WO2003039386A1

WO2003039386A1 - Stereotactic localisation system

Info

Publication number: WO2003039386A1
Application number: PCT/GB2002/005077
Authority: WO
Inventors: M. S. Eljamel; Francis Mark Tulley
Original assignee: Tayside University Hospitals Nhs Trust
Priority date: 2001-11-08
Filing date: 2002-11-08
Publication date: 2003-05-15
Also published as: GB0126850D0

Abstract

The present invention concerns apparatus and a method for use in stereotatic surgery. The apparatus comprises an implantable device which can be permanently implanted in the skull and a microdrive unit mountable on the implantable device. The apparatus and method of the present invention can be used to introduce probes, electrodes, catheters or other such means into the brain.

Description

STEREOTACTIC LOCALISATION SYSTEM

The present invention concerns apparatus and a method for use in stereotactic surgery. In particular the present invention provides apparatus comprising an implantable device and a co-operating micro drive for use in stereotactic surgery.

A number of illnesses and diseases require surgery to be performed on the brain (neurosurgery) to treat the disease or improve the health of the patient. Brain tumours can be treated using neurosurgery to remove tumour mass, alternatively radioactive treatment can be delivered to lesions, or probes able to produce radiofrequencies can be introduced into the brain. Further, psychosurgery can be employed or stimulating electrodes can be positioned at distinct points in the brain to treat neurophysiological disorders.

Classical surgery on brain tissue usually employed large skin flaps and openings in the skull such that the surgeon could be certain of the area of the brain on which they were operating.

Although endoscopic techniques have advanced at a rapid rate in general surgery, gynaecologic surgery and urological surgery where there are large gas filled or fluid filled cavities in which to work and anatomical structures can be identified by visualisation, the solid mass of brain tissues does not generally allow this.

However, the advent of computer tomography (CT scanning) and MRI scanning has allowed three dimensionally precise data to be used together with a known fixed point to create a stereotactically defined surgical field. This has been used to allow minimally invasive surgical techniques to be used on brain tissues.

These minimally invasive techniques mean that the operation on the brain tissues can be performed via a small drill hole in the skull. This small drill hole allows objects such as needles, electrodes, catheters or probes to be inserted through the skull and into the tissue of the brain.

Stereotactic surgical techniques have minimised the side effects of neurosurgery in comparison to classical techniques, however even when these minimally invasive techniques are employed the patient still suffers considerable trauma in that such an operation may take around 24 hours to perform.

As discussed above, to perform stereotactic neurosurgery it is required to precisely determine the position in the brain where probes or other means such as needles, electrodes, and/or catheters should be positioned in relation to a fixed point outside of the skull .

To enable a reference point and a defined surgical field to be established a stereotactic frame is attached to the patient's skull, while the patient is under anaesthetic. A CT or RI scan of the patient's skull is performed to determine the co- ordinates of the location where the probe is to be positioned in relation to the frame. The surgeon can then determine where the opening in the skull should be made such that the path of the probe causes a minimum amount of tissue damage. A portion of the skull is removed and a guide device fitted to allow the neurosurgeon access to the brain. The neurosurgeon waits until the patient awakens from the anaesthetic such that when the neurosurgeon introduces the probe into the patient's brain, the neurosurgeon can monitor the neurological status of the patient.

In addition to providing a reference point to indicate to the surgeon where an access hole in the skull should be drilled, the stereotactic frame is also required to support microdrive units which allow precise movement of the probe or other means into the brain to the desired location. Microdrive units are generally heavy and in order to ensure that they are held firmly in relation to the skull the microdrive is typically supported by the stereotactic frame.

The method of operation employed to position alternative means such as catheters or electrodes into a particular region of the brain is similar to that described above.

Following suitable positioning of the probe, electrode, catheter or other such means into the brain, the neurosurgeon may either remove the probe or other means from the brain or alternatively secure the means introduced into the brain to the skull. Once the means is secured the surgeon typically removes the guide device from the skull, as guide devices typically have considerable bulk, are visible from outside the skull and further prevent the use of CT or MRI scans to analyse the patient's brain. The stereotactic frame from the patient's skull is also typically removed at this point.

The operation of attaching the frame, waiting for the patient to wake up, inserting the probe into the brain and further removing the frame from the patient, is generally a 24 hour procedure. This long operation may subject the patient to considerable stress and/or trauma. In addition the use of valuable theatre space for such a period of time, particularly when a portion of that time is to allow the patient to awaken from anaesthetic is very costly.

