Patent Publication Number: US-2020282179-A1

Title: Flexible surgical sheath and multi-part insertion cannula

Description:
BACKGROUND 
     Neurosurgical techniques involve precise manipulations in confined spaces. For surgical procedures in the brain, precision is particularly important due to the density of neurological structures. Further, the relative sensitivity of brain tissue, coupled with the potential severity of degraded tissue, make precise procedures that minimize collateral effects to surrounding tissue of utmost importance. In recent decades, usage of endoscopic surgical instruments have gained popularity over traditional procedures which removed a portion of the skull for open access; Minimally invasive procedures using endoscopic techniques employ narrow, elongated instruments through smaller incisions, rather than open techniques. Surgical procedures with endoscopic techniques have been mostly performed for intraventricular procedures in the brain. There are many types of endoscopes which generally share some common features: light source, lens system, attached camera and working channels to introduce the surgical instruments. For example, a craniotomy is surgical procedure where a small opening is made in the skull to gain access to a tumor. The craniotomy is the fundamental technique used in tumor resection. It involves making an incision in the patient&#39;s scalp and then an opening in the skull. This is done using specialized endoscopic drills. Such an opening allows access to the intracranial cavity where the brain and ventricle are located. On the other hand 
     SUMMARY 
     Neurosurgical procedures involving the brain tend to involve highly specialized surgeons and surgical instruments, due to the concentration of functionally eloquent neurological tissue and the likelihood of disturbing surrounding tissue. Often, however, large drilled skull openings and access tunnels are required for gaining surgical access to a central or deep location of a surgical site. Particularly in the case of a craniotomy, for example, removal of a tumor necessarily requires compromise of some brain tissue by purposefully or unintentionally retracting brain tissue for affording access to the targeted area. Nonetheless, it is beneficial to minimize application of pressure to brain tissue as mush as practicable to mitigate collateral effects of surgery. 
     Configurations herein are based, in part, on the observation that conventional neurosurgical techniques tend to exert force on adjacent tissue, potentially causing undesired collateral effects. Neurological tissue tends to be sensitive to pressure, therefore neurosurgical procedures strive to avoid disturbing adjacent tissue outside the surgical target. Particularly in brain surgery operations, such as a craniotomy, it can be problematic to leave surrounding tissues undisturbed. 
     Neuroendoscopic techniques are commonly used in many neurosurgical procedures and represent a minimally invasive surgical technique. The standard approach in this technique is insertion of an operating sheath and then introduction of the neuroendoscope (a particular type of endoscope) with a working channel for surgical instruments through this sheath. The first step of this approach is cannulating the ventricle (fluid spaces in the brain) with an introducer to maintain a passageway for an endoscope and related instruments. This can be accomplished with a peelaway catheter introducer or with a reusable rigid obturator/operating sheath. Both provide a passageway to repeatedly insert and withdraw the instruments and endoscope without any need to recannulate the tissue during the surgery. This technique is sufficient for many procedures but conventional introducers or obturator/operating sheaths have particular shortcomings and disadvantages. 
     Since the conventional sheaths are rigid tunnels with a fixed, small size (diameters 4-7 mm), working channels of operating sheaths accept only very small instruments (e.g. having diameters of approximately 1.7-2.8 mm). Therefore only very tiny pieces from the lesions, such as tumors, can be removed with these thin instruments during the procedures. Further, only one or two instruments can be used because of small size of the operating sheath, and no standard suction tube can be introduced for tumor suctioning. Usage of two or more instruments simultaneously is extremely difficult if not impossible, and if attempted, both instruments and the scope must remain parallel in the operating sheath throughout the procedure. Due to the small clearance, instruments cannot maneuver significantly without also moving the operating sheath. Maneuvers of the surgical instruments tend to force the rigid sheath to move with the instruments and push/retract the surrounding tissue which may cause undesired collateral effects such as tissue damage. Because of these limitations, endoscopic resection of some intraventricular solid/semi-solid lesions, such as tumor or colloid cysts, with endoscopic techniques becomes a very challenging procedure and may not be performed both quickly and safely. 
