8.1
Introduction
Literature includes some studies about the use of an exoscope in neurosurgery, either as an exclusive instrument or in combination with the microscope.
The use of the operative exoscope has recently been introduced in head and neck surgery, and there are only a few studies in the literature regarding this kind of exoscopic surgery. Lateral skull-base surgery is traditionally performed mainly using the operative microscope, in some cases with endoscopic assistance.
Some of the limitations of the operative microscope are its large frame and its fixed cumbersome design. It also forces the primary surgeon and his assistants to have fixed positions around the operative field with limited visual angles. Moreover, the operative microscope screens oblige the assistants to follow the surgical procedure with a two-dimensional view because only the surgeon has a stereoscopic vision.
Conversely, endoscopic surgery allows for an ergonomic position of the surgeon with a horizontal gaze and an angled vision “behind the corner.”
Exoscopic surgery is a new surgical technique that has the purpose of using the exoscope to replace the microscope during surgical approaches, it requires the use of a classic two-handed surgery, as it happens in microscopic surgery, while looking at the monitor, where the exoscopic vision is shown.
Exoscopic surgery combines the features of an endoscopic surgical approach as the surgeon works looking at the monitor positioned in front of him/her and the microscopic surgical technique, because the surgeon works with two hands.
However, exoscopic surgery requires adequate training to learn the simultaneous coordination of the hands with the images appearing on the monitor. This technique needs previous training on endoscopic and microscopic surgery because the skills deriving from both techniques are necessary to perform surgery using the exoscope.
Exoscopes are produced by various companies and provide high-resolution imaging and two different kinds of view: two-dimensional (2D) or three-dimensional (3D).
In both the 2D and 3D exoscopes, the images are displayed on 4K high-definition monitors that can enhance anatomical details and make them more realistic.
A 2D exoscope has a 2D vision that is not overcome by the movement of the instrument in the surgical field, as it happens in endoscopic surgery, so it is especially used for video recordings and teaching reasons. On the other hand, the use of a 3D exoscope has 3D vision and allows both residents and fellows to follow the surgical procedure in the same way as the first surgeon.
This chapter is based on our experience with the VITOM 3D exoscope (Karl Storz GmbH, Tuttlingen, Germany) system on lateral skull-base surgical management. We will here describe the use of exoscopic surgery in the surgical treatment of lateral skull-base lesions.
8.2
Exoscopic approaches to lateral skull base
A 3D exoscope can be used as an operative tool to perform surgical procedures in the lateral skull base, replacing the microscope in the majority of cases.
Like every operative tool, the exoscope presents both advantages and disadvantages.
8.2.1
Advantages
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The use of a 3D exoscope provides the surgeon and his assistants with the same three-dimensional images. It allows fellows and residents to follow the surgery in the same way as the first surgeon
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The anatomical structures are more realistic and the recognition and differentiation of the structures are better through a 3D exoscopic view than through a microscopic one.
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It has a small frame with a large depth of field, which reduces the need to refocus during periods of dissection.
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Shifting from a microscopic to a macroscopic vision can be rapidly and easily done without moving the scope or completely losing microscopic vision.
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Its wide operative fields and focal distances are long enough to provide unobstructed operative corridors and enable the surgeon to have a considerable amount of mobility to work with the necessary tools.
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It allows for an ergonomic position of the surgeon with a horizontal gaze throughout the surgical operation. The horizontal gaze may be also maintained throughout surgery using an operative microscope; however, the use of fixed optics limits head and neck movement causing discomfort to the surgeon.
8.2.2
Disadvantages
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A high-intensity light can cause homogenization of the colors and the anatomical structures in the surgical field, so a proper regulation of the light is necessary.
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Lighting is low in the case of small surgical corridors, and pixelation can occur at high magnification in lateral skull base and mastoid surgery (e.g., in the case of posterior tympanotomy).
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The depth perception using a 3D exoscopic visualization at the highest magnification is inferior to the one provided by a standard operative microscope.
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Minimal dizziness, little nausea, fatigue, or vertigo have been described in some studies using a 3D vision during surgery.
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It provides a direct view of the surgical field, like the microscope while the endoscope allows visual control around corners.
In this complex area, both the microscope and the exoscope present the same difficult visualization of the hidden areas (medial to the tympanic and labyrinthine tracts of the facial nerve, medial to the vertical and horizontal segments of the internal carotid artery in the petrous bone). For this reason, it is often necessary to perform an endoscopic check of the surgical field with an angled endoscope at the end of the exoscopic or microscopic procedures to detect any potential residual pathology, which might be located in nonvisualized areas.
