Introduction

Endoscopy derives its origin from the Greek words endon (inside) and scopein (to watch carefully) and has a long history in surgery and in neurosurgery—full of intrigue, intense rivalries, and courage, culminating in remarkable advancements in patient care. In this review, we trace the origins of the field to ancient times and show how it has taken bold challenges to the status quo, close collaborations between clinicians and scientists and some good luck to propel neureondoscopy to where it stands now—an invaluable tool in the armamentarium of neurosurgeons to help solve a wide array of clinical problems.

Ancient origins

There has been a long interest in examining the human body and a rich history of using minimally invasive techniques to allow for less traumatic incisions, less handling of tissue, better wound healing, and better aesthetic results. Perhaps the earliest example of minimally invasive surgery is the Egyptians’ method of transnasal excerebration through the nasal cavity using hook-shaped rods as early as 2000 BC [1, 2] (Fig. 1). This was done so that the soul would recognize the body and unite with it in the afterlife. Abdominal organs were extracted using similar minimally invasive procedures. As ancient Egyptian religious beliefs gave way to the rise of Christianity, the art of these minimally invasive procedures was eventually lost. This art is currently being revived in an explosive manner. In a careful analysis of CT scans of mummies of different eras, it seems that the Egyptians at first used a transethmoidal approach to the calvarial contents but later modified it to the more familiar transsphenoidal approach [1].

Fig. 1
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a An Egyptian mummy in the City of Liverpool Museums. No external damage to the nose or face is visible. This immaculate mummification process was done so that the soul would recognize the body in the afterlife, as was the belief at that time. b X-ray of the same head in (a) showing the piercing through the cribiform plate of the ethmoid bone (between two white arrows) [2] Permission from Egyptian Exploration Society

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The Talmud, which dates back to 1300 BC has a description of an instrument thought to be a precursor to today’s speculum which is used for examination of the uterus and there are reports of this instrument being used by Jewish women to see if they were “pure” or able to participate in sexual intercourse.

Hippocrates (460BC–370BC) clearly understood the importance of surgery when he stated, “what medicines do not heal, the lance will” (Hippocrates Aphorisms). Hippocrates and his disciples used a speculum to investigate the rectum and remove condylamata. In fact, a recent archaeological excavation of Dion, a city in northern Greece unveiled bronze instruments dating from approximately 200 BC that look astonishingly similar to modern speculums (Fig. 2). Hippocrates’ famous saying “First, do no harm”, may have pointed towards minimalistic surgery, as during that time, large operations were often fraught with complications such as infections, sepsis, and death.

Fig. 2
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Ancient Greek specula found in the ruins of Pompei, thought to be date around 70 AD. These instruments are similar to the instruments used today

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Endoscope-like instruments were not always used the way they are used today. This is best understood by taking into account the prevalent early Greco-Roman thought—namely that human disease was a direct consequence of imbalance of the human humors. Thus, there are reports of inserting a trochar-like instrument into the abdomen to drain out the bad humors. Aulus Celsus (25 BC–50 AD), a Roman physician wrote about such incisions: “Some perform it below the navel…some perforate the navel itself; some cauterize the integument and make their opening into the abdomen by incision…” [3].

Around this time, a Chinese philosopher by the name of Mozi (Mo-Ti; 470 BC–390BC) and the founder of Mohism, described the camera obscura, an important concept in endoscopy, where with a pinhole in a room or a box, the light from the external scene strikes a surface inside where it is reproduced, albeit upside-down [3]. He called this concept “the locked treasure room”.

Although there is a paucity of information about the development of minimally invasive instruments during the Middle Ages, it is clear that the Greeks did influence Arab physicians at the time. Abulkasim (962–1013 AD) developed a speculum that sought to improve upon Hippocrates’ design by using reflected light [4]. Tulio Caesare Aranzi in 1585 improved upon this design, by using sunlight, reflected through a glass of water, to examine the nasal cavity [3, 5].

The development of the modern endoscope

During the ensuing 500 years the two major obstacles to furthering endoscopic development were the prevalent prohibitions on examining human anatomy and the inability to harness enough energy or light to make such examinations worthwhile. With the advent of the Renaissance, the first obstacle was struck down. With the Scientific Revolution, the last remaining hurdles—namely that of harnessing enough energy to see deep into the human body and the use of advanced optics to reflect this back, would be similarly smitten.

