19 3D Stereoendoscopic Pituitary Surgery*

Seth Brown, Vijay K. Anand, Jonathan Roth, and Theodore H. Schwartz

Recent years have seen a rapidly growing interest in both endoscopic and robotic surgery, not only in neurosurgery and otolaryngology, but also in nearly every surgical field. Advances have facilitated increasing surgical precision and decreasing operative times in select procedures. The early results of endoscopic pituitary surgery, in terms of length of stay, tumor control, and complications, compare favorably with microscopic surgery.^1–6 Additionally, endoscopic pituitary surgery allows for preservation of important nasal structures including the turbinates, the olfactory fibers, and the anterior septum to maximize sinonasal function postoperatively. Neurosurgeons performing endoscopic pituitary surgery are quite familiar with the excellent visualization an endoscope provides because of the ability to bring light to the source of the lesion, as well as the ability to look “around the corner” via angled scopes. Essentially, the endoscope addresses some of the limiting factors of traditional transsphenoidal surgery: the long, narrow operative corridor, which limits the field of view, and the inability to adequately assess extension of the pathology behind and around critical neurovascular structures. Despite these advances, conversion of many neurosurgeons to this technology has been limited, due partly to the nature of monocular vision of endoscopes. Monocular endoscopes create a two-dimensional (2D) image that impairs the surgeon’s perception of depth, spatial relations, and the size of the anatomical structures.^7,8

The majority of practicing neurosurgeons were trained to perform transsphenoidal surgery with the aid of a microscope, allowing for binocular vision. Using an endoscope requires surgeons to train their hand–eye coordination to respond to visual cues received by the interaction of the operative instruments within the environment to accurately understand the relative depth of structures in the 2D projection. This leads to steeper learning curves for trainees, such as residents and neurosurgeons, attempting neuroendoscopic procedures.

There is little debate that depth perception is of the utmost importance in many surgeries. Depth perception is thought to be critical to precise motor movement. This has been demonstrated in one study that showed the primary cause of error in laparoscopic surgery is secondary to a visual perceptual illusion.⁹ Perhaps the best device would be one that has the capacity of the endoscope to provide a minimally invasive approach to the tumor with a panoramic viewing capacity, yet provides the surgeon with depth perception to judge tumor size and location in reference to surrounding structures. This would more closely mimic direct vision, which remains the gold standard in task completion.⁸

The distinct aspects of the control of fine surgical movements involve initiation of a gross movement in the general desired direction, followed by multiple correctional movements that are modified based on a combination of visual cues.¹⁰ The number of required movements and accuracy of each movement are affected by the clarity of the visual feedback and experience of the surgeon. In endoscopic surgery, tactile cues must be obtained via long instruments. This, combined with 2D visualization, represents a significant barrier to efficient and accurate movements. The acquisition of endoscopic skills inherently involves the ability to translate a 2D image into a mental three-dimensional (3D) representation of a given area. This occurs partially through monocular signals, including variations in color, size, and overlap between the various displayed objects. Trained surgeons also learn to infer spatial relations from haptic cues and surgical movements. Despite these compensatory factors, 2D visualization does not match the depth perception afforded by binocular cues, including vergence, stereopsis, and vertical disparities.¹¹ Studies of human kinematics have demonstrated the negative consequences of monocular vision, including longer movement times and a tendency to underestimate distances between objects.¹²

Initial studies comparing 2D to 3D in surgical task completion have been performed based on laparoscopic procedures. In using direct vision as a baseline, researchers have found a significant decrease in the “endoscopic handicap” both in novice and experienced surgeons using 3D as compared with 2D endoscopes.⁸ Furthermore, even physicians used to 2D surgery are able to complete motor skill tasks faster with binocular vision.¹³ Studies have also shown that 3D vision reduces performance time and error rates in surgical tasks for both resident and attending surgeons^7,14 This appears to be more sensitive as tasks increase in complexity.¹⁵ In looking at vascular anastomosis, 3D vision was found to facilitate quicker and more precise movements, reducing surgical times.¹⁶ Other studies have demonstrated a benefit in speed, efficiency, and learning when using the 3D as compared with the 2D scopes.7,8,17 These findings of reduced surgical times and improved efficiency have been replicated in a study comparing 2D and 3D endoscopic visualization in a model of endoscopic skull base surgery using a group of practicing skull base surgeons and residents performing surgical tasks designed to simulate the transsphenoidal surgery environment.¹⁸

Nevertheless, surgeons with significant experience in 2D endoscopic surgery overcome these limitations by using visual and tactile cues. Hence, as demonstrated in other studies, the 3D stereoendoscope makes a more significant difference for novice users.^8,14,17–21 Likewise, several independent laboratories and clinical studies using experienced laparoscopic surgeons reported improved subjective depth perception but failed to identify any difference in task performance using 2D versus 3D visualization.^22–24 Therefore, it is likely that the greatest impact of a 3D stereoendoscope would be in decreasing the learning curve for new users. In fact, experienced 2D endoscope users may actually find the 3D scopes disorienting if they are used to working with 2D scopes. For these reasons, it can be difficult to find any objective significant endpoints when comparing experienced user outcomes between 2D and 3D scopes.

Although stereoendoscopes exist, their use in neurosurgery has been limited based on the larger diameter and poor resolution of earlier generations.^7,8,17 Consequently, only one report exists of using stereoendoscopes in neurosurgery and only as an adjunct to the microscope.²⁵ It appears that this technology, though slow to enter the mainstream due to some of the limitations described previously, could become the wave of the future for all endoscopic procedures if de-signed with some minor changes in specifications.

Three-Dimensional Technology

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