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Instrumentation: Endoscopes and Equipment
Peer-Review Reports
Instrumentation: Endoscopes and Equipment Michael R. Gaab
Key words 䡲 Accessories 䡲 Application 䡲 Endoscopy 䡲 Instruments 䡲 Principles 䡲 Scopes 䡲 Sterilization 䡲 Technology
䡲 OBJECTIVE: The technology and instrumentation for neuroendoscopy are described: endoscopes (principles, designs, applications), light sources, instruments, accessories, holders, and navigation. Procedures for cleaning, sterilizing, and storing are included.
Abbreviations and Acronyms CCD: Charge-coupled device CJD: Creutzfeldt-Jakob disease CNS: Central nervous system CSF: Cerebrospinal fluid EFIS: Electronic flight instruments ETV: Endoscopic third ventriculostomy HD: High-definition LED: Light-emitting diode
䡲 RESULTS: The main work horses in neuroendoscopy are rigid glass rod endoscopes (Hopkins optics) due to the optical quality, which allows full high-definition video imaging, different angles of view, and autoclavability, which is especially important in neuroendoscopy due to the risk of CreutzfeldtJakob disease infection. Applications are endoscopy assistance to microsurgery, stand-alone endoscopy controlled approaches such as transnasal skull base, ventriculoscopy, and cystoscopy in the cranium. Rigid glass rod optics are also applicable in spinal endoscopy and peripheral nerve decompression using special tubes and cannulas. Rigid minifiberoptics with less resolution may be used in less complex procedures (ventriculoscopy, cystoscopy, endoscopy assistance with pen-designs) and have the advantages of smaller diameters and disposable designs. Flexible fiberoptics are usually used in combination with rigid scopes and can be steered, e.g. through the ventricles, in spinal procedures for indications including syringomyelia and multicystic hydrocephalus. Upcoming flexible chip endoscopes (“chip-in-the-tip”) may replace flexible fiberoptics in the future, offering higher resolution and cold LED-illumination, and may provide for stereoscopic neuroendoscopy. Various instruments (mechanical, coagulation, laser guides, ultrasonic aspirators) and holders are available. Certified methods for cleaning and sterilization, with special requirements in neuroapplications, are important.
Neurosurgical Department, Hannover Nordstadt Hospital, Hannover, Germany To whom correspondence should be addressed: Michael R. Gaab, M.D., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2013) 79, 2S:S14.e11-S14.e21. http://dx.doi.org/10.1016/j.wneu.2012.02.032 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2013 Elsevier Inc. All rights reserved.
INTRODUCTION Endoscopes were the first optical instruments used in neurosurgery. They were used much earlier than microscopes: Lespinasse performed endoscopic plexus coagulation in 1910 (5, 11), Mixter (17) introduced endoscopic third ventriculostomy (ETV) in 1923, and at the same time Grant and Fay (10) used photographic documentation in ventriculoscopy. All of these surgeons used Nitze-Leiter–type cystoscopes with an array of lenses (Figure 1A). This scope was improved for a special ventriculoscope by Scarff in 1936 (23). In 1934, Putnam (19) designed a 7-mm ventriculoscope with a rod of optical glass resulting in wider optical aperture. Before World War II, the principles of neurosurgical endoscopes were known: an optical system inside a tube with an inte-
䡲 METHODS: The description is based on the author’s own technical development and neuroendoscopic experience, published technology and devices, and publications on endoscopic surgery.
䡲 CONCLUSIONS: Neuroendoscopic instrumentation is now an established technique in neurosurgical practice and is experiencing rapid development (stereoscopy, integrated operating room).
grated illumination, channels for instruments and for irrigation to avoid the frequently deadly ventricle collapse with Dandy’s simple tube ventriculoscope (4), special coagulation devices (19), and endoscopic photography. The technique of plexus coagulation and ETV proved to be the first effective treatment for hydrocephalus. Although endoscopy showed decreased surgical mortality of ⬍ 10% (24, 25), which compared well with hydrocephalus shunt
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implants, and was associated with much lower secondary failure and complication rates (20, 26), it did not yet become routine in clinical practice. Reasons were surgical discomfort, risk of infection with the eye at the scope, burns by the heat of the lamp in the tip, and less optical quality compared with the stereoscopic microscope. However, with the introduction of more powerful optics, tolerance of glass rod optics to autoclaving, cold light, and mini color
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ments, and accessories used for different indications are shown in Table 2.
Figure 1. Types of endoscopes. (A) Initial lens scope with external illumination (Nitze & Bénèche, 1877). (B) Traditional lens scope. (C) Hopkins rod lens endoscope. (D) SELFOC lens (Nippon Sheet Glass, Tokyo, Japan) rigid endoscope (“needle scope” based on gradient fiber). (E) Flexible fiberscope. (Endoscopes depicted in B–E are used with external cold light and fiberglass light cable.) (F) Video-endoscope (“chip-in-the-tip”), with integrated LED light.
video cameras in the late 20th century, endoscopy has become an essential part of neurosurgery with dynamic development. ENDOSCOPES The endoscopes used in neurosurgery today are classified as rigid lens endoscopes, “semirigid” mini-fiberscopes, flexible fiberscopes, and video-endoscopes (“distal chip”) (Figure
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1A–F); upcoming innovations are stereoscopic endoscopes, either with conventional scopes (glass rods) using dual charge-coupled device (CCD) cameras/rapidly alternating views with dual “chips on the tip,” or with a microscopic array of lenses in front of a single video chip on the tip (“bee eyes technology”) (21). Features, advantages, and disadvantages of these scope technologies are summarized in Table 1. Endoscopes, instru-
Rigid Lens Endoscopes The area of vision of rigid endoscopes with glass lenses can be increased by using more lenses (Figure 1B). However, these endoscopes have limited image quality and low light transmittance; the small lenses (relay and field lenses) inside the endoscopes require supporting rings, which obscure the train of lenses; are difficult to assemble with the required precision; and are rapidly damaged in clinical use. After initial success with a glass rod instead of lenses by Putnam (19), the breakthrough to today’s superb quality of rod-lens endoscopes was achieved by Hopkins’ patents (British Patent No. 954629; U.S. Patent No. 3247906; both obtained in 1959) on using several glass rods to fill the former air spaces between the lenses. The glass rods as relay lenses are much longer compared with the diameter of traditional lenses (Figure 1C); the optically shaped ends produce an image in the center between two glass rods, and the final image is viewed through the ocular. These rods of optical glass fit exactly to the endoscope tube and are self-aligning without the need of other support, and different glass types of the rods correct for image distortions that occur in every optical system. Karl Storz, who bought Hopkins’ patents, introduced this technique into clinical practice in the 1960 (1). Hopkins’ rod lens optics, now Hopkins II with a still wider angle of vision, are the present gold standard in optical quality, area of vision, light transmission, and color fidelity. In deep-seated lesions, these optics “move the eye of the surgeon in front of the lesion,” with a large focus range and with the complete amount of xenon light available in the depth, in contrast to microscopes, which have only a small focus range at higher magnification and lose most light on the surface. A perfect optical quality achieving full high-definition (HD) video resolution requires an outer diameter of the rod lens scopes of ⬎ 3 mm (with integrated light fibers), which are recommended for initial anatomic information. Multirod lens scopes with smaller diameters of ⬍ 2 mm still provide a good optical quality with much more brightness and resolution than fiberscopes and are used in small ap-
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Table 1. Types and Characteristics of Endoscopes and Advantages and Disadvantages Type of Endoscope Rigid lens scopes (Hopkins optics)
Advantages
Disadvantages
Remarks
Excellent optics, HD video quality
Mechanically sensitive, may break
Gold standard in endoscopy—image equivalent to microscope quality
Wide area of vision (up to140°)
Expensive with high quality
Large focus range
Minimal optics diameter around 2 mm
Various angles of view (0°–120°)
Length not individual, must be calculated and specially designed
Use with effective rigid instruments Neuronavigation control Easy to clean; autoclavable Flexible fiberscopes
Flexible and steerable
Limited resolution, ⱕ 320 ⫻ 320 pixels
Available at any length
Mechanically sensitive, limited lifetime (fibers break)
Small optics, ⱕ 2 mm
Expensive
Passage trough smaller for curved or irregular cavities (e.g., aqueduct, syrinx)
No fixed anatomic image
Mainly secondary use combined with rigid endoscopy
No neuronavigation control* Difficult to clean and to sterilize; not autoclavable Semirigid minifiberscopes
Relatively cheap; disposable designs available
Limited resolution, ⱕ 320 ⫻ 320 pixels, but more than flexible scopes
Reuse designs autoclavable
Restricted area of vision
Disposable devices do not need special care; cleaning and sterilization not required, but at the expense of limited optical quality
Easy to set up Small optics (⬍ 1 mm) allow large spaces for straight instruments and irrigation Video-endoscopes (“chipin-the-tip”)
Increasing resolution (today about standard definition-resolution [SD], 720 ⫻ 57 px)
Not autoclavable
Rapid development, already HD resolution with 4-mm chip
Any design possible (flexible, rigid, tip flexible), any length
Still large with small channel (about 5 mm with 2-mm channel)
Most promising for stereoendoscopy (e.g., bee’s eye technique)
Direct image transmission, not separate
Might become future standard if sterilization problem is solved
Camera, no optics—only objective lens HD, high-definition. *Magnetic navigation might be possible.
proaches (e.g., in ventriculoscopy below the foramen of Monro), which limit the maximal outer diameter of the endoscope sheath containing the endoscopes, instrument, and irrigation channels to ⬍ 7 mm. In these procedures, ⬍ 2-mm Hopkins optics for surgical manipulation with angulated ocular (surgical scope, Figure 2A–C) allow the use of straight instruments with diameters up to 3 mm or of dual instruments with ⬍ 2 mm diameter (Figure 2B).
