Patent Publication Number: US-2005119603-A1

Title: Surgical implant for accessing cerebrospinal fluid and method of surgically inserting same

Description:
FIELD OF THE INVENTION  
      This invention generally relates to an implant for gaining access to cerebrospinal fluid (csf) in the brain, and in particular relates to a surgical implant which serves as a guide for directing a surgical instrument, such as a needle, into the lateral ventricle of the brain.  
     BACKGROUND OF THE INVENTION  
      It is often necessary for research and treatment purposes to have access to cerebrospinal fluid from conscious patients or subjects. For example, by sampling or collecting cerebrospinal fluid, the progression of various brain diseases, infections, or other ailments can be monitored on a regular basis. In research, cerebrospinal fluid sampling is often required to monitor drug levels as well as to monitor changes in physiological parameters in the cerebrospinal fluid. Further, it is often desirable or necessary to administer therapeutic agents directly into the cerebrospinal fluid to bypass the blood-brain barrier.  
      Various devices and methods have been developed for the purpose of accessing cerebrospinal fluid in humans and animals. One such device is a guide cannula which is intended for implanting within the skull of a canine. One or more of these guide cannulas are secured in the skull of the animal and extend to touch the surface of the dura mater on the surface of the brain so that each of the guides is aligned (but not in contact) with one of the lateral ventricles of the brain. These guides are implanted for the purpose of permitting repeated sampling of cerebrospinal fluid over a predetermined span of time, and thus the guides are left within the skull of the animal and are accessed via a collection needle placed through the skin and muscle located above the respective guides following a surgical-style preparation of the skin over the guides. The needle is inserted into the guide cannula and is guided thereby into the corresponding lateral ventricle to collect cerebrospinal fluid. One of the disadvantages of this arrangement is that the guide cannula locks to the skull of the animal with screw-threads, which can cause difficulty with respect to successfully aligning the needle guide in relation to the lateral ventricle. Further, the screw-threads often result in improper placement of the guide cannula when the sloped surface of the skull catches the threads and pulls the implant out of proper alignment.  
      The present invention is directed to an implant or needle guide for accessing cerebrospinal fluid from the brain which overcomes or at least minimizes the disadvantages of known devices. The implant includes an upper head or housing having a flange-like base which projects sidewardly from the housing and is fixed to the skull, and a tube or stalk which projects through a hole formed in the skull. In a preferred embodiment, the head and tube together define a lumen which serves as a guide for a surgical instrument, such as a needle. The implant is positioned in the skull over one of the lateral ventricles in the brain based upon predetermined coordinates with the implant head located subcutaneously on the skull, so that when a needle is inserted into the lumen, the implant precisely guides the needle into the lateral ventricle for collection of cerebrospinal fluid or for dosing therapeutic agents directly into the cerebrospinal fluid.  
      The implant is dimensioned so that when properly positioned in the skull, the free end of the tube is spaced from, and does not penetrate, the lateral ventricle. Thus, the implant itself makes no direct contact with the ventricle. This lack of contact with the ventricle advantageously maintains sterility with repeated use. Further, the flange-like base positioned on the outer surface of the skull allows accurate and reliable positioning of the implant via adhesive such as surgical glue and/or surgical resin, which causes less skull trauma. The free end of the stalk or tube is blunt and rests upon or is disposed closely adjacent the dura mater located beneath the skull which also results in less trauma to the patient, as compared with the above-discussed guide which includes a pointed lower edge which penetrates the dura mater.  
      Other objects and purposes of the invention will be apparent to persons familiar with devices of this type upon reading the following description and inspecting the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a front elevational view of the implant according to the invention.  
       FIG. 2  is a plan view of the implant.  
       FIG. 3  is a cross-sectional view of the implant taken generally along line  3 - 3  in  FIG. 2 .  
       FIG. 4  is a vertical cross-sectional view of the brain of an animal, such as a canine.  
       FIG. 5  is an enlarged, fragmentary, vertical cross-sectional view of the brain of  FIG. 4 , with a pair of implants in position in the skull.  
       FIG. 6  is a vertical cross-sectional view of the brain of a human.  
       FIG. 7  is an enlarged, fragmentary, vertical, cross-sectional view of the brain of  FIG. 6 , with a pair of implants in position in the skull. 
    
    
      Certain terminology will be used in the following description for convenience in reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.  
     DETAILED DESCRIPTION  
      Referring to  FIGS. 1-3 , an implant or guide  10  is illustrated according to the present invention. The implant  10  generally includes a rigid head or housing  11 , a flange-like base  12  positioned at one end of the housing  11 , and a tube or stalk  13  which depends downwardly from the base  12  and terminates in a lower free end  14 .  
