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Robot-assisted endo- and transnasal surgery
The challenge of endo- and transnasal surgery
Endonasal surgery refers to surgery of the nasal cavities and sinuses, while transnasal surgery here refers to surgery using an endonasal approach to anatomic structures lying beyond the nasal cavities and paranasal sinuses: infratemporal fossa, endo-orbital structures anterior and ventral skull base, and petrous apex.
In current practice, endonasal surgery remains strongly affected by its origins: Messerklinger, Agrifolio and Terrier were modest in their aims, however innovative, seeking to approach the maxillary and sphenoid sinuses and ethmoid labyrinth using the recently developed panoramic endoscope. Despite the advantages of this new technique ( Figure 10.1 ), many teams long remained faithful to the operative microscope, especially for sphenoid and ethmoid surgery, as it enabled two-handed surgery. However, as surgeons mastered the technique, transnasal surgery came gradually to be extended to regions hitherto requiring external neurosurgical approaches, sometimes involving craniotomy and its sequelae. In France, Jankowski [ ] was probably the first to see that endonasal surgery had possibilities going beyond mere rhinology; he described a strictly naso-sphenoidal sellar region approach, opening the way to the advent of rhinoneurosurgery. Other teams, including those of Castelnuovo and Nicolai [ ] in Italy, Kassam, Carau and Snyderman in the United States [ ], and Herman in France [ ], realized and developed the possibilities of such surgery, pushing the bounds, refining indications and teaching the technique.
Despite tremendous progress in this field, endonasal surgery mostly relies upon the conventional instrumentarium of its earliest days, with few changes so far, the only noticeable exception being the advent of surgical navigation.
In this chapter, we will try to see how robotized systems could improve endonasal surgery and what attempts are being made in this direction.
What to expect from a robotized manipulator in endonasal surgery
As a general rule, robots are expected to be more accurate and possibly faster than surgeons. In endo- and transnasal surgery, some specific reasons suggest that a robot could improve the way that this surgery is currently performed.
Improving surgical workflow by restoring two-hand surgery
Analyzing the gestures of senior surgeons, even those highly skilled in this surgery, shows that a significant part of the procedure time is spent on tasks not directly consisting in dissecting or resecting tissue to be removed or repaired. Analyzing videos of real procedures ( Figure 10.2 ) shows that 20% to 50% of overall surgery time is spent aspirating accumulated blood to allow visualization of the surgical field, washing the field with water, and trying to find the right-shaped instrument for anatomical structures that are difficult of access. Another frequent difficulty is the impossibility of distracting tissue before cutting, a requirement obvious to any dressmaker. There is obviously much room for improvement in endo-transnasal surgery workflow.
It is strongly suspected that most of these limitations could be overcome by allowing the surgeon to use both hands rather than working single-handed. And it is reasonable to expect that improving surgical workflow could reduce total operating time.
Management of the introduction and removal of surgical instruments
The insertion of instruments inside the nasal tract is a tedious task that has to be done hundreds of times during a procedure. Each introduction can inflict trauma on the nasal mucosa, especially in the nasal vestibule, which usually cannot easily be seen directly or endoscopically. It is guessed that a surgical manipulator could speed up the introduction and removal of instruments while at the same time constantly controlling optimal orientation to minimize unwanted contact with the patient's nasal tract.
Managing several instruments simultaneously
While most open conventional surgeries use many instruments simultaneously for retracting, dissecting and sucking, conventional endonasal surgery is usually performed using a single instrument at a time, manipulated by the surgeon's dominant hand, while the non-dominant hand is devoted to endoscope manipulation. However, simultaneous use of several instruments is a powerful means to enhance surgical workflow, improve tissue dissection, and maintain a clean surgical field even when drilling bone.
Some authors suggest using both hands, with an assistant surgeon holding the endoscope [ ]. Although justified for sophisticated 2-surgeon 2-nostril procedures, this technique is unsuited to more common surgeries such as ethmoidectomy. Manipulating the suction cannula and forceps in the same hand has been suggested [ ], but with obvious limitations. Some static arms are available, with various locking technologies to hold endoscopes; but, being immobile once secured, they cannot adapt to the course of co-working instruments. Further, due to their static nature, they cannot move out of the endoscope when instruments are extracted from the nostril, and thus require special endoscopes with extended length to allow the normal manipulation of forceps [ ]. This makes them useful only in certain contexts, such as resection of a pituitary adenoma by a trans-sphenoidal approach.
Another significant expectation of robots is the possibility of letting them find the best possible instruments orientations so as to increase the number of those usable via the same nostril ( Figure 10.3 ). This is merely vector calculus, for which human beings have poor capabilities, unlike numerical systems which can very quickly and in real time compute the best solution if the anatomical space, instrument geometries and their current positions are known.
Navigation-based endonasal robotics
Except for neurosurgical transcranial approaches [ ], navigation has rarely been linked to robotics despite the very promising enhancement such an association could provide. We believe that endo- and transnasal robotic surgery is a perfect candidate for such combined technologies, providing the robot controller with a map so as to define which prerequisites have been to be taken into account to optimize safety and minimize trauma for the patient. This concept is exactly the same as the flight plan used in aerospace contexts.
Once a trajectory solution is provided by the computer, some spatial limits may be added as virtual fixtures obliging the robot to adjust its motion with respect to these boundaries with adjustable levels of priority: free area with maximum velocity allowed, unsafe area with limited speed, strictly forbidden areas.
While automated tissue segmentation ( Figure 10.4 ) is in a mature state [ ], the main current limitation to the development of this technology is our limited knowledge of how to model endonasal soft-tissue elasticity efficiently. Using the finite elements method (FEM), some studies of a simplified 3D biomechanical model to estimate forces and torques induced by deforming nasal tract soft tissues have been published, but no clinical evidence of the reliability of such a method has yet been demonstrated [ , ].
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