Endoscope

Instrument to visually examine the interior of a hollow space

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Drawing of an endoscope for fetal detection, or "fetoscope"

An endoscope is an inspection instrument composed of image sensor, optical lens, light source and mechanical device, which is used to look deep into the body by way of openings such as the mouth or anus. A typical endoscope applies several modern technologies including optics, ergonomics, precision mechanics, electronics, and software engineering. With an endoscope, it is possible to observe lesions that cannot be detected by X-ray, making it useful in medical diagnosis. An endoscope uses tubes only a few millimeters thick to transfer illumination in one direction and high-resolution video in the other, allowing minimally invasive surgeries.[1] It is used to examine the internal organs like the throat or esophagus. Specialized instruments are named after their target organ. Examples include the cystoscope (bladder), nephroscope (kidney), bronchoscope (bronchus), arthroscope (joints) and colonoscope (colon), and laparoscope (abdomen or pelvis).[2] They can be used to examine visually and diagnose, or assist in surgery such as an arthroscopy.

Etymology

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"Endo-" is a scientific Latin prefix derived from ancient Greek &#;νδο- (endo-) meaning "within", and "-scope" comes from the modern Latin "-scopium", from the Greek σκοπε&#;ν (skopein) meaning to "look at" or "to examine".[3]

History

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Drawings of Bozzini's "Lichtleiter", an early endoscope

The first endoscope was developed in by German physician Philipp Bozzini with his introduction of a "Lichtleiter" (light conductor) "for the examinations of the canals and cavities of the human body".[4] However, the College of Physicians in Vienna disapproved of such curiosity.[5] The first effective open-tube endoscope was developed by French physician Antonin Jean Desormeaux.[6] He was also the first one to use an endoscope in a successful operation.[7]

After the invention of Thomas Edison, the use of electric light was a major step in the improvement of endoscope. The first such lights were external although sufficiently capable of illumination to allow cystoscopy, hysteroscopy and sigmoidoscopy as well as examination of the nasal (and later thoracic) cavities as was being performed routinely in human patients by Sir Francis Cruise (using his own commercially available endoscope) by in the Mater Misericordiae Hospital in Dublin, Ireland.[8] Later, smaller bulbs became available making internal light possible, for instance in a hysteroscope by Charles David in .[9]

Hans Christian Jacobaeus has been given credit for the first large published series of endoscopic explorations of the abdomen and the thorax with laparoscope () and thoracoscope ()[10] although the first reported thoracoscopic examination in a human was also by Cruise.[11]

Laparoscope was used in the diagnosis of liver and gallbladder disease by Heinz Kalk in the s.[12] Hope reported in on the use of laparoscopy to diagnose ectopic pregnancy.[13] In , Raoul Palmer placed his patients in the Trendelenburg position after gaseous distention of the abdomen and thus was able to reliably perform gynecologic laparoscope.[14]

Georg Wolf, a Berlin manufacturer of rigid endoscopes established in , produced the Sussmann flexible gastroscope in .[15][16] Karl Storz began producing instruments for ENT specialists in through his company, Karl Storz GmbH.[17]

Fiber optics

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A Storz endoscopy unit used for laryngoscopy exams of the vocal folds and the glottis

Basil Hirschowitz, Larry Curtiss, and Wilbur Peters invented the first fiber optic endoscope in .[18] Earlier in the s Harold Hopkins had designed a "fibroscope" consisting of a bundle of flexible glass fibres able to coherently transmit an image. This proved useful both medically and industrially, and subsequent research led to further improvements in image quality.