Philipp Bozzini (1773–1809), an Italian born to a well-to-do family in Germany is considered the ‘Godfather’ of modern endoscopy. He developed the “Lichtleiter” or light-carrier, an instrument which consisted of a wax candle in a cradle, a set of reflective mirrors on one end and various examining tubes that could be fitted to the other end. Bozzini, who was also an aspiring artist, designed his Lichtleiter as a beautiful vase decorated with symbols of the sun, moon, and stars (Fig. 3) [3, 6].

Fig. 3
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a Philipp Bozzini (1773–1809), considered by many the ‘Godfather’ of the modern endoscope. b Bozzini’s original design of his ‘Lich tleiter’, or light carrier, an instrument which consisted of a wax candle in a cradle, a set of reflective mirrors on one end and various examining tubes that could be fitted to the other end (Bush et al. [6]), used with permission. c Prototype of Lichtleiter

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Bozzini’s invention was first tested in cadavers and was to be approved for use in live patients. However, in a second round of testing, where the church played a role, the new instrument was not approved. Due to the prevalence of internecine rivalry in nineteenth century Vienna, Bozzini’s invention was ridiculed by the Alert Faculty of the University of Vienna. He was criticized for his inappropriate curiosity and his “magic lantern” was rejected [7]. Bozzini was forced to work as a general practitioner, caring for many people from rural areas. At the young age of 36, he succumbed to typhoid—leaving his wife and three children with little in terms of monetary assets. This was an unfortunate end to the first chapter in endoscopy. However, Bozzinis’ three part design principal—that of a light source, reflective mirrors, and an investigative piece would form the basis for endoscopes even to this day.

Bozzini’s instrument was to be reintroduced close to a half-century later by the French urologist Antoine Jean Desormeaux (1815–1894). Desormeaux, an accomplished French urologist saw the benefits of the Lichtleiter, but instead of using a wax candle as his source of lighting, he used an alcohol and kerosene burning candle with a “chimney” [3]. The lamp was placed between the reflector and the lenses and the light generated was focused down the shaft of the scope with a lens. The surgeon was able to see the illuminated field through an opening in the center of the mirror. Desormeaux used this device to examine the genitourinary (GU) tract and is credited as the first person to coin the term “l’endoscopie” and he presented his work to the Academie des Sciences in Paris on July 20th, 1853 to wide acclaim. A pertinent reason for Desormeaux’s success was that he was able, for the first time, to use such an instrument to remove pathologies of the GU tract, making it the first endoscope to be used for surgical procedures or therapeutic endoscopy.

Desormeaux was a prolific author and with his position as chief surgeon at the Necker Hospital in Paris, his instrument quickly became available to many urologists and gynecologists. He briefly considered using electricity for the light source, but stated “it is too cumbersome to be carried around and it requires an assistant to regulate the batteries” [3]. Also, from a business perspective, he noted that using electricity would “double the price of the instrument” [7]. Nevertheless, because of his ability to show clinical relevance and importance, Desormeaux played a critical role in the evolution of endoscopy.

Sword swallowers and upper gastroenterological endoscopes

Interestingly, if one goes back to and examine Bozzini’s original Lichtleiter, one sees that he envisioned varied uses—for the GU system, for the upper gastroenteral (GI) system, and for the anorectal system. His immediate torch bearers, particularly Desormeaux, were most interested and found the best uses of the endoscope in the GU system. However, the next push in endoscopic technology came from those most interested in examining and treating ailments of the upper GI system. The reason that this push came later is best understood by considering the anatomical barriers to such investigations. The esophagus is a long, dark tube that is not straight. It cannot be dilated and any false turns can quickly turn into disaster. Also, most people cannot voluntarily relax the cricopharyngeal muscle—making it very difficult to go past it.

