Patent Publication Number: US-9427572-B2

Title: Implantable medical device with connector blocks

Description:
This application is a continuation application of U.S. patent application Ser. No. 12/183,214, filed Jul. 31, 2008, now U.S. Pat. No. 9,008,782, which claims the benefit of U.S. Provisional Application No. 61/000,533, filed Oct. 26, 2007. The entire contents of both of these applications is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to implantable medical devices, and more particularly, to implantable medical devices for delivery of electrical stimulation therapy. 
     BACKGROUND 
     Electrical stimulation systems may be used to deliver electrical stimulation therapy to patients to treat a variety of symptoms or conditions such as chronic pain, tremor, Parkinson&#39;s disease, multiple sclerosis, spinal cord injury, cerebral palsy, amyotrophic lateral sclerosis, dystonia, torticollis, epilepsy, pelvic floor disorders, gastroparesis, muscle stimulation (e.g., functional electrical stimulation (FES) of muscles) or obesity. An electrical stimulation system typically includes one or more implantable medical leads coupled to an external or implantable electrical stimulator. 
     The implantable medical lead may be percutaneously or surgically implanted in a patient on a temporary or permanent basis such that at least one stimulation electrode is positioned proximate to a target stimulation site. The target stimulation site may be, for example, a nerve or other tissue site, such as a spinal cord, pelvic nerve, pudendal nerve, stomach, bladder, or within a brain or other organ of a patient, or within a muscle or muscle group of a patient. The one or more electrodes located proximate to the target stimulation site may deliver electrical stimulation therapy to the target stimulation site in the form of electrical signals. 
     Electrical stimulation of a peripheral nerve, such as stimulation of an occipital nerve, may be used to mask a patient&#39;s feeling of pain with a tingling sensation, referred to as paresthesia. Occipital nerves, such as a lesser occipital nerve, greater occipital nerve or third occipital nerve, exit the spinal cord at the cervical region, extend upward and toward the sides of the head, and pass through muscle and fascia to the scalp. Pain caused by an occipital nerve, e.g. occipital neuralgia, may be treated by delivering electrical stimulation therapy to the occipital region via an implanted stimulation lead. 
     SUMMARY 
     This disclosure includes techniques for implanting an electrical stimulation system including a housing with a stimulation generator and electrical stimulation leads inferior to the inion of a patient. The disclosed techniques may be used to treat alleviate occipital neuralgia. 
     In one embodiment, an implantable medical device comprises one or more electrical stimulation generators, and a housing that contains the one or more electrical stimulation generators. The implantable medical device also includes a first medical lead no greater than about 6 inches in length, and a second medical lead no greater than about 6 inches in length. The housing includes a first connector block that electrically connects the first medical lead to at least one of the one or more electrical stimulation generators, and a second connector block that electrically connects the second medical lead to at least one of the one or more electrical stimulation generators. 
     In another embodiment, an electrical stimulation system comprises an electrical stimulator. The electrical stimulator comprises a housing having a width and a length that are each greater than a thickness of the housing, one or more stimulation generators within the housing, and at least two connector blocks. Each connector block accepts a medical lead. The electrical stimulation system further comprises at least two medical leads extending from the housing and electrically coupled to the stimulation generator via the connector blocks. Two of the medical leads connect to the housing at separate locations, wherein the separate locations are separated by at least a third of the length of the housing, wherein each of the at least two medical leads are no greater than about 6 inches in length. 
     In another embodiment, a method for implanting an electrical stimulation system in a patient comprises making an incision in the skin of a patient inferior to the inion of the patient. The paths are sized to accept medical leads of the electrical stimulation system. The method further includes forming an inferior pocket under the skin inferior to the inion, wherein the pocket is sized to accept a housing of an electrical stimulator of the electrical stimulation system, inserting the medical leads of the electrical stimulation system into the lateral paths, inserting the housing into the inferior pocket and closing the incision. 
     The details of one or more aspects of the present disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosed techniques will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a schematic diagram of a therapy system, which includes an electrical stimulator coupled to two stimulation leads that have been implanted in a body of a patient for occipital nerve stimulation. 
         FIG. 1B  illustrates a patient prior to implantation of the therapy system of  FIG. 1A . 
         FIGS. 1C-1E  illustrate the therapy system of  FIG. 1A  prior to implantation within the patient. 
         FIG. 2  is a block diagram illustrating various components of an electrical stimulator and medical leads of a therapy delivery system. 
         FIGS. 3A and 3B  respectively illustrate a top view and a side view of an electrical stimulator. 
         FIG. 4  is a block diagram illustrating an exemplary control module included in an on-site electrical stimulator for the treatment of a patient such as the electrical stimulator of  FIG. 2 . 
         FIG. 5  illustrates a therapy system including an electrical stimulator with a different shape than the electrical stimulator shown in  FIGS. 1A and 1C-1E . 
         FIG. 6  illustrates a therapy system including an electrical stimulator having a housing with two paddle electrode sets coupled directly to the housing. 
         FIG. 7  illustrates a therapy system including an electrical stimulator coupled to two axial leads. 
         FIGS. 8A-8B  illustrate a medical lead introducer including a blunt dissection element and a tab configured to engage a distal end of a medical lead. 
         FIGS. 9A-9B  illustrate a medical lead configured for insertion within a patient using the medical lead introducer of  FIGS. 8A-8B . 
         FIG. 10  illustrates a kit including a medical lead and a medical lead introducer packaged in a sterile container. 
     
    
    
     DETAILED DESCRIPTION 
     In general, the disclosure is directed to techniques for delivering electrical stimulation therapy to an occipital region of a patient via an implanted stimulation device. An electrical stimulator, once implanted, provides stimulation site treatment of head, neck, or facial pain or tension, including pain or tension caused by occipital neuralgia. The stimulation site may generally reside within the upper cervical region of the spine, e.g., C1-C4, and may target occipital nerves and branches in that region. For example, targeted nerves may include trigeminal nerves, greater occipital nerves, lesser occipital nerves, third occipital nerves and suboccipital nerves. An electrical stimulator can be implanted at the selected stimulation site adjacent a neuralgic region of the patient, and deliver neurostimulation therapy to treat pain and tension symptoms. 
