Table 1.
Demographics and clinical presentation of subjects studied.
Figure 1.
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.
Figure 2.
Target ROI is characterized by focal diffusivity changes.
Comparison of diffusivities change across all ROIs reveal statistically significant decrease in FA and rise in RD in “target” post-radiosurgery treatment. Rise in RD and non-significant changes in AD point to changes in myelination as main contributor of diffusivity changes. (*denotes statistically significant changes, FA p = 0.027, RD p = 0.002; two-tailed t-test. NS = no statistical significance. RD,AD scalar values are multiplied ×1000 for ease of representation).
Table 2.
Effect of GKRS treatment on trigeminal nerve diffusivities.
Figure 3.
Changes in FA after GKRS treatment are dynamic.
Sequential images for subject S1 are shown at 0, 1, 7 and 14 months after Gamma Knife radiosurgery (GKRS) treatment. Top panel depicts serial MR images, showing similar gadolinium enhancement in the midcisternal portion of the nerve after treatment with time (yellow triangles). Middle panel shows reconstructed trigeminal nerve tracts for the same time points. At one month, marked FA decrease is seen in the target area (high FA pre-treatment, blue now appearing as low FA, orange) and tract-pruning due to fall-off of FA value. At 14 months the FA values trends towards baseline, with a longer reconstructed trigeminal segment. The area of low FA has also resolved. Lower panel shows a graph of the scalar values of FA with time. At 14 months, subject S1 has experienced full recurrence of her pain.
Figure 4.
Tractography outlines detailed FA changes in the trigeminal nerve after GKRS treatment.
Panels A–D depict the trigeminal nerve tracts pre and post-treatment for subjects S1(A,B) and S2 (C,D). The area between the yellow and blue arrows delineates the cisternal segment, with the yellow arrow being proximal to the brainstem and the blue arrow distal. The red arrow denotes the target area, which corresponds to the region where the greatest change in FA was observed. In S1, FA change affects primarily the outlying fibers of the nerve, while for S2, FA changes are seen in the inferior portion of the cisternal segment of the trigeminal nerve.
Figure 5.
Tractography can detect changes in the trigeminal nerve in the absence of post-treatment gadolinium enhancement: Panels A to E delineate FA changes seen after treatment. Subject S2 did not show post-treatment MR gadolinium enhancement.
Panel A shows location of radiosurgical target during treatment planning. Panels B, C depict post-treatment MR and lack of gadolinium-enhancement (yellow arrowhead). Reconstructed trigeminal tracts are shown in panel D (pre-treatment) and E (post-treatment), with clear FA changes in the target area (blue arrowhead).