Aesculap Unitrac

Single space lumen

1.3 mm

0°-12°

Wolf5

pediatric neuroendoscope

3.3 mm x 4.5 mm

1 0, 1 or 2 W, 2 I/A

1.6 mm

0°, 25°, 70°

1 Aesculap - Tuttlingen, Germany; Wolf, Knittlingen, Germany.

2 Codman & Shurtleff (Johnson & Johnson) New Brunswick, NJ.

3 NeuroNavigational ( Integra NeuroSciences) Plainsboro, NJ.

4 Karl Storz GmbH & Co., Tuttlingen, Germany.

5 Richard Wolf, Henke-Sass, Tuttlingen, Germany.

* O Optic channel; W Working channel; 0/ W Optic and Work channel; I/A Irrigation/Aspiration channel.

This allows for the extreme simplification of the optical system, without the need for complex and long rod lenses systems improving at the same time significatively the quality of vision if compared to the fiberscopes. Although the 1 CCD camera is somehow less performant than the 3 CCD camera (see below) that can be used with rigid rod lenses systems and fiber-scopes, the proximity of the camera to the target of vision allows for excellent magnification and sharpness of the image. Moreover, the steerable properties of the device are preserved because of the lack of rigid lens systems. Some videoscope are already commercially available for ENT use in some countries, with an outer diameter of 6-8 mm; prototypes with smaller outer diameter for neuroendoscopic use are under clinical validation studies and should be available commercially in the next 2-3 years (Kamikawa et al. 2001a, Kamikawa et al. 2001b). The real, significant advantage of this device is the excellent quality of vision (1 CCD camera like), comparable to the 1 CCD rod lens systems, associated with the steer-able properties, allowing for perfect fusion of rigid and steerable systems (Fig. 12a-d).

Camera and Monitor

Two basic cameras are available: a single chip charged coupled device (CCD) and a three chip CCD. A good resolution for neuroendoscopy is available with 0.5 inches single chip cameras (resolution of 500 lines) (Schroeder et al. 2001). If the resolution is poor, the image needs computer-enhancement. The three chip CCD produces images of better quality (more than 800 horizontal lines) but is more expensive and heavier. So, most endoscopic system use single chip cameras. Some manifacturers produce both the type of digital cameras (David 1 and David 3, Aesculap, Tuttlingen, Germany; Image1 and Image3, Karl Storz GmbH & Co., Tut-tlingen, Germany). In some models all the function can be controlled by the surgeon in the operative field. Zoom endo-lens is useful to enlarge the image section.

To achieve good quality images, a monitor with the highest possible resolution should be selected. However, the resolution of the monitor should not greatly exceed that of the camera. The size of the screen is limited by the loss of quality when an image is enlarged. In fact, one should remember that the images of the camera are displayed over an area larger than cross section of the optic cable. In monitor larger than 13 inches, the picture is enlarged too much and decreases in quality. This is especially true in case of fiberoptic endoscopes, where the spaces among the pixels may become evident. Larger monitors (19 or 20 inches) are useful for displaying multiple images (Cinalli 2004, Nobles 1998, Schroeder and Gaab 1999, Siomin and Constantini 2004).

Gene Thrapy Images

Illumination

Xenon light sources provide the best illumination for neuroendoscopic procedures. The light is transmitted via fiber bundles from the light fountain to the endoscope. Setting the light source to between 300 and 500 W provides a superior picture quality. Other types of light source, such as halogen, are not able to generate a light bright enough for neuroendoscopy. Siomin and Constantini (Siomin and Constantini 2004) have calculated that, due to the significant light loss in the fiberoptic system, only 30% of the light generated within the light source reaches the distal tip of the endoscope.

Accessories (Irrigation, Holders)

Imaging with an endoscope requires the clearest possible medium for optimum light with the lowest diffraction. So, irrigation is important to assure good visualization. It should be balanced by the egress of fluid. Care should be given to avoid entrapment of fluid inside the ventricle: it may lead to disastrous sequels (Cinalli 2004, Teo 2004). Irrigation can be performed simply by hand with a catheter connected to the irrigation channel of the endoscope. It can be also provided with the use of a pump irrigator for which the flow is easily controlled using a foot switch (The Malis CMS-II Irrigation Module, Codman and Shurtleff, Inc., Randolph, MA; Endoscopy Pump, Medtronic, Minneapolis, USA).