       FIG. 1A  is a schematic diagram of therapy system  10 , which includes an electrical stimulator  12  coupled to stimulation leads  14 A,  14 B (collectively referred to as “leads  14 ”). In the example of  FIG. 1A , electrical stimulator  12  is implanted in a human patient  16  proximate to an occipital region  11  within patient  16 , below inion  20 , the craniometric point that is the most prominent point at the occipital protuberance on the back of the head of patient  16 . In the example of  FIG. 1A ,  FIG. 1B  illustrates patient  16  prior to implantation of therapy system  10 , and  FIGS. 1C-1E  illustrate the therapy system  10  prior to implantation within patient  16 . 
     Paddles  17 A,  17 B (collectively referred to as “paddles  17 ”) include electrode sets  7 A,  7 B (collectively referred to as “electrodes  7 ”) to deliver stimulation therapy to a therapy region, which generally encompasses occipital nerve sites and trigeminal nerve sites of patient  16 . Such nerve sites may include, for example, an occipital nerve (e.g., a greater occipital nerve, lesser occipital nerve, third occipital nerve and suboccipital nerves), a trigeminal nerve, tissue adjacent to the trigeminal or occipital nerves, or a nerve branching from the occipital and/or trigeminal nerves. Thus, reference to an “occipital nerve” or a “trigeminal nerve” throughout the disclosure also may include branches of the occipital and trigeminal nerves, respectively. In addition, the stimulation therapy may be delivered to both an occipital nerve and trigeminal nerve by a single therapy system  10 . While electrode sets  7  are linear in the example of  FIG. 1D , other examples may utilize paddle electrodes including a two-dimensional array of electrodes. In other embodiments, axial leads with ring electrodes, segmented electrodes, or other electrodes may be used. Other lead and/or electrode configurations may be used. 
     Electrical stimulator  12  generates a stimulation signal (e.g., in the form of electrical pulses or substantially continuous waveforms). The stimulation signal may be defined by a variety of programmable parameters such as electrode combination, electrode polarity, stimulation voltage amplitude, stimulation current amplitude, stimulation waveform, stimulation pulse width, stimulation pulse frequency, etc.) that is delivered to occipital region  11  by implantable stimulation leads  14 , respectively, and more particularly, via stimulation electrodes carried by stimulation leads  14 . Electrical stimulator  12  may also be referred to as a pulse or signal generator, or a neurostimulator. In some embodiments, leads  14  may also carry one or more sense electrodes to permit electrical stimulator  12  to sense electrical signals or other sensors to sense other types of physiological parameters (e.g., pressure, activity, temperature, or the like) from occipital region  11 , respectively. In some implementations, for example, such sensed parameters may be recorded for later analysis, e.g., evaluation of stimulation efficacy, or used in the control of stimulation therapy or therapy parameters. 
     The proximal ends of leads  14  are both electrically and mechanically coupled to separate connection ports  15 A,  15 B (collectively referred to as “ports  15 ”) of electrical stimulator  12 . Connection ports  15  are each located in a separate connector block within the housing of electrical stimulator  12 . The connector blocks including connection ports  15  include terminals at different axial positions within the connector block that mate with contacts at different axial positions at proximal ends of leads  14 . The connection between leads  14  and connection ports  15  also includes fluid seals to prevent undesirable electrical discharge. In different embodiments, leads  14  may be removed from connection ports  15  by a clinician if desired. For example, the removable connection may be a pressure, friction, or snap-fit, e.g., with a spring contacts. In other embodiments, leads  14  may be fixed to connection ports  15  such that simply pulling on leads  14  will not ordinarily release them from connection ports  15 . Examples of relatively fixed connections include solder connections, set screws or other techniques. 
     In any event, conductors disposed in the lead body of each of leads  14  electrically connect stimulation electrodes (and sense electrodes, if present) adjacent to the distal ends of leads  14  to electrical stimulator  12 . Connection ports  15  are located at least approximately a third of the length of the housing of electrical stimulator  12  apart from each other. For example, if the length of the housing is X, connection ports  15  are located at least ⅓*X apart from one another. Length may generally refer to a transverse or horizontal dimension of the housing of stimulator  12  in the example of  FIG. 1A . 
     In the example of therapy system  10  shown in  FIG. 1A , target tissue sites  18  and  19  are located within the patient&#39;s head or neck (e.g., proximate to one or more occipital nerve) and on opposite sides of midline  9  of patient  16 . Midline  9  is a schematic representation of the line that divides patient  16  into about equal and symmetrical left and right halves. Delivering therapy to two target tissue sites, such as sites  18  and  19 , may be used to deliver therapy to two nerve branches that branch from the same nerve. Nerves may branch into left and right branches that extend to opposite sides of midline  9 , and therapy is delivered to two nerve branches on opposite sides of midline  9  (such as at target tissue sites  18  and  19 ). Stimulation of two nerve branches on opposite sides of midline  9  may be referred to as bilateral stimulation. However, bilateral stimulation may also refer to stimulation of any two regions of patient  16  either sequentially or simultaneously. Delivering therapy after nerves branch, e.g., closer to the nerve endings, may allow more targeted therapy delivery with fewer side effects. Therapy may also be delivered unilaterally to sites  18 ,  19 . For example, stimulation therapy may be delivered to site  18  by paddle  17 B simultaneously or alternately with stimulation of site  19  by paddle  17 A. In addition, therapy may be delivered using an electrode set including at least one electrode from both paddle  17 A and  17 B. 
     Stimulation of the occipital region  11  (i.e., in regions of patient  16  proximate to occipital nerves, a trigeminal nerve or other cranial sites) may help alleviate pain associated with, for example, chronic migraines, cervicogenic headaches, occipital neuralgia or trigeminal neuralgia. 
