Anatomic Skull Base Education Using Advanced Neuroimaging Techniques

Peer-Review Reports

Anatomic Skull Base Education Using Advanced Neuroimaging Techniques Matteo de Notaris1,2, Thomaz Topczewski1, Michelangelo de Angelis 3, Joaquim Enseñat1, Isam Alobid 4, Amer Mustafa Gondolbleu 2, Guadalupe Soria5, Joan Berenguer Gonzalez 6, Enrique Ferrer1, Alberto Prats-Galino2

Key words 䡲 3D anatomy 䡲 Endoscopic endonasal approach 䡲 Neuroanatomy 䡲 Pituitary surgery 䡲 Skull base surgery 䡲 Suprasellar area 䡲 Surgical anatomy 䡲 Transsphenoidal surgery Abbreviations and Acronyms 3D: Three-dimensional From the 1Department of Neurosurgery, Hospital Clinic, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain; 2Laboratory of Surgical Neuroanatomy (LSNA), Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain; 3 Università degli Studi di Napoli Federico II, Department of Neurological Sciences, Division of Neurosurgery, Naples, Italy; 4 Department of Otorhinolaryngology, Rhinology Unit, Hospital Clinic de Barcelona, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain; 5Department of Brain Ischemia and Neurodegeneration, Institut d’Investigacions Biomèdiques de Barcelona (IIBB)–Consejo Superior de Investigaciones Científicas (CSIC), Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain; 6Department of Radiology, Neuroradiology Division, Hospital Clinic, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain To whom correspondence should be addressed: Matteo de Notaris, M.D. [E-mail: [email protected]]. Citation: World Neurosurg. (2013) 79, 2S:S16.e9-S16.e13. DOI: 10.1016/j.wneu.2012.02.027 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2013 Elsevier Inc. All rights reserved.

INTRODUCTION History of Surgical Education Surgical education has always been an exciting, challenging, and dynamic discipline. It has a long history of innovative transformations that dramatically improved the way patients were treated and surgery was practiced. A variety of more or less formal educational practices have evolved over time. Above all, the dissection laboratory provides a venue to demonstrate technique and enhance surgical skills. Indeed, cadaveric dissection still remains the gold standard for training

䡲 OBJECTIVE: The goal of the present article was to describe our dissection training system applied to a variety of endoscopic endonasal approaches. It allows one to perform a 3D virtual dissection of the desired approach and to analyze and quantify critical surgical measurements. 䡲 METHODS: All the human cadaveric heads were dissected at the Laboratory of Surgical Neuro-Anatomy (LSNA) of the University of Barcelona (Spain). The model surgical training protocol was designed as follows: 1) virtual dissection of the selected approach using our dissection training 3D model; 2) preliminary exploration of each specimen using a second 3D model based on a preoperative computed tomographic scan; 3) cadaveric anatomic dissection with the aid of a neuronavigation system; and 4) quantification and analysis of the collected data. 䡲 RESULTS: The virtual dissection of the selected approach, preliminary exploration of each specimen, a real laboratory dissection experience, and finally, the analysis of data retrieved during the dissection step was a complete method for training manual dexterity and hand– eye coordination and to improve the general knowledge of surgical approaches. 䡲 CONCLUSIONS: The present model results are found to be effective, providing a valuable representation of the surgical anatomy as well as a 3D visual feedback, thus improving study, design, and execution in a variety of approaches. Such a system can also be developed as a preoperative planning tool that will allow the neurosurgeon to practice and manipulate 3D representations of the critical anatomic landmarks involved in the endoscopic endonasal approaches to the skull base.

physicians in the field of neurosurgery. Computer simulation cannot substitute the study in a dissection laboratory, because the latter provides a unique experience with a wide range of sensorial inputs (4). Nevertheless, the way of teaching surgical anatomy has been markedly influenced by the rapid development of neuroimaging techniques that have opened new possibilities for learning anatomy and simulating interventions. At the same time, nothing could have prepared the surgical community for the revolutionary advances of the past three decades. Indeed, as a result of the extraordinary technological advances, the concept of minimally invasive surgery has replaced the classic and unquestioned “open” approach in every field of surgery. In the same way, the features of anatomic dissection labora-

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tories have changed, being upgraded by modern imaging systems: nowadays, peer knowledge of anatomy as well as a detailed, complete preoperative planning via imaging can be considered equal contributors for a successful surgical procedure. Various efforts have been made to improve surgical education and training. As interest in the development of technical skills training laboratories has grown in the recent years, several investigators have worked to develop methods to objectively evaluate surgical skill and to improve dissection techniques and instrumentation (1-3, 8, 10, 11, 13, 15-17). Currently, classical training methods such as cadaver dissection and modeling techniques are being combined by modern software systems that emphasize three-dimensional (3D) ana-

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PEER-REVIEW REPORTS MATTEO DE NOTARIS ET AL.