Adolph Kussmaul (1822–1902) was a German physician and known for Kussaul breathing (in diabetic ketoacidosis), Kussmaul sign (paradoxical raise in jugular veinous press on inhalation in chronic obstructive pulmonary disease, or constrictive pericarditis), Kussmaul disease (polyarteritis nodosa), and Kussmaul’s dyslexia (word blindness). He sought to overcome the anatomical problems of the upper GI tract by enlisting the help of a unique element of society—sword swallowers. These extraordinary people are able to make the path from the larynx to the esophagus to the stomach a straight path and are able to voluntarily relax their cricopharyngeal muscle—making the long, arduous trek more fathomable and safe (Fig. 4). Though Kussmaul’s accomplishments were notable, especially since he was the first to perform a gastroscopy in 1868, by which he was able to directly visualize the stomach, there are other notable names worth mentioning in the development of GI endoscopy.

Fig. 4
figure 4

Sword swallowers were used by Kussmaul in his introduction of the esophagoscope, partly due to their ability to make the path from the larynx to the esophagus to the stomach a straight path and are able to voluntarily relax their cricopharyngeal muscle. Image used with permission, Copyright 2006 Dan Meyer, Sword Swallowers Association International

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The Spanish orator Manuel Garcia, who despite having no formal medical education, was well known for his oratory skills and is famous for demonstrating to the Royal Society of Medicine in London a direct visualization of his own larynx in 1854. For this, he used a device that was not much more advanced than a dental mirror and another mirror to reflect sunlight [7].

The conflict between Turck and Czermack

As is the case when a new technology is introduced, there is often a group of people who claim primacy. This is seen in the contestation between Ludwig Turck and Johann Czermack. Turck, an Austrian physician, heard about Garcia’s success and after visiting him, made a few adjustments, including enlarging the reflecting mirror thus allowing for more light. History remains unclear about Turck’s total contribution to the field, but a young Czech, Johann Czermak, came blazing onto the scene right at that same time in 1857 with a modified laryngoscope that did not rely on sunlight, as did Turck’s. When he presented his work at the Vienna Medical Society in 1858 and claimed to be the first to visualize the larynx, Turck loudly objected and there was almost a scuffle [3]. Czermack ultimately relented on his claim, but it is clear that no love was lost between these two men.

Although Czermak’s claim to be first to visualize the larynx may have been hyperbole, he does deserve credit for numerous reasons. He used an innovative artificial light source and a tubular design. His most significant contribution to the field of endoscopy however, is that he was the first person to take an endoscopic photograph, something called stereoscopy at that time [3]. This is quite remarkable considering that he only used magnified candlelight as his light source, and many physicians at that time were unable to even visualize the larynx, let alone take pictures of it. Thus, for the first time, descriptions of anatomy and disease processes could be studied by physicians who did not have to be immediately present. Czermak is credited with the emergence of video endoscopy—a large and extremely valuable adjunct to endoscopy.

Collaborations between physicians and engineers

Prior to Thomas Edison’s invention of the light bulb, one of the solutions to the problem of insufficient light was the use of galvanized platinum wires, which could produce glowing hot light. These galvanized platinum wires formed the basis of electrocautery, as developed by the Viennese dentist Moritz Heider in 1845 and the German urologist Theodor Middeldorpf in 1854. However, these galvanized platinum wires were too hot to put into the human body.

One of the key contributors to the solution of this problem was the suggestion by the German dental surgeon Julius Bruck (1840–1902) to encase these galvanized platinum wires within a glass cooling system, which can be thought of as a precursor to the light bulb as we know it. Another important contribution credited to Bruck was his suggestion to bring the light source inside the body, which is distinctly different from earlier iterations of the endoscope, which had placed the light source outside the body [3]. There is some controversy about whether Bruck was able to use his clever design in a clinically practical application, but nonetheless, his contributions are noteworthy.

The end of the nineteenth century was an important time in the evolution of endoscopy, due mostly to the explosion of scientific and technological advancements. Of greatest note was the invention of the light bulb in 1879 by the “Wizard of Menlo Park”, Thomas Edison.