Also, a second flexible endoscope with a diameter ⬍ 3 mm might be used in combination with the rigid scope in a “motherdaughter” setup (Figure 2C), where the rigid scope controls the movement of the flexible scope (e.g., for maneuvering through the aqueduct). A diameter of rigid glass scopes ⬍ 1 mm is achieved with the SELFOC lens (Nippon Sheet Glass, Tokyo, Japan) (Figure 1C) based on gradient index glass (obtained by ion ex-
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change) (18), primarily used for high-speed fiberglass data transmission. The index of refraction is highest in the center of the lens and decreases with the distance from the axis; this results in sinusoidal ray paths within the lens, so the system does not require field lenses and creates a wide field of vision compared with the diameter of the fiber. Such “needlescopes” might be used for very small puncture approaches, as in arthroscopy. However, the optical quality is limited because the single
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Table 2. Types of Endoscopes, Indications, Instruments, and Accessories Type
Indications
Ventriculoscopy
Endoscopes Used
Instruments and Accessories
Diagnostic ventriculoscopy
Rigid lens scopes, coaxial in sheath with special instruments, or single optics for endoscopy assistance; various angles of view
Sheath with trocar, tracker optics
Hydrocephalus: ETV; aqueductoplasty/stent placement; Monroiplasty; plexus coagulation (plus ETV); multicystic hydrocephalus; shunt insertion (ventricle, peritoneum); catheter removal
Rigid lens scopes for standard and complex procedures; semirigid fiberscopes for simpler ETV, ostomies, biopsies
Mechanical instruments
Tumors, cysts, parasites: biopsy (with CSF bypass by ETV, stent placement); resection
Rigid lens scopes for standard and complex procedures; flexible fiberscopes for aqueductoplasty (control), biopsy fourth ventricle, plexus coagulation, multicyst opening
Monopolar and bipolar coagulation
Balloons for ostomies Catheters for stent placement Laser guides and fibers Ultrasound aspirator and dissector Holding devices Navigation connection Cystoscopy
Subdural
Parenchymal
Diagnostic inspection, biopsy
Similar to ventriculoscopy
Arachnoid cysts (and other): ventriculostomy, cisternostomy, stent
Similar to ventriculoscopy—usually rigid lens scopes, often with navigation
Diagnostic inspection
Rigid lens scopes
Irrigation and drainage catheters
Hematoma plus hygroma evacuation, with irrigation
Rigid lens scopes for endoscopy assistance, angulated optics; or minifiber disposables
Coagulation
Drainage insertion
Flexible for looking around
Hematoma and abscess removal
Similar to ventriculoscopy
Deep-seated tumor removal
Abscess: Minifiber disposable
Similar to ventriculoscopy; less complex instrumentation
Navigation Sucker Forceps Catheters Coagulation Ultrasonic aspirator
Transnasal, or also via midface degloving/maxillary sinus
Tumor removal: pituitary, other sellar/perisellar tumors; skull base from behind frontal sinus to lower clivus (also aneurysms) Injuries (frontobasal), basal CSF leaks
Rigid lens scopes (wide angle, 4mm high resolution, different angles of view)
Navigation; microsurgical instruments (adapted to endoscope length) Angulated suckers Ultrasonic aspirator Holding device Special specula or dilators
CSF, cerebrospinal fluid; ETV, endoscopic third ventriculostomy. Continues
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Table 2. Continued Type Endoscope-assisted/controlled
Indications
Endoscopes Used
Instruments and Accessories
Dissection
Rigid lens scopes, also side view; less complex lesions also minifiber pen-designs
Adapted microsurgical instruments
Trephination
Pen minifiber scopes
Holding devices
Spinal discs, stenosis, stabilization
Rigid lens scopes
Adapted microsurgical instruments
Intradural diagnostics; syringomyelia
Small flexiscopes (ⱕ 3 mm)
Carpal tunnel syndrome
Rigid lens scopes, angulated view (30°)
Dilators, slit cannula, hook knife
Ulnar nerve entrapment; neurolysis
Rigid lens scopes, angulated view (30°)
Illuminated special spatula, microsurgical instruments
Tumor resection Aneurysm clip Microvascular decompression Spinal
Nerve entrapment
CSF, cerebrospinal fluid; ETV, endoscopic third ventriculostomy.
gradient glass rod and fiber cannot be corrected for optical aberrations but must be accepted “as is.” Hopkins II rod lens endoscopes with ⬎ 3 mm total outer diameter achieve a wide area of vision of up to 100 degrees and are available with different angles of view by prisms in the tip (Figures 2A–C and 3). Our “workhorses” are mainly 0-degree (direct view), 30-degree, and 45-degree optics. With their large area of vision, these “fore-oblique” (forward oblique) endoscopes still look “straight ahead” and may safely be guided optically. By turning around, 45-degree optics achieve an almost 300-degree (2 ⫻ [100 ⫹ 45]) overview of the whole cavity being approached. Optics with an angle of view of 70 degrees (lateral view) and 120 degrees (retrograde view) do not look forward and are advanced safely only with external optical control or through a positioned sheath and tube. Optics with an angle of view of 70 degrees and 120 degrees with a large area of vision allow a view “backward” (e.g., to check the choroid plexus on top of the third ventricle for foramen of Monro cyst remnants). The newest development consists of rod lens endoscopes with a variable adjustment of viewing direction from 0 –120 degrees (Figure 2A–C). In sheath-guided coaxial ventriculoscopy, instruments are safely controlled “straight forward” with 0-degree optics or better with slight angles of 6 –12 degrees (which focus the surgical instrument in the center of the image; Figure 2A–C). In endo-
scope-assisted microsurgery, lens optics with a lateral view are used under microscopic control to work “around the corner” as first described by Apuzzo et al. (2) (e.g., for lateral dissection, aneurysm clipping, or removal of tumors from cavities, such as from the internal acoustic meatus or Meckel cave) (28). In transnasal skull base surgery, 30-degree, 45degree, and 70-degree optics might be used for surgical manipulation with angled microsurgical instruments and suckers (e.g., inside the sella or intracranially for lateral tumor resection and for hemostasis). Light is usually transmitted to the tip of the endoscope via glass fibers around the optical system coupled to a fiber light cable near the ocular. These round-shaped optics are ideal for diagnostic vision including turning around straight endoscopes with angled vision (Figures 2A–C and 3), but they waste space in the narrow sheath. The use of two separate rods of light fibers creates a “U” shape of the operation scope, providing more space for larger instruments (Figure 2A–C). A disadvantage of glass rod endoscopes is the mechanical sensitivity. The glass rods may break or become misaligned. These endoscopes should never be dropped or bent.
Flexible Fiberscopes Flexible fiberscopes transmit the “image” by a bundle of glass fibers; each fiber has a “core glass” with a high refractive index in the center surrounded by “cladding glass” with lower refraction. The interface be-
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tween the two glass types acts like a mirror, and by total internal reflection the light follows the glass fiber independently from the angle of bending (Figure 1D). Fiberoptics, which were developed by Hopkins in 1955 and 1956 (13, 14), transmit a light point in every fiber with more or less brightness in a specific color resulting in a “pixel-image” (no real image, one looks to the surface of the fiber bundle) (Figure 1D). The resolution of the image depends on the number of glass fibers (minimal diameter 7–10 m). The maximum number of fibers in a flexible fiberscope is about 50,000, which corresponds to a resolution of ⬍ 240 ⫻ 240 pixels. In smaller flexible fiberscopes, which can be advanced through the aqueduct or in the spinal canal (⬍ 3 mm, steerable and with an instrument and irrigation channel, Figure 4A), the resolution is still less. The image quality is decreased further by the Moiré effect—the interference of the fiberoptic pixels with the CCD raster of the camera. This adverse effect increases with the CCD resolution, so HD video cameras are not useful for fiberscopes. Fiberscopes were first introduced into gastroscopy by Debray and Housset in 1955 (6) and by Hirschowitz et al. in 1958 (12), who devised a method of creating optical quality glass-coated fibers and produced practical instruments with American Cystoscope Manufacturing Inc. In 1973, Fukushima et al. (9) was the first to use a fiberscope in the brain ventricles for tumor biopsy and ventriculostomy. Continuous ir-
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rigation facilitates the fiberscope moving forward through narrow spaces and reduces the risk of damage. Instruments in a flexible fiberscope cannot be advanced through a bent tip and must be pushed out of the tip before significant bending. The angle of bending is considerably reduced with the instrument in this position, and the scope must be moved with care to avoid damages by the sharp instrument tip. When the flexible endoscope is retracted, the curvature must be adjusted to the anatomy. Withdrawing a flexible endoscope with a bent tip out of the ventricles, especially out of the fourth ventricle, aqueduct, or foramen of Monro, may severely damage the soft brain in these eloquent areas because the bent tip acts like a hook.
Disadvantages of Fiberscopes The main disadvantages of fiberscopes are the low resolution and the lower brightness of the image. Fiberscopes must be handled with care and should not come in touch with sharp edges because the sensitive glass fibers easily break. After each use, the condition of the optics should be checked; broken fibers are seen as black dots. Surface damage may result in destruction during sterilization. The channels for instruments and irrigation are especially difficult to clean, and fiberscopes cannot be autoclaved. Proper sterilization is of paramount importance because use of fiberscopes in the central nervous system (CNS) requires safe sterilization against prions (e.g., Creutzfeldt-Jakob disease [CJD]) (see later) (22, 29).
Figure 2. Complete set of Hopkins optics with instrumentation and holder for ventriculoscopy and intracranial cystoscopy (Gaab-Storz). (A) Set on operating table: (1) sheath; (2) puncture solid and hollow trocars for stereotaxy (wire channel) or for tracker optics (2-mm channel); (3) small 2-mm tracker optics for trocar (below) and 4-mm diagnostic optics with 0 degrees, 30 degrees, 45 degrees, and 70 degrees of vision, all autoclavable; (4) operation optics, 1.7 mm, U-shaped (see B and C), autoclavable; (5) standard rigid instruments, 1.7 mm, including monopolar and bipolar coagulation rod, inserted, head of ventriculostomy forceps; (6) large instruments, 2.7 mm (see B); (7) puncture cannula, 1.7 mm; (8) irrigation (small) and sucking tube (large); (9) flexible-tip laser guide, 2.8 mm; (10) optical adapter for sterile change of scopes with draped camera; (11) mechanical friction holder. (B) Tip of sheath with operation scope and large forceps. (C) Tip of sheath with flexible endoscope controlled by rigid operation scope.
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Rigid Mini-Fiberscopes The larger diameter and the mechanical sensitivity of the powerful but expensive rod lens scopes resulted in fiberoptic devices with a rigid design. The protection by the outer rigid tube allows a dense packing of fibers in a small diameter (⬍ 1 mm) with an acceptable resolution and an outer diameter of ⱕ 4 mm for a ventriculoscope including the sheath. The optical qualities do not reach the lens optics; the resolution of about 200 ⫻ 200 pixels with 35,000 tiny fibers is not adequate for complex procedures such as resection of ventricle tumors and skull base procedures. However, for a “first view” with a small approach, for pen scopes in endoscopy assistance, and for less
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mor biopsies. It is useful in very large heads because of its usable length of 20 cm.