The use of a holder is sometimes advised when using a rigid rod lens endoscope. During these procedures it allows the surgeon to use both hands and two instruments through two different working channels (Fig. 13). The disadvantages of use of holders is the minor freedom of movements, especially when configuration needs to be frequently changed. However, holders with pneumatic (Fig. 14a) or electromagnetic (Fig. 14b) brakes offer a significant improvement over the mechanical systems, combining the advantages of freehand movements with the possibility of very secure and firm positioning, and are certainly the gold standard for both beginners and expert surgeons (Fig. 14c). With traditional holding devices, a precise steering of the neuroendoscope is not possible, but only a rough positioning. A new device has been developed (NeuroPilot, Aesculap, Tut-tlingen, Germany) that used in combination with a pneumatic holder

Fig. 12. Images of a Neuroendoscopic third ventriculostomy and pineal tumor biopsy obtained with a prototype of videoscope (Olympus opt, Tokyo, Japan). (a) foramen of Monro. (b) ventricular trigone with choroids plexus. (c) from up to down, stoma of the ETV, mammillary bodies, mesencephalic roof. (d) pineal tumor. (e) prototype of video-scope during manipulation (images courtesy of Professor Shuji Kamikawa, Isesaki Sawa Medical Association Hospital, Japan)

Two Working Channel Neuroendoscope

Fig. 13. The use of a holder allows working with both hands if two working channels are available (image courtesy of Dr. Philippe Decq, Hopital Henri Mondor, Paris,

France)

Fig. 13. The use of a holder allows working with both hands if two working channels are available (image courtesy of Dr. Philippe Decq, Hopital Henri Mondor, Paris,

France)

(Unitrac, Aesculap, Tuttlingen, Germany) allows, after positioning of the neuroendoscope, fine, sub-millimetric adjustment in the three dimensional space by three screws.

Neuronavigation and Stereotaxy

Stereotactic guidance was used before the advent of neuroendoscopy to perform third ventriculostomy (Hoffman et al. 1980, Kelly 1991) and was used in association with neuroendoscopy by several authors at the beginning of their experience (Grunert et al. 1994, Hellwig et al. 1998b, Hopf 1999a). In fact, stereotactic guidance can be of some value only in choosing the correct entry point and entering the lateral ventricle in a small-sized ventricular system. The limit of the technique is that the stereotactic frames are bulky and sometimes interfere with the endoscopic procedures and most importantly, frame-based stereotactic systems do not provide an ongoing intraoperative feedback to the surgeon about anatomical structures encountered in the surgical field (Tirakotai et al. 2004).

A good alternative to traditional stereotactic frames can be the combination with frameless neuronavigation (Alberti et al. 2001, Broggi et al. 2000, Hopf et al. 1999a, Riegel et al. 2000, Riegel et al. 2002, Schroeder et al. 2001, Tirakotai et al. 2004). Unlike based stereotaxis, frame-less navigation is still useful for intraoperative orientation, especially in cases of impaired visualization, distorted anatomy or narrowed ventricles. In endoscopic third ventriculostomy, the use of neuronavigation may not be

Unitrac Aesculap

Fig. 14. (a) Holder Unitrac Aesculap: Pneumatically assisted holder (image courtesy of Aesculap - Tuttlingen, Germany). (b) the Storz-Mitaka arm. (c) the Endo-Arm from Olympus

Fig. 14. (a) Holder Unitrac Aesculap: Pneumatically assisted holder (image courtesy of Aesculap - Tuttlingen, Germany). (b) the Storz-Mitaka arm. (c) the Endo-Arm from Olympus necessary (Schroeder et al. 2001); however, in cases with thickened, non-translucent third ventricular floors, neuronavigation is useful for anatomical orientation (Alberti et al. 2001, Tirakotai et al. 2004). Brain shift can be a major factor in influencing the accuracy of the target localization. This problem occurs less often if some precautions are taken to prevent the abrupt change of CSF compartments or cystic lesion. The position of the burr hole should be at the highest point in order to minimize CSF loss. Moreover, brain distortion occurs rarely in midline structures and most endoscopic procedures use midline structures as anatomical landmarks.

