Intraoperative 3D Navigation Using Virtual Endoscopy for Endoscopic Transsphenoidal Pituitary Surgery

Objective: Virtual endoscopy has been successfully applied for preoperative planning of endoscopic transsphenoidal approaches. This advanced visualization method provides a pseudo-3D view of the nasal and sinus anatomy and displays important anatomic objects behind the transparent walls of the sphenoid sinus cavity, such as the pituitary gland, tumor, and internal carotid arteries. The intraoperative application of virtual endoscopy may therefore enhance the safety of the procedure. This project was designed to implement a virtual endoscopy system to standard neuronavigation to provide enhanced visualization feedback intraoperatively.

Patients and Methods: The existing system STEPS (simulator for transsphenoidal endoscopic pituitary surgery) uses computed tomography radiographic data for calculation of the virtual endoscopy images via a first-hit ray-casting algorithm. For delineation of background anatomic objects, magnetic resonance T1-weighted, contrast-enhanced imaged data (for pituitary gland and tumor) or magnetic resonance angiography (for internal carotid artery anatomy) was applied. Intraoperatively, STEPS was connected to the Medtronic Stealth Station using the Stealth Link interface. The spatial position coordinates of the endoscope and a surgical instrument were transmitted from the navigation software to a stand-alone personal computer running STEPS. The virtual images were created using a 120-degree viewing angle from the tip of the endoscope, and the position of the instrument was visualized by superimposed crosshairs. The STEPS software was adapted to solve issues such as registration, calibration, and deviations between virtual and real anatomy.

Initially, a pilot study on a cadaver specimen was performed. Then, the system was tested during endoscopic transsphenoidal interventions on 10 patients with sellar pathologies (9 pituitary adenomas, 1 craniopharyngioma).

Results: During the period of this study, STEPS was advanced to an intraoperative, fully applicable system for virtual endoscopy. Additional time expenditure for system setup was minimal.

The intraoperative real-time 3D images proved beneficial for direct guidance to the sphenoid ostium; for 3D delineation of the individual patient anatomy, which was especially useful in cases of reoperations with distorted anatomy; and for placing an optimally tailored opening of the sellar floor in relation to the pathology, pituitary gland, and internal carotid arteries.

Conclusion: According to our experience, intraoperative application of virtual endoscopy is feasible. By 3D delineation of individual patient anatomy, this advanced navigation method may add to the safety of the procedure.