Instrumentation (Micro, Endo, IGS, MRI Application)

Keywords: skull base surgery, meningiomas, instrumentation, endoscope, operating microscope, imageguided surgery

Oreste de Divitiis, Phillip A. Bonney, Teresa Somma, Federico Frio, and Gabriel Zada

Abstract

Resection of skull base meningiomas represents a complex surgery in which the best surgical approach requires knowledge of all the possibility offered by modern neurosurgery. Traditional microneurosurgical approaches have taken advantages of technological evolution, for example, neuronavigation systems, to gain lesser bone removal and safer tumor debulking of such skull base lesions (minimally invasive surgery). On that way, the evolution of the extended endoscopic endonasal approaches, nowadays, offer minimal bone removal with safe debulking and dissection away from neurovascular structures. Besides, in selected procedures, the endoscope can be managed as an adjunct tool in traditional keyhole microsurgical approaches to obtain a detailed view of the structures in the shadow of the microscope beam, for inspection at the depth of a resection cavity (endoscope-assisted microneurosurgery).

Advances in technology have complemented the development of dedicated equipment and microinstruments designed for each approach. In an effort to lessen surgical trauma and to expand the mobility within such narrow corridors, low-profile shaft with well-established ergonomic features of newer micro-instruments have improved the surgical results and reduced brain damage.

In this chapter, we analyze the state-of-the-art of the instrumentation utilized in microscopic and endoscopic skull base surgery.

5.1 Introduction

Meningiomas are common intracranial tumors often arising along the skull base or convexity regions. ¹ The most challenging task confronting contemporary neurosurgeons remains the selection of the most appropriate surgical approach: multiple factors including surgeon’s preference and experience, tumor size consistency and location, extent of dural attachment and relation with neurovascular structures should take in account for choosing the best corridor.

Traditional microsurgical approaches for resection of skull base meningiomas involve open microscopic craniotomy with fine tumor microdissection. Recently, extended endoscopic approaches have been utilized successfully to access and resect selected skull base meningiomas. Nowadays, the operating microscope, as well as the endoscope, are essential components of visual integration in the modern operating room (OR). The endoscope is the sole visualizing tool in pure extended endoscopic approaches and, in selected procedures, can be used in supporting the traditional microsurgical approaches, to simplify control of deep and hidden structures (endoscope-assisted microneurosurgery) (▶ Fig. 5.1). ²^, ³

Fig. 5.1 Drawing representing a schematic disposition of the staff and equipment into the operating theater during endoscope-assisted microsurgical approach.

Preparation for complex skull base tumor surgery includes ensuring that the surgical team has access to all required equipment and instrumentation—the so-called “clock-gear mechanism” described by Cappabianca et al. A variety of optical equipment (e.g., microscopic or endoscopic), tumor resection devices, and microdissection instruments must be available to the surgeon to safely and efficiently perform complex meningioma resection procedures.

The growing technological developments brought the light on the concept of minimally invasive surgery. On that way, great attention has been focused on the idea of image-guided surgery (IGS), and it has been facilitated by the introduction of the neuronavigation systems ( ▶ Fig. 5.2). It allows the transfer of increasingly refined presurgical image information into the operating theater, to guide surgical procedures with a better knowledge of spatial orientation inside the skull base.

Fig. 5.2 Intraoperative photographs during a transcranial approach: the neuronavigation system guides the stereotactic centered craniotomy for a convexity meningioma.

Future direction in skull base surgery, with improvements in technology, will led to robotic-assisted approaches that may become useful to enhance the surgeon expertise. ⁴^, ⁵^, ⁶

5.2 The Role of the Microscopy in Skull Base Surgery

5.2.1 Positioning

The operative environment is an important “tool” for achieving a satisfactory operative result. ⁷^, ⁸

Positioning the patient foresees methodic and consecutive steps, with the aim of achieving a comfortable working position for surgeon and the best working angle for reaching depth structures.

The head should be positioned using Sugita Head holder or three-pin Mayfield head holder, to get the best surgical operative angle, as regard to tissues and permitting gravity-assisted retraction. ⁹^, ¹⁰ Therefore, pin-fixation sites of the frames, as well as the arch and the counter arch of the Sugita frame, should allow total access to the operative field without hindering free movements of the neurosurgeon’s hands or instruments or the operating microscope. ¹⁰

The elevation of the head (20–30 cm over the level of the heart) facilitates venous drainage and the head should not be turned too much, to avoid arterial and venous compression.

Most intracranial procedures are performed with the patient in the supine, three-quarters prone (lateral oblique or park-bench), or prone/concorde position, with the surgeon sitting at the head of the table. ¹¹^, ¹² Otherwise, modern operating tables offer easy and versatile adjustments, such as back elevation, lateral tilt, Trendelenburg, and anti-Trendelenburg position, which allow variations of working angle during surgery without moving the microscope. ¹³

5.2.2 Operating Microscope

The operating microscope was first introduced in neurosurgical OR in 1957 by T. Kurze, which first removed a neurilemmoma of the eighth cranial nerve, and a crucial contribution provided by M.G. Yasargil, managed to overcome unwieldiness of the operating microscope, by permitting translational movements in the three planes. ¹⁴ It is the opening era of the modern neurosurgery. ¹⁵^, ¹⁶ Surgical procedures became more fluent and effective by the possibility of making fine adjustments to the position without repetitive use of the hands. ¹⁷^, ¹⁸

Modern surgical microscopes provide the possibility of high magnification of the surgical field and stereoscopic perspective. Thanks to motorized zoom system, surgeon can suddenly change surgical field magnification to visualize small structures such as tumor vascular supplies. Equally important is also the possibility to visualize the depth of field by the stereoscopic perspective; this allows visualization of deep structures reducing brain retraction.