Neuronavigation requires a rigid three-pin head fixation, difficult to obtain in case of younger babies. Moreover the neuronavigation can be coupled only with rigid endoscopes.

Equipment for neuronavigation coupled with neuroendoscopy has been discussed in a recent paper by Tirakotai et al. (Tirakotai et al. 2004).

Operative Instruments

Operative instruments for neuroendoscopy include sharp micro scissor, blunt micro scissor, biopsy forceps, grasping forceps, monopolar and bipolar electrodes.

Floor Perforation

The perforation of the floor can be achieved mechanically (by either a sharp instrument or, in combination with more force, a blunt instrument), electrically or with the aid of a laser.

Perforation With the Endoscope Itself

The endoscope can be gently pushed through the floor behind the clivus, stretching the fibers of the floor progressively until complete perforation is achieved and entry into the subarachnoid spaces is ensured by the sudden, direct visualization of the anatomical structures of the interpeduncular cistern (El-Dawlatly et al. 1999, El-Dawlatly et al. 2000, Teo and Jones 1996). This technique has several inconveniences: the traction on the floor can be significant and it is directly transmitted to the hypothalamic structures situated above. Until perforation is achieved this is a blind procedure, with no visual control of the depth reached by the endoscope or of the space remaining behind the membrane to be perforated.

Monopolar or Bipolar Coagulation

It is the most widely used technique (Cinalli 2004, Hellwig et al. 1999, Sainte-Rose and Chumas 1996). The advantages are evident. The point at which to perforate can be precisely chosen: if the floor is translucent, the tip of the coagulating wire can be positioned where the interpeduncular cistern is wider, as far as possible from the basilar bifurcation. Without applying cautery current, the tip of the wire can be used as a probe to ''palpate'' the floor of the third ventricle or to pierce it (Siomin and Constantini 2004). The coagulation is especially useful when the floor is very large and floating in the lumen of the ventricle: it allows the catheter tip to adhere to the chosen point, avoiding the natural tendency of the tip to slide. Coagulation should be used at the lowest effective energy to bring about coagulation of the floor. In most cases it is not necessary to maintain the coagulation until the perforation is achieved. A very short coagulation (<1 s) is usually sufficient to weaken the floor enough to allow perforation easily and atraumatically with the inactive probe, avoiding the risk of entering the interpe-duncular cistern with an electric device on.

Both monopolar and bipolar coagulation are useful in this regard. Coagulation is also useful to achieve hemostasis. Most bleedings are venous with a slow flow, and can be managed only with irrigation. Sometimes a Fogarty balloon can be used to tamponade a bleeding vessel or the margins of a cutting (i.e. the stoma in the floor of the third ventricle). However, in some instances, neurosurgeon must appeal to coagulation to achieve hemo-stasis. Monopolar cautery can be used in both cutting and coagulation modes to achieve fenestration, dissection or cauterisation. The use of electrical current can be associated with some problems (Vandertop et al. 1998). The pathway of the currents flowing out of a tip cannot be controlled because the fluid in the ventricles is conductive and the current flows along the way of least resistance. Moreover energy losses caused by resistance in the leads makes them less efficient, so that very high currents could be necessary. Thus, tissue adherence and thermal damage of surrounding neural tissue are the major limitations of these instruments. However, the thermal damage to the hypothalamic region following coagulation has never been accurately studied. It may perhaps explain the fever sometimes observed after third ventriculostomy (Decq et al. 2000, Decq 2004, Sainte-Rose and Chumas 1996). Because of these problems, Heilman and Cohen (Heilman and Cohen 1991) invented a ''saline torch'': a device that sends a jet of saline past a monopolar wire. The saline acts as a conductor and coagulation can be achieved without direct contact with the probe (Shiau and King 1998).