Figure 3. Hopkins rod lens endoscopes (Storz), area of vision, and different angles of vision: 0 degrees, direct view; 30 – 45 degrees, fore-oblique; 70 degrees, lateral; 120 degrees, retrograde; 0 – 120 degrees, variable adjustment.
complex procedures (e.g., ventriculostomies and cystostomies, ventricle drain positioning, and tumor biopsies in uncomplicated anatomy), these mini-fiberscopes offer an alternative with simple handling. The Clarus-Medtronic scopes (Clarus Medical Systems Inc., Minneapolis, Minnesota, USA [licensed to Medtronic PS Medical, Goleta, California, USA]) are single-use disposable scopes and avoid sterilization problems. The Channel Neuroendoscope with 30,000 fibers and two channels (irrigation inflow and instrument outflow) can be used with straight mechanical instruments for ventriculostomy or cystostomy and biopsies. Pen designs are the MurphyScope with a rounded end (e.g., for endoscopy assistance) and the NeuroPEN
(1.3 mm diameter) with stylet handle (e.g., for endoscopic positioning of ventricle catheters). With only 10,000 fibers, the pen designs have a low resolution. The Gaab Pediatric Neuroendoscope (Storz) is not disposable, but it is easy to clean similar to rigid lens scopes and can be autoclaved. This neuroendoscope has 35,000 fibers, separate irrigation inflow and outflow channels, and an instrument channel that allows the use of rigid and flexible instruments (Figure 5). Its overall outer diameter including the sheath is 4 mm and allows a passage of rigid and flexible instruments including coagulation devices and Fogarty balloons (2-F). We use it especially in infants for ETVs, cystostomies, and tu-
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Video-Endoscopes (“Distal Chip,” “Chipin-the-Tip”) In video-endoscopes, the video CCD is mounted in the tip of the endoscope directly behind the objective lens (Figures 1E and 4B). These scopes initially required ⬎ 10 mm diameter (3), but smaller chip scopes are now used in gastroenterology and otorhinolaryngology; actual diagnostic flexible endoscopes without channels and standard resolution (around video graphics array resolution 640 ⫻ 480 px) have a diameter ⬍ 4 mm (Figure 4B) and are offered with a 2-mm working channel with an outer diameter ⬍ 5 mm (e.g., Olympus ENF-VT [Olympus Corporation, Tokyo, Japan], diameter 4.9 mm). Such flexible chip scopes were found to be superior in optical quality compared with fiberoptics in laryngoscopy and are comparable to rigid lens scopes (27). Chip scopes may be offered with an HD video chip up to a resolution of 1080p, also with a flexible tip and rigid main part but with an outer diameter still ⱖ 10 mm (e.g., Olympus HD EndoEYE LTF-VH). Considering the rapid development in recent years, chip scopes are likely to be used in neuroendoscopy soon; flexible chip scopes with ⬍ 5 mm and working space could already be used for ventriculoscopy including ETV. The resolution is higher than with a fiberscope; the image with direct electronic transmission does not have a Moiré effect; and with lightemitting diode (LED) illumination, no camera or light cable is attached (Figure 4B). Before replacing conventional glass rod endoscopes or flexible fiberscopes, problems with sterilization must be solved. Chips must be miniaturized further for designs with larger instrument and irrigation spaces.
TYPES OF VENTRICULOSCOPE SYSTEMS For endoscope-assisted and endoscopecontrolled surgery (e.g., endoscopic transnasal approach) in a normal “air environment,” the surgeon selects among rigid lens scopes with different diameters, lengths, angle of view, and straight or angled ocular. The set is completed by adequate microsurgical instruments (preferably bayonet-type to prevent interference of the surgeon’s hand with scope and camera; biportal/binasal approaches may use straight
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ure 2A). The endoscopic part starts after removal of the trocar with insertion of the endoscope. Any flexible fiberscope with an adequate diameter fitting the sheath can be used; rigid scopes are offered with individual working tubes and sheaths, where the scope is locked in during surgery. One has to differentiate between “channel types” and “space types” of rigid scope systems.
Channel Scopes Channel scopes use round lens scopes in the optic canal, surrounded by channels for irrigation inflow and outflow (should be separate) and for instruments. Examples include the following:
y Camaert ventriculoscope (Richard Wolf Ltd., Knittlingen, Germany), with 6-mm outer diameter of the sheath, two irrigation channels, and a 2.2-mm (7 Charriere) working channel;
y Aesculap ventriculoscope (Aesculap, Division of B. Braun AG, Melsungen, Germany) (similar to Camaert) in a short (160 mm, for freehand use) and long (250 mm, for stereotactic frame) version, with 6.2-mm outer diameter, two irrigation channels, and a working channel with 2.2 mm for exchangeable 0-degree or 30-degree wide-angle lens scopes;
y DECQ ventriculoscope (Karl Storz GmbH & Co. KG, Tuttlingen, Germany), available with three different diameters of the oval operations sheaths (4.7 mm, 5.2 mm, and 7 mm); in the largest version, two (small) instruments can be used for bimanual dissection;
y OI HandyPro endoscope (Storz), with
Figure 4. (A) Flexible fiberscope for ventriculoscopy, diameter 2.8 mm, with instrument channel, tip bending up 170 degrees and down 120 degrees, and 90-degree area of vision. (B) Video-endoscope with monitor 800 ⫻ 480 pixels, “chip-in-the-tip,” bending up and down 140 degrees, 85-degree area of vision, and integrated light—meaning no camera or light cable is required.
4-mm outer diameter, with three channels (inflow and outflow), 1.3-mm instruments, and 0-degree and 12-degree optics (to center the instrument); this scope is especially designed for freehand ventriculoscopy and ventriculostomy;
y Perneczky’s Minop-Design with Aescuinstruments with the advantage to be simply turned around). Ventriculoscopy and Cystoscopy Ventriculoscopy and cystoscopy are usually based on a puncture approach using a tube
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(sheath) with a blunt trocar. The cavity is punctured without internal optical guidance based on the diagnostic images, often with neuronavigation. A small tracker optic inside the trocar can be used to check the penetration of the ventricle or cyst wall (Fig-
lap, also with three different but round diameters of the sheaths, the largest with 6 mm containing two irrigation channels and one 2.2-mm working channel. The 0-degree and 30-degree optics have a 90-degree angulated ocular for the use of straight instruments;
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Figure 5. Rigid minifiber ventriculoscope, 3.8 mm, autoclavable, in 4.5-mm sheath (pediatric size) with rigid instrument, 1.3 mm, in instrument channel (3); two additional channels for irrigation and outflow (2); and mini-fiberoptics 35.00 fibers, diameter 0.8 mm (1).
y Channel scopes by Clarus-Medtronic (Clarus Medical Systems Inc.) with mini-fiberoptics;
y Gaab (pediatric) Minifiber Ventriculoscope (Karl Storz GmbH & Co. KG) (Figure 5). Special sets of instruments are available for these channel endoscopes. Advantages of channel scopes are the protection of the scope and the guidance of the instruments in the separate channels. The disadvantage is the limited space available for material removal (tumors, cysts, clots) or for the insertion of catheters or stents.
Space Scopes “Space” scopes are based on the principles of Dandy and Kelly (15), who used tubes with the microscope to visualize and remove deep-seated parenchymal lesions with a small approach avoiding spatula retraction. The use of a rigid endoscope should leave as much space as possible for effective surgery in a small sheath in which the diameter is limited (e.g., by the size of the foramen of Monro). The Gaab-Storz ventriculoscope (Karl Storz GmbH & Co. KG) (Figure 2A–C) uses a 6.5-mm sheath (outer diameter). After initial puncture with a blunt trocar (or a hollow
trocar with a 2-mm “tracker” scope to control the puncture), 4-mm straight diagnostic scopes (easy to turn around) with different angles of view (0 degrees, 30 degrees, 45 degrees, 70 degrees, or 120 degrees) and 100 degrees area of vision are used at HD video quality for anatomic orientation and for irrigation. For surgical manipulation, a 1.7-mm Hopkins optics with two rod light guides in a “U” shape is used, with a 6-degree angle of view to have the instrument in the center of vision. The entire space in the sheath is available for instruments up to 3 mm diameter (Figure 2B) for removal of tissue, cysts, and clots or for the insertion of catheters. With an additional top tool with two guiding channels, two straight instruments with 1.3 mm can be used simultaneously. A similar design was the Frazee ventriculoscope (mainly designed for endoscopy in lateral ventricles with larger lesions; disadvantage: too large to pass the foramen of Monro [Karl Storz GmbH & Co. KG]; production ended) with a larger diameter of 8.8 mm.
first produced and named “cold light” by Storz in 1963 (16). Cold light sources produce less heat, but not zero; infrared (heat) is transmitted through the light cable. Heat transmission is reduced further by dichroic mirrors for light focusing and by filters; nevertheless, the end of the light cable may burn owing to the transmission of high light energy without becoming hot itself (7, 8); the free end of the light cables should be handled with care. Also, light from the endoscope tip might damage sensitive structures when coming too close with a fullpower light beam. Xenon lamps have replaced halogen bulbs in cold light sources. Halogen is limited to effective 150 –250 W and has a yellowish color temperature of 5000 –5600 K; xenon light with a color temperature of 5500 – 6400 K corresponds to sunlight and is available with up to 300 W, with longer lifetime of the lamp compared with halogen. Fiberglass cables usually are used for cold light transmission. Theoretically, gel cables filled with clear optical gel (liquid crystal) transmit more light, but they also transmit more heat and may crack.
ENDOSCOPE CAMERAS Small video cameras in sterile covers provide sterile video-optical surgery. Cameras directly attached to the scope ocular are available with three-chip and full HD quality. Some of these cameras can be autoclaved. However, cameras that can be autoclaved are more expensive, and heat sterilization reduces the lifetime. We prefer to use sterile covers. However, to allow a sterile change between different scopes, an autoclavable optical adapter (Figure 2A) is required to connect the endoscope ocular with the camera head. The camera side of the sterile optical adapter (a plastic device with glass plates) is covered with the camera cover, and the endoscope side remains free and sterile; this allows a quick change between different endoscopes without loss of optical quality.
