2.2.1 Rigid Endoscopes

Early endoscopes had an array of glass lenses—which were difficult to assemble, with supporting rings wasting space (Fig. 2.1a). The gold standard now is rod-lens endoscopes based on Hopkins patents.7 The numerous glass rods (Fig. 2.1b) with optically shaped ends are self-aligning; different glass types correct for image distortions. Karl Storz developed this technique for clinical practice in the 1960s,10 and today we use improved Hopkins II endoscopes (enlarged format, increase in lateral view > 30%), which offer full HD video imaging with sufficient diameter of the rods. The large focus range and wide area of vision give the impression of “the eye at the front of the lens,” in contrast to the view offered by microscopes.

Different angles of view are achieved, for example, by prisms (Fig. 2.1c and Fig. 2.2). Most frequently used are 0º (direct view), 30º, and 45º optics (“fore-oblique”), which look “straight ahead” for safe guidance; by turning around, 45º optics achieve an almost 300º overview. Optics with 70º or 120º optics allow a view “backward,” for example, to check the complete removal of cysts or tumors from the ventricle. The most versatile are Hopkins endoscopes with a variable direction of view, for example, the 15º to 90º EndoCAMeleon NEURO ( Fig. 2.2 , Karl Storz GmbH & Co. KG; fits to the GAAB-Set, Fig. 2.3 ).

As instruments are inserted aside of the optics, a slight angle of view of the operation scope (e.g., 6º, Fig. 2.2 ) is preferred to see the instrument in the center. A second flexible endoscope (fiberoptic or videoendoscope) with an adequate diameter can be used in combination with the rigid scope (“mother-daughter principle,” Fig. 2.3d ), which controls the movement of the flexible endoscope.

Optics with light from an external light source via glass fibers surrounding the optics are ideal for diagnostic vision, but they reduce the space in the sheath. The use of two fiberglass light rods aside the optics creates a C-shape of the operation scope, leaving more space (Fig. 2.3).

Rigid lens scopes are fragile; they should never be dropped or bent and should always be picked up by the ocular, not by the shaft, supporting the long axis with one hand. For use in the brain, autoclavable Hopkins optics should be used (see 2.7 Hygiene). Autoclaving decreases the service time (due to strains caused by pressure and heat); a second endoscope should be available in case of damage to the primary endoscope.

Types of Rigid Ventriculoscopes with Sheath

In a monoportal approach, imaging, irrigation, and instrumentation are done through one sheath. Sets of scopes with sheath, instruments (for complex procedures and also for “dual instrument technique”9) and irrigation and/or overflow may be classified into channel scopes or space scopes.7 Channel scopes have separate channels, larger for instruments, smaller for irrigation/overflow, and some with an additional channel for a smaller instrument. The advantage of channel scopes includes precise guidance of instruments; the disadvantage is the limitation of the main working space. In space scopes, a larger channel or a wide space aside the C-shaped Hopkins optics is provided for instruments with ≥ 3-mm diameter, including, e.g., ultrasonic aspirators11 or additional flexible optics to look around and/or through narrow areas. Irrigation and use of dual instruments is integrated in the large space with separate lateral nozzles, which allows an outer diameter of the sheath of < 7 mm, or additional small channels may be provided (then the overall diameter is > 7 mm).

Examples of channel scopes include:

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  The DECQ Ventriculoscope (Karl Storz GmbH & Co. KG, Tuttlingen, Germany), straight Hopkins II optics, 2.9-mm diameter, with 3 different 14-cm operation sheaths (diameter 4.7–7 mm), for 1-mm to 2.5-mm instruments (inset for 7-mm sheath with two small channels for dual instrumentation).

  
  
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  The LOTTA Ventriculoscope (Karl Storz GmbH & Co. KG) by Schroeder, diameter 6.1 mm, 45º angled eyepiece of the operation optics for various straight instruments in a 6.8-mm sheath with 2.9-mm working channel, 1.6-mm irrigation and/or overflow channel. For diagnostic imaging, 3.3-mm Hopkins II scopes with 0º, 30º, or 45º angle of vision can be used; an optical obturator for 2-mm straight 0º Hopkins optics allows one to position the sheath under visual control.

  
  
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  The MINOP Ventriculoscope (Aesculap, a division of B. Braun AG, Melsungen, Germany) by Perneczky: Rod-lens Endoscopes (0º or 30º angle of view) with a diameter of 2.7 mm and a 90º angled ocular for straight instruments. The sheath with an outer diameter of 6 mm has a 2.8-mm working channel, and two 1.4-mm channels for irrigation and/or outflow; one may be used by 1-mm flexible instruments for bimanual instrumentation.

  
  
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  The OI HandyPro Endoscope (Karl Storz GmbH & Co. KG) is designed for freehand ventriculoscopy (removable handle), with straight 0º Hopkins II optics, diameter 2 mm, angle of view 0º or 12º (centered instruments) in a 4-mm operating sheath (15-cm working length) with three channels (for 1.3-mm instruments, irrigation, or suction).