A further disadvantage of the current procedure is that around 1.5% of patients that undergo this procedure require re-operation. One cause of re- operation is the unsuccessful positioning of the probe or other means within the brain. Unsuccessful positioning of the probe or other means can occur due to movement of the electrode on removal of the guide device from the patient's skull.

Patients that require re-operation must undergo re- attachment of the frame, and further CT and MRI scans to obtain the precise location where the probe should be placed in relation to the newly fixed frame. A new guide device must then be re-attached, which may require another hole to be drilled in the patients skull before the probe or other means can be entered. This subsequent operation may take the same length of time as the first operation, therefore the patient experiences further trauma.

In view of the trauma caused to the patient due to both the length of a first operation and the length of any subsequent operations it would be advantageous if the duration of these operations could be reduced. Further, in addition to reducing the trauma suffered by patients, a reduction in the time of the first or subsequent operations would reduce the expense of the operations both in respect of the monetary cost and the surgeon' s time required.

According to a first aspect of the present invention there is provided an implantable device capable of permanent implantation into a skull comprising a first and a second face wherein, in use the first face of the implantable device lies at the exterior of the skull and the second face located opposite to the first face lies at the interior of the skull, the device comprising at least one passage extending continuously from the first face to the second face, the passage allowing at least one suitably sized object to be moved through the passage from the outside of the skull to the inside of the skull.

Preferably the implantable device is implantable into the skull of a human in need of treatment.

Preferably the implantable device is comprised of materials compatible for use with medical imaging equipment.

Preferably the materials used to do show up on MRI scans or are non-metallic.

More preferably the implantable device is comprised of PTFE, plastics material or ceramic material.

Preferably the implantable device may be secured into the skull using bone cement. 1

2. In an alternative embodiment, the implantable device

3 may be secured into the skull using glue .

4

5 In a further embodiment, the side walls of the

6 implantable device are threaded to allow the

7 implantable device to be screwed into the skull. 8

9 A device is considered capable of permanent 0 implantation if the device can be left in situ 1 within the skull of a patient for extended periods 2 of time for example, greater than a week, 3 4 More preferably the device can be left in situ 5 within the skull of a patient for one month. 6 7 More preferably the device can be left in situ within the skull of a patient for one year. 9 Most preferably the device can be left in situ within the skull of a patient for the life of the patient.

Devices which are implanted in the skull, but that project from the plane of the skull may cause abrasion of surrounding skin tissue.

Preferably the first face of the implantable device does not substantially protrude from the plane of the skull.

The implantable device may comprise a plurality of passages .

Preferably the passage can be of any suitable cross section dependant on that required by the probe or other means .

Preferably the passage has width of between 0.05mm to 30mm.

More preferably the passage has width of between 0.2 to 30mm.

More preferably the passage has width of between 0.5mm to 20mm.

Most preferably the passage has width of between 1mm to 15mm.

Preferably the passage is of suitable width such that there is a close transition fit between the exterior of the probe or other means and the walls of the passage.

In a particular embodiment a central passage passes continuously through the implantable device from the first face to the second face and one or more, for example, four further passages surround the central passage and extend from the first face to the second face allowing the passage of suitably sized objects from the outside of the skull to the inside of the skull. Preferably the implantable device comprises at least one removable cap means which is capable of sealing the passage (s) of the implantable device to prevent entry of objects into at least one of the passages.

More preferably the removable cap means are capable . of fixing probe means such as needles, electrodes or catheters in position when suitably located in the brain tissue.

Alternatively a plate can be fixed to the first face of the implantable device to prevent entry of objects into at least one of the passages.

Preferably the implantable device comprises movement limiting means, for example, a flange on the first face to prevent the implantable device being implanted beyond a fixed depth into the skull .

In a first embodiment the implantable device is a single unit.

In a second embodiment the implantable device is comprised of multiple portions .

Preferably the device is comprised of an outer portion to be fixed in the skull and an inner portion adapted to cooperate with and be movable in relation to the outer portion.

^' Preferably the movable inner portion comprises a first face which lies at the exterior of the skull and a second face located opposite to the first face which lies at the interior of the skull, the inner portion comprising at least one passage extending continuously from the first face to the second face, the passage allowing at least one suitably sized object to be moved through the passage from the outside of the skull to the inside of the skull.

