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. 2017 May;19(5):592-605.
doi: 10.3171/2016.11.PEDS16312. Epub 2017 Mar 17.

A Systematic Evaluation of Intraoperative White Matter Tract Shift in Pediatric Epilepsy Surgery Using High-Field MRI and Probabilistic High Angular Resolution Diffusion Imaging Tractography

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A Systematic Evaluation of Intraoperative White Matter Tract Shift in Pediatric Epilepsy Surgery Using High-Field MRI and Probabilistic High Angular Resolution Diffusion Imaging Tractography

Joseph Yuan-Mou Yang et al. J Neurosurg Pediatr. .

Abstract

OBJECTIVE Characterization of intraoperative white matter tract (WMT) shift has the potential to compensate for neuronavigation inaccuracies using preoperative brain imaging. This study aimed to quantify and characterize intraoperative WMT shift from the global hemispheric to the regional tract-based scale and to investigate the impact of intraoperative factors (IOFs). METHODS High angular resolution diffusion imaging (HARDI) diffusion-weighted data were acquired over 5 consecutive perioperative time points (MR1 to MR5) in 16 epilepsy patients (8 male; mean age 9.8 years, range 3.8-15.8 years) using diagnostic and intraoperative 3-T MRI scanners. MR1 was the preoperative planning scan. MR2 was the first intraoperative scan acquired with the patient's head fixed in the surgical position. MR3 was the second intraoperative scan acquired following craniotomy and durotomy, prior to lesion resection. MR4 was the last intraoperative scan acquired following lesion resection, prior to wound closure. MR5 was a postoperative scan acquired at the 3-month follow-up visit. Ten association WMT/WMT segments and 1 projection WMT were generated via a probabilistic tractography algorithm from each MRI scan. Image registration was performed through pairwise MRI alignments using the skull segmentation. The MR1 and MR2 pairing represented the first surgical stage. The MR2 and MR3 pairing represented the second surgical stage. The MR3 and MR4 (or MR5) pairing represented the third surgical stage. The WMT shift was quantified by measuring displacements between a pair of WMT centerlines. Linear mixed-effects regression analyses were carried out for 6 IOFs: head rotation, craniotomy size, durotomy size, resected lesion volume, presence of brain edema, and CSF loss via ventricular penetration. RESULTS The average WMT shift in the operative hemisphere was 2.37 mm (range 1.92-3.03 mm) during the first surgical stage, 2.19 mm (range 1.90-3.65 mm) during the second surgical stage, and 2.92 mm (range 2.19-4.32 mm) during the third surgical stage. Greater WMT shift occurred in the operative than the nonoperative hemisphere, in the WMTs adjacent to the surgical lesion rather than those remote to it, and in the superficial rather than the deep segment of the pyramidal tract. Durotomy size and resection size were significant, independent IOFs affecting WMT shift. The presence of brain edema was a marginally significant IOF. Craniotomy size, degree of head rotation, and ventricular penetration were not significant IOFs affecting WMT shift. CONCLUSIONS WMT shift occurs noticeably in tracts adjacent to the surgical lesions, and those motor tracts superficially placed in the operative hemisphere. Intraoperative probabilistic HARDI tractography following craniotomy, durotomy, and lesion resection may compensate for intraoperative WMT shift and improve neuronavigation accuracy.

Keywords: AB = anterior bundle; AH-CING = anterior horizontal CING; CING = cingulum; CSD = constrained spherical deconvolution; DNET = dysembryoplastic neuroepithelial tumor; DTI = diffusion tensor imaging; EPI = echo-planar imaging; ET-CO2 end-tidal carbon dioxide; FOD = fiber orientation distribution; Fx = fornix; HARDI = high angular resolution diffusion imaging; ICV = intracranial volume; IFOF = inferior fronto-occipital fasciculus; ILF = inferior longitudinal fasciculus; IOF = intraoperative factor; MB = middle bundle; OR = optic radiation; PB = posterior bundle; PH-CING = parahippocampal CING; PS = probability of superiority; PT = pyramidal tract; R2mar = marginal R2; ROI = region of interest; SE = standard error; SLF = superior longitudinal fasciculus; UF = uncinate fasciculus; WMT = white matter tract; diffusion tractography; high angular resolution diffusion imaging; intraoperative high-field MRI; pediatric epilepsy surgery; probabilistic tractography algorithm; white matter tract shift.

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