     Therapy system  10 , however, may be useful in other neurostimulation applications. Thus, in alternate embodiments, target tissue sites  18  and  19  may be at locations proximate to any other suitable nerve in body of patient  16 , which may be selected based on, for example, a therapy program selected for a particular patient. For example, in other embodiments, therapy system  10  may be used to deliver neurostimulation therapy to other areas of the nervous system, in which cases lead  14  would be implanted proximate to the respective nerve(s). As one example, leads  14  may be implanted proximate to other nerves and/or structures of the head and neck of patient  16 . As another example, system  10  may be implanted at other locations in a patient and used for sacral stimulation, pelvic floor stimulation, peripheral nerve field stimulation, spinal cord stimulation, deep brain stimulation, gastric stimulation, or subcutaneous stimulation other than occipital stimulation. 
     Accurate lead placement may affect the success of occipital nerve stimulation. If lead  14  is located too deep, i.e., anterior, in the subcutaneous tissue, patient  16  may experience muscle contractions, grabbing sensations, or burning. Such problems may additionally occur if one of leads  14  migrates after implantation. However, because electrical stimulator  12  is located proximate to target tissue sites  18  and  19 , leads may be less than approximately six inches in length, which may provide a low electrical resistance and improve the efficiency of therapy system  10 . Additionally, the short length of leads  14  also limits the potential for lead migration because patient movement does not create a significant stress on leads  14 . In some embodiments, leads  14  may include fixation elements such as tines. 
     Therapy system  10  also may include a clinician programmer  26  and a patient programmer  28 . Clinician programmer  26  may be a handheld computing device that permits a clinician to program neurostimulation therapy for patient  16 , e.g., using input keys and a display. For example, using clinician programmer  26 , the clinician may specify stimulation parameters for use in delivery of electrical stimulation therapy. Clinician programmer  26  supports telemetry (e.g., radio frequency telemetry) with electrical stimulator  12  to download neurostimulation parameters and, optionally, upload operational or physiological data stored by electrical stimulator  12 . In this manner, the clinician may periodically interrogate electrical stimulator  12  to evaluate efficacy and, if necessary, modify the stimulation parameters. 
     Like clinician programmer  26 , patient programmer  28  may be a handheld computing device. Patient programmer  28  may also include a display and input keys to allow patient  16  to interact with patient programmer  28  and electrical stimulator  12 . In this manner, patient programmer  28  provides patient  16  with an interface for control of neurostimulation therapy by electrical stimulator  12 . For example, patient  16  may use patient programmer  28  to start, stop or adjust neurostimulation therapy. In particular, patient programmer  28  may permit patient  16  to adjust stimulation parameters such as duration, amplitude, current, waveform, pulse width and pulse rate, within an adjustment range specified by the clinician via clinician programmer  28 , or select from a library of stored stimulation therapy programs. 
     Electrical stimulator  12 , clinician programmer  26 , and patient programmer  28  may communicate wireless communication, as shown in  FIG. 1A . Clinician programmer  26  and patient programmer  28  may, for example, communicate via wireless communication with electrical stimulator  12  using RF telemetry techniques known in the art. Clinician programmer  26  and patient programmer  28  also may communicate with each other using any of a variety of local communication techniques, such as RF communication according to the 802.11 or Bluetooth specification sets, infrared communication, e.g., according to the IrDA standard, or other standard or proprietary telemetry protocols. 
     In other embodiments, programmers  26  and  28  may communicate via a wired connection, such as via a serial communication cable, or via exchange of removable media, such as magnetic or optical disks, or memory cards or sticks. Further, the clinician programmer  26  may communicate with patient programmer  28  via remote telemetry techniques known in the art, communicating via a local area network (LAN), wide area network (WAN), public switched telephone network (PSTN), or cellular telephone network, for example. 
       FIG. 1B  illustrates techniques for implantation of the therapy system  10  of  FIG. 1A  by a surgeon, physician, clinician or other caregiver. First, a clinician shaves the back of patient  16 &#39;s head to ensure hair stays out of the way during the implantation. Then, as illustrated in  FIG. 1B , incision  31  is made in the skin scalp of patient  16  along midline  9  of patient  16  inferior to inion  20 . For example, incision  31  may start about 1 cm (e.g., a finger width) below the inion in the scalp of the patient. After incision  31  is made, lateral paths  38 A and  38 B (collectively referred to as “lateral paths  38 ”) are tunneled to both the left and the right of incision  31  for leads  14  ( FIG. 1A ). For example, lateral paths  38  may be formed using blunt dissection. Inferior pocket  36  is also made for electrical stimulator  12  immediately below pockets  38 . The distal ends of leads  14  including paddles  17  are inserted into pockets  38 . Electrical stimulator  12  is rotated 180 degrees to twist leads  14  as shown in  FIG. 1A . This rotation takes up slack in leads  14  to allow leads  14  to lie flat against the skull of patient  16  after implantation. Next, electrical stimulator  12  is inserted into pocket  36  via incision  31  by the clinician. Incision  31  only needs to be large enough so that electrical stimulator  12  may fit through incision  31 . Then, incision  31  is closed over the implanted leads  14  and electrical stimulator  12 . For example, incision  31  may be closed using glue and a vertical mattress suture technique. Other techniques such as taping or stapling may also be used. 
     Optionally, the distal ends of leads  14  may be secured in place. For example, leads  14  may include tines or the distal ends of leads  14  may be secured directly with a suture. In addition the housing of electrical stimulator  12  may also be secured in place using a suture. 
     Alternatively, a lateral incision may be used instead of lateral paths  38 . Other embodiments may comprise using a lateral incision with paddle leads or using a midline incision with leads including ring electrodes instead of paddle leads. 
     In all embodiments, fluoroscopy may be used to locate the leads adjacent the target sites during the implantation. Additionally, patient  16  may be located on his or her side during implantation, which would allow an anesthesiologist to see his or her face. 
       FIG. 1C  illustrates a side view of therapy system  10  including leads  14  and electrical stimulator  12 .  FIG. 1D  illustrates a top view of therapy system  10 .  FIG. 1E  illustrates a perspective view of therapy system  10 . The connector blocks associated with connector ports  15  are oriented in about the same direction such that the leads  14  connect to a common side of electrical stimulator  12 . As shown in  FIG. 1E , paddles  17  are flexible to conform to the curvature of the skull of a patient. Electrical stimulator  12  may include rounded corners and/or a curved major surface to facilitate implantation inferior to the inion of a patient. For example, such a configuration may reduce the likelihood of necrosis to a patient&#39;s scalp adjacent the implant site. 