Using this arrangement the inner portion may be easily replaceable with different inner portions of a different overall size or size of passages, orientation of passages, or position of passages. The implantable device may therefore be more flexible and not require to be repositioned in the skull.

According to a second aspect of the present invention there is provided a microdrive unit comprising a base portion mountable on an implantable device as described herein, the base portion including at least one passage which extends through the base portion, a guide member mounted on the base portion, a carriage, the carriage being slidably mounted on the guide member and drive means, the drive means able to co-operate with the carriage such that movement of the drive means causes the linear translation of the carriage along the guide member.

According to a third aspect of the present invention there is provided a kit comprising an implantable device according to the first aspect of the present invention and a microdrive unit according to the second aspect of the present invention.

Preferably at least one of the passages present in the base portion can co-operate with at least one of the passages present in the implantable device, such that objects can pass through the passage in the base portion and the co-operating passage in the implantable device, thus allowing an object to pass from the exterior to the interior of the skull. Preferably the base portion comprises at least one aperture, which extends continuously through the base portion, into which fastening means, such as cannulae or screws, may be passed such that the micro drive unit can be secured to the skull or the implantable device.

Preferably drive means is provided by a screw rod such that rotation of the screw rod causes a linear translation of the carriage along the guide member.

Preferably the guide member is perpendicularly mounted onto the base portion.

Preferably rotation of the screw rod in one direction causes the linear translation of the carriage toward the base portion and rotation of the screw rod in the other direction causes linear translation of the carriage in the opposite direction. Preferably rotation of the screw rod is performed manually.

Alternatively rotation of the screw rod is performed by a motor .

Preferably the carriage includes passages through which probes or other means including electrodes, needles or catheters can pass through towards the base portion.

Preferably the passages of the carriage through which the probe means including electrodes, needles or catheters can pass are positioned such that the probe means which pass through the carriage towards the base portion can enter the passages in the upper face of the base portion and further pass through the skull by means of the implantable device.

Preferably the carriage includes a slideable comb portion or other means, by which probes, or other means including electrodes, needles or catheters may be fixed to the carriage such that they can pass through the passages of the carriage towards the base portion.

Preferably the guide member is marked such that the linear translation of the carriage along the guide member by the drive means can be quantified.

According to a further aspect of the present invention there is provided a method of gaining repeatable access to the interior of the skull, the method comprising the steps of

permanently implanting an MRI -compatible implantable device into the skull,

mounting a microdrive unit onto the implantable device,

positioning a probe, electrode, catheter or other means in the slideable carriage of the microdrive unit,

advancing the probe, electrode, catheter or other means through the implantable unit into the interior of the skull.

The microdrive unit can be removed and the passage (s) of the implantable device sealed using removable cap means or other means, such as a plate element, such that the implantable device is capable of being left in position in the skull to allow later access to the brain tissue, or the interior of the skull.

Preferably this method is capable of being used to position electrodes able to provide stimulus to regions of the brain.

Alternatively this method is capable of being used to deliver cells, for example, foetal cells to the brain. A further alternative is that this method is capable of being used to deliver treatment including pharmaceuticals or radioactive compounds to the brain.

An embo.diment of the present invention will now be described by way of example only, with reference to the accompanying figures in which ;

Figure la is an isometric perspective view of an implantable device;

Figure lb is a side view of an implantable device ,-

Figure lc is a plan view of an implantable device;

Figure 2 is an isometric perspective view of a micro drive unit, which can be mounted onto the implantable device ;

Figure 3 is a front view of the guide member;

Figure 4 is a side view of a guide member;

Figure 5 is an opposite side view of a guide member,-

Figure 6 is a plan view of the base portion along section I- I; Figure 7 is a front view of the base;

Figure 8 is a plan view of the base portion along section II-II;

Figure 9 is a front view of a cap plate ;

Figure 10 is a plan view of the cap plate of Figure 9;

Figure 11 is a front view of a keeper plate;

Figure 12 is a plan view of the keeper plate ;

Figure 13 is a front view of the carriage;

Figure 14 is a side view of the carriage ,-

Figure 15 is a plan view of the carriage ;

Figure 16 is a plan view of the slideable comb portion;

Figure 17 is a side view of the slideable comb portion;

Figure 18 is a view of the screw rod; and

Figure 19 is a side view of the depth control knob . As shown in figure 1, an implantable device 10 may comprise of square first face 12 and square second face 14, although the first and second faces could be a variety of shapes including and not limited to circular, ellipsoid, rectangular, triangular and star shapes. Further, it is not necessary that the first 12 and second 14 faces of the implantable device be of the same shape. It can also be envisaged that the implantable device might be tapered such that the first face 12 is of greater area than the second face 14.

