Entry-based Planning of Neurosurgical Trajectories

Abstract

Purpose In cases of brain trauma or hydrocephalus an external ventricular drain (EVD) is often inserted through the skull and brain to drain excess cerebrospinal fluid from the ventricles to relieve pressure. Most often, EVDs are inserted free-hand, without guidance, at a point on the skull named Kocher’s point, perpendicular to the skull surface. Previous freehand EVD insertion studies have reported insertions in ideal target locations in only 40-50% of cases. We developed a visualization method to identify regions on the skull surface that will result in successful intersection with the ventricles during the ventriculostomy procedure, while also allowing for pre-calculated uncertainties in the trajectory. Methods Using preoperative head CT scans, we estimated entry sites on the skull surface giving surgeons the best chance of reaching the ventricles, while incorporating uncertainty between 5 and 10 degrees. We performed a technical feasibility trial on 60 retrospective ventriculostomy patient cases consisting of hydrocephalus and traumatic brain injury patients and compared to 30 retrospective asymptomatic patient cases. The method was evaluated by calculating the portion of trajectories still feasible after incorporating uncertainty, and by comparing the calculated average catheter length to the typical catheter length measured in ventriculostomy studies. Results There was no significant difference in hit rate (HtR) between hydrocephalus and trauma patients for the region of high accuracy and the region of high dispersion (p = 0.49, 0.32). There also was no significant difference in catheter length between hydrocephalus and trauma patients for the region of high accuracy (p = 0.17) and the region of high dispersion (p = 0.16). Conclusion A new planning system to perform ventriculostomies was created to help facilitate decision-making in regard to the site of insertion of EVDs. The visualization tool identifies new insertion sites but also confirms the validity of existing insertion sites used in the current standard of care. The average simulated catheter length measured falls within the accepted depth at which EVDs are measured to be inserted into the brain.