LIGHT SOURCES “Cold light” avoids the direct heat of lamps in the scopes and provides more power by transmitting light via glass fibers from an outside light source. This technique was
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INSTRUMENTS AND ACCESSORIES In open spaces, microsurgical instruments with appropriate length can be used with the endoscope; often bayonet instruments
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are preferred to avoid interference with the scope. In coaxial surgery in ventricles and cysts with the instruments running along the endoscope in the endoscope sheath, special sets of instruments are available to fit to the different scopes (length, diameter; Figure 2A, 5). Straight rigid instruments are more powerful and easier to control with rigid scopes, and so some scopes have an angulated ocular. The transition from microsurgery to this coaxial type of endoscopic surgery is difficult and requires training because the instrument hand can control only the depth of the instrument position; the lateral position is mainly controlled by the other hand with the endoscope sheath, which guides the instruments. Standard instruments (Figure 2A) are forceps of different shape and size (spoon type for biopsy and tissue removal; crocodile type for grasping membranes and catheters), blunt-tip and sharp-tip scissors with unilateral or bilateral movement, and needles for puncture and aspiration. A special ventriculostomy forceps is used for membrane opening (ETV, cystostomy), which has tiny outside grooves to prevent the membrane from slipping along (Figure 2A). For minimally invasive enlargement of ventriculostomies and septostomies, Fogarty balloons (2-F to 3-F) are recommended. These should be inflated only with water or saline and not with compressible air to avoid a sudden “pop off.” The equator of the balloon is difficult to position exactly in the membrane perforation. Special double-balloon catheters are easier to use, with the membrane placed between the two balloons for widening the stoma. However, these catheters are expensive and have the risk of asymmetric inflation (e.g., of the lower balloon close to the basilar artery in ETV). Monopolar and bipolar instruments are used for hemostasis, which must be preventive in fluid-filled ventricles and cysts; bleeding in the cerebrospinal fluid (CSF) rapidly obscures the endoscopic vision. For precise irrigation during coagulation, a small separate irrigation tube (Figure 2A) positioned close to the bleeding helps clear the vision. For coagulation and piecemeal resection of tumors, laser fibers can be used with flexible-tip laser guides (Figure 2). Some surgeons also use laser for ETV and septostomy. However, the considerable depth penetration of neodymium:yttriumaluminum-garnet (Nd:YAG) and holmium:
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YAG lasers is a risk within the sensitive diencephalon and on top of the basilar artery. For irrigation in intracranial endoscopy, gravity-controlled infusions or roller pumps can be used; in addition, manual bolus injection may clear the vision more rapidly. However, irrigation should not increase the intracranial pressure, and a free outflow must be guaranteed. If increased intracranial pressure is suspected, the scope should be removed, providing the scope channel for additional outflow. For irrigation in adults, 0.9% sodium chloride can be used, which should be warmed close to but not above body temperature. In infants, larger amounts of sodium chloride and low-temperature irrigation should be avoided.
Ultrasonic Dissectors and Aspirators The small space available in minimally invasive endoscopic neurosurgery in the ventricles and in transnasal skull base approaches interferes with effective resection of larger tumors. Special long, tiny ultrasonic aspirators can be used (e.g., handpiece to the SONOCA Ultrasonic Aspirator [Soering, Hamburg, Germany]). Tiny ultrasonic aspirators do not have their own irrigation, but with central aspiration channels they allow the fragmentation and aspiration of tumors with limited vascularization; simultaneously, CSF can be removed in the nonoscillating sucking mode. In an air environment, hemostasis on the surface and in tumors is easier than with blood spreading through the CSF. However, sucking must be carefully adjusted to low levels with intermittent irrigation to avoid a ventricle collapse.
Navigation Systems For the “blind” puncture of ventricles and cysts through small burr holes, computerized neuronavigation, which replaces stereotactic frames, is used routinely in intracranial endoscopy and is mandatory with small ventricles and for orientation in unstructured cysts and multilocular hydrocephalus. Any infrared-based or mechanical navigation system can be used with rigid endoscopes or endoscopy sheath. Magnetic navigation is attempted for precise intracranial location also of the tip of flexible endoscopes.
Endoscope Holders Some neurosurgeons use freehand ventriculoscopy (special designs such as the OI HandyPro ventriculoscope). However, many endoscopic neurosurgeons prefer an endoscope holder for precise, stable positioning during manipulation, especially for more complex procedures. Holding devices must reliably fix the endoscope but should not delay position changes much. The cheapest solution is the use of two microsurgical Leyla arms attached to a plate that holds the endoscope— our first technique used. The Leyla arm can also be used for retractors in cases of transition to microsurgery. Simple, inexpensive friction holders (Figure 2A) are easier to use and more universal (also for microsurgical assistance and transnasal skull base approach). These allow (similar to Leyla arms) a different friction adjustment from “fully fixed” via “slowly movable” to “fully free.” The more expensive holders with pneumatic (UnitracR Pneumatic Holding Arm [Aesculap, Division of B. Braun AG]) or electromagnetic brakes (Point setter [Mitaka Kohki Co., Ltd., Tokyo, Japan], or Endo-Arm [Olympus Medical Systems Corp.,Tokyo, Japan]) allow an easy control with a single switch but not individually adjustable intermediate positions for slow “holder-supported” motions.
CLEANING, STERILIZATION, AND STORAGE The fiberscope channels are especially difficult to clean, to dry, and to sample microbiologically and cannot be inspected. The use of fiberscopes that usually do not withstand temperatures ⬎ 60°C and are sensitive to many chemicals (which may also lead to degradation of lens cement) should be avoided in infectious lesions. For sterilization and storage, special trays should be used providing fixed positions for each endoscope (not mixed among surgical instruments without protecting sheaths), with fiberscopes if possible in a straight position. Rigid lens scopes should be able to be autoclaved at 134°C. Although the scopes themselves are easy to clean and to inspect, the spaces in the endoscope sheaths must carefully be cleaned and inspected after use. A special problem of CNS endoscopy is the risk of transmission of CJD and its variants (variant CJD— bovine spongi-
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form encephalopathy), which might not be discovered owing to the long incubation time. The prion protein (PrPSc) is extremely resistant to most sterilization procedures; gas sterilization might even increase the infectivity. Because flexible endoscopes cannot be autoclaved at 134°C with 3 bar for 1 hour and cannot withstand aggressive chemical disinfection with sodium hydroxide, sodium hypochlorite, or guanidinium-isothiocyanate (GdnSCN), flexible scopes must be destroyed after CJD or CNS use in any case with suspicion of variant CJD (22, 29).
FUTURE PERSPECTIVES Neuroendoscopy can be improved by still smaller optics with high resolution giving more space. Scopes, cameras, and light cables can be made more compact by modifying the traditional, large ocular coupling and separate light cable connection. However, different scopes used during an operation with one draped camera and one light cable interfere with a “handy” design. The solution will probably come with the rapid development of chip scopes; with flexible tips or swiveling lens or chip, changing between rigid scopes with different angles of view would no longer be required. Chip endoscopes may also be the solution for threedimensional neuroendoscopy with LED illumination without heat problems. Initial designs have been presented but still with low resolution (e.g., with ⬙bee’s eye technology⬙ [21]). Endoscopy should also move away from “stand-alone” endoscopy towers and should be integrated in multifunction displays of the future operation room combining endoscopic, microscopic, and diagnostic images and patient monitoring and control data, similar to a cockpit with multifunction electronic flight instruments (EFIS).
ENDOSCOPES AND EQUIPMENT
18. Nishizawa K: Chromatic aberration of the Selfoc lens as an imaging system. Appl Optics 19:10521055, 1980.
REFERENCES 1. Abbott R: History of neuroendoscopy. Neurosurg Clin N Am 15:1-7, 2004. 2. Apuzzo MLJ, Heifetz M, Weiss MH, Kurze T: Neurosurgical endoscopy using the side-viewing telescope. Technical note. J Neurosurg 16:398-400, 1977. 3. Berci M, Paz-Partlow M: Electronic imaging in endoscopy. Surg Endosc 2:227-233, 1988. 4. Dandy WE: Cerebral ventriculoscopy. Bull Johns Hopkins Hosp 33:189, 1922. 5. Davis LE: Neurological Surgery. Philadelphia: Lea & Febiger; 1936. 6. Debray C, Housset P: New flexible gastroscope [in French]. Arch Mal Appar Dig Mal Nutr 44:561-563, 1955. 7. ECRI: OR fires caused by fiberoptic illumination systems [hazard]. Health Devices 11:148-149, 1982. 8. Eggen MA, Brock-Utne JG: Fiberoptic illumination systems can serve as a source of smoldering fires. J Clin Monit 10:244-246, 1994. 9. Fukushima T, Ishijima B, Hirakawa K, Nakamura N, Sano K: Ventriculofiberscope: a new technique for endoscopic diagnosis and operation. Technical note. J Neurosurg 38:251-256, 1973. 10. Grant FC, Fay T: Ventriculoscopy and intraventricular photography in internal hydrocephalus. JAMA 80:461-463, 1923. 11. Grant JA: Victor Darwin Lespinasse: a biographical sketch. Neurosurgery 39:1232-1233, 1996.
19. Putnam TJ: Treatment of hydrocephalus by endoscopic coagulation of the choroid plexus. N Engl J Med 210:1373-1376, 1934. 20. Putnam TJ: Surgical treatment of infantile hydrocephalus. Calif Med 78:29-32, 1953. 21. Roth J, Singh A, Nyquist G, Fraser JF, Bernardo A, Anand VK, Schwartz TH: Three-dimensional and 2-dimensional endoscopic exposure of midline cranial base targets using expanded endonasal and transcranial approaches. Neurosurgery 65:11161139, 2009. 22. Rutata WA, Weber DJ: Reprocessing endoscopes: United States perspective. J Hosp Inf 56:527-539, 2004. 23. Scarff JE: Endoscopic treatment of hydrocephalus: description of a ventriculoscope and preliminary report of cases. Arch Neurol Psychiatry 35:853-861, 1936. 24. Scarff JE: Non-obstructive hydrocephalus: treatment by endoscopic cauterization of the choroid plexus. J Neurosurg 9:164-173, 1952. 25. Scarff JE: Treatment of hydrocephalus: an historical and critical review of methods and results. J Neurol Neurosurg Psychiatry 26:1-26, 1963. 26. Scarff J: The treatment of nonobstructive (communicating) hydrocephalus by endoscopic cauterisation of the choroids plexus. J Neurosurg 33:1-18, 1970. 27. Schröck A, Stuhrmann N, Schade G: Flexible chipon-the-tip endoscopy for larynx diagnostics [in German]. HNO 56:1239-1242, 2008.