One advantage of a square first and second face is that the implantable device is unable to rotate when it is being fixed into the skull. Alternatively a cylindrically shaped implant would allow rotation of the implantable device when it was being fixed into the skull. Threading of such a cylindrically shaped implantable device may be advantageous in enabling the implantable device to be secured into the skull, as rotation of a threaded cylindrically shaped implantable device would enable the implantable device to be screwed into the skull .

The side faces 16 of the implantable device 10 may be grooved or contain indentations 18 such that the implantable device 10 is held in place, in the skull more easily by fixing means such as bone cement or glue.

The grooves can be any suitable dimension or shape. Further, the device can comprise a plurality of grooves on each side face of the implantable device, and different numbers of grooves on each of the side faces of the implantable device.

In the embodiment shown in figure lb the grooves are 2mm in width and 1mm in depth. The side walls of the grooves are angled at around 45° from an axis perpendicular to the plane of the side walls of the implantable device.

Typically, the length of the implantable device 10 between its first face 12 and second face 14 is in the range of 8mm to 15mm.

The embodiment of the implantable device 10 shown is comprised from material such as PTFE, which is both biocompatible and MRI compatible. However, any non- metallic material may be used to form the implantable device. The implantable device is preferably not formed from metallic materials as these would be seen during the MRI scan.

In preferred embodiments, the implantable device 10 may be formed from plastics material or ceramic material .

The implantable device 10 comprises at least one aperture in the first face 12, which extends towards second face 14 to form a passage 24 through the implantable device through which an object such as probe means may be passed. In the embodiment of the implantable device 10 shown in figure 1, four apertures 20 surround a central aperture 22 in the first face 12, each of the apertures extending towards the second face 14 to form distinct passages 24 between the first 12 and second 14 faces through which an object may be passed.

Embodiments of the present invention can be envisaged which include screw threading on the side faces 16 of the implantable device 10, which contact the skull when the implantable device 10 is positioned in the skull in use. The implantable device 10 may also be shaped such that it may be fixed to the skull by screwing the implantable device either directly into the skull or into a tapped co-operating element, which had been previously attached to the skull .

The design of the present invention means that it is small enough to be incorporated into the skull bone and thus in si tu it is not easily visible. This contrasts with devices in the prior art, which are typically easily visible, having bulky portions outside of the skull which, as well as potentially being cosmetically unacceptable to a patient, may represent a hazard liable to damage. The design of the implantable device 10 of the present invention, such that it can be incorporated discretely into the skull, means that it may be permanently implanted by the neurosurgeon into the skull of the patient and need not be removed following positioning of the probes or other means into the brain.

Further, as the implantable device 10 is comprised of biocompatable and MRI compatible material it does not need to be removed by the neurosurgeon if the patient requires subsequent MRI scans following fitting of the implantable device 10.

The permanent nature and compatibility of the implantable device 10 enabling the device to be left in situ during MRI scans means that the implantable device 10 allows significant changes in operational procedure to position probes and other means into the patients brain to be adopted by the neurosurgeon to the advantage of the patient.

As discussed above, a stereotactic operation to introduce a probe or other such means into the brain typically takes around 24 hours with the operation comprising a period of time between fitting of the frame and introducing the probe into the patients brain when the patient is allowed to recover from the anaesthesia.

Using the implantable device 10 of the present invention, the procedure can be split into two shorter operations comprising a first operation of, β attaching a stereotactic frame to the patient while they are under anaesthetic, * performing a CT or MRI scan of the patient's skull to determine the position where the probe is to be inserted in relation to a fixed point on the patients skull or on the frame, β making a hole in the patient's skull and fixing the implantable device 10 into the skull, removing the frame , • allowing the patient to recover from the anaesthetic (this need not be done in the operating theatre) ,

and a second operation of introducing the probe or other means through the implantable device 10 into the patient's brain. This second operation does not require the stereotactic frame to be re-attached to the patient.

