most position of the snare handle  90  and, consequently, the distal-most position of the snare  80 . Similarly, the stop  110  contacts the needle handle  75  to define the proximal-most position of the needle handle  75  and, consequently, of the needle  60 . Those skilled in the art will understand that the rod  110  may be formed as a separate piece bonded to, or molded into, the interior of the handle body  100 . In addition, an increased diameter portion  112  of the needle  60  is provided to further define the proximal and distal limits of travel of the needle  60 . Specifically, the proximal end  114  of the increased diameter portion  112 , which is formed as a seal to seal the interior lumen  70  of the needle  60 , facilitates contact between the stop  110  and the needle  60  and includes a receiving cavity  113  to ensure that the needle  60  does not travel proximally past the stop  110 . A distal end  116  of the increased diameter portion  112  abuts a shoulder formed on a distal end of the handle body  100  when the needle  60  is in a distal-most position. In addition, when the needle actuator  75  is retracted to the proximal-most position, it can be rotated about the longitudinal axis of the housing  100  so that the needle actuator  75  is locked into a locking bay  118 . 
     FIG. 17 shows a device similar to that of FIG. 16 except that the increased diameter portion  112  of the needle  60  includes a detente  120  extending from the proximal end  114 . This detente  120  cooperates with a latch  122  formed on a portion of the snare handle  90  extending within the housing  100  so that as the snare  80  is pushed distally, the latch  122  will abut the proximal end  114  of the increased diameter portion  112  pushing the needle  60  out to the fully deployed position. of course, the needle  60  may be independently deployed by moving the needle handle  75  distally. In any case, when the needle  60  reaches the fully deployed position and the distal end  116  abuts the shoulder formed on the distal end of the handle body  100 , the latch  122  moves underneath the detente  120  and locks the snare handle  90  to the needle  60 . Thus, when the snare  80  is withdrawn proximally, the needle  60  is also drawn back into the sheath  1  until further proximal travel of the needle  60  is stopped by contact between the distal end  114  and the stop  110  at which point the latch  122  is released from the detente  114  and the snare  80  is retracted into the interior lumen  70  of the needle  60 . 
     Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the above-recited detailed description, wherein the preferred embodiment of the invention has been shown and described. 
     The description of the preferred embodiment is simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various respects, all without departing from the invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive.