Abstracts

Rationale: Subdural implantation of electrodes is commonly performed to localize an epileptic focus in preparation for resective surgery. Although generally safe, complications are not uncommon and techniques vary between centers. Whether to temporarily explant or leave implanted the bone plate and whether to employ peri-operative steroids is unclear. Methods: We retrospectively reviewed records on all unilateral intracranial implants performed between November 2001 and June 2011. Patients were divided into three groups: Group 1: (n=24) Bone explanted, no peri-operative steroids; Group 2: (n=42) Bone implanted, no peri-operative steroids; Group 3: (n=25) Bone implanted, given peri-operative steroids. Rates of infection, time to first seizure, number of seizures in first three days, severity of headache in first three days, midline shift and size of subdural hematoma on post-operative CT scan, and rate of emergency re-operation were correlated with each group using ANOVA, Fisher's exact and Generalized Estimating Equation (GEE) statistics. Results: Out of a series of 324 cranial epilepsy surgeries, there were 91 unilateral implants, of which 86 met inclusion criteria. Average (SD) number of seizures in the entire monitoring sessions was 4.7 (8.3), and 66.3% of patients had a seizure within the first three days. Headaches were severe in 33.7%, and 18.7% had > 4 mm midline shift. 41.8% of patients had a subdural hematoma > 10 mm in thickness, the rate of early re-operation was 7.7%, and the rate of infection was 12.1%. There was a statistically higher rate of infection when the bone was explanted (33.3%) compared with when the bone was left in place (4.5%; p<0.01). Leaving the bone in place also increased the number of seizures and decreased the time to first seizure but also increased the size of the subdural hematoma, although there was no increase in midline shift, severity of headache or emergency re-operation. The use of steroids did not appear to have any effect on any of our outcome measures. Conclusions: Temporary bone flap explantation during craniotomy for implantation of subdural electrodes can result in high rates of infection, possibly due to the frequent change of hands in transferring the bone to the bone bank. Leaving the bone in place may increase the size of subdural hematoma and frequency of seizures but does not increase the rate of complications. These results may be institution-dependent.