Abstracts

Rationale:
The use of SEEG for invasive intracranial monitoring has gained popularity in many centers around the world. As in other stereotactic procedures, correct placement of the electrodes is essential for diagnosis, treatment, and avoidance of complications. Registration in frame-based systems is a critical step to ensure the accuracy and  is routinely done by merging a CT scan with the preoperative MRI. 3D fluoroscopy (XT) has emerged as a method for intraoperative electrode localization following implantation and more recently has been shown to be useful in the registration process with some advantages over the CT such as decrease radiation dose, and avoidance of transportation of the patient to the radiology department. To date there are no studies comparing the two modalities for frame-based registration in SEEG surgery.
Method:
During the last year, our group has implemented the use of a portable intraoperative XT imaging system (Medtronic OARM®) for registration of all stereotactic procedures. A retrospective analysis was done to compare the accuracy of SEEG electrode placement by registration with CT and XT imaging. We analyzed the Euclidean distance between planned and post-implantation trajectories to calculate the error in both the entry point (EP) and target point (TP) for each electrode. Other variables evaluated included radiation dose measured by the dose length product (DLP), time of registration (defined as the time anesthesia started to skin incision) and complications. A one-way ANOVA was used for statistical analysis.  
Results:
Twenty-seven patients, 13 in the CT group and 14 in the XT group,  underwent placement of SEEG electrodes for investigation of refractory epilepsy. In total, 319 electrodes were implanted, 157 in the CT group and 162 in the XT group, with a mean of 12 electrodes per patient in both groups.  The mean EP and TP errors for the CT group were 2.3 mm and 3.3 mm, respectively. In the XT group the errors were calculated to be 1.9 mm and 2.9 mm, with no statistically difference between groups (p=0.75 and p=0.246). The registration time was similar in both groups (XT group, 82±10 min; CT group, 84±22 min (p=0.858). The average radiation exposure with XT (234±55 mGy*cm) was significantly lower than CT (1245±123 mGy*cm) (p< 0.000). Four complications were documented, 2 patients in each group had intracranial hemorrhage on the postop CT, but only one was symptomatic with a transient headache and no neurological deficits.
Conclusion:
The use of XT as a method for registration in frame-based SEEG resulted in similar implantation accuracy compared with CT. Overall accuracy of frame-based SEEG was 2.1 mm for EP and 3.1 mm for TP which is in concordance with previous studies. Incidence of complications was similar in both groups and was consistent with previous reports for SEEG surgery. The main advantages of XT are the substantial reduction in radiation dose and the elimination of the need to transfer the patient out of the room which may have an impact on patient safety and OR efficiency.
Funding:
:No