At around this time, there was an important collaboration between a German physician, Maximilian Nitze and an Austrian engineer, Josef Leiter. Nitze was born in 1848 in Berlin and obtained his medical license in 1874. He is described as sometimes “shy” or “irascible”, with a hot temper [3], but nonetheless he was unmistakably brilliant [8]. Nitze realized that there were two main problems that had to be overcome for endoscopic investigations to become practical. The first was that the field of view was too small. While cleaning the dusty eyepiece of his microscope he found that he could see through it clear across to a neighboring church. He thus realized that by including a telescoping system within the existing optical system, a much larger field of view could be obtained. The second problem had to do with the limited illumination that could be obtained by using the prevalent design, with a light source outside the body. As Nitze stated, “to light up a room one must carry the lamp inside” [7].

To solve these problems, Nitze began collaborating with the Austrian inventor and they were able to produce a cystoscope with a telescoping optical system that had a much larger field of view (Fig. 5). However, they still had the problem of insufficient illumination and although they used the available cooled platinum wires, their instrument was very cumbersome and expensive. As is sometimes the case when two large personalities come together, Nitze and Leiter had a falling out and Nitze subsequently returned to Berlin. Leiter tried to claim the cystoscope as his own, asserting “the microscope and rifle are named for their designers not after the inventors of the idea” [7].

Fig. 5
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Prototype of Nitze’s cystoscope, introduced in 1877 [8], used with permission

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Shortly thereafter, Leiter went on to collaborate with the Polish physician, Johan von Mikulicz-Radecki (1850–1905). Together, they designed a clinically practical endoscope capable of gastroscopy that consisted of a distally placed galvanized wire and an ingenious cooling system. There is still some debate about whether the Mikulicz-Leiter gastroscope was much different than that made by Nitze and Leiter. In an ironic twist of fate, Mikulicz died at the young age of 55 of stomach cancer—precisely the type of disease that his gastroscope was designed to detect and treat.

It took Nitze 8 years from the invention of the light bulb by Edison to try it on his cystoscope. Once Nitze was able to attach such a bulb to the distal end of his cystoscope, the instrument became much more manageable and Nitze gained widespread acclaim. Nitze is also given credit, or shares credit, for designing electrocautery forceps and ureteral balloon catheters. However, it is clear that he was not the most easy man to get along with, as evidenced by his split with Leiter and later his heated exchange with the American urologist Hugh Hampton Young (1870–1945). Young, who had just recently joined the faculty at Johns Hopkins went to visit Nitze in 1903 in order to get his opinion regarding a better endoscope design. Although he was warned by one of Nitze’s assistants not to show him his design, he did and Nitze exploded, “this is an old idea and a very bad construction”. Young responded in broken German with a recommendation about where Nitze could place his endoscope! As later recounted by Young, these two luminaries came very close to a “knock down, drag-out fight” [3].

Kelling and Jacobaeus

At the turn of the twentieth century, there were large advances in asceptic techniques, anesthesia, and electrocautery. Large open surgeries became much safer. This caused the field of endoscopy to take a back seat to the explosive improvements in open techniques. However, with the widespread spread of tuberculosis, many patients were doomed to have open explorative laparotomies. Georg Kelling (1866–1945), a German gastroenterologist is credited as the first to perform a successful laparoscopy [9]. Kelling got most of his early training under the tutelage of Mikulicz, of “Mikulicz-Leiter” fame. At first, Kelling’s main problem was the inability to see “around corners”, especially as it pertained to the greater curvature of the stomach. To solve this problem, he designed a flexible esophagoscope/gastroscope in 1897, which consisted of several segmented tubes that could be angulated or straightened by the operator. Kelling was also a forefather of insufflation, which is critical in modern day laparoscopy, recognizing that by using air, one could accomplish much—including helping with hemostasis and causing an artificial pneumothorax—a treatment of choice at that time for tuberculosis. One detractor from Kelling’s fame is that he was slow to publish his clinical results [3].

Hans Christian Jacobaeus was a Swedish internist who was unaware of Kelling’s work and published his experience with a laparoscopic device in 1910. He claimed to be the first one to perform a laparoscopy, but this was heatedly contested by Kelling, who stated that he had performed several laparocopies previously, but had not published his results [3]. Kelling, in fact, did not publish a comprehensive review of his laparoscopic experience until 1923, where he states that the laparoscope found increased use in the years after World War I, as Germany’s economic downfall made laparotomies prohibitively expensive [9].

