Abstract:
A deep brain stimulation lead system has a medical lead, or similar elongate medical insertion device, securable with a lead lock through a cannula slit, thereby allowing a lead to remain electrically operative and preventing movement of the lead during removal of a stylet, recording microelectrode, or cannula.

Description:
The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/404,692, filed Aug. 20, 2002, which application is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to systems and methods for inserting a medical device into the brain for deep brain stimulation. 
     BACKGROUND OF THE INVENTION 
     Deep brain stimulation (DBS) and other related procedures involving implantation of leads and catheters are increasingly used to treat Parkinson&#39;s disease, dystonia, essential tremor, seizure disorders, obesity, depression, restoration of motor control, and other debilitating diseases. During these procedures, a catheter, lead, or other medical device is strategically placed at a target site in the brain. Locating the “best” target for stimulation in the brain can be a painstaking procedure. 
     Implantation of a lead for DBS generally involves the following preliminary steps: (a) anatomical mapping and (b) physiological mapping. Anatomical mapping involves mapping segments of an individual&#39;s brain anatomy using non-invasive imaging techniques, such as magnetic resonance imaging (MRI) and computed axial tomography (CAT) scans. Physiological mapping involves localizing the brain site to be stimulated. Step (b) can be further divided into: (i) preliminarily identifying a promising brain site by recording individual cell activity with a microelectrode and (ii) confirming physiological stimulation efficacy of that site by performing a test stimulation with a macroelectrode or microelectrode, however a macroelectrode is preferred. 
     Microelectrode recording is generally performed with a small diameter electrode with a relatively small surface area optimal for recording single cell activity. The microelectrode may be essentially a wire which has at least the distal portion uninsulated to receive electrical signals. The rest of the body or wire of the microelectrode may be insulated. The microelectrode functions as a probe to locate a promising brain site. Since a number of attempts may be required to locate the precise target site, it is desirable that the microelectrode be as small as possible to minimize trauma when the microelectrode is placed into the brain, in some cases, multiple times. 
     Once a brain site has been identified, a macroelectrode is used to test that the applied stimulation has the intended therapeutic effect. Once macrostimulation confirms that stimulation at the brain site provides the intended therapeutic effect, the macroelectrode is withdrawn from the brain and a DBS lead is permanently implanted at the exact site. 
     A conventional procedure for carrying out the microelectrode recording phase of DBS may involve the following detailed steps: (1) placing a stereotactic frame on the subject, which stereotactic frame is a device temporarily mounted on the head to assist in guiding the lead system into the brain; (2) performing MRI or equivalent imaging of the subject with the stereotactic frame; (3) identifying a theoretical target using a planning software; (4) placing the subject with the stereotactic frame in a head rest; (5) using scalp clips, cutting the subject&#39;s skin flap in the head, exposing the working surface area of the cranium; (6) placing the stereotactic arc with target coordinate settings and identifying the location on the skull for creation of a burr hole; (7) removing the arc and drilling a burr hole in the patient&#39;s skull; (8) placing the base of the lead anchor; and (9) with the microelectrode recording drive attached, and with an appropriate stereotactic frame adaptor inserted into the instrument guide, placing the stereotactic arc. 
     Next, (10) advancing a microelectrode cannula (or several at a time) and an insertion rod into the brain until they are approximately 25-35 mm above the target; (11) removing the insertion rod, and leaving the cannula in place; (12) inserting a recording microelectrode such that the tip of the microelectrode is flush with the tip of the microelectrode cannula; (13) connecting the connector pin of the recording microelectrode to a microelectrode recording system; (14) starting approximately 25 mm above the target, advancing the microelectrode into a recording tract at the specified rate using the microdrive; and (15) if the target is identified, removing the recording microelectrode cannula and recording microelectrode and leaving a stimulation or recording lead or similar device in their place. 
     Some physicians might use additional steps, fewer steps, or perform the steps in a different order. 
     On average, a single microelectrode recording tract takes approximately 30 minutes to perform. Each microelectrode recording tract requires placement of a larger diameter insertion cannula at a distance of 25-35 mm above the target site through viable brain tissue. Each time an object is inserted into the brain there is approximately a 5% risk of hemorrhage. Creating multiple tracts increases the risk for intracranial bleeding, duration of operation, post-operative infection, and operative risk. Creating new tracts is fraught with misalignment/misplacement problems because the introduction cannulas may not trace the exact pathways desired. 