     Therefore, there is a need for a soft, non-rigid sheath which would provide a larger passageway to the ventricle to accommodate standard size surgical instruments such as suction tips, forceps, scissors, and coagulators, and generally, to use multiple instruments simultaneously and to allow maneuvers without significant retraction to surrounding tissue. 
     Unfortunately, conventional approaches suffer from the shortcoming that rigid access devices such as rigid sheaths impose constant pressure on the brain tissue as force from the sheath tends to displace brain tissue. Narrow access resulting from smaller diameter surgical access tunnels tends to limit instrument mobility in the surgical site, while larger drilled holes for accommodating a larger sheath compromise additional neurological tissue. Accordingly, configurations herein substantially overcome the shortcoming of displacement pressure, imposed by conventional rigid sheaths, by providing a flexible sheath that mitigates constant pressure on the brain tissue around the surgical tunnel. The flexible sheath as disclosed herein conforms to the surgical access tunnel while the tissue is at rest, and allows temporary deformation as the surgical instruments are manipulated while accessing the surgical site. Although the surgical instruments may need to be angled during the procedure, and thus exert force against the flexible sheath and corresponding adjacent tissue, such forces are temporary and not for the duration of the procedure. 
     In further detail configurations discussed further below disclose a surgical device including an obturator adapted for insertion through surgical tissue to a surgical site, and a plurality of rigid sheath portions disposed around the obturator, such the rigid sheath portions are in circumferential engagement around the obturator for defining a surgical passageway through the surgical tissue. Configurations herein employ a two part rigid sheath including an inner sheath portion and an outer sheath portion. A flexible sheath is adapted for insertion between the rigid sheath portions following withdrawal of the obturator, using an introducer or other mechanism for drawing the flexible sheath between the rigid sheath portions. The inserted flexible sheath is periodically deformable in response to biasing forces from surgical instruments, such that the periodic deformation relieves constant pressure on the surgical tissue. The plurality of rigid sheath portions are slideably removable following insertion of the flexible sheath. 
     Installation of the flexible sheath invokes a method of providing surgical access that includes inserting an obturator assembly including an obturator disposed between the plurality of elongated, rigid sheath portions, such that the rigid sheath portions encase or encircle the obturator for defining a surgical passageway through surgical tissue. Following insertion, the surgeon withdraws the obturator, and inserts, in the defined surgical passageway, a flexible sheath having a resilient tubular shape of slightly smaller diameter than a drilled surgical channel that the obturator was extended through. The surgeon then withdraws each of the portions of the rigid sheath portions in succession, in which the rigid sheath portions are adapted to slideably pass between the flexible sheath and surgical tissue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIGS. 1 a -1 c    show the assembled components of the flexible sheath and insertion mechanism; 
         FIGS. 2 a -2 e    show the individual components of the sheath of  FIG. 1 ; 
         FIG. 3  is a flowchart of a method of installing the flexible sheath of  FIG. 1 ; 
         FIGS. 4 a -4 k    show a method of inserting the flexible sheath of  FIGS. 1 a   - 2   e;    
         FIGS. 5 and 6  describe a method of employing the flexible sheath in a surgical procedure as in  FIGS. 4 a   - 4   k;    
         FIGS. 7 a -7 f    shown an alternate single piece sheath configuration; and 
         FIGS. 8 a -8 h    show alternate linkage arrangements of the sheath portions. 
     
    
    
     DETAILED DESCRIPTION 
     Configurations disclosed herein relate to neuroendoscopic instruments and surgical techniques used in neurosurgical operations in human brains. It more particularly relates to the introducer/obturator/operating sheaths used in neuroendoscopic procedures to provide a passageway for inserting, withdrawing and reinserting the neuroendoscopes and surgical instruments during these procedures. The disclosed flexible sheath and method of insertion thereof includes three components: the outer sheath, obturator and inner/operating sheath, referred to herein as the flexible sheath. The outer sheath has at least two portions of slightly different diameters such that engage by sliding the smaller diameter inner sheath into the larger diameter outer sheath. 
