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Tractography delineates microstructural changes in the trigeminal nerve after focal radiosurgery for trigeminal neuralgia.

Hodaie M, Chen DQ, Quan J, Laperriere N - PLoS ONE (2012)

Bottom Line: Assessment of treatment effectiveness is primarily clinical, given the paucity of investigational tools to assess trigeminal nerve changes.Radiosurgery resulted in 47% drop in FA values at the target with no significant change in FA outside the target, demonstrating highly focal changes after treatment.This study is a proof of principle for further assessment of DTI parameters to understand the pathophysiology of TN and treatment effects.

View Article: PubMed Central - PubMed

Affiliation: Division of Neurosurgery, Toronto Western Hospital and University of Toronto, Toronto, Ontario, Canada. mojgan.hodaie@uhn.on.ca

ABSTRACT

Purpose: Focal radiosurgery is a common treatment modality for trigeminal neuralgia (TN), a neuropathic facial pain condition. Assessment of treatment effectiveness is primarily clinical, given the paucity of investigational tools to assess trigeminal nerve changes. Since diffusion tensor imaging (DTI) provides information on white matter microstructure, we explored the feasibility of trigeminal nerve tractography and assessment of DTI parameters to study microstructural changes after treatment. We hypothesized that trigeminal tractography provides more information than 2D-MR imaging, allowing detection of unique, focal changes in the target area after radiosurgery. Changes in specific diffusivities may provide insight into the mechanism of action of radiosurgery on the trigeminal nerve.

Methods and materials: Five TN patients (4 females, 1 male, average age 67 years) treated with Gamma Knife radiosurgery, 80 Gy/100% isodose line underwent 3Tesla MR trigeminal nerve tractography before and sequentially up to fourteen months after treatment. Fractional anisotropy (FA), radial (RD) and axial (AD) diffusivities were calculated for the radiosurgical target area defined as the region-of-interest. Areas outside target and the contralateral nerve served as controls.

Results: Trigeminal tractography accurately detected the radiosurgical target. Radiosurgery resulted in 47% drop in FA values at the target with no significant change in FA outside the target, demonstrating highly focal changes after treatment. RD but not AD changed markedly, suggesting that radiosurgery primarily affects myelin. Tractography was more sensitive than conventional gadolinium-enhanced post-treatment MR, since FA changes were detected regardless of trigeminal nerve enhancement. In subjects with long term follow-up, recovery of FA/RD correlated with pain recurrence.

Conclusions: DTI parameters accurately detect the effects of focal radiosurgery on the trigeminal nerve, serving as an in vivo imaging tool to study TN. This study is a proof of principle for further assessment of DTI parameters to understand the pathophysiology of TN and treatment effects.

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Baseline MR imaging, tractography of the trigeminal nerve, target and ROI definition.Image processing commenced with baseline anatomical 3TMR images (A, axial section, midpontine level). Diffusion tensor images with overlaid colour-by-orientation fibers are shown in B. Reconstructed tracts of the trigeminal nerve onto colour-by-orientation images are shown in C. Panel D depicts the contour of the trigeminal nerve (blue) and location of the radiosurgical shot. Yellow circle denotes the 80% isodose line, representing the “target” of Gamma radiation to the nerve. Panel E shows focal area of post-gadolinium enhancement on the trigeminal nerve (yellow arrowhead), defining the “target” ROI. Panel F shows the location of the “proximal” ROI, proximal to the area of gadolinium enhancement (B, white arrow), and “unaffected” ROI, contralateral nerve.
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pone-0032745-g001: Baseline MR imaging, tractography of the trigeminal nerve, target and ROI definition.Image processing commenced with baseline anatomical 3TMR images (A, axial section, midpontine level). Diffusion tensor images with overlaid colour-by-orientation fibers are shown in B. Reconstructed tracts of the trigeminal nerve onto colour-by-orientation images are shown in C. Panel D depicts the contour of the trigeminal nerve (blue) and location of the radiosurgical shot. Yellow circle denotes the 80% isodose line, representing the “target” of Gamma radiation to the nerve. Panel E shows focal area of post-gadolinium enhancement on the trigeminal nerve (yellow arrowhead), defining the “target” ROI. Panel F shows the location of the “proximal” ROI, proximal to the area of gadolinium enhancement (B, white arrow), and “unaffected” ROI, contralateral nerve.

Mentions: Figure 1 shows an axial image of the brainstem at the level of the trigeminal nerve. The overlaid tracts of the trigeminal nerve (panel C) demonstrate adequate concordance with the location and size of the tracts. The location of the radiosurgical target, and corresponding selection of ROIs are shown in panels D-F. The small ROI size was not a limitation in trigeminal tract reconstruction or calculation of scalar DTI parameters.