       FIG. 2  is a block diagram illustrating a general example of various components of electrical stimulator  12  and medical leads  14 . Electrical stimulator  12  may include power source  47  and control module  39  including therapy delivery module  40 , processor  42 , memory  44  and telemetry module  46 . As one example, all or a portion of control module  39  may be implemented in an integrated circuit. In some embodiments, electrical stimulator  12  may also include a sensing circuit (not shown in  FIG. 2 ). Medical paddle  17 A includes electrodes  7 A, which are each electrically coupled to therapy delivery module  40  via a separate conductor of conductor  49 A of lead  14 A. Likewise, medical paddle  17 B includes electrodes  7 B, which are each electrically coupled to therapy delivery module  40  via a separate conductor of conductor  49 B of lead  14 B. Conductors  49 A and  49 B are collectively referred to as conductors  49 . 
     As one example, an implantable signal generator or other stimulation circuitry within therapy delivery module  40  delivers electrical signals (e.g., pulses or substantially continuous-time signals, such as sinusoidal signals) to targets stimulation sites  18  and  19  ( FIG. 1 ) via selected combinations of at least some of electrodes  7  under the control of a processor  42 . For example, electrical stimulator  12  may be configured to produce electrical pulses having one or more of the following attributes: a current amplitude between approximately 1 milliamps and 100 milliamps, a voltage amplitude between approximately 0.1 volts and 10 volts, a pulse frequency between approximately 10 Hz and 800 Hz and/or a pulse width between approximately 20 microseconds and 800 microseconds. 
     The implantable signal generator may be coupled to power source  47 . Power source  47  may take the form of a small, rechargeable or non-rechargeable battery, or an inductive power interface that transcutaneously receives inductively coupled energy. In the case of a rechargeable battery, power source  47  similarly may include an inductive power interface for transcutaneous transfer of recharge power. In addition to a rechargeable battery, in some cases, power source  47  may include power supply circuitry to produce appropriate operating voltages and/or currents. 
     The stimulation energy generated by therapy delivery module  40  may be formulated as neurostimulation energy, e.g., for treatment of any of a variety of neurological disorders, or disorders influenced by patient neurological response. The signals may be delivered from therapy delivery module  40  to various, selected combinations of electrodes  7  via a switch matrix and conductors carried by leads  14  and electrically coupled to respective electrodes  7 . 
     Processor  42  may include one or more microprocessors, controllers, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic circuitry, or the like, or any combination thereof. Processor  42  controls the implantable signal generator within therapy delivery module  40  to deliver neurostimulation therapy according to selected stimulation parameters. Specifically, processor  42  controls therapy delivery module  40  to deliver electrical signals with selected amplitudes, pulse widths (if applicable), and rates specified by the programs. In addition, processor  42  may also control therapy delivery module  40  to deliver the neurostimulation signals via selected subsets of electrodes  7  with selected polarities. For example, electrodes  7  may be combined in various bipolar or multi-polar combinations, including combinations of electrodes on the same lead or different leads, to deliver stimulation energy to selected sites, such as nerve sites adjacent an occipital nerve, spinal column, pelvic floor nerve sites, or cranial nerve sites. Electrodes  7  may also be combined in various bipolar or multi-polar combinations to deliver stimulation energy to selected sites, such as nerve sites adjacent the spinal column, pelvic floor nerve sites, or cranial nerve sites. 
     Processor  42  may also control therapy delivery module  40  to deliver each signal according to a different program, thereby interleaving programs to simultaneously treat different symptoms or provide a combined therapeutic effect. For example, in addition to treatment of one symptom such as migraine headaches, electrical stimulator  12  may be configured to deliver neurostimulation therapy to treat other symptoms such as back pain. In such an embodiment, electrodes  7 A of paddle  17 A may be positioned to deliver stimulation therapy for treating one symptom, and electrodes  7 B of paddle  17 B may be positioned to deliver stimulation therapy for treatment of another symptom. 
     Memory  44  of electrical stimulator  12  may include any volatile or non-volatile media, such as a RAM, ROM, NVRAM, EEPROM, flash memory, and the like. In some embodiments, memory  44  of electrical stimulator  12  may store multiple sets of stimulation parameters that are available to be selected by patient  16  via patient programmer  28  ( FIG. 1 ) or a clinician via clinician programmer  26  ( FIG. 1 ) for delivery of neurostimulation therapy. For example, memory  44  may store stimulation parameters transmitted by clinician programmer  26  ( FIG. 1 ). Memory  44  also stores program instructions that, when executed by processor  42 , cause electrical stimulator  12  to deliver neurostimulation therapy according to selected programs or program groups. Accordingly, computer-readable media storing instructions may be provided to cause processor  42  to provide functionality as described herein. 
     Processor  42  may control telemetry module  46  to exchange information with an external programmer, such as clinician programmer  26  and/or patient programmer  28  ( FIG. 1 ), by wireless telemetry. In addition, in some embodiments, telemetry module  46  supports wireless communication with one or more wireless sensors that sense physiological signals and transmit the signals to electrical stimulator  12 . 
       FIG. 3A  illustrates a top view of an example of electrical stimulator  12 .  FIG. 3B  illustrates a side view of electrical stimulator  12 . Electrical stimulator  12  may be subcutaneously implanted at a stimulation site adjacent a neuralgic region of a patient. In particular, electrical stimulator  12  may be subcutaneously implanted at the back of the neck of the patient, as in the example of  FIG. 1A . 
     As shown in  FIGS. 3A-3B , electrical stimulator  12  comprises a housing  71  that may contain a control module  39 , a battery  74 , and a telemetry and/or recharge coil  76  encircling an inner perimeter of housing  71 . Electrical stimulator  12  may also include flexible circuit  73  and connector blocks  75 A and  75 B (collectively “connector blocks  75 ”). Connector blocks  75  each include a connection port to accept one of leads  14 . In other embodiments, leads  14  may be permanently attached to connector blocks  75 . Connector blocks  75  may be separated by a distance of at least one-third of the length of housing  71 . For example, Connector blocks  75  may separated by a distance of at least one-half, two-thirds or three-fourths of the length of housing  71 . The combination of flexible circuit  73  and connector blocks  75  provide an electrical connection path, e.g., via copper traces, between control module  39  and leads  14 . As one example, components of control module  39  may be mounted directly to flexible circuit  73 . 