     There is, therefore, a need to provide a system and method for implanting a medical device such as a lead into the brain that reduces the duration of the operation, reduces the number of repetitive invasive tracts created to find the “best” target site, reduces post-operative infection, and reduces operative risk to provide optimal physiological therapy. 
     SUMMARY OF THE INVENTION 
     The present systems and methods address the above and other needs by providing systems and methods for implanting a medical device such as a lead into the brain and avoids lead displacement once the “best” target site in the brain is located and components such as a recording microelectrode and a cannula are removed from the stereotactic frame. 
     The present systems and methods include a slit cannula, an elongated medical device within the lumen of the slit cannula, and a lock for securing the elongated medical device through the slit in the cannula. The lock is fastened to a reference platform, which reference platform is attached to a stereotactic frame. 
     In one aspect of the present systems and methods, the elongated medical device is a lead or catheter with an offset portion. The offset portion may be a tab, knob, bulge, parallel lead, or any other structure along the side of the lead to which the lock may attach. The offset portion may also be a paddle electrode connector or other electrode connector of the lead. The electrode connector is capable of forming an electrical connection with an operating room cable connected to an external trial stimulator. 
     In another aspect of the present systems and methods, the elongated medical device has a lumen through its axis, and the lumen does not continue through the offset portion. The lumen of the lead may be dimensioned to permit a microelectrode to be inserted into the lead lumen. 
     Conventionally, when a cannula enveloping a lead is removed from a stereotactic frame, the cannula is pulled upward, away from the brain, as it slides like a sleeve off of the lead. Before the distal tip of the cannula exits the skull, the proximal tip of the cannula has covered the proximal end of the lead. Thus, as the proximal length of the lead is cloaked by the cannula and the distal length of the lead is cloaked by the skull, dura mater, and brain, no portion of the lead is visible to the surgeon. Yet in order to insure that the lead does not move during removal of the cannula and other structures, e.g., the recording microelectrode, it is critical that at least a portion of the lead be seen by the surgeon at all times, and if possible, locked into place. The present systems and methods avoid lead displacement by permitting a surgeon to view and lock the lead into place at all times during the removal of a cannula and other structures such as the recording microelectrode. 
     The present systems and methods allow a surgeon to remove a recording microelectrode before or after a cannula is removed. The present systems and methods also allow a surgeon to place a non-isodiametric lead within a cannula lumen. Further, the present systems and methods prevent fluid ingress into the connector end of a lead. Further still, the present systems and methods allow a surgeon to deliver continuous stimulation and receive continuous recording signals through the lad during removal of the surgical insertion tools (i.e., the cannula, recording microelectrode, and other devices) in order to continuously monitor any potential changes in stimulation efficacy of the lead during removal of the insertion tools. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects of the present systems and methods will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1A  shows a front view of an offset lead of the present systems and methods 
         FIG. 1B  shows a front view of a DBS lead system of the present systems and methods; 
         FIGS. 2A-2D  represent front views of the DBS system showing a sequence for removal of the surgical insertion tools of  FIG. 1B ; 
         FIG. 3  shows a perspective view of the lead and lead lock of the DBS lead system shown in  FIG. 1B ; 
         FIG. 4  shows a close-up, perspective view of the removal of the slit cannula from the offset lead/lead lock assembly of  FIG. 1B ; 
         FIG. 5  shows a top view of the lead, lead lock, and slit cannula of  FIG. 1B ; and 
         FIG. 6  shows a close-up, side view of the slit cannula and the base of the offset portion of the lead of  FIG. 4 . 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description includes the best mode presently contemplated for carrying out the present systems and methods. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the present systems and methods. The scope of the invention should be determined with reference to the claims. 
     The systems and methods described herein that allow for visualization and locking of a deep brain stimulation (DBS) lead, or other elongated medical structure, during a surgical tool removal process of a DBS procedure, hence eliminating the risk of lead movement. Visualization and locking of the lead during the surgical removal process can be accomplished using a unique lead system. 
     For this disclosure, the lead system refers to (1) a lead, (2) a slit cannula, (3) a lead lock, and (4) a recording microelectrode or stylet. The lead may have a lumen for receiving the recording microelectrode. The lead is also dimensioned to fit within the lumen of the slit cannula. The lead lock is capable of attaching to the lead through the slit of the cannula. Alternatively, the lead has an offset portion that extends from the main body of the lead, through the slit cannula, to the lead lock. The lead lock is capable of attaching to the offset portion of the lead. The lead lock is, in turn, anchored to a stereotactic frame, or other permanent reference point. 
