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  • Author or Editor: Eric M. Thompson x
  • By Author: Selden, Nathan R. x
  • By Author: Roberts, Colin M. x
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Eric M. Thompson, Gregory J. Anderson, Colin M. Roberts, Matthew A. Hunt and Nathan R. Selden

Object

Surgery to monitor and resect epileptogenic foci may be undertaken in 2 stages, providing an opportunity to use skull-fixated fiducials implanted during the first stage to improve the accuracy of cortical resection during the second stage. This study compared the intrinsic accuracy of skin-based and skull-fixated fiducial markers in registering frameless stereotaxy during pediatric epilepsy surgery. To the authors' knowledge, these modalities of registration have not previously been directly compared in this population.

Methods

The authors undertook a retrospective review of pediatric patients who underwent resection of epileptogenic foci in 2 stages with frameless stereotactic assistance, performed by a single surgeon at Oregon Health & Science University. For the first stage (subdural grid implantation), 9 skin fiducial markers were used to register anatomical data in a frameless stereotactic station. Intraoperatively, four 3-mm screws were placed circumferentially around the craniotomy. Postoperatively, thin-slice brain MR and CT images were obtained and fused. For the second stage, the 4 screws were used as fiducial markers to register the stereotactic anatomical data. For both stages, accuracy (difference in millimeters from zero of the manual fiducial registration compared with the computer model) was determined using navigation software. The intrinsic accuracy of these 2 methods of fiducial registration was compared using a paired Student t-test.

Results

Between 2004 and 2009, 40 pediatric patients with epilepsy underwent frameless stereotactic surgical procedures. Fourteen patients who had 2-stage procedures using skin-based and skull-fixated registration with complete accuracy data were included in this retrospective review. Mean registration error was significantly lower using skull-fixated fiducials (1.35 mm, 95% CI 1.09–1.60 mm) than using skin-based fiducials (1.85 mm, 95% CI 1.56–2.13 mm; p = 0.0016).

Conclusions

A significantly higher degree of accuracy was achieved using 4 skull-fixated fiducials compared with using 9 skin-based fiducials. This simple and accurate method for registering frameless stereotactic anatomical data does not involve the potential time, expense, discomfort, and morbidity of extraoperative skull-fixated fiducial placement. The method described in this paper could also be extrapolated to other planned 2-stage cranial surgical procedures such as combined skull base approaches.

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Eric M. Thompson, Susan E. Wozniak, Colin M. Roberts, Amy Kao, Valerie C. Anderson and Nathan R. Selden

Object

Vagus nerve stimulation (VNS) is approved by the FDA for the treatment of partial epilepsy in patients older than 12 years. Authors of the current study performed a large retrospective analysis and comparison of VNS outcomes in children with an age ≥ and < 12 years, including those with partial and generalized epilepsy.

Methods

A retrospective review of the records of pediatric patients (age < 18 years) who had undergone primary VNS system implantation between 2001 and 2010 by a single pediatric neurosurgeon was undertaken. Considered data included demographics, epilepsy type (partial vs generalized), seizure frequency, seizure duration, postictal period duration, and antiepileptic medication use.

Results

One hundred forty-six patients (49% female) were followed up for a mean of 41 months after VNS implantation. Thirty-two percent of patients had partial epilepsy and 68% had generalized epilepsy. After VNS system implantation, seizure frequency was reduced in 91% of patients, seizure duration in 50%, postictal period in 49%, and antiepileptic medication use in 75%. There was no significant difference in age, sex, or duration of follow-up according to epilepsy type. Neither was there any significant difference in seizure frequency reduction, seizure duration, postictal period, medication use, overall clinical improvement, or improvement in quality of life based on an age ≥ or < 12 years or epilepsy type.

Conclusions

Vagus nerve stimulation reduced both seizure frequency and antiepileptic medication use in the majority of pediatric patients regardless of sex, age cohort, or epilepsy type. Vagus nerve stimulation also reduced seizure duration and postictal period in approximately half of the pediatric patients. Contrary to expectation, children with partial epilepsy do not benefit from VNS at higher rates than those with generalized epilepsy.