12. Hirschowitz BI, Curtiss IF, Peters CW, Pollard HM: Demonstration of a new gastroscope, the “fiberscope.” Gastroenterology 35:50, 1958.
28. Schroeder HWS, Oertel J, Gaab MR: Endoscopeassisted microsurgical resection of epidermoid tumors of the cerebellopontine angle. J Neurosurg 101:227-232, 2004.
13. Hopkins HH, Kapany NS: Transparent fibres for the transmission of optical images. J Modern Optics (Optica Acta) 1:164-170, 1955.
29. Working Group Hygiene in Hospital and Practice: AWMF guidelines Register No. 029/025. Hyg Med 32:301-306, 2007.
14. Hopkins HH, Kapany NS: A flexible fibrescope using static scanning. Nature 173:39-41, 1956. 15. Kelly PJ: Tumor Stereotaxis. Philadelphia: Saunders; 1991. 16. Kieser CW: Introduction of cold light to endoscopy. Aktuel Urol 39:130-134, 2008. 17. Mixter WJ: Ventriculoscopy and puncture of the floor of the third ventricle. Boston Med Surg J 188: 277-278, 1923.
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Conflict of interest statement: Michael R. Gaab is a consultant of Karl Storz Company, Tuttlingen, Germany. Received 16 August 2011; accepted 03 February 2012 Citation: World Neurosurg. (2013) 79, 2S:S14.e11-S14.e21. http://dx.doi.org/10.1016/j.wneu.2012.02.032 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2013 Elsevier Inc. All rights reserved.
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Instrumentation: Endoscopes and Equipment Michael R. Gaab
Key words 䡲 Accessories 䡲 Application 䡲 Endoscopy 䡲 Instruments 䡲 Principles 䡲 Scopes 䡲 Sterilization 䡲 Technology
䡲 OBJECTIVE: The technology and instrumentation for neuroendoscopy are described: endoscopes (principles, designs, applications), light sources, instruments, accessories, holders, and navigation. Procedures for cleaning, sterilizing, and storing are included.
Abbreviations and Acronyms CCD: Charge-coupled device CJD: Creutzfeldt-Jakob disease CNS: Central nervous system CSF: Cerebrospinal fluid EFIS: Electronic flight instruments ETV: Endoscopic third ventriculostomy HD: High-definition LED: Light-emitting diode
䡲 RESULTS: The main work horses in neuroendoscopy are rigid glass rod endoscopes (Hopkins optics) due to the optical quality, which allows full high-definition video imaging, different angles of view, and autoclavability, which is especially important in neuroendoscopy due to the risk of CreutzfeldtJakob disease infection. Applications are endoscopy assistance to microsurgery, stand-alone endoscopy controlled approaches such as transnasal skull base, ventriculoscopy, and cystoscopy in the cranium. Rigid glass rod optics are also applicable in spinal endoscopy and peripheral nerve decompression using special tubes and cannulas. Rigid minifiberoptics with less resolution may be used in less complex procedures (ventriculoscopy, cystoscopy, endoscopy assistance with pen-designs) and have the advantages of smaller diameters and disposable designs. Flexible fiberoptics are usually used in combination with rigid scopes and can be steered, e.g. through the ventricles, in spinal procedures for indications including syringomyelia and multicystic hydrocephalus. Upcoming flexible chip endoscopes (“chip-in-the-tip”) may replace flexible fiberoptics in the future, offering higher resolution and cold LED-illumination, and may provide for stereoscopic neuroendoscopy. Various instruments (mechanical, coagulation, laser guides, ultrasonic aspirators) and holders are available. Certified methods for cleaning and sterilization, with special requirements in neuroapplications, are important.
Neurosurgical Department, Hannover Nordstadt Hospital, Hannover, Germany To whom correspondence should be addressed: Michael R. Gaab, M.D., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2013) 79, 2S:S14.e11-S14.e21. http://dx.doi.org/10.1016/j.wneu.2012.02.032 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2013 Elsevier Inc. All rights reserved.
INTRODUCTION Endoscopes were the first optical instruments used in neurosurgery. They were used much earlier than microscopes: Lespinasse performed endoscopic plexus coagulation in 1910 (5, 11), Mixter (17) introduced endoscopic third ventriculostomy (ETV) in 1923, and at the same time Grant and Fay (10) used photographic documentation in ventriculoscopy. All of these surgeons used Nitze-Leiter–type cystoscopes with an array of lenses (Figure 1A). This scope was improved for a special ventriculoscope by Scarff in 1936 (23). In 1934, Putnam (19) designed a 7-mm ventriculoscope with a rod of optical glass resulting in wider optical aperture. Before World War II, the principles of neurosurgical endoscopes were known: an optical system inside a tube with an inte-
䡲 METHODS: The description is based on the author’s own technical development and neuroendoscopic experience, published technology and devices, and publications on endoscopic surgery.
䡲 CONCLUSIONS: Neuroendoscopic instrumentation is now an established technique in neurosurgical practice and is experiencing rapid development (stereoscopy, integrated operating room).
grated illumination, channels for instruments and for irrigation to avoid the frequently deadly ventricle collapse with Dandy’s simple tube ventriculoscope (4), special coagulation devices (19), and endoscopic photography. The technique of plexus coagulation and ETV proved to be the first effective treatment for hydrocephalus. Although endoscopy showed decreased surgical mortality of ⬍ 10% (24, 25), which compared well with hydrocephalus shunt
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implants, and was associated with much lower secondary failure and complication rates (20, 26), it did not yet become routine in clinical practice. Reasons were surgical discomfort, risk of infection with the eye at the scope, burns by the heat of the lamp in the tip, and less optical quality compared with the stereoscopic microscope. However, with the introduction of more powerful optics, tolerance of glass rod optics to autoclaving, cold light, and mini color
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ments, and accessories used for different indications are shown in Table 2.
Figure 1. Types of endoscopes. (A) Initial lens scope with external illumination (Nitze & Bénèche, 1877). (B) Traditional lens scope. (C) Hopkins rod lens endoscope. (D) SELFOC lens (Nippon Sheet Glass, Tokyo, Japan) rigid endoscope (“needle scope” based on gradient fiber). (E) Flexible fiberscope. (Endoscopes depicted in B–E are used with external cold light and fiberglass light cable.) (F) Video-endoscope (“chip-in-the-tip”), with integrated LED light.
video cameras in the late 20th century, endoscopy has become an essential part of neurosurgery with dynamic development. ENDOSCOPES The endoscopes used in neurosurgery today are classified as rigid lens endoscopes, “semirigid” mini-fiberscopes, flexible fiberscopes, and video-endoscopes (“distal chip”) (Figure
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1A–F); upcoming innovations are stereoscopic endoscopes, either with conventional scopes (glass rods) using dual charge-coupled device (CCD) cameras/rapidly alternating views with dual “chips on the tip,” or with a microscopic array of lenses in front of a single video chip on the tip (“bee eyes technology”) (21). Features, advantages, and disadvantages of these scope technologies are summarized in Table 1. Endoscopes, instru-
Rigid Lens Endoscopes The area of vision of rigid endoscopes with glass lenses can be increased by using more lenses (Figure 1B). However, these endoscopes have limited image quality and low light transmittance; the small lenses (relay and field lenses) inside the endoscopes require supporting rings, which obscure the train of lenses; are difficult to assemble with the required precision; and are rapidly damaged in clinical use. After initial success with a glass rod instead of lenses by Putnam (19), the breakthrough to today’s superb quality of rod-lens endoscopes was achieved by Hopkins’ patents (British Patent No. 954629; U.S. Patent No. 3247906; both obtained in 1959) on using several glass rods to fill the former air spaces between the lenses. The glass rods as relay lenses are much longer compared with the diameter of traditional lenses (Figure 1C); the optically shaped ends produce an image in the center between two glass rods, and the final image is viewed through the ocular. These rods of optical glass fit exactly to the endoscope tube and are self-aligning without the need of other support, and different glass types of the rods correct for image distortions that occur in every optical system. Karl Storz, who bought Hopkins’ patents, introduced this technique into clinical practice in the 1960 (1). Hopkins’ rod lens optics, now Hopkins II with a still wider angle of vision, are the present gold standard in optical quality, area of vision, light transmission, and color fidelity. In deep-seated lesions, these optics “move the eye of the surgeon in front of the lesion,” with a large focus range and with the complete amount of xenon light available in the depth, in contrast to microscopes, which have only a small focus range at higher magnification and lose most light on the surface. A perfect optical quality achieving full high-definition (HD) video resolution requires an outer diameter of the rod lens scopes of ⬎ 3 mm (with integrated light fibers), which are recommended for initial anatomic information. Multirod lens scopes with smaller diameters of ⬍ 2 mm still provide a good optical quality with much more brightness and resolution than fiberscopes and are used in small ap-
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Table 1. Types and Characteristics of Endoscopes and Advantages and Disadvantages Type of Endoscope Rigid lens scopes (Hopkins optics)
Advantages
Disadvantages
Remarks
Excellent optics, HD video quality
Mechanically sensitive, may break
Gold standard in endoscopy—image equivalent to microscope quality
Wide area of vision (up to140°)
Expensive with high quality
Large focus range
Minimal optics diameter around 2 mm
Various angles of view (0°–120°)
Length not individual, must be calculated and specially designed
Use with effective rigid instruments Neuronavigation control Easy to clean; autoclavable Flexible fiberscopes
Flexible and steerable
Limited resolution, ⱕ 320 ⫻ 320 pixels
Available at any length
Mechanically sensitive, limited lifetime (fibers break)
Small optics, ⱕ 2 mm
Expensive
Passage trough smaller for curved or irregular cavities (e.g., aqueduct, syrinx)
No fixed anatomic image
Mainly secondary use combined with rigid endoscopy
No neuronavigation control* Difficult to clean and to sterilize; not autoclavable Semirigid minifiberscopes
Relatively cheap; disposable designs available
Limited resolution, ⱕ 320 ⫻ 320 pixels, but more than flexible scopes
Reuse designs autoclavable
Restricted area of vision
Disposable devices do not need special care; cleaning and sterilization not required, but at the expense of limited optical quality
Easy to set up Small optics (⬍ 1 mm) allow large spaces for straight instruments and irrigation Video-endoscopes (“chipin-the-tip”)
Increasing resolution (today about standard definition-resolution [SD], 720 ⫻ 57 px)
Not autoclavable
Rapid development, already HD resolution with 4-mm chip
Any design possible (flexible, rigid, tip flexible), any length
Still large with small channel (about 5 mm with 2-mm channel)
Most promising for stereoendoscopy (e.g., bee’s eye technique)
Direct image transmission, not separate
Might become future standard if sterilization problem is solved
Camera, no optics—only objective lens HD, high-definition. *Magnetic navigation might be possible.
proaches (e.g., in ventriculoscopy below the foramen of Monro), which limit the maximal outer diameter of the endoscope sheath containing the endoscopes, instrument, and irrigation channels to ⬍ 7 mm. In these procedures, ⬍ 2-mm Hopkins optics for surgical manipulation with angulated ocular (surgical scope, Figure 2A–C) allow the use of straight instruments with diameters up to 3 mm or of dual instruments with ⬍ 2 mm diameter (Figure 2B).
