4.1 Introduction

Much has been said in recent years regarding the endoscope and its applications in brain surgery. Despite this, only limited numbers of neurosurgeons have successfully incorporated the endoscope into their craniotomies. Some of this is due to a lack of comfort and experience, which can only be obtained with persistence and time. However, one of the biggest barriers to widespread use of the endoscope in transcranial operations is the general challenge of determining a time and method for best incorporating the endoscope in a meaningful and useful way. There are few resources specifically advising people how and when to bring in the endoscope during a craniotomy, and therefore, while most neurosurgeons are aware that the endoscope is able to look around corners, they generally do not have specific knowledge to guide them on how best to harness this trait for their own benefit.

The present chapter introduces the endoscope and its essential features. It further defines the principal situations where we use the endoscope and provides some basic techniques we use to accomplish this safely and effectively. These principles are described in more detail for each specific location in subsequent chapters. However, it is important to grasp the basic ideas and techniques outlined in this chapter.

4.2 A Brief Introduction to the Endoscope

In transcranial surgery, when we refer to the endoscope, we usually mean the angled rigid endoscope (generally 30 degrees or more). The 0-degree endoscope is easier to steer and remains well oriented; however it generally does not provide visualization around corners, and thus provides little advantage over the microscope. Nevertheless, as emphasized in Chapter 3 and elsewhere in this book, the microscope is the principle working device of keyhole surgery, and we only bring in the endoscope when there is a specific need that cannot be easily addressed with the microscope.

Two characteristics of the 30-degree endoscope which are initially challenging to beginners are firstly that it only looks ahead (and thus has a blind spot behind the lens), and secondly that it is aimed in a direction below what is seen on the screen, and so is not aimed at what you are looking at (Fig. 4.1). These two features raise significant safety concerns, particularly when working near delicate structures such as the optic nerve, and for this reason some training outside actual patients (namely in cadavers) is highly recommended to develop safe technique. Novices must learn to steer the endoscope slightly upward in order to move toward the structure on the screen, and to do so slowly to avoid striking anything in the brain with the endoscope. This simply takes practice.

4.3 Safe Endoscope Technique

Many common methods for visualizing around tight corners, including drilling of bony protuberances or removal of structural impediments such as the orbital rim, are both time consuming and potentially morbid. While the endoscope can be a powerful tool for accessing these awkward angles, it may also become a dangerous weapon when used incorrectly. Thus, regardless of how safe and wide open the field you are working in appears to be, it is important to develop good habits, and to use good technique consistently.

Most importantly, the endoscope is a fencing instrument, not a slashing instrument. By that we mean that because the sides of the endoscope are out of its field of view, it is important not to change viewing angles by merely swinging the scope, because anything in the angle subtended by these two axes, be it optic nerve, perforators, bridging veins, etc., is at risk of being slashed by the endoscope shaft (Fig. 4.2). Changes in the angle of the endoscope should therefore be made by first removing the endoscope and then reinserting it at the new desired angle (see Video 4.1). For deep visualization, especially those maneuvers which require a view past important structures, it is often useful to introduce the endoscope under microscopic visualization, and to have the assistant serve as a spotter to ensure that the angle is not changing inadvertently and injuring something behind the scope tip. Similarly, while rotation along the long axis of a 30-degree endoscope can provide a view around corners (Fig. 4.3), it is difficult to be sure that you have not changed the angle while doing so, and we therefore typically remove the endoscope and rotate the viewing angle externally (see Video 4.2).

Due to the challenges of safely steering a 30-degree endoscope straight ahead, it is wise to do so slowly, with small steady adjustments, to avoid disaster. Introducing the endoscope with the aid of the microscope is a safe method of solving this problem (Fig. 4.4).

Finally, due to the blind spots which are inherently present with all endoscopes, it is risky to introduce instruments blindly once the endoscope is in position (Fig. 4.5). The safe method of introducing an instrument is therefore to place the instrument in front of the endoscope in a safe spot, and follow the instrument into the field with the endoscope (see Video 4.3).