Space scopes have the rod-lens optics positioned aside, to leave as much space as possible for a large channel or free area aside the scope in the sheath. Examples include:

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  The GAAB Ventriculoscope (Karl Storz GmbH & Co. KG; Fig. 2.2 and Fig. 2.3 ), with 6.5-mm sheath (outer diameter). Straight 4-mm Hopkins II scopes with 0º, 30º, 45º, 70º, or 120º angle of view or the EndoCAMeleon® NEURO with a variable view of 15º to 90º (Fig. 2.2) are inserted for diagnosis (full HD quality; may be turned around). For the operation, a 1.7-mm Hopkins II optics with two fiberglass light guides aside (C-shaped) is used, 6º angle of view (instrument in the center) with 45º angled eyepiece for the use of straight instruments. The space of 3 mm in the sheath allows instruments with ≤ 3-mm diameter (Fig. 2.3), a 2.8-mm rigid Hopkins “tracker” optics, or flexible endoscopes (Fig. 2.3e and Fig. 2.6). An obturator with a 2-mm channel may be used for stereotactic guidance, an “optical” obturator with a 2.7-mm channel for straight Hopkins II “tracker” optics to position the sheath under visual control. An additional top tool with two channels allows the simultaneous use of two small straight instruments. Two lateral anozzles to the “space” are used for overflow and irrigation (a Teflon catheter may be introduced, e.g., close to a bleeding source for easier hemostasis), or a second flexible instrument (1.3 mm) for bimanual instrumentation combined with a large instrument in the “space.”

  
  
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  The MINOPInVent ventriculoscopy system (Aesculap, a division of B. Braun AG, Fig. 2.4 ) has a sheath with an outer diameter of 8.3 mm; it uses the same MINOP ventriculoscope(s) as described above, positioned at the lower margin of the sheath (Fig. 2.4). The working channel with 3.7 × 6.5-mm diameter is used for various 3.1-mm instruments, also with deflection or lateral extensions, etc., in the oval channel; for example, forceps; dissectors; hook knife with 3.0-mm height; 90º blunt hook with 3.5-mm deflection; monopolar coagulation with straight and hook electrodes; or bipolar with 0º, 30º, and 40º deflection, height 3.2 mm. A second channel (2.2 mm) is provided for an additional instrument (bimanual instrumentation) and a third (1.4 mm) for irrigation.

2.2.2 Flexible Fiberscopes

Fiberoptics transmit one light point with every fiber—one looks to the surface of the fiber bundle. Each fiber has a core glass with a highly refractive index surrounded by cladding glass with a lower refractive index. The interface between the two glass types acts as a mirror; by total reflection the light is transmitted independently from the angle of bending (Fig. 2.1d). Hopkins12,13 arranged the fibers in matching locations at either end, resulting in an anatomical fiberoptic pixel image in the eyepiece. The resolution therefore depends on the number of glass fibers (minimal diameter 7–10 mm). In a larger flexible ventriculoscope with a diameter of 4 mm allowing a working channel of ≤ 2 mm for more effective instruments, the number of available fibers is ~ 50,000, which corresponds to a resolution of < 240 × 240 fiberoptic pixels; such a flexible fiberscope, however, is quite large, for example, for a use through the aqueduct or in the spine. The resolution of fiberscopes with < 3-mm diameter is < 200 × 200 fiberoptic pixels. The image quality is further decreased by the Moiré effect, the interference of the fiberoptic pixels with the raster of the CCD14 camera chip. This interference increases with the CCD resolution, resulting in reduced image quality with full HD video cameras (pixel filters are not effective).

Fiberscopes were initially used in gastroscopy by Debray and Housset15 and by Hirschowitz et al in 1958.16 Fukushima17 was the first to use a flexible fiberscope for ventriculoscopy in 1973, performing ventriculostomy and tumor biopsy. We use a steerable 70-cm Neuro-Fiberscope (Nr. 11161 C, Karl Storz GmbH & Co. KG) with a diameter of 2.8 mm, a working channel of 1.2 mm, and an angle of vision of 90º, with a possible deflection up/down of 170º/120º. It can be introduced in the working channel of some rigid space-type ventriculoscopes—for example, a space-type scope in a “mother-daughter principle.” The powerful rigid optics then provide a detailed anatomical overview and control the flexible scope, for example for moving it through the foramen of Monro to and through the whole third ventricle (e.g., to control a complete removal of cysts or tumors), and via the aqueduct to the fourth ventricle, and even to the upper spine via the foramen of Magendie. The instruments are powerful enough to open tiny membranes (e.g., for an aqueductoplasty18) or for a biopsy of a tumor in the fourth ventricle. Irrigation facilitates the movement of flexible endoscopes through narrow spaces. Instruments in a flexible endoscope cannot be advanced in the flexed tip, and the bending angle is reduced by the instrument.19 When retracting a flexible endoscope, the curvature must be adjusted; retraction with a bent tip may severely damage the brain—it acts like a hook!

The disadvantages of flexible fiberscopes are low resolution and brightness. The glass fibers break easily, and the tiny surface cover on each may get damaged. The fiberoptics should be checked before and after use (broken fibers result in black dots). Channels for instruments and irrigation should immediately be cleaned after an operation. Flexible fiberscopes cannot be autoclaved (see 2.7 Hygiene); videoendoscopes with higher resolution will probably replace fiberscopes.