Also, a second flexible endoscope with a diameter ⬍ 3 mm might be used in combination with the rigid scope in a “motherdaughter” setup (Figure 2C), where the rigid scope controls the movement of the flexible scope (e.g., for maneuvering through the aqueduct). A diameter of rigid glass scopes ⬍ 1 mm is achieved with the SELFOC lens (Nippon Sheet Glass, Tokyo, Japan) (Figure 1C) based on gradient index glass (obtained by ion ex-
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change) (18), primarily used for high-speed fiberglass data transmission. The index of refraction is highest in the center of the lens and decreases with the distance from the axis; this results in sinusoidal ray paths within the lens, so the system does not require field lenses and creates a wide field of vision compared with the diameter of the fiber. Such “needlescopes” might be used for very small puncture approaches, as in arthroscopy. However, the optical quality is limited because the single
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Table 2. Types of Endoscopes, Indications, Instruments, and Accessories Type
Indications
Ventriculoscopy
Endoscopes Used
Instruments and Accessories
Diagnostic ventriculoscopy
Rigid lens scopes, coaxial in sheath with special instruments, or single optics for endoscopy assistance; various angles of view
Sheath with trocar, tracker optics
Hydrocephalus: ETV; aqueductoplasty/stent placement; Monroiplasty; plexus coagulation (plus ETV); multicystic hydrocephalus; shunt insertion (ventricle, peritoneum); catheter removal
Rigid lens scopes for standard and complex procedures; semirigid fiberscopes for simpler ETV, ostomies, biopsies
Mechanical instruments
Tumors, cysts, parasites: biopsy (with CSF bypass by ETV, stent placement); resection
Rigid lens scopes for standard and complex procedures; flexible fiberscopes for aqueductoplasty (control), biopsy fourth ventricle, plexus coagulation, multicyst opening
Monopolar and bipolar coagulation
Balloons for ostomies Catheters for stent placement Laser guides and fibers Ultrasound aspirator and dissector Holding devices Navigation connection Cystoscopy
Subdural
Parenchymal
Diagnostic inspection, biopsy
Similar to ventriculoscopy
Arachnoid cysts (and other): ventriculostomy, cisternostomy, stent
Similar to ventriculoscopy—usually rigid lens scopes, often with navigation
Diagnostic inspection
Rigid lens scopes
Irrigation and drainage catheters
Hematoma plus hygroma evacuation, with irrigation
Rigid lens scopes for endoscopy assistance, angulated optics; or minifiber disposables
Coagulation
Drainage insertion
Flexible for looking around
Hematoma and abscess removal
Similar to ventriculoscopy
Deep-seated tumor removal
Abscess: Minifiber disposable
Similar to ventriculoscopy; less complex instrumentation
Navigation Sucker Forceps Catheters Coagulation Ultrasonic aspirator
Transnasal, or also via midface degloving/maxillary sinus
Tumor removal: pituitary, other sellar/perisellar tumors; skull base from behind frontal sinus to lower clivus (also aneurysms) Injuries (frontobasal), basal CSF leaks
Rigid lens scopes (wide angle, 4mm high resolution, different angles of view)
Navigation; microsurgical instruments (adapted to endoscope length) Angulated suckers Ultrasonic aspirator Holding device Special specula or dilators
CSF, cerebrospinal fluid; ETV, endoscopic third ventriculostomy. Continues
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Table 2. Continued Type Endoscope-assisted/controlled
Indications
Endoscopes Used
Instruments and Accessories
Dissection
Rigid lens scopes, also side view; less complex lesions also minifiber pen-designs
Adapted microsurgical instruments
Trephination
Pen minifiber scopes
Holding devices
Spinal discs, stenosis, stabilization
Rigid lens scopes
Adapted microsurgical instruments
Intradural diagnostics; syringomyelia
Small flexiscopes (ⱕ 3 mm)
Carpal tunnel syndrome
Rigid lens scopes, angulated view (30°)
Dilators, slit cannula, hook knife
Ulnar nerve entrapment; neurolysis
Rigid lens scopes, angulated view (30°)
Illuminated special spatula, microsurgical instruments
Tumor resection Aneurysm clip Microvascular decompression Spinal
Nerve entrapment
CSF, cerebrospinal fluid; ETV, endoscopic third ventriculostomy.
gradient glass rod and fiber cannot be corrected for optical aberrations but must be accepted “as is.” Hopkins II rod lens endoscopes with ⬎ 3 mm total outer diameter achieve a wide area of vision of up to 100 degrees and are available with different angles of view by prisms in the tip (Figures 2A–C and 3). Our “workhorses” are mainly 0-degree (direct view), 30-degree, and 45-degree optics. With their large area of vision, these “fore-oblique” (forward oblique) endoscopes still look “straight ahead” and may safely be guided optically. By turning around, 45-degree optics achieve an almost 300-degree (2 ⫻ [100 ⫹ 45]) overview of the whole cavity being approached. Optics with an angle of view of 70 degrees (lateral view) and 120 degrees (retrograde view) do not look forward and are advanced safely only with external optical control or through a positioned sheath and tube. Optics with an angle of view of 70 degrees and 120 degrees with a large area of vision allow a view “backward” (e.g., to check the choroid plexus on top of the third ventricle for foramen of Monro cyst remnants). The newest development consists of rod lens endoscopes with a variable adjustment of viewing direction from 0 –120 degrees (Figure 2A–C). In sheath-guided coaxial ventriculoscopy, instruments are safely controlled “straight forward” with 0-degree optics or better with slight angles of 6 –12 degrees (which focus the surgical instrument in the center of the image; Figure 2A–C). In endo-
scope-assisted microsurgery, lens optics with a lateral view are used under microscopic control to work “around the corner” as first described by Apuzzo et al. (2) (e.g., for lateral dissection, aneurysm clipping, or removal of tumors from cavities, such as from the internal acoustic meatus or Meckel cave) (28). In transnasal skull base surgery, 30-degree, 45degree, and 70-degree optics might be used for surgical manipulation with angled microsurgical instruments and suckers (e.g., inside the sella or intracranially for lateral tumor resection and for hemostasis). Light is usually transmitted to the tip of the endoscope via glass fibers around the optical system coupled to a fiber light cable near the ocular. These round-shaped optics are ideal for diagnostic vision including turning around straight endoscopes with angled vision (Figures 2A–C and 3), but they waste space in the narrow sheath. The use of two separate rods of light fibers creates a “U” shape of the operation scope, providing more space for larger instruments (Figure 2A–C). A disadvantage of glass rod endoscopes is the mechanical sensitivity. The glass rods may break or become misaligned. These endoscopes should never be dropped or bent.
Flexible Fiberscopes Flexible fiberscopes transmit the “image” by a bundle of glass fibers; each fiber has a “core glass” with a high refractive index in the center surrounded by “cladding glass” with lower refraction. The interface be-
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tween the two glass types acts like a mirror, and by total internal reflection the light follows the glass fiber independently from the angle of bending (Figure 1D). Fiberoptics, which were developed by Hopkins in 1955 and 1956 (13, 14), transmit a light point in every fiber with more or less brightness in a specific color resulting in a “pixel-image” (no real image, one looks to the surface of the fiber bundle) (Figure 1D). The resolution of the image depends on the number of glass fibers (minimal diameter 7–10 m). The maximum number of fibers in a flexible fiberscope is about 50,000, which corresponds to a resolution of ⬍ 240 ⫻ 240 pixels. In smaller flexible fiberscopes, which can be advanced through the aqueduct or in the spinal canal (⬍ 3 mm, steerable and with an instrument and irrigation channel, Figure 4A), the resolution is still less. The image quality is decreased further by the Moiré effect—the interference of the fiberoptic pixels with the CCD raster of the camera. This adverse effect increases with the CCD resolution, so HD video cameras are not useful for fiberscopes. Fiberscopes were first introduced into gastroscopy by Debray and Housset in 1955 (6) and by Hirschowitz et al. in 1958 (12), who devised a method of creating optical quality glass-coated fibers and produced practical instruments with American Cystoscope Manufacturing Inc. In 1973, Fukushima et al. (9) was the first to use a fiberscope in the brain ventricles for tumor biopsy and ventriculostomy. Continuous ir-
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rigation facilitates the fiberscope moving forward through narrow spaces and reduces the risk of damage. Instruments in a flexible fiberscope cannot be advanced through a bent tip and must be pushed out of the tip before significant bending. The angle of bending is considerably reduced with the instrument in this position, and the scope must be moved with care to avoid damages by the sharp instrument tip. When the flexible endoscope is retracted, the curvature must be adjusted to the anatomy. Withdrawing a flexible endoscope with a bent tip out of the ventricles, especially out of the fourth ventricle, aqueduct, or foramen of Monro, may severely damage the soft brain in these eloquent areas because the bent tip acts like a hook.