The birth of neuroendoscopy

By 1910, endoscopy had made advances in the fields of urology, gastroenterology, pulmonology, and obstetrics and gynecology. The endoscopes at that time consisted of both flexible and rigid tubes, with various optical instruments and mostly distal light sources. The first reported case of neuroendoscopy was by Victor Lespinasse, a urologist at the Wesley Hospital of Chicago, who introduced a cystoscope into the lateral ventricles of two infants and performed bilateral fulgurations of the choroid plexus to treat hydrocephalus [10].

However, Lespinasse only presented his work at a local meeting and did not publish it. It turns out that Lespinasse became more interested in testicular transplantation for rejuvenation, and considered his choroid plexus fulgurations an “intern’s stunt”, though he performed this a full 3 years before Dandy and Blackfan published their work on dogs. Lespinasse is remembered for his highly publicized case of testicular transplantation. In 1922, he transplanted the testicles of a blacksmith into Harold McCormick, son of Cyrus McCormick (the inventor of the reaper). At that time, McCormick was married to Edith Rockfeller, the daughter of John D. Rockfeller. Supposedly, McCormick was in awe of his father-in-law’s vigor, but in a twisted way, wanted the operation so that he could pursue the Polish opera singer Ganna Walska [11]. McCormick did end up marrying the Polish singer, but they quickly divorced. This story was immortalized by Chicago locals, who modified the classic work by Henry Wadsworth Longfellow: “Under the spreading chestnut tree; The village smithy stands; The smithy a gloomy man is he; McCormick has his glands” [12].

Walter Dandy, a neurosurgeon at Johns Hopkins Hospital worked out the physiology of cerebrospinal fluid (CSF) dynamics with Kenneth Blackfan in 1914 using dogs (Fig. 6) [13]. In 1918, Dandy published a manuscript describing his technique of ventriculoscopy and extirpation of the choroid plexus. However, his method at that time was crude—he used a nasal dilator to keep the cortex open and had to remove the entire CSF volume before the choroid plexus was removed using forceps, ligated with a silver clip and avulsed (Fig. 7) [14]. This original paper cited four patients; three of whom died within 1 month and the last one showed no signs of hydrocephalus 10 months after the surgery. Improving on his original technique, Dandy described the use of a cystoscope for looking into the lateral ventricles and performing choroid plexectomy in a one paragraph article published in the Johns Hopkins Hospital Bulletin in 1922 [15].

Fig. 6
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Method by which Dandy and Blackfan caused hydrocephalus in dogs [13]. By making a small incision and craniectomy into the posterior fossa, they obstructed the acqueduct of Sylvius using a cotton pledget covered with a gelatin cap

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Fig. 7
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Dandy’s original technique of ventriculoscopy and extirpation of the choroid plexus, published in 1918 [14]. The technique at that stage was rather crude, using a nasal dilator to keep the cortex open and had to remove the entire CSF volume before the choroid plexus was removed using forceps, ligated with a silver clip and avulsed

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W. Jason Mixter, the founding Chair of Neurosurgery at Massachusetts General Hospital and most famous for his work on intervertebral disk disease, published the first report of an endoscopic third ventriculostomy (ETV) in 1923 [16]. Here, he used a urethroscope in a 9-month old with non-communicating hydrocephalus and made a puncture in the floor of the third ventricle. Mixter had diagnosed non-communicating hydrocephalus by injecting indigo carmine into the lateral ventricle by puncturing the anterior fontanelle, but noted the absence of the dye on lumbar puncture. After puncturing the third ventricular floor, he was able to recover the dye on a subsequent lumbar puncture [16]. Mixter’s instruments were cumbersome and his report did not have much traction with the practitioners of the day.

Twelve years after Mixter’s original paper describing ETV, John Scarff of Columbia University described an improved endoscope, complete with an irrigation system that prevented the collapse of the ventricular system. It also had a movable electrocautery and operating tip. Scarff was able to achieve a rapid decrease in head circumference on his first patient, but unfortunately, the patient died. On autopsy, there was a healed scar over the site of the ventricular puncture. This caused Scarrf to realize that he would need to create a larger perforation of the third ventricular floor—a concept that still rings true today [17].

