Abstracts

RATIONALE: Image-guidance has come into widespread use in neurosurgery over the past years. For epilepsy surgery, image-guidance provides an additional tool to assure radical resection of brain tumors and other lesions presenting with chronic seizures. The usefulness of frameless stereotactic guidance depends on the clarity of the imaging data set. Non-enhancing brain lesions can be relatively poorly defined on volumetric data sets routinely used for surgical guidance. In addition, sulcal anatomy is not always clear on routine volumetric imaging studies.
METHODS: Fluid-attenuated inversion recovery (FLAIR) MR imaging has proven to be a very sensitive sequence for diagnostic MRI studies with an ability to highlight a number of subtle pathologies including non-enhancing tumors or vascular malformations, gliosis, and mesiotemporal sclerosis. Although highly sensitive, the resolution of FLAIR sequences does not ideally lend itself to image-guidance during surgery. Using an image-fusion program ([dsquote]ImMerge[dsquote]TM, StealthStation), we combined data sets of SPGR or volumetric CT with volumetrically acquired FLAIR sequences and subsequently used the fused data set for image guided surgery. This was performed in 30 patients with epilepsy, 16 with non-enhancing intrinsic brain lesions, 13 with non-lesional epilepsy and one with post-traumatic gliotic changes.
RESULTS: Image-guidance using the fused data set was accurate in all 30 patients. Despite the lack of enhancement, one of the 16 lesions was found to be a high grade (grade III , mixed oligodendroglioma-astrocytoma) glioma. One of the low-grade tumors was associated with considerable areas of gliotic change, not considered to represent tumor on permanent histology. The patient with post-traumatic epilepsy and gliotic changes remained seizure-free 24 months after selective resection of gliotic tissue. Gross total or radical ([gt]95%) tumor resection was achieved in all tumor cases. Intra-operative sulcal identification was facilitated by FLAIR fusion on the non-lesional epilepsy cases.
CONCLUSIONS: Non-enhancing lesions are often poorly demarcated not only on imaging studies, but also during surgery. FLAIR-SPGR fusion allows resection of such lesions using computer image-guidance intra-operatively and also helps clarify sulcal anatomy. Radical lesion resection correlates with better seizure control both in our patients and in prior reports by others. We believe FLAIR fusion to be a simple technique to expand the useful applications of frameless stereotaxis in epilepsy surgery.