2 Cognitive Principles of Planning Keyhole Approaches

10.1055/b-0035-104214

2 Cognitive Principles of Planning Keyhole Approaches

Michael E. Sughrue and Charles Teo

2.1 Introduction

Most people who try keyhole surgery and give up do so because they incorrectly plan and/or execute the approach, and then struggle, leading them to conclude that keyhole surgery is dangerous or unnecessarily difficult. Presently, there are very few texts, or other sources of instruction, on how to plan a perfect keyhole opening, so it is not surprising that many surgeons have not switched over to keyhole surgery. The present chapter introduces the basic principles of planning a keyhole approach that are emphasized throughout the rest of this text in different contexts to address various disease processes.

Principle 1: Study the Films Closely

This principle is not unique to keyhole surgery; it is always wise to study the films closely. In keyhole surgery the principle is even more important, as mistakes are not very well tolerated working through small openings. The onset of keyhole surgery has put an end to the era of telling your resident to perform a large, standard pterional craniotomy and then showing up when the dura is open: planning the craniotomy is critical to success, and mistakes are punished. Every keyhole case is slightly different, and minor variations matter. Thus, while it is easier to perform the same large opening for many patients as one will always get more than enough exposure, we would suggest that this is an intellectually lazy approach which puts the patient through unnecessary pain and tissue injury, simply to avoid having to put more thought and care into planning the operation.

Principle 2: Find the Long Axis of the Tumor

Regardless of tumor type, ergonomically it is always easiest to work down the long axis of the tumor, regardless of the size of the craniotomy (Fig. 2.1 a). Working down the long axis reduces the number of uninvolved structures which need to be retracted or manipulated, especially if the patient is positioned with the long axis oriented vertically (Fig. 2.1 b). Working down the long axis allows one to remove the bulk of the tumor without looking around difficult corners, or sweeping blindly. While the long axis is not always the best approach for all situations—keyhole approaches do not always work down the long axis—it is always best to consider it first. At the very least, by completing this mental exercise you will have defined the basic location and projection of the tumor.

**Fig. 2.1** **a, b** Schematic demonstrating the principle of orienting the approach to a cerebral tumor. Down the long axis of the tumor, as opposed to the closest point to the surface the long axis of the tumor, as opposed to the closest point to the surface (a). When the long axis is oriented vertically, the brain tends to fall away from the cavity (b).

Principle 3: Catalog the Tumor and Its Component Parts

When first starting tumor surgery, it is easy to focus on the large part of the tumor, and to overlook smaller parts that may extend from the main mass. With experience, one finds that these small parts are often the areas which cause the greatest difficulty and pose the greatest risk (Fig. 2.2). They are often the pieces which get inadvertently left behind after an otherwise excellent tumor resection (Fig. 2.3). One should make a mental catalog of every portion of the tumor, and think about how the initially selected approach would address these portions if the goal of surgery is to remove them. Sometimes this reveals the need for a change in approach. Other times it highlights a requirement to use the endoscope. Regardless, it is a mistake to view the tumor as one single mass, as it is often really several discrete masses, which pose different surgical issues. Sometimes, the right approach for accessing 98% of the tumor is the wrong approach for 100% of it.