Stagnation in neuroendoscopy

The 1950s represented a stage of stagnation for the field of neuroendoscopy. This was due to the advent and popularization of shunting procedures, the development of microneurosurgery, and perhaps most importantly, the limitations and problems with early neuroendoscopic instrumentation. In 1949, Frank Nulsen and Eugene Spitz placed the first successful ventricular shunt to treat hydrocephalus, diverting CSF from the cerebral ventricles into the venous system [18].

The development of microneurosurgery in the 1960s helped push neuroendoscopy further into the background. The microscope provided neurosurgeons with what the neuroendoscope lacked: high magnification, adequate illumination, and the ability to work in deep structures with little damage to surrounding vital structures. Although the 1960s represented a time during which publications on neuroendoscopy were sparse, it was also a time that key technological advances were made that has allowed neuroendoscopy to make a strong resurgence [19]. These technological advances included the invention of variable refractive index lenses by Harold Hopkins, the invention of charged-coupling devices (CCDs) and improved fiber optic technology [20].

The British optical phyisicist Harold Hopkins deserves a lot of credit for the advancement of neuroendoscopy [20]. Similar to pioneering geniuses like Bozzini, Hopkins has an intriguing personal history. The last of six children born to a baker’s assistant in Leicester, Hopkins’ family faced financial difficulties through much of the 1920s and 1930s. His mother insisted that he concentrate on his education and he later won a scholarship to University College in Leicester, where he graduated in 3 years with degrees in physics and mathematics [21]. His PhD in applied physics was interrupted by war, and it was during his enlistment that he befriended a soldier named of Nairs Craig. After completing his PhD, Hopkins continued his research and teaching endeavors at the Imperial College in London. In 1948, he developed a zoom lens used by the BBC to televise sporting events. Coincidentally, at a dinner party in 1951 hosted by his war friend Craig, Hopkins was seated next to Hugh Gainsborough, a gastroenterologist who complained of the inadequacies of the then available gastroscopes. Gainsborough complained that the gastroscopes were highly rigid and unable to provide much illumination. Working with a research student Narinder Kapany, Hopkins came up with the idea of using coherent bundles of glass fibers to provide light and an image. They published this as a letter to Nature [22, 23]. Hopkins was later approached by James Gow, a urologist from Liverpool, who provided him with a £3,000 grant to improve the illumination of cystoscopes. Previous to Hopkins’ work, endoscopic designs consisted of a tube of air with thin glass lenses and required precise placements to create an image. This made them clinically impractical and unable to provide a large working area. Initially, by mistake, Hopkins realized that by using thicker lenses he could design a sturdier system. Furthering his work, he found that the ideal system consisted of a tube of glass with thin air lenses, or the rod–lens system (Fig. 8) [24]. This rod–lens system forms the basis of the rigid endoscope currently used today. Hopkins’ original system was bought by Karl Storz [25]. Hopkins’ design was able to increase the field of vision as well as increase the illumination almost 10 times. It was said that Hopkins was nominated for the Nobel Prize in Physics twice [21].

Fig. 8
figure 8

a Harold Hopkins, an English physicist deserves a lot of credit for the development of modern endoscopic theory and instrumentation. b Hopkins understood the importance of coherent light sources, showing how, depending on their relative phase, light intensity could be increased (dashed lines) or decreased (dashed, dotted lines, Hopkins [23] used with permission). c Hopkins realized that instead of using an air rod, with interspersed lenses, using glass rods with interspersed ‘air lenses’ or the rod–lens system, one could obtain a larger field of view and higher magnification (Apuzzo et al. [24], used with permission). d Modern day endoscopes make use of many of Hopkins’ ideas

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Charged-couple devices, with their ability to convert optical signals to electrical impulses, became invaluable in the design of modern neuroendoscopes as they allowed for further miniaturization. Being more than 10 times more sensitive to light than standard photographic film, CCDs were perfect for the low illumination systems they were being used in [20, 26].

Thus, advances in fiber-optic technology allowed for the use of powerful light sources that could be placed distally and transmitted with increasing efficiency to the structures of interest. The addition of advanced optical systems that minimized loss of reflected light and improved video capture methods created an explosion of interest in the field of neuroendoscopy over the last 20 years.