      Upper housing  11  is generally annular in shape, and defines an outer cylindrical and generally vertically oriented surface  17 , a generally planar and annular upper surface  18  which in the illustrated embodiment is generally perpendicular to surface  17 , and a generally planar and annular lower surface  19  which is spaced downwardly from and is generally parallel to upper surface  18 . Housing  11  has an opening  20  which projects completely therethrough, and is defined by an inner annular surface  21  which is tapered or funnel-shaped when viewed in cross-section as in  FIG. 3 , and an inner cylindrical surface  22  which adjoins surface  21  at a transition point  23  and projects downwardly therefrom. Surface  22  is generally parallel to outer surface  17 .  
      Base  12  is a thin and flexible plate-like member, and defines thereon generally planar, parallel and annular upper and lower surfaces  26  and  27 , and a generally vertically oriented side surface  28  which interconnects surfaces  26  and  27 . Base  12  defines therein an opening  29  which projects completely through the thickness of base  12  as defined between the surfaces  26  and  27 .  
      Tube  13  is generally cylindrical in shape and defines inner and outer cylindrical and generally parallel surfaces  32  and  33 . Inner surface  32  defines an opening  34  which extends completely through tube  13 . As shown in  FIG. 3 , the outer diameter of tube  13  as well as the diameter of opening  29  of base  12  are similar in dimension to the diameter of the lower portion of housing opening  20  as defined by lower surface  22 . Dimensioning the implant components in this manner allows same to be assembled to one another without the use of adhesives or other fasteners. More specifically, the implant  10  is assembled by inserting the tube  13  downwardly through the upper portion of the housing opening  20 , and then forcing the tube  13  into the lower constricted part of the opening  20  until an uppermost end  38  of tube  13  is positioned generally at the transition point  23 . The base  12  is then fitted over the lower free end  14  of tube  13  until same engages and abuts the lower surface  19  of housing  11 . The tube  13  thus effectively serves as a fastening device which secures housing  11  and base  12  to one another through a force-fit arrangement. However, adhesive may be used to further secure housing  11 , base  12  and tube  13  to one another, if desirable or necessary. Further, it will be appreciated that housing  11 , base  12  and tube  13  may alternatively be secured to one another through a mechanical interlock arrangement.  
      When housing  11 , base  12  and tube  13  are assembled to one another as discussed above, opening  20  of housing  11  and opening  34  of tube  13  together define a lumen  37  which extends through the implant  10  and serves as a guide channel through which a surgical instrument can be inserted.  
      It will be appreciated that housing  11  and base  12  can instead be constructed as a unitary component, for example by milling a suitably sized cylinder to define base  12 . Housing  11 , base  12  and tube  13  may also be constructed as a unitary, one-piece component.  
      In the illustrated embodiment, housing  11 , base  12  and tube  13  are constructed of surgical-grade stainless steel. However, these components may alternatively be constructed of non-reactive, injection-molded rigid plastic, resin or titanium.  
       FIGS. 4 and 5  illustrate a brain  40  of an animal, such as a canine and  FIGS. 6 and 7  illustrate the brain  41  of a human. The same reference numbers are used in these drawings to refer to the same or similar parts of brains  40  and  41 . The brain  40 ,  41  is contained within the skull  42  covered by skin  43 , and includes three primary parts, the cerebrum which is defined by the cerebral hemispheres  45 , the cerebellum  46  and the spinal cord or brain stem (not shown). A thick and fibrous membrane called the dura mater  47  lines the interior of the skull  42 . The most common sites for accessing cerebrospinal fluid in the brain are the lateral ventricles  48 , which are respectively located in the lower and inner parts of the cerebral hemispheres  45  and contain cerebrospinal fluid therein.  
      The guide  10  according to the invention is implanted into the brain  40 ,  41  of a patient as follows, with reference to  FIGS. 5 and 7 . The anesthetized patient is placed in a conventional stereotaxic apparatus and aseptically prepped for surgery. A longitudinal midline incision is made over the center of the skull  42 , and dissection is employed to extend the incision down to the surface of the skull  42 . The musculature is then laterally peeled away from the skull  42  to clear the area for the implant  10 . Using predetermined brain coordinates, a bone drill positioned in the stereotaxic apparatus is used to drill a hole  50  in the skull  42  of the same or similar diameter as the tube  13  at the appropriate position above one of the lateral ventricles  48 . The drill is removed, and a syringe and needle, such as manufactured by the Hamilton Company, is assembled to the implant  10  by inserting the needle through the lumen  37  of the implant  10 . This assembly is then mounted to the stereotaxic apparatus and the needle advanced into the hole  50  in the skull  42  until cerebrospinal fluid is obtained. The needle is then backed off until same has exited the lateral ventricle  48 , and the implant  10  is advanced down the needle until the tube  13  is located about halfway into the hole  50  in the skull  42 . Surgical adhesive or gel  51 , such as cyanoacrylate gel, is then applied to the exposed upper portion of the tube  13  and to lower surface  27  and the side edge  28  of base  12 , and the implant  10  is then advanced down the needle and into position in the skull  42 . In this regard, the implant  10  is properly positioned when the lower free end  14  of tube  13  penetrates the skull  42  and rests on the surface of the dura mater  47 . The lower free end  14  of the tube  13  is preferably rounded or blunt, so as not to damage or otherwise cause trauma to the skull  42  and the membranes beneath the skull  42 .  