ANATOMIC SKULL BASE EDUCATION

Figure 1. (A) Scheme of the workstation at the laboratory. The microscope and endoscope are connected to the video and photo camera to acquire the images and simultaneously connected to the work screen and the computer workstation for the acquisition and editing of images during the final work process. (B) Position of the screws as permanent bone markers

tomic relationships using advanced neuroimaging techniques (6, 12). In the current chapter, we describe our novel laboratory-based surgical training method integrated with a computer-based 3D anatomic model for the study and analysis of endoscopic endonasal approaches to the skull base. The use of this model for other skull base approaches has been reported previously by our group (7).

MATERIAL AND METHODS Dissections were performed at the Laboratory of Surgical Neuroanatomy in the Department of Human Anatomy and Embryology, Faculty of Medicine, University

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for the neuronavigation step. (C) Photograph showing the laboratory during one of the dissection process. The work screen and the neuronavigation system are connected to the microscope or endoscope. (D) Photograph during the execution of the endoscopic endonasal approach with the aid of the neuronavigation system.

of Barcelona (Barcelona, Spain). Endoscopic endonasal approaches were performed using a rigid endoscope 4 mm in diameter, 18 cm in length, with 0-degree optics (Karl Storz, Tuttlingen, Germany). The endoscope was connected to a light source through a fiberoptic cable and to a camera (endovision Telecam SL; Karl Storz) fitted with three charge-coupled device sensors. A real-time digital recording and editing system allowed creating high-definition videos and photos of the entire dissection process. An integrated network connection provided for secure remote connectivity between the dissection laboratory and other postproduction offices within the department (Figure 1A).

Before dissection, all specimens underwent a multislice helical computed tomographic scan (SOMATOM Sensation 64, Siemens, Forchheim, Germany) with axial spiral sections 0.6 mm thick and a 0-degree gantry angle. To allow the coregistration with the neuronavigation system, five screws were implanted in the skull as permanent bone reference markers. Three screws were positioned on the midline: the first was set 2 cm above the nasion (on upper horizontal plane), the second screw was set 5 cm above the first, and the third screw was set 5 cm behind the second; two other screws were set 3.5 cm lateral to the first on the upper rim of the orbit (Figure 1B). Image data were transferred to the laboratory navigation planning workstation (Figure 1C)

WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2012.02.027

PEER-REVIEW REPORTS MATTEO DE NOTARIS ET AL.

ANATOMIC SKULL BASE EDUCATION

Figure 2. Virtual computer-based 3D models of areas of the different endoscopic endonasal approaches to the midline skull base and cavernous sinus. Red, Transcribiform approach; pale blue, transplanum/transtuberculum approach; yellow, sellar approach; dark blue, transclival approach; purple, craniovertebral junction approach; green, cavernous sinus approach. (A) Posterolateral view. (B) Anterior view. (C, D) Endonasal anteroinferior perspective.

Figure 3. A virtual preoperative exploration of each specimen using the 3D endoscopy module supported by the OsiriX software. (A) Before entering the left nostril. (B) Exposure on the nasal septum and left inferior

and point registration was performed using the bone-implanted fiducials. A registration correlation tolerance of 2 mm was considered acceptable. Thereafter, the approach can be performed in the dissection laboratory (Figure 1D). Once the surgical approach was chosen, a virtual dissection was performed using an in-house interface designed through specific imaging software for the manipulation of biomedical data (Amira Visage Imaging Inc., San Diego, California, USA). Our system allows to select between varieties of skull base approaches and to perform a step-by-step virtual dissection (Figure 2). After that, a preliminary analysis of the pre-dissection computed tomographic scan was performed using an open-source software for navigating in multidimensional DICOM images (Osirix, Advanced Open-Source PACS Workstation DICOM viewer) to meaningfully evaluate the anatomic individual variability (Figure 3). After the dissection step in the anatomic laboratory, a postprocessing quan-

turbinate. (C) The left choana is reached. (D) The sphenoethmoidal recess is disclosed moving the endoscope upward.