Bipolar cautery may represent a more controlled method of coagulation: it has demonstrated minimal current spread; it permits sharply demarcated coagulation fields and precise cuts; damage to lateral or underlying structures is kept to a minimum. Therefore, bipolar coagulator should be preferred (Shiau and King 1998). The simplest way to achieve bipolar coagulation is through a fork electrode (Aesculap 2.1-mm fork electrode). The use of grasping bipolar forceps (2.5 mm - Codman & Shurtleff, Johnson & Johnson, Raynham, MA) allows the surgeon to pick up tissue for dissection and fenestration, and to coagulate vessels of more than 2 mm in diameter. Riegel et al. (Riegel et al. 2002) developed a new microbipolar forceps (ERBE Elektromedizin GmbH, Tübingen, Germany) that can be used for grasping, dissection, dilation, shrinkage of tissue, and precise coagulation even of larger vessels. The branches of the forceps are moved via elastic deformation of the metal without the use of a mechanical joint of

Codman Bipolar Forceps

Fig. 15. The lack of mechanical joint allows very slow and delicate movements in this bipolar forceps produced by ERBE (Courtesy of ERBE Elektromedizin GmbH,

Tübingen, Germany)

Fig. 15. The lack of mechanical joint allows very slow and delicate movements in this bipolar forceps produced by ERBE (Courtesy of ERBE Elektromedizin GmbH,

Tübingen, Germany)

any kind (Fig. 15). The instrument has a outer diameter of 1.5 mm along its entire length and is compatible with most working channels of neuroendoscopes. It can be opened up to a width of 6 mm. So, it can be used either to perforate or to enlarge the stoma. Bipolar electrodes of different shape are also available and are extremely effective for coagulation and perforation (Fig. 16).

Decq Forceps

Also this instrument can perforate the floor and enlarge the stoma (Decq et al. 2000). It is a modified endoscopic flexible grasping forcep with an outer diameter less than 1 mm, allowing it to be used with working channels of virtually all endoscopes. The tip is thin enough to allow easy perforation of the floor of the ventricle by the application of gentle pressure, while its pointed but blunt shape do not damage structures like vessels as a needle could.

The peculiarity of this forcep is that the inner surface is smooth whereas the outer surface presents indentations: this avoids accidental catching of vessels during closure and slipping of the edges of the stoma during opening, allowing easy dilatation with one single movement and avoiding the repeated manoeuvers that are often necessary to enlarge the first opening and that are potentially hazardous (Fig. 17a-c). The opening is approximately 4 mm in diameter. The advantage of this forcep is that it combines a thin, almost pointed tip with the potential for performing a gentle dissection by opening the jaws, especially when the floor is thick and difficult to puncture (Cinalli 2004, Decq et al. 2000).

Aesculap Unitrac
Fig. 16. Single, smooth tip bipolar electrodes allow atraumatic and small coagulation and perforation (Courtesy of ERBE Elektromedizin GmbH, Tübingen, Germany)

Laser

The physics of lasers in medicine has been reviewed by Nobles (Nobles 1998) and Siomin and Constantini (Siomin and Constantini 2004). Application of laser to tissue causes an instantaneous increase in temperature, leading to vaporization of the cells. Most lasers cannot be used in neuro-endosopy, because they are not able to work through water and transmit through a miniature fiberoptic cables (600 mm and 400 mm). The only lasers suitable for neuroendoscopy are the neodymium: yttrium aluminum garnet (Nd:YAG) laser, the argon laser and the potassium-tetanyl-phosphate (KTP) laser (Nobles 1998, Shiau and King 1998, Siomin and Constantini 2004, Wharen et al. 1984, Wong and Lee 1996). A sharper-edge tip maximizes the cutting ability, but diminishes its coagulative properties (Shiau and King 1998). The lasers can be used in a contact or non-contact mode. Free laser light would be rapidly absorbed by the CSF with scattering and possible thermal injury to the surrounding structures (Vandertop et al. 1998). The contact probe offers more controlled tissue vaporization and requires less energy (Shiau and King 1998). In this case, the tip of the probe can become heat. The tip may remain hot even when the laser is off, so that care should be given to do not inadvertently damage neural tissue. Some authors have proposed the use of contact tipped Nd:YAG laser (1064 nm) (Miller 1992, Oka and Tomonaga 1992, Ymakawa 1995), although this only offers a partial solution to the problem. Vandertop et al. (Vandertop et al. 1998) propose the use of specially designed laser probes with atraumatic ball-shaped fiber tips coated with a layer of carbon particles. This allows 90% absorption of the laser light that is converted into heat, a