The previous practice of a small filament lamp on the tip of the endoscope had left the choice of either viewing in a dim red light or increasing the light output &#; which carried the risk of burning the inside of the patient. Alongside the advances to the optics, the ability to 'steer' the tip was developed, as well as innovations in remotely operated surgical instruments contained within the body of the endoscope itself. This was the beginning of "key-hole surgery" as we know it today.[19]

Rod-lens endoscopes

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There were physical limits to the image quality of a fibroscope. A bundle of 50,000 fibers would only give a 50,000-pixel image, and continued flexing from use breaks fibers and progressively loses pixels. Eventually, so many are lost that the whole bundle must be replaced at a considerable expense) . Harold Hopkins realised that any further optical improvement would require a different approach. Previous rigid endoscopes suffered from low light transmittance and poor image quality. The surgical requirement of passing surgical tools as well as the illumination system within the endoscope's tube which itself is limited in dimensions by the human body left very little room for the imaging optics.[citation needed] The tiny lenses of a conventional system required supporting rings that would obscure the bulk of the lens' area. They were also hard to manufacture and assemble and optically nearly useless.[citation needed]

The elegant solution that Hopkins invented was to fill the air-spaces between the 'little lenses' with rods of glass. These rods fitted exactly the endoscope's tube making them self-aligning and requiring of no other support.[citation needed] They were much easier to handle and utilised the maximum possible diameter available.

With the appropriate curvature and coatings to the rod ends and optimal choices of glass-types, all calculated and specified by Hopkins, the image quality was transformed even with tubes of only 1mm in diameter. With a high quality 'telescope' of such small diameter the tools and illumination system could be comfortably housed within an outer tube. Once again, it was Karl Storz who produced the first of these new endoscopes as part of a long and productive partnership between the two men.[20]

Whilst there are regions of the body that will always require flexible endoscopes (principally the gastrointestinal tract), the rigid rod-lens endoscopes have such exceptional performance that they are still the preferred instrument and have enabled modern key-hole surgery.[citation needed] (Harold Hopkins was recognized and honoured for his advancement of medical-optic by the medical community worldwide. It formed a major part of the citation when he was awarded the Rumford Medal by the Royal Society in .)

Composition

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The insertion tip of an endoscope

A typical endoscope is composed of following parts:

• A rigid or flexible tube as a body.
• A light transmission system that illuminates the object to be inpsected. For the light source, it is usually located outside the scope body.
• A lens system that transmits the image from the objective lens to the observer, usually a relay lens system in the case of a rigid endoscope or a bundle of optical fibers in the case of a fiberoptic endoscope.
• An eyepiece which transmits the image to the screen in order to capture it. However, modern videoscopes require no eyepiece.
• An additional channel for medical instruments or manipulators (only for a multi-function endoscope, see below in "Classification").

Besides, patients undergoing endoscopy procedure may be offered sedation in to avoid discomfort.

Laparoscopic surgery

Clinical application

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An endoscopy room in a hospital

Endoscopes may be used to investigate symptoms in the digestive system including nausea, vomiting, abdominal pain, difficulty swallowing, and gastrointestinal bleeding.[21] It is also used in diagnosis, most commonly by performing a biopsy to check for conditions such as anemia, bleeding, inflammation, and cancers of the digestive system. The procedure may also be used for treatment such as cauterization of a bleeding vessel, widening a narrow esophagus, clipping off a polyp or removing a foreign object.

Health care workers can use endoscopes to review the following body parts:

Classification

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A rigid endoscope A flexible endoscope

There are many different types of endoscopes for medical examination, so are their classification methods. Generally speaking, the following three classifications are more common:

• According to functions of the endoscope:
  • single-function endoscope: A single-function endoscope refers to an observation mirror that only has an optical system with it.
  • multi-function endoscope: For a multi-functional endoscope, in addition to the function of observation, it also has at least one working channel like lighting, surgery, flushing and other functions.
• According to detection areas reached by the endoscope:
  • enteroscope
  • otoscope
  • colonoscope
  • rhinoscope
  • arthroscope
  • laparoscope
  • etc.
• According to rigidity of the endoscope:
  • rigid endoscope: A rigid endoscope is a prismatic optical system with advantages of clear imaging, multiple working channels and multiple viewpoints.
  • flexible endoscope: A flexible endoscope is an optical-fiber-based system. Notable features of a flexible endoscope include that the lens can be manipulated by the operator to change direction, but the imaging quality is not as good as a rigid one.

