In neurosurgery, the development of endoscopic or keyhole techniques has revolutionised the surgeon’s ability to examine the brain, spine and peripheral nervous system and perform minimally invasive surgical procedures. 

Simply explained, a neuroendoscope is a small rigid or flexible tube that carries a system of optical lenses connected to a high-resolution video camera and a light source. The endoscope relays a clear image of the brain to a computer monitor, allowing surgeons to locate, isolate and remove or repair a lesion without affecting nearby tissues. This technique requires only a small burr hole. There are one or more working channels in the endoscope to allow small instruments to be inserted into the brain to perform the procedure. Endoscopes can be used to access structures that are normally difficult to reach and, by using angled optics, the surgeon can virtually look around the corner and identify structures that otherwise could be not visualised and might be damaged. 

In Ireland, all three neurosurgical centres at Cork University Hospital, Dublin’s Beaumont Hospital and Children’s University Hospital, Temple Street, use neuroendoscopy routinely.

“This minimally invasive neurosurgery has the advantages of a small incision site and minimal trauma to the brain or spinal cord, resulting in a shorter hospital stay for patients and a quicker return to normal activities. Some of the more common neuroendoscopic surgery performed in Ireland would include endoscopic third ventriculostomy (ETV) for hydrocephalus, pineal tumour biopsy, ventricular tumour biopsy or excision, cyst fenestration (arachnoid cyst) and endoscopy-assisted procedures such as trans-sphenoidal resection of pituitary tumours,” explains Dr Chandru Kaliaperumal, a specialist registrar in neurosurgery at Temple Street Hospital. 

“These are mainly for cranial procedures. However, neuroendoscopy is also utilised in spinal surgery,” he added.

The goal of using endoscopes for surgery is to reduce the tissue trauma when compared with traditional open surgery. It also allows for better visualisation and illumination of the operative field through the narrowest practical corridor. 

History of the endoscope

Physicians as far back as Hippocrates have sought minimally invasive ways to peer into a live human body. Just over 200 years ago, that conundrum was cracked by German doctor Philipp Bozzini, who was the first to explore inside body cavities through their natural openings using his Lichtleiter or ‘light conductor’ – a primitive endoscope, which consisted of a thin metal tube that allowed reflected candlelight to shine into an orifice. His invention founded the principles that guided the development of endoscopy.

In 1853, Antoine Jean Desormeaux, a French surgeon, first introduced the Bozzini Lichtleiter to a patient. The light source was a lamp flame; the endoscope burned a mixture of alcohol and turpentine. Consequently, a major complication was burns to the unfortunate patient. The first electrical light bulb as the light source was introduced in 1879 by German doctor Maximilian Nitze. Although his endoscopic system was only suitable for urological procedures, the principle soon became accepted for the inspection of other body cavities.

It was in the early 20th century that the pioneering phase of neuroendoscopy commenced, initially in an effort to diagnose and treat hydrocephalus. In 1910, Victor Darwin Lespinasse, an urologist in Chicago, conducted the first neuroendoscopic intervention when he cauterised the choroid plexus of two severely ill infants diagnosed with communicating hydrocephalus. One patient died post-operatively, but the other was successfully treated. He never published this procedure, thinking it to be ‘an intern’s stunt’, and only reported the case in front of a local surgical society. The method was further developed by American neurosurgeon and scientist Walter Dandy, who implemented ventriculography, which he developed in 1918, in the procedure of choroid plexus removal in hydrocephalic patients. For many, he is considered the father of neuroendoscopy.

Another neurosurgical inventor, Jason Mixter, performed the first purely ETV in 1923 on a child with congenital hydrocephalus. The floor of the third ventricle was attempted with a urethroscope and perforated using a flexible probe. However, his report on this groundbreaking procedure went largely unnoticed, possibly because of the cumbersome size of his instruments and the poor illumination that they offered. 

There were no further reports of ETV until 1935, when John E Scarff performed the procedure with novel instruments: he used an endoscope equipped with a mobile cauterising electrode, an irrigation system that prevented collapse of the ventricle, and a movable operating tip which was used to puncture the floor of the third ventricle.

In one case where dramatic results were achieved (a 3cm decrease in head circumference six weeks post-operatively), the ventriculostomy eventually failed and the patient died. A healed scar over the ventriculostomy site was found at autopsy, prompting Scarff to write: “This case demonstrates clearly the feasibility of the procedure but points out also the necessity of enlarging the opening beyond a mere puncture wound.”

