40.1 Introduction

Neuroendoscopy has had a history of steady growth, evolving from relatively primitive roots to its current level of refinement. While we have achieved much in terms of technical capability, clearly there is still much room for improvement. Despite this, it may be that neuroendoscopy has already passed through its Golden Age. The field’s maturation has been driven by the persistent desire of neurosurgeons to advance the options available to their patients and a parallel movement toward lower impact, minimally invasive treatments. The endonasal endoscopic revolution gave the field more impetus to evolve, and many of the advances impacted intracranial neuroendoscopy positively as well. Yet even while the interest of a new generation of neurosurgeons has remained high, other forces have limited growth. The dilemma facing neuroendoscopy now has a twofold face. On the one hand, technology should make many new and exciting advances possible; on the other, economic forces are limiting its growth.

How will niche treatments like endoscopy, which are heavily dependent on technology but apply to the care of very few patients, find their way forward? Financial pressures in health care give little incentive to advance such treatments. Few patients and few cases means little consumption to drive industry development of revolutionary technologies. In fact, because existing procedures may use more technological resources than the procedures they replace, they may be seen as a detriment in a system where cost considerations dominate. In a value-based system, it will be increasingly critical to show that there is an advantage to these techniques that justifies their expense. Innovation will likely be driven by the practitioners themselves, whose passion may overcome the reluctance that pure economics might dictate. In the end, innovation and pragmatism always must find common ground for any advance to become widespread and broadly applied.

Happily, technology will continue to work in our favor. Even as you read this, industry is making steady improvements in camera technology, and smaller, lighter, brighter, and higher-definition cameras are becoming available on a regular basis. While these advances are not driven by the demands of neuroendoscopy, these advances are easily applied to our field. Chip-on-the-tip cameras have the potential to replace bulky camera heads. Light-emitting diode (LED) lighting is bright but cool and very reliable. Tracking technologies may allow us to know where the endoscope is and how it is moving. Three-dimensional (3D) imaging and virtual imaging are combining in our favor to give us added understanding and overcoming one of the major liabilities of neuroendoscopy, namely, disorientation.

Technical challenges still facing neuroendoscopy include operating around corners, seeing through blood, and achieving a microscopic-level degree of dexterity. As a field, we see several areas where advances can be anticipated. We will detail them in the rest of this chapter.

40.2 Three-Dimensional Neuroendoscopy

One of the problems with current endoscopes is the lack of stereoscopic view. Three-dimensional systems provide surgeons realistic images of the anatomical structures. The “insect eye” technology (Visionsense Corp., New York, New York, USA) is the most notable of the 3D lens systems. This system incorporates a lenticular array of microscopic lenses into a chip—referred to as “chip-on-the-tip” at the distal end of the endoscope. The right-handed and the left-handed images are generated from a single charge-coupled device (CCD) and overlaid on a dual–flat-screen system with stereoscopic monitors.1 This new technology eliminates the dizziness, fatigue, and eye strain observed when surgeons used previous 3D technology. Surgeons remained divided as to the advantages of 3D endoscopy in actual use, though one of us (PN) is a proponent.

40.3 Neuronavigation and Image-Guided Neuroendoscopy

With the use of advances in neuronavigation and image-guided surgery, neuroendoscopy has the potential to overcome the limitations of lack of stereoscopic view and the ability to track the tip of the endoscope. Loss of orientation or view, with consequent inability to achieve surgical goals, is a source of anxiety and consumes valuable operating time, as well as a source of potential morbidity. Technologies are available to define terrain and thereby identify what the view is of, reducing the potential for disorientation. Advanced rendering could allow the surgeon to continue to work with virtual guidance, despite the reduced view. Surgeons will be able to plan their approach and trajectory and visualize the range of manipulation of the endoscope and endoscopic instruments through virtual reality or from real-time images. Virtual preoperative rehearsal neuroendoscopy would involve generating a simulation of patient’s anatomy and allowing surgeons to review the structures of interest before proceeding to the actual operation, now with better training and planning.

For flexible neuroendoscopy, there would be an advantage to a technology that would allow the surgeon to know where the entire shaft is so that it does not negatively impact critical structures behind the field of view. This kind of virtual representation, or even definition of “no-fly zones” for the back of the endoscope could help promote this technology among surgeons who are not currently comfortable with it.