Should any subsequent operations be required to introduce further probes or other means into the patient's brain then there is no need to re-operate in order to re-attach the frame, as the complete implantable device 10, which can be left in situ provides a reference point, which has not altered since the first operation. During this subsequent operation additional further probes may be introduced through the implantable device positioned in the skull.

The division of the first operation into two shorter operations significantly reduces the trauma of the operation on the patient. Further, any subsequent operation is considerably shorter in duration than the first operation. This is because a subsequent operation does not require the patient to be treated with anaesthetic, as the stereotactic frame does not require to be re-attached, nor is a further hole required to be drilled in the patient's skull, which is again of advantage to the patient.

In addition to the benefits enjoyed by the patient, the division of the operation into two shorter operations reduces the cost of the operation. Using the system of the present invention comprising the implantable device 10 and microdrive unit, the patient may be awakened from the anaesthetic outside of theatre, freeing up hospital resources. For any subsequent operations, the time and personnel required to introduce a further probe or other means into the skull is significantly reduced leading to a reduced cost of the second operation.

As shown in figure 1 the implantable device 10 may include more than one passage extending through the implantable device 10 from the first face 12 to the second face 14.

In the embodiment shown in figure 1, five apertures extending from the first face 12 to the second face 14 of the implantable device 10 are shown, although the device may comprise any suitable number of apertures.

The implantable device 10 is located in the skull such that the middle passage is directed towards the area into which the probe or other means is to be placed. The four surrounding apertures allow additional exploration of the target area typically around 2 -3mm on each side of the position to which the middle passage is directed.

This means that if placement of the probe or other means is unsuccessful using the central passage of the implantable device 10 further attempts can be made without requiring a new hole to be drilled or an additional implantable device to be inserted into the skull.

Although not shown in any of the drawings it can be envisaged that modifications of the implantable device could be made such that it includes movement limiting means such as a flange to aid in the ^• positioning of the implantable device 10 at the correct depth within the skull .

In addition the implantable device 10 may include sealing means, for example a removable cap means to allow at least one of the passages to be sealed to prevent the movement of suitably sized objects through the passages.

The placement of sealing means, for example, removable cap means over a passage 16 of the implantable device 10 may also fix the probe means introduced into the brain tissues in position.

Alternatively, screws can be inserted into the passages 16 of the implantable device to cap the passages instead of a cover cap, or a plate can be fixed to the implantable device using fixing means to cover the passages 16 in the device. Suitable fixing means include screws.

In order to ensure that the probe or other means is advanced into the brain to the correct depth from the location of the implantable device 10, the probe or other means is preferably attached to a drive unit, which allows the depth of the probe to be determined.

In conventional apparatus for use in steretactic surgery, drive units are typically attached to a stereotactic frame, which is in turn attached to the skull of the patient such that the drive unit is held in a stable position as the probe or other means is advanced. As described above the implantable device 10 of the present invention does not require a stereotactic frame to be attached to the skull of the patient. Thus in preferred embodiments the kit of the present invention comprises a microdrive unit able to co-operate with the implantable device 10 such that the microdrive unit does not require a stereotactic frame to be attached to the patient's skull.

In a further embodiment, the implantable device can comprise at least two portions. A first outer portion is suitably locatable and fixable in the skull, as described above, using fixing means such as bone cement, glue, or screws. An inner portion is located in the outer portion and is moveable within said outer portion. The inner portion comprises at least one passageway which allows passage of a probe or other means from the outside of the skull, through the skull and into the interior of the skull or the brain. Preferably the inner portion of the implantable device comprises a plurality of passages which can receive probes or • . other means .

The inner portion is moveable within and relative to the outer portion of the implantable device to allow the trajectories of any probes inserted through the passageways to be altered. Once the inner portion has been moved such that a suitable trajectory is obtained then the inner portion can be fixed to the outer portion to hold the inner portion in position.

The inner portion can be fixed to the outer portion using a variety of fixing means such as screws, glue or cement. Alternatively the outer and inner portions can include a locking feature which enables the inner portion when locked in place to be held in position relative to the outer portion of the implantable device.

An embodiment of a microdrive unit of the present invention is shown in figure 2 of the drawings.

As shown in figure 2 the microdrive unit comprises a base 110 shaped to co-operate with the implantable device 10. The base 110 has a first face 112 which in use is adjacent to the upper face 12 of the implantable device 10. The base 110 comprises an opposite second face 114 on which a first end 122 of a guide member 120 is perpendicularly mounted.