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ANATOMIC SKULL BASE EDUCATION

Figure 4. Computed tomographic scan showing the calculation of linear and angular measurements. (A) Distance between the pterygoid canals at level of the intrapetrous carotid canal. (B) The angle between the anterior skull base and the limbus sphenoidale.

tification and analysis of data was performed using the points recorded during the dissection procedure to improve the general knowledge of the surgical approaches. Thereafter, a virtual 3D model of the same specimen was created using the

same imaging software as in the first step (Amira). Bony structures were segmented from DICOM images using a semiautomatic thresholds-based procedure, and then a smoothing function was applied to further refine the rendering of the bony surfaces. Later on, on the segmented bone,

different volumes of interest were labeled using a 3D editor so that a computerized surgical geometric triangular model was created automatically. Linear and angular measurements were taken directly on the 3D model (Figure 4A and B). Planar and spherical measurements, mainly used in the field of quantitative analysis, were employed to compare between different approaches (5, 9, 14). The quantitative analysis of every approach was calculated using our in-house developed 3D model based on two main parameters: 1. Area of exposure: considered as the maximal region defined on specific deep anatomic landmarks that can be exposed using a definite surgical approach (Figure 5A and B). 2. Surgical freedom: considered as an estimate of the movement available to the surgeon’s hands and instruments, represented by a partial spherical area through which surgical instruments can be inserted to manipulate a deep target (Figure 5C and D).

Figure 5. Planar and spherical measurements obtained using the three-dimensional reconstruction modules supported by the Amira software. (A) Virtual computer-based multiplanar reconstruction with measurement of area of exposure for the endoscopic endonasal approach to the sellar region. (B) Virtual computer-based sagittal reconstruction disclosing the representation of the area of exposure for the endoscopic endonasal approach to the sellar region. (C) Virtual computer-based reconstruction of the surgical freedom obtained for a point at the level of the tuberculum sellae during an endoscopic endonasal approach. (D) Volume rendering of the same specimen as in C to demonstrate the surgical route through the right nostril.

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DISCUSSION In the current chapter, we have developed a model for the surgical training in the anatomic laboratory based on three main principles: cadaver dissection, virtual surgery simulation system, and postdissection analysis and quantification of data.

WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2012.02.027

PEER-REVIEW REPORTS MATTEO DE NOTARIS ET AL.

Cadaver Dissection The skull base surgeon requires specific training to achieve competency in neurosurgery. Basic skills such as craniotomies, craniectomies, and advanced drill techniques should be acquired during an irreplaceable cadaver dissection experience. Once acquired, these fundamentals skills also can be learned on 3D advanced simulations but dissection on cadavers still remains a valuable experience that one cannot afford to miss even in this era of great medical advances. Virtual Surgery Simulation System During endoscopic endonasal approaches, the operative field is viewed by means of an endoscope in which a small camera relays a video signal to a two-dimensional monitor. During endoscopic surgery, however, the surgeon’s direct view is often restricted, thus requiring a higher degree of manual dexterity. The complexity of the instrument controls, restricted vision and mobility, and difficult hand– eye coordination are major obstacles in performing such procedures. To date, a number of techniques have been developed for the assessment of manual dexterity and hand– eye coordination with the combined use of virtual and mixed reality simulators. These environments offer the opportunity for safe, repeated practice and for objective measurement of performance. Intermediate and advanced skills require simulations using more sophisticated models such as 3D advanced neuroimaging techniques and virtual reality computerized systems. Postdissection Analysis and Quantification of Data This step provides the actual quantification of the approach realized in the dissection laboratory. Data analysis is a fundamental step toward interpreting and critiquing results. In our experience, the data analysis improves the general knowledge and gives us the opportunity to compare skull base surgical approaches.

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CONCLUSIONS

dimensional microsurgical and tractographic anatomy of the white matter of the human brain. Neurosurgery 62(6 Suppl 3):989-1026 [discussion 1026-1028], 2008.

The present model is very effective, providing a depiction of anatomic landmarks as well as a 3D visual feedback, thus improving the study, design, and execution in a variety of endoscopic endonasal approaches to the skull base. Such a system can also be developed as a preoperative planning tool that can allow the neurosurgeon to perceive, practice reasoning, and manipulate 3D representations of the anatomy.

10. Fraser JF, Allen B, Anand VK, Schwartz TH: Threedimensional neurostereoendoscopy: subjective and objective comparison to 2D. Minim Invasive Neurosurg 52:25-31, 2009.

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received 23 September 2011; accepted 03 February 2012

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Citation: World Neurosurg. (2013) 79, 2S:S16.e9-S16.e13. DOI: 10.1016/j.wneu.2012.02.027 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com

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