     In contrast to conventional cannulated access, employing a unitary rigid sheath, the flexible sheath employs a multipart rigid sheath for insertion. An obturator or other elongated insertion member drives a sheath assembly into a surgical tunnel or recess, typically a hole drilled through the skull and brain of the surgical patient. The inserted sheath assembly includes two or more rigid sheath portions disposed around the obturator. The individual rigid sheath portions engage or interlock to define a cannulated access channel through the drilled surgical tunnel. The obturator has a tapered or angled tip for guiding the sheath assembly through the surgical tunnel to a target region such as a ventricle or other brain structure for which surgical intervention is sought. Following insertion, the obturator is withdrawn and a flexible sheath inserted in the surgical tunnel defined by the rigid sheath portions. Alternatively, the flexible sheath may be inserted with the rigid sheath portions and the obturator subsequently withdrawn. 
     Configurations herein therefore disclose a flexible surgical sheath and multi-part insertion cannula, or rigid sheath, for inserting the flexible sheath in the surgical tunnel to gain access to a ventricle or other surgical target. Due to the flexibility of the sheath and the fragility of the surrounding brain tissue, insertion of a sheath assembly facilitates insertion of the flexible sheath into the drilled surgical tunnel, followed by withdrawal of the components of the sheath assembly, according to the method disclosed herein, leaving the flexible sheath in place for the duration of the surgical procedure. An optional depth limiter provides a substantially flush surface at a proximate end of the sheath nearest the skull surface for gauging depth into the surgical tunnel. 
     Configurations herein provide the following features to overcome the shortcomings of conventional neuroendoscopic techniques. The disclosed method provides a large passageway to intracranial fluid spaces, such as the ventricle, which may easily accommodate standard size neurosurgical instruments. Further, the larger passageway allows the surgeon to use multiple instruments simultaneously. The rigid outer sheath, defined by the inner and outer portions, is used only to introduce the flexible inner sheath and is then removed. The flexible inner sheath thereafter imposes little or no tension to surrounding brain tissue, facilitates maneuvers of the instruments, and allows the surgeon to use multiple instruments in non-parallel fashion, thus allowing an angled usage to enhance access, leverage etc. Further, the flexible sheath allows reorientation of the scope and/or instruments to side, up or down as needed by just changing the direction of the scope and/or instrument(s), and provides a safe passageway for repeated insertion and withdrawal of the scope and/or instruments. The usage of the flexible sheath therefore permits endoscopic instrument usage without injuring the surrounding brain tissue. 
     Following insertion, withdrawal of the obturator leaves the surgical tunnel defined by the rigid sheath portions flanking the flexible sheath. Subsequent removal of each of the rigid sheath portions leaves only the flexible sheath, thus eliminating the outward force exerted by the rigid sheath portions on the brain tissue. The brain tissue is therefore relaxed as the flexible sheath occupies the surgical tunnel, while allowing insertion of endoscopic surgical instruments through the flexible sheath. 
       FIGS. 1 a -1 c    show the assembled components of the flexible sheath and insertion mechanism adapted for insertion into a surgical tunnel ( 150 ,  FIG. 4 b   , below). The surgical tunnel may be formed by any suitable means, such as drilling, and has a size based on the sheath assembly. Referring to  FIGS. 1 a -1 c   , the sheath assembly  100  includes two rigid sheath portions, including an inner sheath portion  110  and an outer sheath portion  112  disposed around an obturator  120  having a tip  122 . Referring also to  FIGS. 2 a -2 b   , the inner  110  and outer  112  sheath portions (inner sheath  110  and outer sheath  112 , hereinafter) define an insertion void  114  approximating the diameter of the surgical tunnel. The insertion void  114  is defined by the rigid inner and outer sheaths  110 ,  112  and is adapted to receive the flexible sheath  130  of  FIG. 2 d   , discussed further below. 