     Coil  76  may serve as an inductive power interface to recharge battery  54 , as well as a telemetry coil for wireless communication with an external programmer, e.g., as part of telemetry module  46 . In some embodiments, coil  76  may encircle control module  39 , battery  74 , or both. Battery  74  may form part of power source  47 . Coil  76  inductively receives energy from an external recharging unit (not illustrated) through the skin of the patient to recharge battery  74 . Coil  76  may be formed of insulated windings of copper or another highly conductive material. Electrical stimulator  12  also includes two leads  14  to provide stimulation to the neuralgic region of the patient. Control module  39  receives power from battery  74  to drive the electrodes on leads  14  according to a stimulation program included in control module  39 . In various embodiments, the leads  14  may be paddle, axial or subcutaneous leads. 
     Housing  71  conforms to a substantially rectangular form factor, but may include rounded corners and/or a curved major surface to facilitate implantation inferior to the inion of a patient. For example, such a configuration may reduce the likelihood of necrosis to a patient&#39;s scalp adjacent the implant site. 
     Generally, the larger electrical stimulator  12  is, the higher capacity battery electrical stimulator  12  can hold. A higher capacity battery extends the operational time allowed between recharging. However, smaller devices may allow easier implantation, improved cosmetic appearance and patient comfort. Housing  71  may conform to a miniaturized form factor with a low profile in order to fit directly adjacent the neuralgic region of the patient. The housing may have a volume between approximately 0.5 cubic centimeters (cc) and 5 cc. For example, the housing may have a volume equal to or greater than approximately 1.5 cc and less than or equal to 2.5 cc. An aspect ratio of the length L of the housing to the width W of the housing may be between approximately 1.5:1 and 2:1. In other embodiments, the aspect ratio of the length L of the housing to the width W of the housing may be about 1:1. The width W may be between about 20 mm (0.8 inches) and 76 mm (3.0 inches). For example, the width W may be between about 10 mm (0.4 inches) and 51 mm (2.0 inches). The thickness T may be between about 3 mm (0.12 inches) and about 10 mm (0.40 inches). For example, the thickness T may be between about 4 mm (0.16 inches) and about 5 mm (0.20 inches). 
     Battery  74  may comprise a rechargeable battery with a capacity of at least 20 milliamp-hours, more preferably at least 25 milliamp-hours, and still more preferably at least 30 milliamp-hours. In some embodiments, battery  74  may comprise a lithium ion rechargeable battery. Battery  74  may conform to a miniaturized form factor to fit within housing  71 . Battery  74  may comprise a length of less than or equal to about 25 mm (1.0 inches), a width of less than or equal to about 12.7 mm (0.50 inches), and a thickness of less than or equal to about 3.3 mm (0.13 inches). Battery  74  may conform to one of a variety of designs. 
     Electrical stimulator  12  may be over-discharge protected. However, since battery  74  conforms to an extremely small form factor, the over-discharge protection may be difficult to realize using traditional approaches, such as extra battery capacity. Therefore, electrical stimulator  12  may include a switch to disconnect battery  74  from the load when a predetermined voltage is reached. In other cases, battery  74  may comprise an over-discharge tolerant battery. 
     Control module  39  may also conform to a miniaturized form factor to fit within housing  71 . Control module  39  may comprise a length of less than or equal to about 6.5 mm (0.256 inches), a width of less than or equal to about 9.4 mm (0.37 inches), and a thickness of less than or equal to about 3.6 mm (0.14 inches). Control module  39  also couple to coil  76 , which may operate as both a recharge coil and a telemetry coil. Control module  39  may receive energy via recharge coil  76  to recharge battery  74 . Control module  39  may also receive stimulation programs and other instructions from the patient, the physician, or the clinician via telemetry coil  76 . 
     Control module  39  may comprise an integrated circuit (IC)  81  designed to minimize the number of components within electrical stimulator  12 . For example, IC  81  may perform the functions of control module  39  ( FIG. 2 ) and/or other functions. In some implementations, IC  81  may be formed from an ASIC. IC  81  may be designed using an 0.8 micron process in an effort to reduce the overall size and profile of electrical stimulator  12 . With sufficient processing power, IC  81  may have a footprint of about 5.2 mm (0.204 inches) by 5.2 mm and a thickness of about 0.46 mm (0.018 inches). 
       FIG. 4  is a block diagram illustrating an example control module  39 , which may be similar to the control module of  FIG. 2 . Control module  39  comprises IC  81 , stimulation capacitors and inductors  94 , filter and telemetry components  97 , and a crystal oscillator  98  positioned on a substrate board. One or more memory devices, such as memory  44 , also may be provided. The substrate board may comprise a minimal number of layers, e.g. four layers or less, and comprise a thickness equal to or less than about 0.4 mm (0.014 inches). In one example, the substrate board may be a flexible circuit as shown in  FIGS. 3A and 3B . 
     Control module  39  couples to a rechargeable battery  74 , which may form part of power source  47 , conductors  92  that connect to one or more stimulation electrodes of the electrical stimulator, and a recharge and telemetry coil  76 . As previously mentioned, coil  76  may operate as both a recharge coil and a telemetry coil. In some cases, as described above, coil  76  may encircle control module  39 . IC  81  includes a processor  82 , a power manager  84 , a recharge module  85 , a telemetry coil  76 , a stimulation generator  88 , and a clock  89 . 
