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AJNR - American Journal of Neuroradiology

Published ahead of print on May 1, 2008
doi: 10.3174/ajnr.A1101

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Diffusion Tensor Tractography of the Meyer Loop in Cases of Temporal Lobe Resection for Temporal Lobe Epilepsy: Correlation between Postsurgical Visual Field Defect and Anterior Limit of Meyer Loop on Tractography

T. Taoka^a, M. Sakamoto^a, H. Nakagawa^a, H. Nakase^b, S. Iwasaki^a, K. Takayama^a, K. Taoka^c, T. Hoshida^b, T. Sakaki^b and K. Kichikawa^a

^a Departments of Radiology, Nara Medical University, Nara Japan
^b Departments of Neurosurgery, Nara Medical University, Nara Japan
^c Department of Ophthalmology, Kakogawa Municipal Hospital, Hyogo, Japan

View larger version (13K): [in this window] [in a new window]   Fig 1. Schematic drawing of the classification by visual field defect. Fibers in the anterior part of the Meyer loop correspond to the medial sector, and posterior fibers correspond to the lateral sectors of the upper quadrant visual field on the contralateral side. Because the anterior part of the Meyer loop is more likely to be injured by a temporal lobe resection, visual defects due to temporal lobe resection begin at the medial sector in cases of slight injury, with severe cases spreading into the lateral sector. Group A, no visual field defect in the upper quadrant visual field. Group B, incomplete defect in the medial sector of the upper quadrant visual field. Group C, complete defect in the medial sector and incomplete defect within the lateral sector. Group D, complete defect in both medial and lateral sectors.

View larger version (46K): [in this window] [in a new window]   Fig 2. Right temporal lobe epilepsy. Selective amygdalohippocampectomy was performed. A, The circle shows the seed area for the presurgical tractography. An identical seed area was used for drawing the postsurgical tractography. B, Tractography of the optic radiation (green) and uncinate fascicles is shown. Note that the 2 tracts are close together at the temporal stem. Thus, tractography of uncinate fascicles drawn in advance can be used as an assistant or a guide to draw the Meyer loop. C, The T-M distance is 41 mm for presurgical tractography (arrow). D, Postsurgical tractography of Meyer loop is also achieved in this patient.

View larger version (51K): [in this window] [in a new window]   Fig 3. Right temporal lobe epilepsy. Anterior temporal lobectomy was performed. A, Presurgical tractography. Tractography of the Meyer loop is shown as the green tract. T-M distance is 35.6 mm. Uncinate fascicles are shown in the yellow tract. Note that there is no gap between the 2 tractographies. B, Postsurgical spin-echo sagittal image. An anterior temporal lobectomy has been performed. The T-R distance is 38 mm (arrow). Because the T-M distance is 35.6 mm on the presurgical tractography, the M-R distance is calculated to be +2.4 mm. C, For the postsurgical tractography, the Meyer loop could not be delineated; thus, only the dorsal optic radiation could be drawn. D, The visual field 2 months after the surgery. There is a complete visual field defect in the medial sector and a partial visual field defect in the lateral sector of the lateral upper quadrant visual field.

View larger version (5K): [in this window] [in a new window]   Fig 4. Correlation between the extent of the visual field defect and the T-R distance. Although there is a slight tendency for the T-R distance to appear larger in cases that have more severe visual field defects, overlap between the groups is quite large. No statistically significant differences could be observed by the ANOVA test. (Cases with anterior temporal lobectomy are shown in black, and cases with selective amygdalohippocampectomy are shown in white.)

View larger version (10K): [in this window] [in a new window]   Fig 5. Interindividual variation of the T-M distance. A, The reproducibility of tractography by 2 operators. The correlation coefficient between the measurement of T-M distance by 2 operators is 0.97. B, Interindividual variations of mean T-M distances by 2 operators on a presurgical tractography. The mean T-M distance is 36.6 mm (SD = 4.45 mm). Variation ranges from 30.0 to 43.2 mm.

View larger version (10K): [in this window] [in a new window]   Fig 6. Correlation between the extent of the visual field defect and the M-R distance. A plus value for the M-R distance indicates that there is a resected area of optic tract due to temporal lobe resection. A minus value for the M-R distance indicates that there are still spaces between the anterior limit of the Meyer loop and the posterior limit of the temporal lobe resection. The more severe the postsurgical visual field defect (groups C and D), the larger is the amount of resection of the Meyer loop. In contrast, minus values are seen for all the cases within groups A (no defect) and B (partial defect in the medial sector). ANOVA showed statistically significant differences (P < .01) between groups A and C, groups A and D, groups B and C, and groups B and D. (Cases with anterior temporal lobectomy are shown in black, and cases with selective amygdalohippocampectomy are shown in white.)