      The surgical gel  51  serves to anchor the implant  10  in place and provides a build-up of material below the housing  11  and base  12  to fill the gap created by the natural curvature of the skull  42 . This build-up of surgical gel  51  is necessary since the orientation of the base  12  should preferably be parallel with the horizontal to ensure proper guidance of the surgical instrument into the respective lateral ventricle  48 . The enlarged base  12  of the implant  10  advantageously provides an edge or lip which is gripped by the adhesive  51  to firmly lock the implant  10  in the proper angular orientation relative to the skull  42 . Additional implants  10  can then be placed within the skull  42  at other coordinates, as shown in  FIGS. 5 and 7 . Once the implant  10  is in position, an infusion of radio-opaque dye can be infused via the implant  10  and observed with fluoroscopy to confirm the proper directional orientation of tube  13  relative to the respective ventricle  48 .  
      The incision is then closed, and after the skin  43  is fully closed over the skull  42  but prior to the patient&#39;s recovery from the anesthesia, a collection needle is inserted into the implant  10  and slowly advanced until cerebrospinal fluid begins welling up in the needle. This needle depth, as measured between the skin  43  to the point at which sufficient fluid flow is achieved, is recorded for the particular implant  10  and is subsequently used to provide the proper needle depth for post-surgical collections or dosings. These recorded needle depths constitute default depths for the particular implants  10  and needles are either specially cut to length for accessing fluid or dosing, or suitable spacers are utilized on standard needles to provide the proper penetration depth as discussed below.  
      When sampling of cerebrospinal fluid is desirable or necessary, the skull  42  of the patient is felt with the fingers in order to locate the bump or nodule created by the upper housing  11  of the implant  10  under the skin  43 . Using standard aseptic practices, a collection needle  60  ( FIGS. 5 and 7 ) is then pushed through the skin  43  and into the lumen  37  of the implant  10  and is guided downwardly by the tapered surface  21  of housing  11  and into the opening  34  of the tube  13 . As the needle  60  is advanced, the tube  13  then guides the needle  60  as same penetrates the brain and ultimately enters the lateral ventricle  48 . Cerebrospinal fluid is then withdrawn from the lateral ventricle  48  with the needle  60 . As discussed above, an appropriately-sized spacer  61  defining a through-hole  62  therein may be utilized in conjunction with needle  60  to ensure proper insertion depth into the ventricle  48 . The same procedure is utilized when dosing of a drug or drugs is desirable or necessary, except that a dosing needle is utilized instead of a collection needle and serves to deliver a drug directly into the cerebrospinal fluid located within the lateral ventricle  48 .  
      It will be appreciated that the implant  10  according to the invention may be utilized with humans and canines as discussed above, and the dimensions thereof will be based upon the brain size and structure of the particular animal. In this regard, the implant  10  is also usable with animals other than canines, such as rabbits and non-human primates. When utilized in a human, typical dimensions of the implant  10  are as follows: the upper housing has an outer diameter of approximately 8-10 mm, and a height of approximately 4-6 mm; the base  12  has an outer diameter of approximately 10-12 mm; and the tube  13  projects outwardly from the base  12  over a distance of about 6-8 mm. When used in a canine, typical dimensions of the implant  10  are as follows: the upper housing  11  has an outer diameter of approximately 5 mm, and a height of approximately 4 mm; the base  12  has an outer diameter of approximately 8 mm; and the tube  13  projects outwardly from the base  12  over a distance of about 2-4 mm. When determining the dimensions of the implant  10  for a particular species, the tube  13  should preferably have a length sufficient to permit the tube  13  to penetrate the skull so that the lower free end  14  thereof rests on or adjacent the dura mater  47 .  
      It will be appreciated that the tapered surface  21  defined in the housing  11  enables easy insertion of a surgical instrument into the implant  10 . However, the surface  21  need not necessarily be tapered as shown, and the opening may instead be cylindrical, for example.  
      It will also be appreciated that the implant  10  may be utilized to guide a surgical instrument, such as a needle, into the left ventricle as discussed above, but may alternatively be used to insert a surgical instrument, such as a piezoelectric crystal typically used for obtaining a pressure reading. Further, the implant  10  may be used to insert a fiber-optic camera into the ventricle to visualize same.  
      Further, the implant  10  according to the invention may also be utilized as a temporary port for accessing cerebrospinal fluid from a patient or subject. In this regard, the implant would require a septum or other penetrable barrier at the upper open end of housing  11  so as to create a closed access port, and the skin would then not be closed over the implant. The implant as modified in this manner could be used for research purposes or for treating injuries.  
      Although a particular preferred embodiment of the invention has been disclosed for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.