Disadvantages of Fiberscopes The main disadvantages of fiberscopes are the low resolution and the lower brightness of the image. Fiberscopes must be handled with care and should not come in touch with sharp edges because the sensitive glass fibers easily break. After each use, the condition of the optics should be checked; broken fibers are seen as black dots. Surface damage may result in destruction during sterilization. The channels for instruments and irrigation are especially difficult to clean, and fiberscopes cannot be autoclaved. Proper sterilization is of paramount importance because use of fiberscopes in the central nervous system (CNS) requires safe sterilization against prions (e.g., Creutzfeldt-Jakob disease [CJD]) (see later) (22, 29).
Figure 2. Complete set of Hopkins optics with instrumentation and holder for ventriculoscopy and intracranial cystoscopy (Gaab-Storz). (A) Set on operating table: (1) sheath; (2) puncture solid and hollow trocars for stereotaxy (wire channel) or for tracker optics (2-mm channel); (3) small 2-mm tracker optics for trocar (below) and 4-mm diagnostic optics with 0 degrees, 30 degrees, 45 degrees, and 70 degrees of vision, all autoclavable; (4) operation optics, 1.7 mm, U-shaped (see B and C), autoclavable; (5) standard rigid instruments, 1.7 mm, including monopolar and bipolar coagulation rod, inserted, head of ventriculostomy forceps; (6) large instruments, 2.7 mm (see B); (7) puncture cannula, 1.7 mm; (8) irrigation (small) and sucking tube (large); (9) flexible-tip laser guide, 2.8 mm; (10) optical adapter for sterile change of scopes with draped camera; (11) mechanical friction holder. (B) Tip of sheath with operation scope and large forceps. (C) Tip of sheath with flexible endoscope controlled by rigid operation scope.
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Rigid Mini-Fiberscopes The larger diameter and the mechanical sensitivity of the powerful but expensive rod lens scopes resulted in fiberoptic devices with a rigid design. The protection by the outer rigid tube allows a dense packing of fibers in a small diameter (⬍ 1 mm) with an acceptable resolution and an outer diameter of ⱕ 4 mm for a ventriculoscope including the sheath. The optical qualities do not reach the lens optics; the resolution of about 200 ⫻ 200 pixels with 35,000 tiny fibers is not adequate for complex procedures such as resection of ventricle tumors and skull base procedures. However, for a “first view” with a small approach, for pen scopes in endoscopy assistance, and for less
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mor biopsies. It is useful in very large heads because of its usable length of 20 cm.
Figure 3. Hopkins rod lens endoscopes (Storz), area of vision, and different angles of vision: 0 degrees, direct view; 30 – 45 degrees, fore-oblique; 70 degrees, lateral; 120 degrees, retrograde; 0 – 120 degrees, variable adjustment.
complex procedures (e.g., ventriculostomies and cystostomies, ventricle drain positioning, and tumor biopsies in uncomplicated anatomy), these mini-fiberscopes offer an alternative with simple handling. The Clarus-Medtronic scopes (Clarus Medical Systems Inc., Minneapolis, Minnesota, USA [licensed to Medtronic PS Medical, Goleta, California, USA]) are single-use disposable scopes and avoid sterilization problems. The Channel Neuroendoscope with 30,000 fibers and two channels (irrigation inflow and instrument outflow) can be used with straight mechanical instruments for ventriculostomy or cystostomy and biopsies. Pen designs are the MurphyScope with a rounded end (e.g., for endoscopy assistance) and the NeuroPEN
(1.3 mm diameter) with stylet handle (e.g., for endoscopic positioning of ventricle catheters). With only 10,000 fibers, the pen designs have a low resolution. The Gaab Pediatric Neuroendoscope (Storz) is not disposable, but it is easy to clean similar to rigid lens scopes and can be autoclaved. This neuroendoscope has 35,000 fibers, separate irrigation inflow and outflow channels, and an instrument channel that allows the use of rigid and flexible instruments (Figure 5). Its overall outer diameter including the sheath is 4 mm and allows a passage of rigid and flexible instruments including coagulation devices and Fogarty balloons (2-F). We use it especially in infants for ETVs, cystostomies, and tu-
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Video-Endoscopes (“Distal Chip,” “Chipin-the-Tip”) In video-endoscopes, the video CCD is mounted in the tip of the endoscope directly behind the objective lens (Figures 1E and 4B). These scopes initially required ⬎ 10 mm diameter (3), but smaller chip scopes are now used in gastroenterology and otorhinolaryngology; actual diagnostic flexible endoscopes without channels and standard resolution (around video graphics array resolution 640 ⫻ 480 px) have a diameter ⬍ 4 mm (Figure 4B) and are offered with a 2-mm working channel with an outer diameter ⬍ 5 mm (e.g., Olympus ENF-VT [Olympus Corporation, Tokyo, Japan], diameter 4.9 mm). Such flexible chip scopes were found to be superior in optical quality compared with fiberoptics in laryngoscopy and are comparable to rigid lens scopes (27). Chip scopes may be offered with an HD video chip up to a resolution of 1080p, also with a flexible tip and rigid main part but with an outer diameter still ⱖ 10 mm (e.g., Olympus HD EndoEYE LTF-VH). Considering the rapid development in recent years, chip scopes are likely to be used in neuroendoscopy soon; flexible chip scopes with ⬍ 5 mm and working space could already be used for ventriculoscopy including ETV. The resolution is higher than with a fiberscope; the image with direct electronic transmission does not have a Moiré effect; and with lightemitting diode (LED) illumination, no camera or light cable is attached (Figure 4B). Before replacing conventional glass rod endoscopes or flexible fiberscopes, problems with sterilization must be solved. Chips must be miniaturized further for designs with larger instrument and irrigation spaces.
TYPES OF VENTRICULOSCOPE SYSTEMS For endoscope-assisted and endoscopecontrolled surgery (e.g., endoscopic transnasal approach) in a normal “air environment,” the surgeon selects among rigid lens scopes with different diameters, lengths, angle of view, and straight or angled ocular. The set is completed by adequate microsurgical instruments (preferably bayonet-type to prevent interference of the surgeon’s hand with scope and camera; biportal/binasal approaches may use straight
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ure 2A). The endoscopic part starts after removal of the trocar with insertion of the endoscope. Any flexible fiberscope with an adequate diameter fitting the sheath can be used; rigid scopes are offered with individual working tubes and sheaths, where the scope is locked in during surgery. One has to differentiate between “channel types” and “space types” of rigid scope systems.
Channel Scopes Channel scopes use round lens scopes in the optic canal, surrounded by channels for irrigation inflow and outflow (should be separate) and for instruments. Examples include the following:
y Camaert ventriculoscope (Richard Wolf Ltd., Knittlingen, Germany), with 6-mm outer diameter of the sheath, two irrigation channels, and a 2.2-mm (7 Charriere) working channel;
y Aesculap ventriculoscope (Aesculap, Division of B. Braun AG, Melsungen, Germany) (similar to Camaert) in a short (160 mm, for freehand use) and long (250 mm, for stereotactic frame) version, with 6.2-mm outer diameter, two irrigation channels, and a working channel with 2.2 mm for exchangeable 0-degree or 30-degree wide-angle lens scopes;
y DECQ ventriculoscope (Karl Storz GmbH & Co. KG, Tuttlingen, Germany), available with three different diameters of the oval operations sheaths (4.7 mm, 5.2 mm, and 7 mm); in the largest version, two (small) instruments can be used for bimanual dissection;
y OI HandyPro endoscope (Storz), with
Figure 4. (A) Flexible fiberscope for ventriculoscopy, diameter 2.8 mm, with instrument channel, tip bending up 170 degrees and down 120 degrees, and 90-degree area of vision. (B) Video-endoscope with monitor 800 ⫻ 480 pixels, “chip-in-the-tip,” bending up and down 140 degrees, 85-degree area of vision, and integrated light—meaning no camera or light cable is required.
4-mm outer diameter, with three channels (inflow and outflow), 1.3-mm instruments, and 0-degree and 12-degree optics (to center the instrument); this scope is especially designed for freehand ventriculoscopy and ventriculostomy;
y Perneczky’s Minop-Design with Aescuinstruments with the advantage to be simply turned around). Ventriculoscopy and Cystoscopy Ventriculoscopy and cystoscopy are usually based on a puncture approach using a tube
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(sheath) with a blunt trocar. The cavity is punctured without internal optical guidance based on the diagnostic images, often with neuronavigation. A small tracker optic inside the trocar can be used to check the penetration of the ventricle or cyst wall (Fig-
lap, also with three different but round diameters of the sheaths, the largest with 6 mm containing two irrigation channels and one 2.2-mm working channel. The 0-degree and 30-degree optics have a 90-degree angulated ocular for the use of straight instruments;
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Figure 5. Rigid minifiber ventriculoscope, 3.8 mm, autoclavable, in 4.5-mm sheath (pediatric size) with rigid instrument, 1.3 mm, in instrument channel (3); two additional channels for irrigation and outflow (2); and mini-fiberoptics 35.00 fibers, diameter 0.8 mm (1).
y Channel scopes by Clarus-Medtronic (Clarus Medical Systems Inc.) with mini-fiberoptics;
y Gaab (pediatric) Minifiber Ventriculoscope (Karl Storz GmbH & Co. KG) (Figure 5). Special sets of instruments are available for these channel endoscopes. Advantages of channel scopes are the protection of the scope and the guidance of the instruments in the separate channels. The disadvantage is the limited space available for material removal (tumors, cysts, clots) or for the insertion of catheters or stents.