       FIGS. 1 b  and 1 c    show engagement of the inner and outer rigid sheaths  110 ,  112  of particular sizes. A generally oblong or oval arrangement tends to provide greater mobility, and may be 6 mm*14 mm, as shown in  FIG. 1 b   , or 4 mm*8 mm as shown in  FIG. 1 c   , if a smaller surgical tunnel is sufficient. The inner  110  and outer  112  sheaths will be in different lengths, typically increments of 3, 4, 5 and 6 cm are most likely for typical applications. As shown in  FIGS. 1 b  and 1 c   , the inner sheath  110  has a slightly smaller diameter and extends a lesser arcuate distance than the outer sheath  112 , which has a larger diameter. The inner  110  and outer  112  sheaths overlap in an overlap region  113 , which secures the inner  110  and outer sheaths  112  in a slideable axial engagement for allowing withdrawal while maintaining a continuous supportive encircling around the flexible sheath  130  from the overlap region  113 . 
       FIGS. 2 a -2 e    show the individual components of the sheath of  FIG. 1 . The inner sheath  110  has a slightly smaller elliptical diameter than the outer sheath  112  for insertion thereof. Further, the inner  110  and outer sheaths  112  may be tapered toward a distal end  116 ,  118  that is inserted into a surgical tunnel. The inner  110  and outer sheaths  112  may be any suitable corresponding shape, such as elliptical, oblong or circular, however, an elliptical configuration is shown herein as an example. 
     In the example of  FIGS. 2 a -2 e   , the distal ends  116 ,  118  have a diameter  142  and  146  respectively, which may be slightly smaller than a diameter  141 ,  145  of proximate ends  115  and  117 . An opening  143 ,  147  in the annular surface of the inner  110  and outer sheaths  112  allows slideable communication while maintaining continuous support encircling the flexible sheath because of the overlap region  113 . Once positioned, a depth limiter  140 , substantially flush with the surgical tunnel opening on the skull, may secure the flexible sheath  130  by tabs or slots  142 , and provides a reference working surface for gauging depth within the surgical tunnel  150  and provides protection to tissue and bone structures around the opening of the surgical tunnel. Winglike protrusions or handles  148  on the inner and outer sheaths facilitate removal, as discussed below with respect to  FIGS. 4 a   - 4   k.    
       FIG. 3  shows a method of installing the flexible sheath. Referring to  FIG. 3 , at step  200 , the method of providing surgical access comprising as disclosed herein includes inserting an obturator (sheath) assembly  100  having an obturator  120  disposed between a plurality of elongated, rigid sheath portions  110 ,  112 , in which the rigid sheath portions encase or surround the obturator  120  for defining a surgical passageway through surgical tissue. A surgeon inserts, between the defined surgical passageway, the flexible sheath  130 , in which the flexible sheath  130  has a resilient tubular shape receptive to endoscopic instruments, as depicted at step  201 . The obturator  120  may also be also used for placement of surgical support devices, such as for mounting neuronavigator system sensors. Typically, the obturator is inserted to a depth based on the surgical target (i.e. ventricle), following which the obturator is withdrawn and the flexible sheath  130  inserted with the same obturator  120  or with an introducer. Both the rigid insertion cannula (inner  110  and outer  112  sheath portions) and the obturator  120  will have depth markings for gauging insertion. Alternatively, the flexible sheath may accompany the insertion assembly if the obturator may be withdrawn inside of it. After the obturator  120  has reached a predetermined depth, the surgeon withdraws the obturator and each of the portions of the rigid sheath portions  110 ,  112  in succession, in which the rigid sheath portions  110 ,  112  are adapted to slideably pass between the flexible sheath  130  and surgical tissue, as shown at step  202 . The flexible sheath  130  remains disposed in the surgical tunnel  150  for providing surgical access without exerting constant pressure on the surrounding tissue as conventional, unitary rigid catheters do. 
       FIGS. 4 a -4 k    show a method of inserting the flexible sheath of  FIGS. 1 and 2 . Referring to  FIG. 4 a   , the sheath assembly  100  is shown in a cutaway view. In  FIG. 4 b   , the sheath assembly  100  is inserted into the surgical tunnel  150 , having walls shown by dotted lines  150 ′,  150 ″, by the surgeon via the obturator  120 . In a typically craniotomy, a fluid space defined by a ventricle  152  represents a desired insertion depth for accessing a surgical target. Insertion of the sheath assembly  100  in  FIG. 4 c    disposes the inner sheath  110 , outer sheath  112  and obturator  120  in the surgical tunnel  150  as a single unit. 