Recent developments

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Robot assisted surgery

A capsule endoscope

With the development and application of robotic systems, especially surgical robotics, remote surgery has been introduced, in which the surgeon could be at a site far away from the patient. The first remote surgery was called the Lindbergh Operation.[22] And a wireless oesophageal pH measuring devices can now be placed endoscopically, to record ph trends in an area remotely.[23]

Endoscopy VR simulators

Virtual reality simulators are being developed for training doctors on various endoscopy skills.[24]

Disposable endoscopy

Disposable endoscopy is an emerging category of endoscopic instruments. Recent developments[25] have allowed the manufacture of endoscopes inexpensive enough to be used on a single patient only. It is meeting a growing demand to lessen the risk of cross contamination and hospital acquired diseases. A European consortium of the SME is working on the DUET (disposable use of endoscopy tool) project to build a disposable endoscope.[26]

Capsule endoscopy Capsule endoscopes are pill-sized imaging devices that are swallowed by a patient and then record images of the gastrointestinal tract as they pass through naturally. Images are typically retrieved via wireless data transfer to an external receiver.[27]

Augmented reality

The endoscopic images can be combined with other image sources to provide the surgeon with additional information. For instance, the position of an anatomical structure or tumor might be shown in the endoscopic video.[28]

Image enhancement

Emerging endoscope technologies measure additional properties of light such as optical polarization,[29] optical phase,[30] and additional wavelengths of light to improve contrast.[31]

A low-cost waterproof USB endoscope for non-medical use

Non-medical use

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Industrial endoscopic nondestructive testing technology

The above is mainly about the application of endoscopes in medical inspection. In fact, endoscopes are also widely used in industrial field, especially in non-destructive testing and hole exploration. If internal visual inspection of pipes, boilers, cylinders, motors, reactors, heat exchangers, turbines, and other products with narrow, inaccessible cavities and/or channels is to be performed, then the endoscope is an important, if not an indispensable instrument.[32] In such applications they are commonly known as borescopes.

See also

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References

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Takanori Fukushima from Japan used a fiberscope in for intraventricular as well as subarachnoid space endoscopic surgery with malleable instruments but the poor picture quality in the fiberscope made it unpopular [ 9 ] . The introduction of side viewing wide angled lens by Michael Apuzzo ushered in the era of modern neuroendoscopy, an era which would be subsequently based upon a foundation of clarity, illumination, maneuverability, and allowed widespread application. A channel endoscope dedicated to intraventricular neuroendoscopy was initially developed by Michael Gaab from Germany (for Karl Storz) [Figure 2] . Subsequently, additional channels were modified onto a rigid endoscope by Philippe Decq from Paris in [Figure 3] , and it was clinically applied for ventriculocystocisternostomy in suprasellar arachnoid cysts and for purely endoscopic colloid cyst excision [ 10 , 11 ] . This enabled simultaneous usage of unipolar or bipolar probe biopsy forcepsalong with suction and irrigation and helped expand the armory of neuroendoscopy by allowing bimanual dissection.

The major improvement in optical imaging was bought about by renowned British Physicist, Professor Harold Hopkins. He was the foremost authority in his field and is credited for introducing concepts of zoom lens, rod-lens endoscopes, and rigid/flexible endoscopes. The rights to his work on the lens system for endoscope were purchased by Karl Storz SE & Co. KG from Germany in the s, and, until now, surgeons from the world over are taking benefit of this partnership [ 8 ] .