     Power manager  84  couples to rechargeable battery  74  to provide power to processor  82 , recharge module  85 , telemetry coil  76 , and stimulation generator  88 . Recharge module  85  couples to recharge and telemetry coil  76  and receives power via coil  76  to recharge battery  74 . Telemetry coil  76  also couples to recharge and telemetry coil  76  and receives stimulation programs and other instructions from a programmer operated by the patient or physician via coil  76 . Filter, power management, telemetry components  97  couple to telemetry coil  76  to support reliable wireless communication. Examples of filter, power management and telemetry components  97  include a telemetry tank capacitor, voltage regulation filters, power supply filters, and battery bypass capacitors. Telemetry coil  76  then provides the received stimulation programs to processor  82 , which stores the programs in memory (not shown). 
     Crystal oscillator  98  is coupled to clock  89 , which clocks processor  82  to run the stimulation programs. Processor  82  directs stimulation generator  88  to provide stimulation to the electrodes of the electrical stimulator via stimulation conductors  49 . Processor  82  directs stimulation generator  88  according to the stimulation programs received from telemetry coil  76  and the clock cycle received from clock  89 . Stimulation generator  88  is coupled to stimulation capacitors and inductors  94 , which include capacitors to store stimulation pulses. 
     As an example, a stimulation program may instruct stimulation generator  88  to generate a stimulation waveform having an amplitude of about 1 to 40 milliamps, or even 6 to 10, a frequency of about 10 to 500 Hz, and even 20 to 200 Hz, and a duration of about a few seconds to several minutes. The stimulation waveform may have a substantially square or spiked waveform. In some embodiments, a neurostimulation waveform may have a duty cycle in a range of about 15 to 25 percent, i.e., “on” for 15 to 25 percent of the time, and even 20 percent of the time. 
     In other embodiments, a stimulation program may instruct stimulation generator  88  to generate a stimulation pulse; for example, a duration of about 20 to 800 microseconds, and even 80 to 120 microseconds may be used. 
       FIG. 5  illustrates therapy system  120 , which includes electrical stimulator  132  and paddle leads  134 A,  134 B (collectively referred to as “leads  134 ”). Therapy system  120  may be substantially similar to therapy system  10 . In contrast to electrical stimulator  12  (FIGS.  1 A and  1 C- 1 E), however, electrical stimulator  132  has an about square shape such that its length and width dimensions are similar. For example, electrical stimulator  132  may have a width and a length of between about 0.45 inches to 1.6 inches and a thickness of about 0.120 inches to 0.240 inches. The shape may be rounded at the corners. Other features of therapy system  120  are similar to therapy system  10  ( FIGS. 1A and 1C-1E ). For brevity, these features are not described in detail with respect to therapy system  120 , and in some instances such features are not described at all with respect to therapy system  120 . 
     Electrical stimulator  132  includes two connector blocks, each having one of connection ports  135 A,  135 B (collectively referred to as “connection ports  135 ”). Connection ports  135  provide an electrical connection to leads  134 . For example, connection ports  135  may provide a press-fit with a proximal end of one of leads  134 . Connection ports  135  may include electrical contacts that mate with corresponding electrodes on a proximal end of one of leads  134 . In other embodiments, leads  134  may be permanently attached to separate connector blocks within electrical stimulator  132 . Connection ports  135  are separated by at least a third of the length of the housing of electrical stimulator  132 . In fact, as shown in  FIG. 5 , connection ports  135  are located on opposing surfaces of the housing of electrical stimulator  132  such that the connector blocks are oriented in opposite directions and separated by the entire width of the housing of electrical stimulator  132 . 
     Leads  134  include paddle electrode sets  136 A,  136 B to deliver stimulation therapy to a patient. Like leads  14 , lead  134  are flexible to conform to the skull of a patient. For example, therapy system  120  may be implanted beneath the scalp and inferior to the inion of a patient to deliver stimulation therapy to at least one of an occipital nerve and a branch of the occipital nerve. 
       FIG. 6  illustrates therapy system  140 , which includes electrical stimulator  152  and paddle electrode sets  156 A,  156 B (collectively referred to as “paddle electrode sets  156 ”). Electrical stimulator  152  has an about square shape such that its length and width dimensions are similar. For example, electrical stimulator  152  may have a width of between about 0.45 inches to 1.6 inches, a length of between about 0.45 inches to 1.6 inches and a thickness of about 0.120 inches to 0.240 inches. Other form factors are also possible. 
     In contrast to therapy system  10  ( FIGS. 1A and 1C-1E ) paddle electrode sets  156  may be hardwired to electrical stimulator  152  and are not part of leads. For example, paddle electrode sets  156  may be electrically coupled to a circuit of electrical stimulator  152  via solder connections, set screws or other techniques. Other features of therapy system  140  are similar to therapy system  10  ( FIGS. 1A and 1C-1E ). For brevity, these features are not described in detail with respect to therapy system  140 , and in some instances such features are not described at all with respect to therapy system  140 . 
     Electrical stimulator  152  includes a stimulation generator to deliver stimulation therapy to a patient via paddle electrode sets  156 . For example, therapy system  120  may be implanted beneath the scalp and inferior to the inion of a patient to deliver stimulation therapy to at least one of an occipital nerve and a branch of the occipital nerve. Once therapy system  140  is implanted electrodes sets  156  may be adjacent to target stimulation sites, such as stimulations sites  18 ,  19  ( FIG. 1A ). 
       FIG. 7  illustrates therapy system  160 , which includes electrical stimulator  12  and axial leads  173 A,  173 B (collectively referred to as “leads  173 ”). As also shown in  FIGS. 3A-3B , electrical stimulator  12  includes connector blocks  75 . Connector block  75 A is shown in detail, but the details shown with respect connector block  75 A are also attributable connector block  75 B. Specifically, connector block  75 A includes connection port  15 A, which receives a proximal end of lead  173 A. Connection port  15 A includes a set of terminals  176  at different axial positions that mate with contacts  174  at different axial positions at the proximal end of lead  173 A. The connection between lead  173 A and connection port  15 A includes fluid seals to prevent undesirable electrical discharge. Lead  173 A may be removed from connection port  15 A by a clinician if desired. For example, the removable connection may be a pressure or snap-fit, e.g., with a spring contacts. 