     Referring to  FIGS. 4 b -4 j   , once the sheath assembly  100  is positioned, the surgeon withdraws the obturator  120  in  FIG. 4 d   , leaving the inner  110  and outer sheaths  112  within the surgical tunnel  150  in  FIG. 4 e   . The flexible sheath  130  of  FIG. 4 f    is inserted using an introducer or bayonet  121  in  FIG. 4 g   . The outer sheath  112  is then removed from the surgical tunnel  150  in  FIG. 4 h   , leaving the flexible sheath  130  frictionally engaged between the walls  150 ′ of the surgical tunnel  150  and the inner sheath  110 . A diameter  150 D of the surgical tunnel will tend to decrease as the rigid outer sheath  112  is removed and relieves pressure exerted on it against the wall  150 ′ of the surgical tunnel  150 .  FIG. 4 i    shows the corresponding removal of the inner sheath  110  and subsequent further contraction of the surgical tunnel  150  around the flexible sheath  130 , leaving only the flexible sheath  130  in the surgical tunnel  150  ( FIG. 4 j   ). Removal order of the inner  110  and outer sheaths  112  may be varied; since the outer sheath  112  has greater surface area, it is beneficial to remove first so as to slide past the inner sheath  110  rather than have the entire surface area of the outer sheath  112  frictionally engage the flexible sheath  130 , to minimize the chance of drawing the flexible sheath  130  out of the surgical tunnel  150 . Removal of the sheaths  110 ,  112  permits access to a surgical site  160 , such as a tumor, with instruments, as shown in  FIG. 4 k   . Surgical instruments  162 ,  164  may then be employed to access the surgical site  160 . An insertion angle  166  is facilitated by the diameter  150 D of the surgical tunnel, and the flexible sheath  130  allows a greater insertion angle  166  by permitting a range of motion to temporarily compress the flexible sheath  130  against the tunnel walls  150 ′,  150 ″. Such temporary pressure subsides with instrument repositioning, in contrast to a fixed rigid sheath that exerts constant pressure.  FIG. 4 k    also shows an optional depth limiter  140 , which may be applied at any time for maintaining a known working surface and for anchoring the flexible sheath  130  via slots or tabs  142 . 
       FIGS. 5 and 6  describe a method of employing the flexible sheath in a surgical procedure as in  FIGS. 4 a -4 k   . Referring to  FIGS. 5 and 6 , and continuing to refer to  FIGS. 1 and 4 , at step  300 , the method of providing surgical access via the flexible sheath includes inserting an obturator or sheath assembly  100  including an obturator  120  disposed between a plurality of elongated, rigid sheath portions  110 ,  112  encasing the obturator  120  for defining a surgical passageway or tunnel  150  through surgical tissue. In the example arrangement shown, the plurality of rigid sheath portions includes an inner sheath  110  portion and an outer sheath portion  112 , such that the inner and outer sheath portions are in overlapping engagement for slideably passing adjacent to the other sheath portion for withdrawal, as shown at step  301 . The rigid sheath portions  110 ,  112  may be tapered such that the rigid sheath portions define a smaller opening at a distal end  116 ,  118  inserted into the surgical passageway, and a larger opening at a proximate end  141 ,  145 , as shown at step  302 . The rigid sheath portions  110 ,  112  may further comprise a handle  148  defined by an appendage normal to an outer surface of the rigid sheath portions  110 ,  112 , as depicted at step  303 . The rigid sheath portions  110 ,  112  therefore define a surgical passageway (tunnel  150 ) tapered from a larger elliptical diameter at a proximate end to a smaller elliptical diameter at a distal end adjacent the surgical site, as shown at step  304 . Alternatively, a variety of circular or oblong tunnels may be employed. Generally, the flexible sheath  130  has an unexpanded size less than the surgical passageway defined by the rigid sheath portions  110 ,  112 , as depicted at step  305  so as to be disposed easily into the surgical tunnel  150  following retraction of the rigid sheath portions  110 ,  112 . 