As shown in figure 6 the base 110 of the microdrive unit comprises at least one and preferably a number of apertures 116 which extend from the first face of the base portion 112 to the second face of the base portion 114 to form distinct passages 116 through which objects of a suitable size can be passed. When the base 110 is mounted on the implantable device 10 the passages 116 of the base 110 co- operate with the passages 24 present in the implantable device 10 such that objects of suitable size can be passed from the second face 114 of the base portion to the second face 14 of the implantable device 10, allowing objects to be passed from the outside to the interior of the skull.

In addition to comprising passages 116, which may co-operate with the passages 24 of the implantable device, the second face of the base portion 114 also comprises means by which the microdrive unit can be removably attached to the skull or implantable device 10.

In the embodiment shown, the microdrive unit is held to the implantable device 10 by fastening means. These two fastening means can be cannulae, which pass through apertures 19 in the base 110 such that the microdrive unit can be fixed to the implantable device 10, which is implanted in the skull. The fixing means can also be screw or other suitable means .

As shown in figure 2 the guide member 120 comprises two elongate members perpendicular to the second face 114 of the base portion, set apart such that drive means 150 can be incorporated between them.

Opposite the end of the guide member 122 attached to the base portion 110, the second end of the guide member 124 is fixed to a keeper plate 160. A cap plate 170 is mounted on the keeper plate 160 on the opposite face of the keeper plate to that adjacent to the guide member 120.

As shown in the figures, drive means can be a screw rod 150 rotatably mounted at a first end of the screw rod in the base portion 110 at a section 115 between the two elongate members 120. The screw rod 150 passes between the two elongate guide members 120 through the keeper plate 160 via a channel 162 and through an aperture 172 in the cap plate 170, the screw rod 150 being fixed into handle means 180 at a second end of the screw rod 150. In the embodiment shown the handle means 180 for rotating the screw rod 150_. is a knob.

A carriage 130 is mounted on the thread of the screw rod 150 via an aperture 131, the carriage 130 also being slideably mounted on the guide member 120 via two cut out portions 132. On rotation of the screw rod 150 the carriage 130 is linearly translated along the guide member 120, the cut out portions 132 ensuring the carriage 130 remains both perpendicular to the guide member 120 and further that the rotation of the screw rod 150 causes translation and not rotation of the carriage 130.

It can be envisaged that rotation of the screw rod 150 can be performed using a motor. The microdrive can therefore be motorised to provide movement of the carriage, in addition or alternatively to manual operation to provide movement of the carriage.

The carriage 130 comprises a bottom portion 133 which extends perpendicularly from the elongate guide member 120, and two end stops 134 which protrude normally from opposite edges of the bottom portion such that they form a channel, the bottom portion forming the bed 135 of the channel.

The bed 135 of the channel comprises at least one aperture 136 which is in alignment with at least one aperture in the second face 114 of the base portion 110. In the embodiment shown the five apertures of the base 116 are aligned with co-operating apertures 136 in the bed 135 of the carriage 130.

A comb portion 140 is slidably mounted on the bed 135 of the carriage 130 between the two endstops 134. As shown in figure 17 the comb portion comprises a number of slots 142, which extend away from one edge of the comb 140, but do not extend across the full width of the comb 140. The slots 142 are of suitable size such that they can hold a probe or other means to be introduced into the brain through the implantable device 10.

The microdrive unit of the present invention is both light in weight and has a low inertia about its mounting point. These features allowing the use of the microdrive unit without the need for a stereotactic frame or other means to which the drive unit can be attached. Further, the microdrive unit of the system described by the present invention is able to co-operate with the implantable device 10 of the present invention.

The combination of the lightweight nature, lower inertia about its mount and ability to co-operate with the implantable device described herein means that the microdrive unit of the present invention may be used without the need for a stereotactic frame to be attached to the patient. This is of considerable benefit, as use of the implantable device 10 of the present invention does not require a stereotactic frame for second or subsequent operations to be attached to the patient. Thus use of the microdrive unit of the system of the present invention allows significantly reduced operational times to be achieved. This reduces the trauma suffered by the patients undergoing the procedures described.

It can be envisaged that alternative drive means or alternative means for controlling the screw rod 150 could be used in the microdrive unit to cause translation of the carriage 130.

Further it can be envisaged that the drive means may be computer or electronically controlled.