     Because the lead is anchored by means of a lead lock to a permanent reference point, a surgeon is able to remove both the slit cannula and the recording microelectrode without disturbing the location of the lead within the brain. Even a slight movement of a lead from its target site within the brain of a patient can dramatically decrease the therapeutic effect of the lead for the patient. Thus, the present systems and methods lock the lead into place once the lead has been placed in a location of maximum therapeutic effect for the patient. 
     As shown in  FIG. 1A , the lead may be an offset lead  100  with a lead body  101  and an offset portion  102 . Referring to  FIGS. 1A and 1B , lead body  101  fits within the lumen of a slit cannula  110  while offset portion  102  remains connected to lead body  101  through the slit of cannula  110 . A lead lock  120  attaches to offset portion  102  of lead  100  and thereby anchors lead  100  through cannula  110  to a stereotactic frame  130 . 
       FIG. 1B  shows a front view of an embodiment of the DBS lead system of the present systems and methods. The DBS lead system of  FIG. 1B  includes offset lead  100 , which can also be a catheter or other similar insertable medical device; slit cannula  110 ; and lead lock  120 .  FIG. 1B  also shows stereotactic frame  130 , which holds the components of the DBS lead system during a DBS procedure; a stylet and/or recording microelectrode  140  inserted within the lumen of lead  100 ; and a skull  150 , dura mater  160 , and brain  170  of a patient. The DBS lead system is fully engaged with stereotactic frame  130 , and the distal ends of both offset lead  100  and slit cannula  110  are inserted into brain  170 . 
       FIGS. 2A-2D  illustrate the procedure used to remove microelectrode  140  and/or cannula  110  of the DBS lead system shown in  FIG. 1B .  FIG. 2A  shows the DBS lead system in stereotactic frame  130  with microelectrode  140  and with slit cannula  110  fully inserted.  FIG. 2B  depicts the removal of microelectrode  140  from the DBS lead system.  FIG. 2C  depicts the removal of cannula  110  from the DBS lead system. The steps of removing microelectrode  140  and cannula  110  can be performed in reverse order when the proximal end of microelectrode  140  is moved or bent to the side, through the slit of cannula  110 , and cannula  110  is removed. Cannula  110  has a slit  400  (shown in  FIG. 4 ) along its entire length that, inter alia, permits the body of microelectrode  140  to be moved or bent to the side, i.e., outside the lumen of cannula  110 , in order for cannula  110  to be removed. If connector  200  (see  FIG. 2A ), at the proximal end of microelectrode  140 , has an outer diameter less than the inner diameter of slit cannula  110 , no movement of microelectrode  140  is required.  FIG. 2D  depicts the removal of all the insertion tools of the DBS lead system, thus leaving offset lead  100  securely locked into place by lead lock  120 . 
       FIGS. 1B through 2D  show lead  100  locked to lead lock  120  at an elevated point above the skull of a patient. However, the present systems and methods include invention locking lead  100  to lead lock  120  at locations along lead  100  that are closer to the skull than shown in  FIGS. 1B through 2D . In some examples, lead  100  is locked to lead lock  120  just above the site of entry into the skull. Lead  100 , or another elongated medical device locked by lead lock  120 , may be made of malleable or elastic material. Therefore, lead  100  may move slightly when other devices in contact with lead  100  are moved. Lead  100  may move despite the fact that it is locked into place by icad lock  120 . Locking the lead  100  at or just above the site of entry into the skull minimizes unwanted movement of lead  100  during movement of other structures in contact with lead  100 . Movement is minimized because lead  100  is stabilized by lead lock  120 , the skull, and brain tissue and because the distance between the point at which lead  100  is locked and the target site in the brain is minimized. 
       FIG. 3  is a perspective view of offset lead  100  and lead lock  120  of the DBS lead system shown in  FIG. 1B . In this embodiment of the offset lead, the proximal end of offset lead  100  has a lumen  300  terminating at approximately the same height as an arm  310  of the offset portion  102  of offset lead  100 . Lead lock  120  is attached to an insertion tool holder  320 . Lead lock  120  clamps a base  600  (see  FIG. 6 ) of offset portion  102  of offset lead  100  securely into place. In an alternate embodiment, lead lock  120  may secure offset lead  100  through a spring-loaded clamp, vice, or similar mechanism capable of securing offset lead  100 . In yet another alternate embodiment, offset lead  100  may have a tab, knob, bulge, or any other structure to which lead lock  120  may attach instead of base  600  (see  FIG. 6 ) of offset portion  102 . 