The scope system then underwent several technical modifications before being implemented widely in the field of surgery. Victor Lespinasse, Walter Dandy, and William Mixter were the pioneers for introducing endoscopy in neurosurgery. The earliest instruments used for this purpose were cystoscopes and urethroscopes. Use in neurosurgery was therefore limited due to the rigid nature of the instrument, suboptimal optics, and large size of the scopes. Although the term ventriculoscopy was first used by Walter Dandy in while describing his unsatisfactory experience with a cystoscope, the first ventriculoscope was described a few years later by Tracy Putnam and thereafter perfected by John Scarrf [ 7 ] .

The basic principle of endoscopy lies in the illumination and internal reflection of light in a body cavity. This principle has been worked upon by many scientists even before the era of modern medicine. Greek scientist Hippocrates&#; work published in the book &#;The Art of Medicine&#; and Arab-Spanish surgeon Abu-al-Qasim&#;s techniques from the book &#;Al-Tasrif&#; (The Method) are testament to the fact that endoscopy had its origins many years earlier than previously thought [ 4 ] . For his description and application of the first prototype of an endoscope, German physician Philip Bozzini is widely, albeit contentiously, regarded as the &#;Father of Endoscopy&#; [ 5 ] . The first therapeutic application of endoscopy was in the field of urology in by Joseph Grunfeld from Austria. This was closely followed by the development of the first direct-vision rigid endoscopes (cystoscope) in by Maximilian Nitze [ 6 ] [Figure 1] . The inbuilt light source system effectively corrected the persistent issues with illumination in the application of endoscopy.

Endoscopes and endoscopic procedures

In the s, Claris Corporation was the first to come out with endoscope guided ventricular catheter placement for treating hydrocephalus[12]. These scopes were lightweight, thin with outer diameter of 1.14 mm, and able to be introduced into shunt catheters. Medtronic Company from USA then came out with a similar functioning NeuroPEN endoscope. Correspondingly, slit tip catheters were introduced by Medtronic and Codman (USA) for ventriculoscopic placement. However, they did not attain wide acceptance as the literature consists of experiences mentioning only small case series[13]. This was probably due to the absence of any discernible benefit over routine shunt catheter placements[14], relatively higher costs, and suboptimal vision. However, neurosurgeons have not been deterred from probing avenues for further improvements in endoscopic treatment of hydrocephalus[15]. The multipurpose ventriculoscope described by Henry Schroeder in helps in tackling not only obstructive CSF pathways but the extra channel allows also intraventricular lesion biopsy and resection, among other uses ably aided by the then newly developed high definition (HD) visualization and display system[16,17].

Bauer, Hellwig, and their team from Marburg, Germany published their eight years of experience of stereotactic endoscopy[18] wherein they used it for cystic cerebral pathologies, intracerebral hematoma evacuation, brain abscess, third ventriculostomy, and retrieval of ventricular catheters. Axel Perneczky[19] from Mainz, Germany is credited with bringing &#;minimally invasive neurosurgery&#; to the mainstream in by greater use of narrower (MINOP, Aesculap) endoscopes in ventricles and using them for indications beyond hydrocephalus. He brought stereotaxy and navigation guidance in endoscopy to the forefront[20] and developed the concept of &#;endoscope guided surgery&#; for cases such as colloid cysts. Endoscope assisted microneurosurgery was the next stage in the mid-s and innovations to attain the best dual imaging were highly sought after. Axel Perneczky proposed projection of the endoscopic images into a head mounted LCD device which was not routinely available in that period[1]. His most important contribution was the concept of &#;keyhole surgical approaches&#; with the integration of these visualization methods to the skullbase and development of specially designed shaft instruments for dissection [Figure 4], clip applicators, and a table mounted endoscope holding device to aid bimanual endoscopic surgery.