In use the stereotactic frame is attached to the patients skull, a CT or MRI scan of the patients skull is performed to determine co-ordinates relating the location where the probe means should be positioned relative to a fixed point outside or on the skull. This allows the surgeon to determine the position where a hole should be made in the skull and the path that the probe or other means will take through the brain.

At the point determined by the surgeon in view of the results of the CT or MRI scan, a hole is drilled in the skull. The first part of the system, the implantable device is placed into the hole and secured in position using suitable means such as bone cement, glue or screwing. If the implantable device is to be screwed into the hole, the hole may be drilled by a bit, which taps the hole to allow a threaded implant to be screwed into position. Alternatively a threaded element into which the implantable device can be screwed may be first fixed into the hole.

The stereotactic frame can be removed and the patient moved out of theatre and allowed to recover in a hospital ward. At a later date the patient can be brought back into theatre, for the second operation, to position a probe or other means into the brain. During this second operation the patient need not be under anaesthetic and the second part of the system, the ■ microdrive unit may be mounted onto the implantable device 10 such that the passages 116 of the base portion 110 align with the passages 24 of the implantable device 10.

One or more probe means such as electrode (s) are inserted into the apertures 136 of the carriage 130 and the carriage moved down such that the probe means enter the passages 116 of the base 110 of the microdrive unit. The probe means are then fixed in the carriage by means of the comb 140.

Rotation of the knob 180 causes the probe or other means to pass through the passage 116 of the base 110 of the microdrive unit, into the corresponding aperture (s) 20 or 22 on the upper face 12 of the implantable device 10, and to exit the implantable device 10 via the corresponding aperture on the second face of the implantable device 14, such that the probe or other means passes into the interior of the skull and then into the brain tissue.

Once an implantable probe has been translated into the brain to a suitable depth the microdrive unit may be removed and the probe may be secured in place onto the implantable device 10. The implantable device 10 may be left permanently implanted in the skull, preventing any dislodgement of the probe means that might occur if the implantable device 10 was removed. Removable cap means may be used to seal passages 24 of the implantable device 10.

If further operations to introduce further probe means into the patient's brain tissue (s) are required, the stereotactic frame is not required to be re-attached, as the implantable device 10 provides both a reference point and a means by which probes can be entered through the skull .

As the implantable device 10 is comprised of material compatible with CT or MRI scans subsequent scans can be taken while the implantable device is in place.

This permanent nature and compatibility of the implantable device 10 with CT and MRI scans allows additional probes to be entered into the brain in the future through the implantable device without the need to attach a stereotactic frame.

Various modifications can be made to the system without departing from the scope of the invention for example the implantable device could be of larger area, different shape or comprise of more apertures.

Claims

CLAIMS :

1. An implantable device, capable of permanent implantation into a skull, comprising a first and a second face wherein, in use, the first face of the implantable device lies at the exterior of the skull and the second .face which is located opposite to the first face, lies at the interior of the skull, the device comprising at least one passage extending continuously from the first face to the second face, the passage allowing at least one suitably sized object to be moved through the passage from the outside of the skull to the inside of the skull.

2. An implantable device as claimed in claim 1 comprised of a material (s) compatible for use with medical imaging equipment .

3. An implantable device as claimed in claim 2 wherein said material (s) is one or more of PTFE, plastics material or ceramic material.

4. An implantable device as claimed in claims 1 to 3 capable of being secured into the skull using bone cement.

5. An implantable device -as claimed in any one of claims 1 to 3 capable of being secured into the skull using glue.

6. An implantable device as claimed in any previous claim wherein the side walls of the implantable device are threaded to allow the implantable device to be screwed into the skull.

7. An implantable device as claimed in any previous claim which comprises a plurality of passages .

8. An implantable device as claimed in claim 7 where^'in the implantable device comprises a central passage that passes continuously through the implantable device from the first face to the second face and four further passages surround the central passage and extend from the first face to the second face allowing the passage of suitably sized objects from the outside of the skull to the inside of the skull.

9. An implantable device as claimed in any previous claim which further comprises at least one sealing means for example removable cap means, which is capable of sealing the passage (s) of the implantable device to prevent entry of objects into at least one of the passages.

10. An implantable device as claimed in claim 9 wherein the sealing means is capable of fixing probe means such as needles, electrodes or catheters in position when suitably located in the brain tissue.