Although many reports demonstrated the potential utility of neuroendoscopy, poor magnification and illumination made neuroendoscopy difficult and unreliable. For these reasons, and with the advent of ventricular cerebrospinal fluid (CSF) shunting and the birth of microneurosurgery in the early 1960s, neuroendoscopy entered a stage of hibernation that would last more than two decades. It was not until the technical advances in optics, electronics and image processing that neuroendoscopy resurged. British physicist Harold Hopkins, who invented the zoom lens in the 1940s, applied solid rod lenses in the construction of the endoscope in 1960, ‘opening the door’ to modern keyhole surgery. Seeing promise in this system, Karl Storz bought the patent and in 1967 began to produce endoscopic instruments with a tremendously brilliant image and superb illumination. 

The development and refinement of fiberoptic cables was a major factor in the endoscopy revolution. This important technological breakthrough allowed the light source to be separated from the rest of the endoscope. Light could also be emitted from the tip of the endoscope without significant heating through one set of cables, while other cables could be constructed to conduct images without a loss of luminescence.

Modern flexible neuroendoscopy was pioneered by Takanori Fukushima, working in Tokyo, Japan, in the 1970s. He invented the ‘ventriculofiberscope’ and used it to perform biopsy of tumours of the lateral and third ventricles.

Modern applications

The early efforts of these individuals and others have led to neuroendoscopy becoming an important and expanding field of neurosurgery. Initially, neuroendoscopic procedures were confined to the ventricles of the brain, which contain CSF – the ideal medium: a crystal-clear fluid. These intraventricular neuroendoscopic procedures include biopsy or resection of certain types of tumours, fenestrate (create an opening in) cysts and other structures to allow drainage of fluid, and relieve increased intracranial pressure or hydrocephalus. 

The expansion of neuroendoscopy outside CSF space, and finally also outside cranial space, has resulted in this minimally invasive method being used to treat many neurological pathologies and the indications are rapidly expanding. The modern neuroendoscope can be used alone or in conjunction with an operating microscope. The three major groups of endoscopic techniques are:

• Endoscopic neurosurgery (channel endoscopy) is mainly used in ventricular endoscopy. The surgical instruments are introduced via working channels that are located within the endoscope 
• Endoscope-controlled microneurosurgery means that the endoscope is the only visualisation tool and microsurgical instruments are used along the endoscope. Major applications are endonasal endoscopic skull base surgery, endoport surgery and endoscopic transcranial surgery 
• Endoscope-assisted microneurosurgery means that microscope and endoscope are used in the same surgery.

The navigation and usage of an endoscope through the highly intricate anatomy of the human central nervous system is a complex technique. Neurosurgeons using this technique are trained accordingly, particularly in visuomotor skills, and carry out neuroendoscopic procedures on a regular basis in order to have enough experience and expertise. 

“There is a long learning curve to develop the skill to use neuroendoscopy from a training perspective. Neuroendoscopy training for Irish trainees is a part of the curriculum and there are also courses available to build the skills on neuroendoscopy for trainees interested in this technique. However, when a trainee is working with a consultant who has an interest in neuroendoscopy, then one gets to see and perform the procedure under supervision,” says Mr Kaliaperumal.

In inexperienced hands an endoscopic procedure can be very long, which increases the complication rate. Major risks of neuroendoscopic procedures are intra-operative bleeding, which can be very problematic due to the small approach, and post-operative infection. On the plus side, this minimally invasive neurosurgery has the distinct advantages of a small incision site and minimal trauma to the brain or spinal cord, resulting in a shorter hospital stay for patients, less postoperative pain, minimal scarring, and a quicker return to normal activities.

According to Mr Steven Young, consultant neurosurgeon, Beaumont Hospital: “With the advent of improved endoscopic equipment and high-definition three-chip cameras, the use of neuroendoscopy has extended beyond the treatment of hydrocephalus with third ventriculostomy to endoscope-assisted microvascular decompression for trigeminal neuralgia, endoscope-assisted removal of acoustic neuromas and endonasal pituitary surgery. There is now considerable interest in combining neuroendoscopy with other diagnostic and therapeutic modalities such as ultrasonic microprobes and endovascular coiling of aneurysms and arteriovenous malformations.”