Gene Storz

Fig. 17. The forceps described by Decq (Karl Storz GmbH & Co., Tuttlingen, Germany) present a smooth tip when closed, suitable for floor perforation (a), and indentation on the outer surface, allowing opening of the perforation (b) to a satisfying diameter (c) with one single movement (image courtesy of Dr. Philippe Decq, Hopital

Henri Mondor, Creteil, France)

Fig. 17. The forceps described by Decq (Karl Storz GmbH & Co., Tuttlingen, Germany) present a smooth tip when closed, suitable for floor perforation (a), and indentation on the outer surface, allowing opening of the perforation (b) to a satisfying diameter (c) with one single movement (image courtesy of Dr. Philippe Decq, Hopital

Henri Mondor, Creteil, France)

allowing both the amount of laser light used and the length of exposure to be reduced (Willems et al. 2001). Other authors (Buki et al. 1999) have proposed combined pulsed holmium (Ho)-Nd-YAG laser and claim that it is superior to mechanical cutting of the tissues, both for third ventri-culostomy and for cyst fenestration. According to Siomin and Constantini (Siomin and Constantini 2004), the KTP laser offers some advantages on Nd: YAG laser: the emission of a visible light, that makes it easier to manipulate; an inferior tissue penetration, that makes it safer, and less dependency on tissue pigmentation, that makes it more versatile.

Nd:YAG laser and KTP laser are more useful in case of tumor removal and cyst fenestration than in case of third ventriculostomy. In fact, great care should be given when using a laser to perform a third ventriculostomy, since a case of injury of the vessels of the interpeduncolar cistern has been reported (McLaughlin et al. 1997).

Suction-Cutting (Grotenhuis) Device

The suction-cutting device (Synergetics), developed recently by Grotenhuis, is composed of a thin suction cannula that can be introduced through an operative channel at least 2 mm in diameter. The outer surface and the edges of the inlet of the cannula are smooth, whereas small blades are inserted into the lumen of the cannula. When the tip of the cannula comes into contact with the floor of the third ventricle, the suction hole on the handle is closed and the membrane is sucked into the lumen of the cannula. Rotation of the cannula allows section of only the tissue aspirated into the lumen, limiting the risk of accidental injury to vascular structures.

"Semisharp" Instruments

The cautious blunt perforation is usually safe, but in case of more resistant floor of the third ventricle a forceful pushing of the instruments is necessary and might be dangerous. Surgical tools specifically designed for safe perforation of a resistant and/or thick floor have a semisharp, slightly angulated tip that, directed anteriorly and pushed inferiorly along the clivus, would allow safe perforation minimizing the risk of injury of the basilar artery (Kehler et al. 1998).

Ultrasound Microprobes

Ultrasound microprobes have been specifically designed for use through the working channel of the endoscope (6 French) or paraendoscopically (8 French). These probes offer the major advantage of direct visualization of the anatomical structures of the interpeduncolar and prepontine cisterns and can be used for blunt perforation of the floor. This allows safer perforation under the double control of the floor of the third ventricle (endoscopic) and of the anatomical and vascular structures hidden behind the floor membrane (ultrasonographic) (Paladino et al. 2000, Resch and Reisch 1997, Resch and Perneczky 1998, Resch 2003) (Fig. 18a-c).

Forceps and Scissors

Instruments of various design are commercially available, suitable for rigid or flexible endoscopes. These include: grasping forceps, biopsy forceps

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