     Once the obturator  120  is retracted ( FIG. 4 d   ), the surgeon inserts, within the defined surgical passageway  150 , a flexible sheath  130  having a resilient tubular shape, as depicted at step  306  and shown in  FIG. 4 e   . This may further employ an introducer or bayonet  121  adapted for releasably attaching to the flexible sheath  130 , such that the introducer  121  has markings for inserting the flexible sheath  130  between the rigid sheath  110 ,  112  portions to a predetermined depth, and releasing the flexible sheath  130  for disposing the flexible sheath  130  in communication with a surgical site  160 , as shown at step  307 . 
     The flexible sheath may be of any suitable construction, such as expandable or ribbed, as shown at step  308 . Therefore, the resilient tubular shape may be an expandable shape adapted to respond to surgical instruments biased against the flexible sheath and return to an unexpanded shape, as shown at step  309 . Alternatively, the resilient tubular shape may have alternating folds for responding to biasing by surgical instruments  162 ,  164  as shown step  310  and below in  FIGS. 7 a   ,  7   b.    
     After the obturator  120  has reached and defined a predetermined depth, and been subsequently withdrawn, each of the portions of the rigid sheath portions  110 ,  112  are withdrawn in succession, in which the rigid sheath portions  110 ,  112  are adapted to slideably pass between the flexible sheath  130  and surgical tissue, as shown at step  311  and in  FIGS. 4 h  and 4 i   . The procedure may further include securing a proximate end of the flexible sheath  130  with a portal such as a depth limiter  140  flush with an opening defining the surgical passageway, as depicted at step  312 , such that the portal is adapted to maintain a depth reference by maintaining a constant distance to a distal end of the flexible sheath  130 . The depth limiter  140  is flush with an opening defining the surgical passageway, and thus is adapted to maintain a depth reference by establishing a constant distance to a distal end of the flexible sheath  130 , as depicted at step  313 . 
     Following insertion of the flexible sheath  130 , the surgeon employs the defined surgical tunnel  150  for simultaneous access by a plurality of surgical instruments  162  and  164 , such that the flexible sheath  130  is responsive to the surgical instruments  162 ,  164  for deforming within the surgical passageway, as depicted at step  314 . The flexible sheath  130  then returns to an unexpanded shape upon repositioning of the surgical instruments  162 ,  164  away from biasing against the flexible sheath, as disclosed at step  315 . 
       FIGS. 7 a -7 f    shown an alternate single piece sheath configuration. Referring to  FIGS. 7 a - f   , a fan fold configuration  170  employs alternately folded portions  172  for permitting expansion and retraction of the sheath  170 . Each of rigid sides  170 - 1  and  170 - 2  are coupled by the folding portions  172 . An irrigation channel  174  occupies one of the rigid sides  170 - 1 , and an endoscope channel  176  occupies the opposed rigid side  170 - 2 . Alternate arrangements for the obturator include obturator  120 ′, and obturator  120 ″ having an elongated tip  178 , as shown in  FIGS. 7 e    and  7   f.    
       FIGS. 8 a -8 h    show alternate linkage arrangements of the sheath portions  110  and  112 .  FIGS. 8 a -8 d    show a flap and spine linkage including a rigid spine  182  having a slot  186 . Each of rigid halves  180 - 1  and  180 - 2  has a flap  184 , such that opposed flaps are engaged by the slot  186  of the spine  182  to couple the halves  180 - 1 ,  180 - 2 .  FIG. 8 e    shows a cross section view of the overlap region  113  of the configuration of  FIG. 1  above.  FIG. 8 f    shows a tongue and groove configuration  190  where each of portions  190 - 1  and  190 - 2  are linked by a tongue  192  adapted to be received by a groove or slot  194 .  FIGS. 8 g  and 8 h    disclose a peel away cannula  195  that employs tape-like peel away membranes  196  for installing the rigid sheath. 
     While the apparatus and methods defined herein have been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.