The light intensity is a fundamental aspect of gaining visual resolutions under the operating microscope: incandescent, fiber optic, halogen, and tungsten are available types of illumination.

Furthermore, the stability of the operating microscope permits movements during surgery and is guaranteed by a modern system of adjustable counterweights. This permits to reduce the operation time spent merely adjusting and moving the microscope, improving surgeon comfort. Finally, allows real-time observation and recording of operative details not otherwise visible by the integration with high-resolution 3CCD camera system.

This technical revolution changed the neurosurgery, permitting smaller cortical incisions and less brain retraction (“keyhole surgery”), but also safer and precise coagulation of bleeding points, less neural and vascular damage, and anastomosis of small vessels and nerves. ¹⁹

Today’s operating microscopes mount sophisticated imaging capabilities to better visualize malignant gliomas, such as blue light illumination and infrared technology, with administration of oral 5-aminolevulinic acid (5-ALA) and intravenous indocyanine green (ICG), respectively.

5.2.3 Microsurgical Instruments and Techniques

The instruments become extensions of the surgeon’s own body. Every operation and even every technique for each type of operation requires a dedicated set of instruments (▶ Fig. 5.3). ²⁰^, ²¹ Technological research permitted the realization of suitable handle microsurgical instruments, which are used, according to the “blind hand” technique, without direct visual control. Indeed, the straight bayoneted instruments are designed to avoid conflict between the surgeon’s hands and the lens of the microscope. Bayonet forceps may be used to develop tissue planes, instead of straight scissors with fine blades or circular semisharp arachnoid blade, with a variety of tip sizes, is used for opening the most superficial arachnoid membrane, according to the “sharp dissection” (▶ Fig. 5.4).

Fig. 5.3 Basic set of microsurgical instruments: blunt and sharp dissection instruments, different diameter wraparound tip aspirators, and different size Yasargil’s tumor grasping forceps bayoneted shaped.

Fig. 5.4 Basic set of Yasargil’s style stainless steel bipolar forceps.

The bipolar forceps provide accurate coagulation of bleeding areas in the scalp, muscles, dura, and intradural areas. Choosing the right lengths of bipolar forceps helps for delicate coagulation of brain tissue and tumor; furthermore, it permits arachnoid dissection and tumor manipulation, just adopting opening and closing maneuvers.

1- or 2-mm freer dissector or round-tip microdissector, are two important instruments. They are suitable for “blunt dissection”; indeed, they can be used for separating layers, vessels, and nerves, and surrounded tissue from tumor. In this scenario, the “water-jet” could be considered as one of the most elegant tool for dissection. Indeed, repeated injection of warm Ringer’s solution in the subarachnoid space is currently used for separating arachnoid membranes or tumor from surrounding tissue. ²²

The suction is a multifunctional tool, in both neurosurgeon hands. Indeed, it could be used by right and left neurosurgeon hand for suction, retraction, and dissection. In particular, the modern suction tubes combine an ergonomic, surgeon-friendly design with the freedom and flexibility of many different lengths and diameters (from 3 to 7 French), with wraparound tip to minimize tissue injury. The slim, lightweight handpiece reduces fatigue during long procedures, while providing precise, intraoperative suction control with thumb or forefinger.

Brain retraction can increase the surgical working area but, several reports have claimed that “retractorless surgery” is superior for preserving neural function. Indeed, patient positioning, cerebrospinal fluid (CSF) drainage, neuroanesthesia, and suitable uses of bipolar forceps, suction tubes, cottonoids, and other instruments, provide to constantly move out the brain off the surgical working area. However, in some cases (e.g., subfrontal approach), with the aid of microcottonoids to protect the brain, the intermittent use of gentle brain spatulas or self-retaining retractors (Greenberg retractor, Fukushima holder system, or Sugita-type retractors) offers the necessary operative space in the depth. ⁷

High-speed micro-drill with diamond-tipped burrs is fundamental to gently reduce the thickness of bones, such as the lesser and greater wing of the sphenoid in pterional or fronto-orbito-zygomatic approach, for increasing the surgical working area.

The Cavitron Ultrasonic Surgical Aspirator (CUSA) was introduced in neurosurgery approximately 30 years ago and, nowadays, it is a fundamental tool in modern OR ( ▶ Fig. 5.5). It is composed of an ultrasound generator, a sucker, and an irrigator that, together, combines aspiration, ultrasonic dissection, and irrigation in a single operation. The CUSA destroys selectively tissues with high water and low collagen content, so is used for fragmentation of solid tissues, such as meningioma, with relative sparing of vessels. Its widespread use is due to reduction of surgical time associated to respect of surrounding neural brain structures. ²³

Fig. 5.5 CUSA Excel ultrasonic surgical aspirator system. It allows the selective dissection of target tissues while preserving vessels, ducts, and other delicate structures.

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