11. An implantable device as _claimed in claim 9 or 10 wherein the sealing means is a plate that can be fixed to the first face of the implantable device to prevent entry of objects into at least one of the passages.

12. An implantable device as claimed in any one of the previous claims which further comprises movement limiting means on the first face to prevent the implantable device being implanted beyond a fixed depth into the skull.

13. An implantable device as claimed in claim 12 wherein the movement limited means is a flange.

14. An implantable device as claimed in any one of the previous claims comprised of an outer portion fixable to the skull and an inner portion adapted to cooperate with and be movable in relation to the outer portion.

15. An implantable device as claimed in claim 14 wherein the movable inner portion comprises a first face which in use lies at the exterior of the skull and a second face located opposite to the first face which in use lies at the interior of the skull, the inner portion comprising at least one passage extending continuously from the first face to the second face, the passage allowing at least one suitably sized object to be moved through the passage from the outside of the skull to the inside of the skull.

16. A microdrive unit comprising a base portion mountable on an implantable device as described in any one of claims 1 to 15, the base portion including at least one passage which extends through the base portion, a guide member mounted on the base portion, a carriage, the carriage being slidably mounted on the guide member and drive means, the drive means able to co-operate with the carriage such that movement of the drive means causes the linear translation of the carriage along the guide member.

17. A microdrive unit as claimed in claim 16 wherein at least one of the passages present in the base portion can co-operate with at least one of the passages present in the implantable device, such that objects can pass through the passage in the base portion and the co-operating passage in the implantable device, thus allowing an object to pass from the exterior to the interior of the skull.

18. A microdrive unit as claimed in claims 16 or 17 wherein the base portion comprises at least one aperture, which extends continuously through the base portion, into which fastening means may be passed such that the microdrive unit can be secured to the skull or the implantable device.

19. A microdrive unit as claimed in any one of claims 16 to 18 wherein the drive means is provided by a screw rod such that rotation of the screw rod causes a linear translation of the carriage along the guide member.

20. A microdrive unit as claimed in any one of claims 16 to 19 wherein the guide member is perpendicularly mounted onto the base portion.

21. A microdrive unit as claimed in claim 19 wherein clockwise rotation of the screw rod causes the linear translation of the carriage toward the base portion.

22. A microdrive unit as claimed in claim 21 wherein rotation of the screw rod is performable manually.

23. A microdrive unit as claimed in claim 21 wherein rotation of the screw rod is performable by a motor.

24. A microdrive unit as claimed in claims 16 to 23 wherein the carriage includes a passage (s) through which a probe (s) or other means such as an electrode (s) , needle (s) or catheter (s) can pass towards the base portion.

25. A microdrive unit as claimed in claim 24 wherein the passage (s) of the carriage through which the probe or other means can pass are positioned such that the probe or other means which pass through the carriage towards the base portion can enter the passage (s) in the upper face of the base portion and further pass through the skull by means of the implantable device.

26. A microdrive unit as claimed in claims 16 to 25 wherein the carriage includes a slideable comb portion or other means, by which probes, or other means such as electrode (s) , needle (s) or catheter (s) may be fixed to the carriage such that they can pass through the passage (s) of the carriage towards the base portion.

27. A microdrive unit as claimed in claims 16 to 26 wherein the guide member is marked such that the linear translation of the carriage along the guide member by the drive means can be quantified.

28. A stereotactic surgical kit comprising an implantable device according to any one of the' claims 1 to 16 and a microdrive unit according to any one of the claims 16 to 27.

29. A method of gaining repeatable access to the interior of the skull, the method comprising the steps of,

implanting an MRI compatible permanently implantable device into the skull,

mounting a microdrive unit onto the implantable device, positioning a probe, electrode, catheter or other means in . the slideable carriage of the microdrive unit,

advancing the probe, electrode, catheter or other means through the implantable unit into the interior of the skull .

30. A method according to claim 29 where the implantable device is the device according to any one of claims 1 to 16.

31. A method according to claims 29 or 30 where the microdrive unit is the microdrive unit according to any one of claims 16 to 27.

32. A method as claimed in any one of claims 29 to 31 comprising of positioning of one or more electrodes in a position able to provide stimulation, to a region (s) of the brain.

33. A method as claimed in any one of claims 29 to 31 comprising the delivery of foetal cells to the brain.

34. A method as claimed in any one of claims 29 to 31 comprising the delivery of a medicament to the brain.