Figure 4. MINOP shaft instrument with multiple attachments

Endoscopic third ventriculostomy (ETV) is one of the most widely performed procedures in neuroendoscopy today and its results have been validated worldwide for hydrocephalus[21]. Several techniques and instruments have been described for safe perforation of the ventricular floor and then dilating it, such as with the leucotome, puncturing needle, blunt endoscope, Fogarty balloon, monopolar electrode, wired stone extractor, etc.[22]. Andre Grotenhuis from the Netherlands designed an endoscopic perforator which sucks and lifts the floor before forceps can be introduced to widen the opening[23]. This reduces the chances of basilar artery damage during ETV. Success score systems predicting ETV&#;s outcome in adult and pediatric patients[24] and other criteria for defining its prognosis have been well explained in the literature[25]. ETV has also been attempted via a flexible scope through the lamina terminalis in cases of technical difficulty to perforate the floor via traditional route[26]. Endoscopic biopsy has also been favorably evaluated[27], and occasional resections of tumors are being reported by many centers[28,29].

The first series of cases published of endonasal transsphenoidal approach was by Jankowski et al.[30] from France who presented his experience in three cases of pituitary adenomas in . Subsequently, Jho and Carrau[31] from the University of Pittsburgh, USA successfully used nasal endoscopes for transsphenoidal pituitary surgery and published the first large series of 50 patients in . Immediately following that, the concept of functional endoscopic pituitary surgery was mooted by Cappabianca et al.[32] in from Naples, Italy, which gave a big push forward to endonasal surgery. Thereafter, the preference shifted to the more versatile binostril approach, especially after very good results of 800 cases were put forward by Kassam et al.[33] from USA. Gradually, extended approaches to pathologies of the skullbase came to the fore with the improvement in skullbase defect repair techniques[34,35].

A dedicated pediatric endoscope was developed by Oi et al.[36] from Japan for Karl Storz (Oi Handy Pro endoscope). This system had a smaller working diameter and a 2-mm lens with malleable instruments and a pistol grip for easier holding [Figure 5]. It provides a narrower tract which is extremely important in infants and small children, not only to minimize brain damage but also to reduce the occurrence of postoperative CSF leaks. It is also recommended in cases where the foramen of Monroe is not large enough for safe passage of the larger adult scope.

Figure 5. Oi scope with malleable instruments and pistol grip handle

Pediatric Lotta system from Karl Storz was conceptualized by Henry Schroeder who developed this HD visualization scope with narrow shaft and another one with a wider shaft for adults with an extra channel that can take in two instruments through two channels of the scope apart from the suction-irrigation port [Figure 6A]. This system also has an optical obturator for scope insertion under visualization [Figure 6B][37]. Parallel developments in rigid endoscope were also undertaken by other companies such as Wolf from USA, Rudolf from Germany, and Olympus and Machida from Japan. The use of HD visualization has greatly improved accuracy of endoscopic neurosurgery and the recent introduction of 4K display system is a big stride forward in better visualization. Experience with 3D-HD endoscopy has slowly started gaining momentum in the field of neurosurgery. As compared to the traditional 2D display, 3D system provides a better depth perception especially for those neurosurgeons starting out in this field[38]. This has still not come in wider use because of limited availability and much higher costas well as due to the familiarity of most experienced neurosurgeons with dynamic endoscopy and 2D HD systems. Although this review focuses mainly on cranial endoscopy, a brief overview of spinal endoscopic system is given. One of the earliest innovators in spine endoscopic surgery was Destandau[39] from France. By using the ENDOSPINE System (Karl Storz, Germany), he first described his technique for endoscopic discectomy in , which is currently a widely practiced method. A versatile SMART endoscopic spine system was put forth by Chiu[40] in with a wide variety of applications, viz. degenerative spine disease, spinal fixation, discectomy, etc. In , Oertel et al.[41] described the &#;EASY GO&#; system for spinal endoscopy consisting of dilators of varied sizes, sheaths, 30-degree endoscope, and endoscope holder. This system does not have a long learning curve and has been shown to have excellent postoperative response as per feedback of over 80% of patients.

Figure 6. A: Lotta scope with ceramic bipolar; B: optical obturator for guided insertion

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