     Axial leads  173  provide an alternative to paddle leads  14  ( FIG. 1A ). Axial leads  173  include ring electrodes sets  181 A,  181 B (collectively referred to as “electrodes  181 ”) disposed the distal ends of leads  173 . The configuration, type, and number of electrodes  181  illustrated in  FIG. 7  are merely exemplary. In some embodiments, electrodes  181  may be ring electrodes. In other embodiments, electrodes  181  may be segmented or partial ring electrodes, each of which extends along an arc less than 360 degrees (e.g., 90-120 degrees) around the periphery of leads  173 . 
     Leads  173  may include fixation elements  183 A,  183 B (collectively referred to as “fixation elements  183 ”). Fixation elements  183  may help locally fix electrodes  181  proximate to target stimulation sites  18 ,  19  ( FIG. 1 ). Fixation elements  183  may be expanded or activated by any suitable means. In some embodiments, fixation elements  183  may be restrained or otherwise prevented from premature fixation by a lead introducer, sheath, or other mechanism, prior to introduction into a patient. Upon implantation, fixation elements  183  may be expanded or activated by active or passive means. Fixation elements  183  may each be any suitable actively or passively deployed fixation element that helps prevent migration of leads  173  when leads  173  are implanted in a patient, such as, but not limited to, one or more barbs, hooks, wire-like elements, adhesives (e.g., surgical adhesives), balloon-like fixation elements, tissue receiving cavities, pinning fixation elements, collapsible or expandable fixation structures, and so forth. In addition, fixation elements  183  may be formed in situ (i.e., after leads  173  are implanted in patient  16 ), such as by delivering a solidifying material (e.g., an adhesive or a hardenable structure material) to one or more exit ports along one or more surface of leads  173  to form fixation elements that extend from lead  32  and/or  33  to engage with surrounding tissue. Fixation elements  183  may be composed of any suitable biocompatible material, including, but not limited to, polymers, titanium, stainless steel, Nitinol, other shape memory materials, hydrogel or combinations thereof. 
     In some embodiments, fixation elements  183  are attached directly to leads  173 . However, in other embodiments, fixation elements  183  may not be attached directly to leads  173 , but may be carried by another apparatus that is attached to the leads  173 , such as a sleeve or mounting band. 
       FIGS. 8A-8B  illustrate a medical lead introducer  210  for use in deploying an implantable medical lead, which includes blunt dissection element  218 .  FIGS. 9A-9B  illustrate medical lead  220 , which is configured for insertion within a patient using medical lead introducer  210 .  FIG. 10  illustrates a kit including medical lead  220  and medical lead introducer  210  packaged in sterile container  229 . Medical lead introducer  210  is configured such that one side of medical lead  220  is exposed to patient tissue during a lead introduction procedure. Lead introducer  210  facilitates the positioning of medical lead  220  proximate a target tissue site within a patient simultaneously with the blunt dissection of patient tissue. For example, medical lead  220  may be implanted with medical lead introducer  210  in patient  16  in place of one or both of leads  14  ( FIG. 1A ). 
     In the example of  FIGS. 9A and 9B , medical lead  220  is a paddle lead including one or more electrodes  225  on paddle  224  to deliver stimulation therapy to therapy region within a patient. Medical lead  220  also includes lead body  222 , which includes insulated conductors in electrical communication with electrodes  225 . A proximal end of medical lead  220  is configured to be electrically and mechanically connected to an electrical stimulation therapy delivery device to deliver stimulation therapy to a patient via electrodes  225 . Electrodes  225  may also be used as sensing electrodes to sense one or patient parameters, including, but not limited to, patient parameters related to a patient response to stimulation. In addition medical lead  220  may include fluoroscopic elements to allow a clinician to more easily determine an orientation and position of medical lead  220  using fluoroscopy during implantation. 
     Medical lead introducer  210  is configured to implant medical lead  220  proximate a target tissue site within a patient. Medical lead introducer  210  includes shank  214  and blunt dissection element  218 , which is fixed to the distal end of shank  214 . Lead introducer  210  includes handle  212  on the proximal end of lead introducer  210 . Handle  212  allows a clinician to apply a significant force to lead introducer  210  in order to tunnel through tissue of a patient using blunt dissection element  218 . Generally, the profile of medical lead introducer  210  should be kept to a minimum to limit the size of a tunnel created within a patient when implanting medical lead  220  with medical lead introducer  210 . Limiting the size of the tunnel may not only reduce patient trauma associated within implantation, but may also reduce lead migration after implantation. 
     Shank  214  has a rectangular cross section, although in other examples different cross-sectional shapes may also used. For example, the width W of shank  214  may be at least three times greater than the height H of shank  214 . Generally, the width of shank  214  may be about equal to the width of paddle  224 . The cross section of medical lead introducer  210  may cause shank  214  to have greater flexibility about its height and limited side-to-side flexibility. The uneven flexibility provided by shank  214  may improve the steerablity of lead introducer  210  when tunneling through tissue of a patient by substantially constraining the bending of shank  214  to be within a single plane. In different examples, lead introducer  210  may be may substantially stiff such that it will not bend during a blunt dissection procedure. 
     In the example of  FIGS. 8A and 8B , medical lead introducer  210  also includes tab  216 , which extends from shank  214 . Tab  216  is configured to engage through-hole  226  of medical lead  220  to hold medical lead  220  during a lead introduction procedure. In this manner, tab  216  serves as a carrier structure, whereas through-hole  226  serves as a mating carrier structure. Through-hole  226  is located at the distal end of medical lead  220  in paddle  226 . In other examples, paddle  226  may include a detent as a mating carrier structure to be engaged by tab  216  in place of through-hole  226 . In other examples, carrier structures may include additional tabs similar to tab  216  to engage multiple depressions on a medical lead. 
     Tab  216  extends at a forward angle α relative to the insertion direction of lead introducer  210 . Likewise, through-hole  226  passes through paddle  224  at about the same angle α. As examples, the angle α may be between 10 and 80 degrees, between 30 and 60 degrees, or may be about 45 degrees. In some embodiments, distal surface  6  of tab  216  may be at different angle as compared to proximal surface  5  relative to the insertion direction of lead introducer  210 . For example, distal surface  6  may be at a larger angle than proximal surface  5  of lead introducer  210 . This may increase the strength of tab  216  for a given angle of the proximal surface  5  as a smaller angle of the proximal surface  5  may make it easier to release lead  220  from lead introducer  210 . As examples, distal surface  6  may be at an angle of between 5 and 75 degrees greater than the angle of proximal surface  5 , at an angle of between 15 and 60 degrees greater than the angle of proximal surface  5  or at an angle of about 20 degrees greater than the angle of proximal surface  5 . 
