Powered instrumentation and bipolar technology in endoscopic endonasal skull base surgery

Introduction

Technologic developments in a variety of instruments and tools have been integral in the development and advancement of endoscopic endonasal skull base surgery. From scopes and camera heads to imaging modalities and surgical navigation down to the very instruments necessary to safely and effectively perform these surgeries, it is fair to say that endonasal skull base surgery exists because of these technologic advancements. Although the list of the available technology includes several areas, this chapter focuses specifically on powered instrumentation and bipolar technology currently available for endonasal skull base surgery.

There are several factors to consider when selecting and using both powered instrumentation and bipolar technology in endonasal skull base surgery. One of the greatest challenges in surgery of the skull base is the close proximity to critical neurovascular structures. Therefore, safety and control of the instruments is of paramount importance. This includes consideration of not only the tissue that is to be removed but also the nearby critical structures that could be injured directly or secondarily through either energy or heat transfer. Ideally, the power delivery and action of the instrument can be easily controlled and rapidly stopped if needed. Second, endonasal skull base surgery is done through narrow corridors where concurrent visualization and instrumentation can be a challenge. Furthermore, depending on the location on the skull base, angled instrumentation is necessary to achieve access. Therefore, the size, shape, length, and angles of the instruments are essential and can be a limiting factor. Finally, the instrumentation must be effective. Complex skull base cases can take several hours. Having instruments that quickly, effectively, and safely remove tissue, whether it is bone or soft tissue or tumor, allow for progression of the case, decreased operative time, and in some cases, improved visualization and decreased blood loss. To summarize, the ideal powered instruments for use in endonasal skull base surgery meet some or all the following criteria:

• Predictable depth of energy penetration or heat distribution or scatter

• Reduce collateral damage to nearby structures

• Easy manipulation and control with measures that allow for immediate cessation of instrument action

• Are of the appropriate length, and diameter and are available in a variety of angles to reach different regions of the skull base, through narrow corridors, without compromising visualization

• Effective in tissue removal or control of bleeding

Powered instrumentation

Powered instrumentation includes a variety of instruments used for the purpose of bone or soft tissue removal. Examples include drills, microdebrider (MD) technology (including the NICO), and piezoelectric devices. The following provides a review of the technology, its use in endonasal skull base surgery, and benefits and limitations.

Drills

Endoscopic drills are some of the mainstays in endonasal skull base surgery. Specifically, high-speed drills capable of reaching 10,000 to 100,000 revolutions per minute (RPMs) allow for rapid removal of bone. There are a variety of handpiece options, and control of the drill can either be through the handpiece or via a foot peddle. Drill burrs come in a variety of angles from straight to 70 degrees, allowing for access to all regions of the skull base as shown in Figure 41.1 . The burrs additionally come in variety of shapes, sizes (0.5–7 mm), and types, including diamond (can range from fine to course) and fluted or cutting. For endonasal skull base surgery, 3.0- to 4.0-mm drill bits are most commonly used. Fluted or cutting burrs can remove bone much more rapidly than diamond burrs, which can be beneficial in locations such as the sphenoid face, rostrum, and clivus. Given the rapid rate at which cutting burrs remove bone, the use of such burrs when nearing critical neurovascular structures should be done with great caution, if at all, given the potential for injury to vessels and nerves. Generally, as dissection gets nearer to critical structures, it is recommended that diamond drill burrs be used instead. Diamond drill burrs remove bone in a slower, more controlled fashion, making them safer for use near the carotid arteries and optic apparatus. In addition, diamond burrs can be used to address bone bleeding and achieve hemostasis. This is particularly helpful in cases with bothersome bone bleeding such as clival approaches in which marrow spaces and bleeding are frequently encountered. Finally, some drills have suction and irrigation capabilities, and others do not. The specifications and options for each drill is highly dependent on the manufacturer and vary widely across the market.

Neurovascular injury with the drill or other powered instrumentation is one of the most feared complications of endonasal skull base surgery. Knowledge of the complex anatomy of the skull base and important anatomic relationships is crucial for safe and effective surgery of the skull base. So, too, is a thorough understanding of the specific patient’s anatomy and the relationship of the pathology with nearby structures, which can be achieved with extensive review of preoperative imaging. This along with basic anatomic knowledge allow for a surgeon to decide when and where it is safe to drill. One final important consideration for the drill is heat transfer to surrounding tissues. Irrigation is crucial when drilling near critical neurovascular structures such as the optic nerve to avoid inadvertent injury to the nerve through heat transfer. At our institution, when drilling near critical structures, our preference is to do so with a two-surgeon, four-handed technique, allowing for irrigation, suctioning, and drilling to occur simultaneously.