     Offset lead  100  is described as non-isodiametric because its diameter changes due to an attachable structure along its length. However, in yet another embodiment of the present system, an isodiametric lead, i.e., a lead with no attachable structures along its length, may also be attached to or secured by an embodiment of lead lock  120 . For example, a lead could be pinched by prongs, pierced by hooks or pins, sutured by a pin and thread, or otherwise restrained by a break through a slit  400  (see  FIG. 4 ) of cannula  110 . In some examples, a lead or elongated medical device is secured through the slit  400  (see  FIG. 4 ) in cannula  110  by a structure that may be fastened to the stereotactic frame or a similar reference platform in the case that the surgery is performed without a stereotactic frame. 
       FIG. 4  is a close-up, perspective view of the removal of the slit cannula from the lead/lead lock assembly of  FIG. 1B . The slit  400  of cannula  110  allows for use of an isodiametric or non-isodiametric lead  100 . This allows for use of a lead that has a highly reliable connector such as a silicone paddle  410 , or other paddle electrode connector with electrical contacts  420 . Silicone paddle  410  is capable of being connected to an external trial stimulator via an operating room cable. Silicone paddle  410  forms a silicone to silicone seal between the electrical contacts  420  at the coupling of a lead and an implantable pulse generator. 
     Because silicone paddle  410  is adjacent to the main portion of offset lead  100 , lumen  300  (see  FIG. 3 ) of offset lead  100  does not extend into the arm  310  of offset portion  102  of offset lead  100 . Therefore, it is impossible for fluid to travel through lumen  300  (see  FIG. 3 ) to the implantable pulse generator. Conventionally, unwanted fluid penetration via the lead to an implantable pulse generator is possible, for example, with an isodiametric lead and use of connectors such as those available from Bal Seal Engineering of Foothill Ranch, California. At the coupling of a Bal Seal, a series of circular springs surround the circumference of the lead contacts and are longitudinally spaced by polyurethane, silicone, or epoxy seals. In order for the lead to couple with the implantable pulse generator, the lead contacts must pass each consecutive seal, thereby disturbing the original structure of the spacer seals and compromising the ability of the Bal Seal to prevent fluid penetration. As mentioned earlier, fluid penetration using an offset lead  100  is impossible as lumen  300  (see  FIG. 3 ) does not travel to silicon paddle  410 , which paddle  410  is used to electrically connect to an implantable pulse generator. In an alternate embodiment, offset lead  100  without paddle  410  could be coupled with a Bal Seal connection mechanism, or any other functional connection mechanism, and fluid ingress would still be avoided as lumen  300  (see  FIG. 3 ) does not travel to the site of connection in non-isodiametric offset lead  100 . 
     In summary, the offset feature of offset lead  100  prevents fluid ingress through a paddle, Bal Seal, or other connection mechanism. As shown in the embodiment in  FIG. 4 , because offset lead  100  has an offset portion  102 , paddle  410  may be used, thereby providing a superior sealing mechanism, especially as compared to the Bal Seal mechanism. 
     Slit  400  along the entire length of cannula  110  also allows the physician to visualize the offset lead  100  during removal of cannula  110 . Another advantage of slit cannula  110  is that the stylet or microelectrode  140  (see  FIG. 1B ) can be removed before or after cannula  110  is removed. 
       FIG. 5  is a top view of the offset lead  100 , lead lock  120 , and slit cannula  110  of  FIG. 1B . Arm  310 , silicone paddle  410  with electrical contacts  420 , and insertion tool holder  320  are also shown. 
       FIG. 6  is a close-up, side view of slit cannula  110  with slit  400  and base  600  of offset portion  102  of lead  100  of  FIG. 4 . As previously mentioned, base  600  of offset portion  102  holds lead  100  (referring to  FIGS. 1A and 1B ) stable while the temporary surgical tools are removed. When cannula  110  and microelectrode  140  are removed, a lead anchor lock or burr hole plug can be engaged to lock lead  100  in place, at which time lead lock  120  can safely be disengaged. Then, stereotactic frame  130  (shown in  FIG. 1B ) can be removed without disturbing lead  100 . The stereotactic frame adapters may consist of two halves that facilitate easy removal of the frame without disturbing the position of lead  100 . Referring to  FIG. 4 , lead lock  120  permits silicone paddle  410  to attach to an external trial stimulator via an operating room cable such that clinical efficacy, i.e., physiological response stimulation via lead  100 , can be observed during the removal of the recording microelectrode  140  and insertion cannula  110 . Thus, a change in clinical response to stimulation will immediately be observed and adjustments during the removal process can be made. 
     While the systems and methods herein disclosed have been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.