8.2.3
Exoscopic surgery of the lateral skull base: rationale
Lateral cranial base surgery often requires surgical skills, and a deep knowledge of the anatomy of the neck, the temporal bone, the petrous apex, and of the cerebellopontine angle (CPA). There are quite a few lateral skull-base pathologies; among them, the most frequent ones are acoustic neuromas, cholesterol granulomas, petrous bone cholesteatomas, temporal bone paragangliomas, facial nerve tumors, etc.
In most cases, the approaches to the lateral cranial base require the use of the operative microscope (translabyrinthine, transotic, transcochlear, middle cranial fossa, retrosigmoid approaches). Recently, exclusively endoscopic procedures have been introduced for few selected cases (transcanal transpromontorial approach for limited acoustic neuromas and transcanal suprageniculate approach for limited geniculate ganglion tumors or selected posttraumatic facial palsy for geniculate ganglion injury).
In many cases, because of the complex anatomy, in the same patient, the procedure requires the management of the neck and the temporal bone anatomy, performing a surgical step on the neck to isolate the major blood vessels and the extracranial tract of the nerves, at the exits from the foramina.
After the neck surgical step, it is possible to perform a wide microscopic demolition of the temporal bone to reach the pathological process. A typical example is Type A infratemporal fossa approach that is used for the management of lesions located at the level of the jugular foramen. During these procedures, the microscope is used only during the demolition of the temporal bone.
The introduction of exoscopic surgery has allowed the surgeon to replace the microscope during the demolition of the temporal bone and to perform the surgical steps in the neck with the same surgical instruments, with a more precise surgical outcome, through a 3D view.
Currently, a few studies are present in the literature, but a new promising surgical technique has been introduced for the management of the complex lateral skull-base pathological processes.
8.2.4
Operating room setup
VITOM 3D exoscope (Karl Storz GmbH, Tuttlingen, Germany) is used as an operative tool in lateral skull-base surgery. The system consists of a holding arm for VITOM 3D placed in front of the surgical field (at a distance of 20–50 cm). This is a full HD 3D, 16: 9 modular video system, stereoscopic optics with high-resolution image sensors (4K) and 8–30× magnification. The image is shown on a 3D monitor using the appropriate passive glasses.
The 3D 4K screen is placed in front of the surgeon allowing a direct view during surgery. The surgeon and the assistants wear 3D glasses or clip-on glasses for those wearing corrective glasses ( Figs. 8.1 and 8.2 ).
There is a control unit (IMAGE PILOT), to either regulate the focus or to enlarge or shift the field of view. The latter is located next to the surgeon and kept in place by another holding arm. An assistant or the surgeon usually handles the control unit. If the assistant handles the control unit, the surgeon can focus only on the surgical procedure.
The surgical scrub nurse is on the opposite side of the operating table to the surgeon in front of a second 2D screen, while the anesthesiologist is at the foot of the operating bed ( Fig. 8.3 ).
8.2.5
Surgical approaches to lateral skull base
The exoscope is best suited for approaches with a large surgical field, rather than for small surgical corridors, as in these cases it allows for an optimal replacement of the microscope.
Therefore, the surgeon works by looking at the high-definition monitor (4K) located in front of him/her (as it happens in endoscopic surgery) with a 3D view (as in microscopic surgery) working with two hands. Obviously, 3D exoscopic surgery requires adequate training.
From our experience, the surgical steps on soft tissue, bone tissue, and pathology dissection are easily feasible exclusively using the 3D exoscope instead of the traditional microscope in most of the procedures concerning the lateral skull base, as in the majority of these procedures a large surgical field without narrow corridors is required.
Transpetrous approaches can be divided as follows ( Fig. 8.4 ):
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Posterior: retrosigmoid approach.
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Lateral: retrolabyrinthine or presigmoid, translabyrinthine, transcochlear/transotic, transcanal transpromontorial, Fisch infratemporal fossa approach (type A, B, C, D approaches), subtotal petrosectomy.
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Anterior: middle cranial fossa approach, anterior petrosectomy.
Some of these approaches do not require a large surgical corridor, so exclusive exoscopic surgery is not as effective as the microscope for them (e.g., retrosigmoid approach), while for lateral and anterior transpetrous approaches the exoscope can replace the functions of the microscope. As it happens for microscopic surgery, exoscopic surgery, in some of transpetrous approaches, also needs an endoscopic assistance to explore the hidden areas and exclude any residual pathological process at the end of the procedure.
8.2.5.1
Type A, B, and C Fisch infratemporal fossa approaches
Type A Fisch infratemporal fossa (IFT) approach provides a good exposure of the jugular foramen area, and it is performed for benign or malignant tumor removal of this area (mostly benign tumors of the skull base, such as schwannomas or paragangliomas) ( Figs. 8.5–8.13 ).
