3 Development of a Flexible Neuroendoscope

10.1055/b-0036-141978

3 Development of a Flexible Neuroendoscope

Kazunari Oka

3.1 Introduction

Minimally invasive surgery represents a major advance in the field of neurosurgery. The endoscope has played a major role in neuroendoscopy, one of the minimally invasive techniques. Endoscopic surgery is not unfamiliar to neurosurgeons. In fact, endoscopic surgery was first performed in the early 1900s. However, the lack of suitable options and instruments led to poor operative results and impeded this technique from achieving worldwide popularity. Since the 1970s, endoscopes were used widely in several medical fields, including gastroenterology, pulmonary medicine, and urology, before being reconsidered for neurosurgical purposes.

Neuroendoscopic technique must be adapted to the particular conditions presented by ventricles filled with cerebrospinal fluid (CSF). Additionally, brain tissue is solid, but soft and fragile. Over many years of careful evaluation, the endoscopes and accessories used in neuroendoscopic procedures have undergone multiple modifications aimed at improving their accuracy and safety. The flexible steerable endoscope is currently used to perform many neuroendoscopic procedures safely and effectively.

Herein, we review the development of flexible neuroendoscopes and their accessories.

3.2 Development of a Flexible, Steerable Neuroendoscope

In 1986, working with Olympus Optical Company (Tokyo, Japan), the author contributed to the development of a new endoscope for neurosurgery. The concept underlying the development of this neuroendoscope was that neuroendoscopic surgery was more effective than microscopic surgery for treatment of many neurosurgical pathologies.

The new neuroendoscope design had to enable the visualization possible with a large working channel, to avoid or minimize neurovascular damage. The outer diameter had to be as small as possible to provide a comfortable grip for the neurosurgeon. The neuroendoscope needed an appealing design but also had to meet universal specifications. Accessories therefore were designed with smooth exteriors and interiors, and they were intended for easy use, both lengthwise and widthwise.

Neurosurgeons tend to prefer open surgery, with direct visualization of the lesion and the ability to expand the approach to allow easy observation of its surroundings. Skillful neurosurgeons with proficient techniques often can minimize the size of the operative trajectory. Therefore, the new neuroendoscope design had to allow a further reduction of the operative trajectory compared with the operative microscope. We surveyed Japanese neurosurgeons, who indicated that an endoscope with a 3-mm outer diameter was overly small, whereas one with a 5-mm outer diameter was overly large. The resulting neuroendoscope had an outer diameter of ~ 4 mm and was equipped with a working channel with a 2-mm inner diameter.

Advances in medical imaging technologies continue to be made. These advances include the development and improvement of minimally invasive neuroendoscopic surgical techniques, as well as the addition of commercial materials, such as artificial CSF.

3.2.1 Initial Designs

Initially, we worked on two design concepts for flexible, steerable fiberoptic neuroendoscopes, one for observation (Fig. 3.1) and one for surgery (Fig. 3.2) (Olympus Optical Company, Tokyo, Japan).1 These neuroendoscopes were waterproof and lighter than the fiberoptic endoscopes used in other fields, such as gastroenterology, pulmonary medicine, gynecology, and urology. The neuroendoscopes for observation and therapeutics had outer diameters of 2.8 mm and 4.6 mm, respectively. They were capable of automatic light exposure control when used with an appropriate cold light supply (CLV U20D, Olympus Optical Company). The resulting photographic images (OTV S2D, Olympus Optical Company) could be projected onto a color television (TV) screen. Accordingly, a neuroendoscopic procedure could be simultaneously observed and recorded on videotape and film (Video 3.1). The surgical neuroendoscope had a 1.8-mm working channel that was suitable for most neuroendoscopic operations.

**Fig. 3.1** First-generation of flexible, fiberoptic neuroendoscope for observation.

**Fig. 3.2** Second-generation of flexible, fiberoptic neuroendoscope for surgery.

The following neuroendoscopic instruments2,3 were included: endoscopic grasping forceps for blunt penetration and biopsy sample collection, endoscopic dissecting forceps, endoscopic needle for puncture and aspiration, endoscopic electrode (ME2, Codman & Shurtleff, Inc., Randolph, MA) for cutting and coagulation, a contact (Nd:YAG) laser endoprobe (Surgical Laser Technologies, Tokyo, Japan) for coagulation, vaporization, and cutting, a percutaneous transluminal coronary angioplasty balloon catheter (CardioVascular Dynamics, Inc., Irvine, CA) for third ventriculostomy, and an endoscopic ultrasonic aspirator (prototype, Olympus) for hematoma and tissue aspiration. All of these instruments were sterilized with ethylene oxide gas at 50ºC for 12 hours preoperatively. Dripping irrigation with artificial CSF4 (Artcereb, Otsuka Pharmaceutical Company, Inc., Naruto, Japan) was used intraoperatively to prevent injury to the brain tissue or collapse of the ventricles. Subsequently, this surgical neuroendoscope was upgraded twice, with substantial improvement of the quality of the optical images. The outer diameter of neuroendoscope was enlarged from 4.6 mm to 4.8 mm (Fig. 3.3), and the working channel was widened from 1.8 mm to 2.0 mm.