Endoscopic third ventriculostomy

Recently there has been an increased interest in using endoscopic methods to treat hydrocephalus. The original optimism about shunting procedures has faded somewhat. Shunts are troublesome devices. The complication rates of ventriculoperitoneal shunts are reported to be as high as 40–60 % [27, 28]. The most feared complication of such shunts is failure which can result in serious neurological compromise including death due to hydrocephalus. This is particularly concerning for children in developing countries, as these patients are very far from a center that would have the resources to repair such failures. Thus, in a wide clinical undertaking, hydrocephalic children in Sub-Saharan Africa were treated with endoscopic third ventriculostomy as well as bilateral choroid plexus cauterization [29]. This, and other studies has caused an explosion in the interest in ETV for the management of hydrocephalus of various etiologies even in developed countries. With new endoscopic technology, the visualization of intraventricular anatomy is exceptionally clear (Fig. 9). Combining neuroendoscopy with neuronavigation has made intraventricular surgery much less dangerous [30].

Fig. 9
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a The first published photographs of intraventricular anatomy published by Fay and Grant in 1923. Note the grainy pixilation and low resolution. b Today, much clearer visualization is possible. This is a view through the right lateral ventricle onto the floor of the third ventricle. c Frameless stereotaxy (BrainLAB, Feldkirchen, Germany) allows one to precisely plan the most appropriate trajectory including where to place the burr hole [30], used with permission

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Intraventricular biopsy and resection

There has also been an explosion in the interest in performing more complicated intraventricular operations with new endoscopic technologies. These include the biopsy of difficult tumors, such as tumors of the pineal region [31] and other exophytic tumors. As many patients with these tumors also present with hydrocephalus, there has been an increased use of simultaneous endoscopic third ventriculostomy and biopsy [31, 32]. Similarly, for intraventricular tumors that are soft and friable, there is an increased interest in endoscopic resections as such a technique would result in less damage to cortical structures [33, 34].

Endosocopy has also been a useful tool for resecting colloid cysts. Although transcallosal and transcortical paths are popular, a comparative study revealed that using an endoscopic intraventricular approach resulted in shorter hospital stays with lower rates of complications compared to open techniques [35, 36].

In cadaveric models, we have shown successful selective amygdalohippocampectomy is possible using an occipital burr hole [37] as well as functional hemispherectomy through a parasagittal burr hole [38].

Transsphenoidal surgery

The endonasal, transsphenoidal path to the sella and parasellar structures has been recognized since early times, beginning with the Egyptians’ transnasal excerebration during the mummification process (see above). One of the pioneers to help resurrect the transphenoidal approach to sellar lesions, after it was abandoned by Harvey Cushing, was the French neurosurgeon Gerard Guiot—another academic giant [39]. He has been given the name as Cushing’s “spiritual grandson”, due to the fact that he first learned the transsphenoidal approach to sellar regions as an assistant to Clovis Vincent, who had learned many of these techniques from Cushing in the 1920s as well as 2-week visit to the Royal Infirmary in Edinburgh where he observed Nornan Dott—another former Cushing fellow [40]. Guiot was the first to use a separate light source and endoscope for neuroendoscopic procedures, though he abandoned this due to the large size of the endoscope and sheath [20, 26, 41]. Otorhinolaryngologists were the first to adopt endoscopic methods to examine and perform sinus surgery and even some pituitary surgery [42]. For a long time, the microscope was used for transsphenoidal surgeries as it was felt that it provided better visualization, 3D imaging, and thus safer surgery in this crowded and important corridor. However, neurosurgeons such as Jho and Laws showed that the endoscope could be used as a primary tool to perform pituitary surgery [43, 44]. Further refinements include the use of neuronavigation and 3D technology—allowing the surgeon unprecedented visualization of the vital parasellar and sellar structures. In fact, with increasing microsurgical abilities and improved technologies, extended transsphenoidal exposures are attainable from cervical spine to the olfactory bulb and laterally to the foramen ovale [45].

Conclusion

The evolution of neuroendoscopy has been a long and stuttering one. The field is replete with a rich history of colorful luminaries such as Bozzini and Harold Hopkins. It has advanced as the result of collaborations among clinicians, engineers, and scientists. Such continued collaborations will most likely lead to more novel applications of neuroendoscopy in the future.