40.4 Flexible Neuroendoscopy

Since first being introduced by Fukushima in 1973 into neurosurgery, the flexible neuroendoscope had been used by many neurosurgeons; however, it has not gained as much popularity as the rigid endoscope. The main reasons are the lesser image quality due to the low resolution delivered by fiberoptic cameras, lower brightness, the fragility of the equipment, and the potential for disorientation in the flexed position. On the hardware side, the quality and characteristics of flexible neuroendoscopes have improved considerably over the past years. The recently developed videoscope with an outer and a working diameter of 5.0 mm and 2.0 mm, respectively, is unique due to the high-quality image and 180º rotation of the flexible insertion tube.2 It contains a narrow-band imaging (NBI) technology that uses an optical color separator filter that narrows the bandwidth for spectral transmittance. This digital technology affords the videoscope the capability of delivering magnified views of microscopic textures such as capillary vessels. Future flexible neuroendoscopes will have high-definition (HD) and/or 3D imaging technology. The 3D-Eye-Flex (Olympus, Tokyo, Japan) is a flexible videoscope that produces 3D and HD digital imaging using two CCDs.3 We anticipate that chip-on-the-tip cameras will eventually replace bulky external camera heads. New flexible neuroendoscopes will incorporate neuronavigation using electromagnetic tracking.4 To navigate the tip of the flexible neuroendoscope, miniaturized magnetic field sensors can be mounted on the endoscope tip enabling tracking of the tip without any loss of the function. A prototype of this flexible neuroendoscope is currently being developed by Japanese neurosurgeons.4 This future prototype has one large working channel of 2 mm, range of the movement of 90º up and down, with a very similar method of operation to other flexible neuroendoscopes. Results from the prototype tests have demonstrated a minimal error of 1.2 mm. One major advantage of this kind of tracking technology is that it does not require rigid head fixation, a factor particularly advantageous in pediatric neurosurgery. The sensor mounted on the flexible neuroendoscope is 1.8 mm in diameter and 9 mm in length. This relatively small diameter allows it to be mounted within the neuroendoscope. This electromagnetically tracked flexible neuroendoscope is ideal for biopsy of intraventricular lesions, intraventricular hematoma evacuation, and penetration of cystic intracerebral and intraventricular lesions.

40.5 Hyperspectral Imaging

Modern endoscopes need not be limited to the visual spectrum native to the human eye. Both rigid and flexible neuroendoscopes can also incorporate fluorescence and other technologies. This modality can be very useful identifying normal anatomical structures in patients with distorted anatomy due to hydrocephalus within the lateral ventricles (choroid plexus), third verticle (median eminence, organum vasculosum), and fourth ventricle (area postrema, calamus scriptorius).5,6

Indocyanine green (ICG), fluorescein, and 5-ALA are fluorophores (ICG, fluorescein) or precursors (5-ALA) that allow visual recognition of certain normal and abnormal neurovascular structures not visible to the human eye.5,6,7,8,9,10,11 Indocyanine green has been integrated into the operating microscope and is now familiar to many neurosurgeons. A microscope-integrated light source containing infrared excitation light illuminates the operating field. Intravascular fluorescence from within the blood vessels is imaged using a Video camera attached to the microscope. The principal applications of ICG are in cerebrovascular and, to a lesser degree, neuroncological surgery, including aneurysms, arteriovenous malformations and fistulas, venous circulation around tumors such as meningiomas, and selected high-grade gliomas. Incorporation of ICG into the endoscope could be useful in the endoscopic management of aneurysms (see Chapter 35), intraventricular hypervascular tumors (see Chapter 12), and endoscopic extra-axial and intra-axial tumor surgery (see Chapters 33 and 34). ICG can also be used to visualize deeper structures within tissue due to its infrared excitation–emission, which travels further through tissue without scattering. Fluorescein is a simple fluorophore which serves as a tracer of blood–brain barrier disruption; it was tried but soon abandoned in high-grade glioma surgery years ago; recently, interest in it has undergone resurgence. Fluorescence has recently been adapted to intraventricular endoscopy (see Chapter 36 for more details). For the first time in 2004, circumventricular organs (median eminence, organum vasculosum of the lamina terminalis) were seen during endoscopy for hydrocephalus using fluorescence technique.12 Incorporated into a flexible neuroendoscope, fluorescence angiography in a ventricular endoscope allows identification of additional landmarks and structures that are not visible in white light such as circumventricular organs, subependymal microvascular network, and intraventricular tumors features.5,6 5-aminolevulinic acid (5-ALA) for clinical use is available in Europe and many other countries, but has not in use in the United States, as it has not been FDA approved yet. 5-ALA provides tumor-specific contrast that is more similar to immunohistochemistry. It is concentrated in neoplastic cells and converted to the endogenous fluorophore protoporphyrin IX intracellularly, which provides macrofluorescent contrast of neoplastic cell cytoplasm.13