     Detent  213  also may be provided to help secure medical lead  220  during a lead introduction procedure. Detent  213  is located on handle  212 , and is configured to secure lead body  222  as shown in  FIG. 10 . For example, detent  213  may provide a snap-fit interface with lead body  222 . This snap-fit interface may assist in keeping lead body  222  in line with lead introducer tool  210  and may also hold through-hole  226  in paddle  224  of lead  220  in engagement with tab  216 . 
     Lead introducer  210  is inserted as part of an assembly also including lead  220  into the tissue of a patient. Tab  216  extends from shank  214  and is angled towards the distal end of lead introducer  210 , i.e., towards blunt dissection element  218 . Likewise, through-hole  226  has a similar angled configuration to mate with tab  216 . As a clinician forces lead introducer  210  through patient tissue, friction of patient tissue pulls on lead  220  including paddle  224 . The angled configuration of tab  216  and through-hole  226  holds tab  216  in engagement with paddle  224 . The clinician continues to force introducer  210  in a forward direction through patient tissue until electrodes  225  are positioned adjacent a target tissue site. 
     After advancing lead  220  to the desired location, the clinician withdraws introducer  210 . The angled configuration of tab  216  and through-hole  226  allows tab  61  to withdraw from through-hole  226  and introducer  210  to slide out over lead  220  without significantly disturbing placement of lead  220 . An important feature of lead introducer  210  is that it does not encompass lead  220  during lead placement within a patient, i.e., at least one side of lead  220  is exposed to patient tissue during implantation. This allows lead  220  to be implanted simultaneously while tunneling through patient tissue. It also facilitates implantation of leads that are permanently fixed to a stimulation device since the introducer does not need to slide off the proximate end of the lead. While the specific example of tab  216  and through-hole  226  are suitable as a carrier structure and mating carrier structure respectively, many other structures may also be used for a lead introducer that does not encompass the lead during lead placement within a patient. 
     Blunt dissection element  218  may have a tapered tip to facilitate blunt dissection through tissue of a patient. As best shown in  FIG. 10 , blunt dissection element  218  has a frontal area that extends beyond a frontal area of shank  214 . As referred to herein, a frontal area is the two-dimensional area in the geometric plane that is perpendicular to the insertion direction. In this manner, blunt dissection element  218  provides a frontal area that shields medical lead  220  when medical lead  220  is held by medical lead introducer  210  during a lead introduction procedure. Because blunt dissection element  218  is not centered on the distal end of shank  214 , the insertion force applied by a clinician to handle  212  does not inherently balance with the tunneling force applied to blunt dissection element  218  by tissue of a patient. Instead, the off-center position of shank  214  relative to blunt dissection element  218  biases lead introducer  210  down in the direction of lead  210 . For this reason, blunt dissection element  218  is asymmetrical to balance the insertion force against the blunt dissection force. This limits bending of the medical lead introducer resulting from the combination of the insertion force and the blunt dissection force. For example, blunt dissection element  218  may defined a surface  217  that is proximate to the side of shank  216  that includes tab  216  and surface  219 , which opposes the first surface  217 . In order to balance the insertion force against the blunt dissection force, the frontal area of surface  217  may be greater than the frontal area of the surface  219 . 
     Medical lead introducer  210  may be made of any material suitable for facilitating implantation of a medical lead. In addition, medical lead introducer  210  may include fluoroscopic elements to allow a clinician to more easily determine an orientation and position of the lead introducer  210  using fluoroscopy during implantation of a medical lead. For example, medical lead introducer  210  may be made from stainless steel, titanium, polyester, polyurethane, silicone, and/or plastic, or other biocompatible materials. In some instances, all or a portion of lead introducer  210  may be coated, e.g., with Polytetrafluoroethylene (PTFE), to reduce friction with a patient&#39;s tissue during a lead introduction procedure. 
     As shown in  FIG. 10 , medical lead introducer  210  may come packaged as a kit including medical lead  220  packaged in sterile container  229 . As examples, sterile container  229  may be a flexible plastic enclosure, foil packaging or other suitable sterile container. In such an example, lead introducer  210  may be disposable after implantation of lead  220 . In other examples, lead introducer  210  may be reused to implant multiple leads. 
     Embodiments of the invention may provide one or more advantages. For example, in embodiments where the stimulation therapy system including an electrical stimulator and leads is sized to be located adjacent the occipital region of a patient, embodiments of the invention allow for stimulation therapy system including an electrical stimulator and leads to be implanted via a single incision. Implanting both the electrical stimulator and leads via a single incision may reduce patient discomfort during recovery from the implantation procedure as well as reduce surgery time compared to systems in which the electrical stimulator is not located adjacent to the target stimulation region of a patient. 
     Furthermore, locating the electrical stimulator adjacent the target stimulation region of a patient, allows for relatively short leads. Short leads can limit lead migration due to patient movement. Short leads allow have a lower resistance for a given diameter electrical conductor, which can improve the efficiency to reduce power consumption. 
     Furthermore, because the electrical stimulator and leads are implanted via a single incision, the invention allows embodiments in which the leads are permanently attached to the electrical stimulator. Permanently attached leads may provide for therapy systems that are more reliable because there can be a permanent seal between the permanently attached leads may provide therapy systems with reduced manufacturing cost compared to systems with detachable leads. 
     Various embodiments of the invention have been described. The foregoing description of the exemplary embodiments of the invention has been presented for the purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. For example, although application of various embodiments of the invention to occipital neuralgia has been described for purposes of illustration, the invention may be applied to treat a variety of disorders. The scope of the invention is not limited with this detailed description, but rather by the claims. These and other embodiments are within the scope of the following claims.