Space Scopes “Space” scopes are based on the principles of Dandy and Kelly (15), who used tubes with the microscope to visualize and remove deep-seated parenchymal lesions with a small approach avoiding spatula retraction. The use of a rigid endoscope should leave as much space as possible for effective surgery in a small sheath in which the diameter is limited (e.g., by the size of the foramen of Monro). The Gaab-Storz ventriculoscope (Karl Storz GmbH & Co. KG) (Figure 2A–C) uses a 6.5-mm sheath (outer diameter). After initial puncture with a blunt trocar (or a hollow
trocar with a 2-mm “tracker” scope to control the puncture), 4-mm straight diagnostic scopes (easy to turn around) with different angles of view (0 degrees, 30 degrees, 45 degrees, 70 degrees, or 120 degrees) and 100 degrees area of vision are used at HD video quality for anatomic orientation and for irrigation. For surgical manipulation, a 1.7-mm Hopkins optics with two rod light guides in a “U” shape is used, with a 6-degree angle of view to have the instrument in the center of vision. The entire space in the sheath is available for instruments up to 3 mm diameter (Figure 2B) for removal of tissue, cysts, and clots or for the insertion of catheters. With an additional top tool with two guiding channels, two straight instruments with 1.3 mm can be used simultaneously. A similar design was the Frazee ventriculoscope (mainly designed for endoscopy in lateral ventricles with larger lesions; disadvantage: too large to pass the foramen of Monro [Karl Storz GmbH & Co. KG]; production ended) with a larger diameter of 8.8 mm.
first produced and named “cold light” by Storz in 1963 (16). Cold light sources produce less heat, but not zero; infrared (heat) is transmitted through the light cable. Heat transmission is reduced further by dichroic mirrors for light focusing and by filters; nevertheless, the end of the light cable may burn owing to the transmission of high light energy without becoming hot itself (7, 8); the free end of the light cables should be handled with care. Also, light from the endoscope tip might damage sensitive structures when coming too close with a fullpower light beam. Xenon lamps have replaced halogen bulbs in cold light sources. Halogen is limited to effective 150 –250 W and has a yellowish color temperature of 5000 –5600 K; xenon light with a color temperature of 5500 – 6400 K corresponds to sunlight and is available with up to 300 W, with longer lifetime of the lamp compared with halogen. Fiberglass cables usually are used for cold light transmission. Theoretically, gel cables filled with clear optical gel (liquid crystal) transmit more light, but they also transmit more heat and may crack.
ENDOSCOPE CAMERAS Small video cameras in sterile covers provide sterile video-optical surgery. Cameras directly attached to the scope ocular are available with three-chip and full HD quality. Some of these cameras can be autoclaved. However, cameras that can be autoclaved are more expensive, and heat sterilization reduces the lifetime. We prefer to use sterile covers. However, to allow a sterile change between different scopes, an autoclavable optical adapter (Figure 2A) is required to connect the endoscope ocular with the camera head. The camera side of the sterile optical adapter (a plastic device with glass plates) is covered with the camera cover, and the endoscope side remains free and sterile; this allows a quick change between different endoscopes without loss of optical quality.
LIGHT SOURCES “Cold light” avoids the direct heat of lamps in the scopes and provides more power by transmitting light via glass fibers from an outside light source. This technique was
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INSTRUMENTS AND ACCESSORIES In open spaces, microsurgical instruments with appropriate length can be used with the endoscope; often bayonet instruments
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are preferred to avoid interference with the scope. In coaxial surgery in ventricles and cysts with the instruments running along the endoscope in the endoscope sheath, special sets of instruments are available to fit to the different scopes (length, diameter; Figure 2A, 5). Straight rigid instruments are more powerful and easier to control with rigid scopes, and so some scopes have an angulated ocular. The transition from microsurgery to this coaxial type of endoscopic surgery is difficult and requires training because the instrument hand can control only the depth of the instrument position; the lateral position is mainly controlled by the other hand with the endoscope sheath, which guides the instruments. Standard instruments (Figure 2A) are forceps of different shape and size (spoon type for biopsy and tissue removal; crocodile type for grasping membranes and catheters), blunt-tip and sharp-tip scissors with unilateral or bilateral movement, and needles for puncture and aspiration. A special ventriculostomy forceps is used for membrane opening (ETV, cystostomy), which has tiny outside grooves to prevent the membrane from slipping along (Figure 2A). For minimally invasive enlargement of ventriculostomies and septostomies, Fogarty balloons (2-F to 3-F) are recommended. These should be inflated only with water or saline and not with compressible air to avoid a sudden “pop off.” The equator of the balloon is difficult to position exactly in the membrane perforation. Special double-balloon catheters are easier to use, with the membrane placed between the two balloons for widening the stoma. However, these catheters are expensive and have the risk of asymmetric inflation (e.g., of the lower balloon close to the basilar artery in ETV). Monopolar and bipolar instruments are used for hemostasis, which must be preventive in fluid-filled ventricles and cysts; bleeding in the cerebrospinal fluid (CSF) rapidly obscures the endoscopic vision. For precise irrigation during coagulation, a small separate irrigation tube (Figure 2A) positioned close to the bleeding helps clear the vision. For coagulation and piecemeal resection of tumors, laser fibers can be used with flexible-tip laser guides (Figure 2). Some surgeons also use laser for ETV and septostomy. However, the considerable depth penetration of neodymium:yttriumaluminum-garnet (Nd:YAG) and holmium:
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YAG lasers is a risk within the sensitive diencephalon and on top of the basilar artery. For irrigation in intracranial endoscopy, gravity-controlled infusions or roller pumps can be used; in addition, manual bolus injection may clear the vision more rapidly. However, irrigation should not increase the intracranial pressure, and a free outflow must be guaranteed. If increased intracranial pressure is suspected, the scope should be removed, providing the scope channel for additional outflow. For irrigation in adults, 0.9% sodium chloride can be used, which should be warmed close to but not above body temperature. In infants, larger amounts of sodium chloride and low-temperature irrigation should be avoided.
Ultrasonic Dissectors and Aspirators The small space available in minimally invasive endoscopic neurosurgery in the ventricles and in transnasal skull base approaches interferes with effective resection of larger tumors. Special long, tiny ultrasonic aspirators can be used (e.g., handpiece to the SONOCA Ultrasonic Aspirator [Soering, Hamburg, Germany]). Tiny ultrasonic aspirators do not have their own irrigation, but with central aspiration channels they allow the fragmentation and aspiration of tumors with limited vascularization; simultaneously, CSF can be removed in the nonoscillating sucking mode. In an air environment, hemostasis on the surface and in tumors is easier than with blood spreading through the CSF. However, sucking must be carefully adjusted to low levels with intermittent irrigation to avoid a ventricle collapse.
Navigation Systems For the “blind” puncture of ventricles and cysts through small burr holes, computerized neuronavigation, which replaces stereotactic frames, is used routinely in intracranial endoscopy and is mandatory with small ventricles and for orientation in unstructured cysts and multilocular hydrocephalus. Any infrared-based or mechanical navigation system can be used with rigid endoscopes or endoscopy sheath. Magnetic navigation is attempted for precise intracranial location also of the tip of flexible endoscopes.
Endoscope Holders Some neurosurgeons use freehand ventriculoscopy (special designs such as the OI HandyPro ventriculoscope). However, many endoscopic neurosurgeons prefer an endoscope holder for precise, stable positioning during manipulation, especially for more complex procedures. Holding devices must reliably fix the endoscope but should not delay position changes much. The cheapest solution is the use of two microsurgical Leyla arms attached to a plate that holds the endoscope— our first technique used. The Leyla arm can also be used for retractors in cases of transition to microsurgery. Simple, inexpensive friction holders (Figure 2A) are easier to use and more universal (also for microsurgical assistance and transnasal skull base approach). These allow (similar to Leyla arms) a different friction adjustment from “fully fixed” via “slowly movable” to “fully free.” The more expensive holders with pneumatic (UnitracR Pneumatic Holding Arm [Aesculap, Division of B. Braun AG]) or electromagnetic brakes (Point setter [Mitaka Kohki Co., Ltd., Tokyo, Japan], or Endo-Arm [Olympus Medical Systems Corp.,Tokyo, Japan]) allow an easy control with a single switch but not individually adjustable intermediate positions for slow “holder-supported” motions.
CLEANING, STERILIZATION, AND STORAGE The fiberscope channels are especially difficult to clean, to dry, and to sample microbiologically and cannot be inspected. The use of fiberscopes that usually do not withstand temperatures ⬎ 60°C and are sensitive to many chemicals (which may also lead to degradation of lens cement) should be avoided in infectious lesions. For sterilization and storage, special trays should be used providing fixed positions for each endoscope (not mixed among surgical instruments without protecting sheaths), with fiberscopes if possible in a straight position. Rigid lens scopes should be able to be autoclaved at 134°C. Although the scopes themselves are easy to clean and to inspect, the spaces in the endoscope sheaths must carefully be cleaned and inspected after use. A special problem of CNS endoscopy is the risk of transmission of CJD and its variants (variant CJD— bovine spongi-
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form encephalopathy), which might not be discovered owing to the long incubation time. The prion protein (PrPSc) is extremely resistant to most sterilization procedures; gas sterilization might even increase the infectivity. Because flexible endoscopes cannot be autoclaved at 134°C with 3 bar for 1 hour and cannot withstand aggressive chemical disinfection with sodium hydroxide, sodium hypochlorite, or guanidinium-isothiocyanate (GdnSCN), flexible scopes must be destroyed after CJD or CNS use in any case with suspicion of variant CJD (22, 29).
FUTURE PERSPECTIVES Neuroendoscopy can be improved by still smaller optics with high resolution giving more space. Scopes, cameras, and light cables can be made more compact by modifying the traditional, large ocular coupling and separate light cable connection. However, different scopes used during an operation with one draped camera and one light cable interfere with a “handy” design. The solution will probably come with the rapid development of chip scopes; with flexible tips or swiveling lens or chip, changing between rigid scopes with different angles of view would no longer be required. Chip endoscopes may also be the solution for threedimensional neuroendoscopy with LED illumination without heat problems. Initial designs have been presented but still with low resolution (e.g., with ⬙bee’s eye technology⬙ [21]). Endoscopy should also move away from “stand-alone” endoscopy towers and should be integrated in multifunction displays of the future operation room combining endoscopic, microscopic, and diagnostic images and patient monitoring and control data, similar to a cockpit with multifunction electronic flight instruments (EFIS).
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18. Nishizawa K: Chromatic aberration of the Selfoc lens as an imaging system. Appl Optics 19:10521055, 1980.
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14. Hopkins HH, Kapany NS: A flexible fibrescope using static scanning. Nature 173:39-41, 1956. 15. Kelly PJ: Tumor Stereotaxis. Philadelphia: Saunders; 1991. 16. Kieser CW: Introduction of cold light to endoscopy. Aktuel Urol 39:130-134, 2008. 17. Mixter WJ: Ventriculoscopy and puncture of the floor of the third ventricle. Boston Med Surg J 188: 277-278, 1923.
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Conflict of interest statement: Michael R. Gaab is a consultant of Karl Storz Company, Tuttlingen, Germany. Received 16 August 2011; accepted 03 February 2012 Citation: World Neurosurg. (2013) 79, 2S:S14.e11-S14.e21. http://dx.doi.org/10.1016/j.wneu.2012.02.032 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2013 Elsevier Inc. All rights reserved.
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