Computer Modeled Multiportal Approaches to the Skull Base

Surgical approaches to the skull base have evolved significantly to minimize collateral tissue damage and improve access to complex anatomic regions. Technological advancements in optics and materials have mirrored and been critical in enabling this progress. Recently, transorbital portals that allow safe, direct pathways to skull base pathology have been described. These offer opportunities to approach regions that were previously inaccessible endoscopically. These can be combined in multiportal approaches that allow improved angles for visualization and instrumentation, thereby optimizing the ability to safely achieve the surgical goal. The decision of which portal and pathway to use to access a target is becoming more complex as more options are becoming available.

To assist in this decision making, a 3-dimensional computer model was created to analyze transorbital and transnasal surgical approaches. Pituitary targets were modeled as they are relatively common, and the standard treatment involves surgical resection, often via a transnasal or open approach. Eleven specific regions were defined around the pituitary gland as locations that would typically demand an open craniotomy approach in the surgical treatment. Virtual surgery was performed on 10 adult CT scans with normal skull base anatomy to access the 11 regions through multiportal endoscopic approaches. Data were collected on length of approach, angle between instruments, instrument collision, and approach angle to the target plane. Optimal configurations of instruments and endoscope portals were derived using the computer model. Four cadaver dissections were performed with navigation to validate the measurements and feasibility of the surgical approaches.

The data demonstrated that in many cases the shortest, most direct pathway to pituitary targets was through transorbital portals. For example, the length of the pathway to the posterior chiasmatic region was 105 mm through a transnasal portal, compared with 75 mm using the precaruncular transorbital approach. The addition of transorbital portals allowed the angle between instruments to increase substantially. In the case of accessing the lateral cavernous sinus, the angle between two transnasal instruments was 12 degrees. Adding a precaruncular transorbital port increased that angle to 31 degrees, and adding a lateral retrocanthal portal increased it to 56 degrees.

Depending on the location of the pathology, multiple configurations are possible to maximize target visualization and instrumentation. A computer model may play an important role in surgical planning as complex multiportal endoscopic approaches become more common in the treatment of skull base pathology.