Tractography delineates microstructural changes in the trigeminal nerve after focal radiosurgery for trigeminal neuralgia.

Hodaie M, Chen DQ, Quan J, Laperriere N - PLoS ONE (2012)

Baseline MR imaging, tractography of the trigeminal nerve, target and ROI definition.Image processing commenced with baseline anatomical 3TMR images (A, axial section, midpontine level). Diffusion tensor images with overlaid colour-by-orientation fibers are shown in B. Reconstructed tracts of the trigeminal nerve onto colour-by-orientation images are shown in C. Panel D depicts the contour of the trigeminal nerve (blue) and location of the radiosurgical shot. Yellow circle denotes the 80% isodose line, representing the “target” of Gamma radiation to the nerve. Panel E shows focal area of post-gadolinium enhancement on the trigeminal nerve (yellow arrowhead), defining the “target” ROI. Panel F shows the location of the “proximal” ROI, proximal to the area of gadolinium enhancement (B, white arrow), and “unaffected” ROI, contralateral nerve.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3295766&req=5

pone-0032745-g001: Baseline MR imaging, tractography of the trigeminal nerve, target and ROI definition.Image processing commenced with baseline anatomical 3TMR images (A, axial section, midpontine level). Diffusion tensor images with overlaid colour-by-orientation fibers are shown in B. Reconstructed tracts of the trigeminal nerve onto colour-by-orientation images are shown in C. Panel D depicts the contour of the trigeminal nerve (blue) and location of the radiosurgical shot. Yellow circle denotes the 80% isodose line, representing the “target” of Gamma radiation to the nerve. Panel E shows focal area of post-gadolinium enhancement on the trigeminal nerve (yellow arrowhead), defining the “target” ROI. Panel F shows the location of the “proximal” ROI, proximal to the area of gadolinium enhancement (B, white arrow), and “unaffected” ROI, contralateral nerve.
Mentions: Figure 1 shows an axial image of the brainstem at the level of the trigeminal nerve. The overlaid tracts of the trigeminal nerve (panel C) demonstrate adequate concordance with the location and size of the tracts. The location of the radiosurgical target, and corresponding selection of ROIs are shown in panels D-F. The small ROI size was not a limitation in trigeminal tract reconstruction or calculation of scalar DTI parameters.

Bottom Line: Assessment of treatment effectiveness is primarily clinical, given the paucity of investigational tools to assess trigeminal nerve changes.Radiosurgery resulted in 47% drop in FA values at the target with no significant change in FA outside the target, demonstrating highly focal changes after treatment.This study is a proof of principle for further assessment of DTI parameters to understand the pathophysiology of TN and treatment effects.

View Article: PubMed Central - PubMed

Affiliation: Division of Neurosurgery, Toronto Western Hospital and University of Toronto, Toronto, Ontario, Canada. mojgan.hodaie@uhn.on.ca

ABSTRACT

Purpose: Focal radiosurgery is a common treatment modality for trigeminal neuralgia (TN), a neuropathic facial pain condition. Assessment of treatment effectiveness is primarily clinical, given the paucity of investigational tools to assess trigeminal nerve changes. Since diffusion tensor imaging (DTI) provides information on white matter microstructure, we explored the feasibility of trigeminal nerve tractography and assessment of DTI parameters to study microstructural changes after treatment. We hypothesized that trigeminal tractography provides more information than 2D-MR imaging, allowing detection of unique, focal changes in the target area after radiosurgery. Changes in specific diffusivities may provide insight into the mechanism of action of radiosurgery on the trigeminal nerve.

Methods and materials: Five TN patients (4 females, 1 male, average age 67 years) treated with Gamma Knife radiosurgery, 80 Gy/100% isodose line underwent 3Tesla MR trigeminal nerve tractography before and sequentially up to fourteen months after treatment. Fractional anisotropy (FA), radial (RD) and axial (AD) diffusivities were calculated for the radiosurgical target area defined as the region-of-interest. Areas outside target and the contralateral nerve served as controls.

Results: Trigeminal tractography accurately detected the radiosurgical target. Radiosurgery resulted in 47% drop in FA values at the target with no significant change in FA outside the target, demonstrating highly focal changes after treatment. RD but not AD changed markedly, suggesting that radiosurgery primarily affects myelin. Tractography was more sensitive than conventional gadolinium-enhanced post-treatment MR, since FA changes were detected regardless of trigeminal nerve enhancement. In subjects with long term follow-up, recovery of FA/RD correlated with pain recurrence.

Conclusions: DTI parameters accurately detect the effects of focal radiosurgery on the trigeminal nerve, serving as an in vivo imaging tool to study TN. This study is a proof of principle for further assessment of DTI parameters to understand the pathophysiology of TN and treatment effects.

Show MeSH
Related in: MedlinePlus