Subacute Degeneration of Fibers After Vertical Parasagittal Hemispherotomy.

Abstract

After vertical parasagittal hemispherotomy arestricted diffusion is often seen ipsilaterally and even distant from the adjacent resection margin. This retrospective cohort study analyses the anatomic site and the time course of the diffusion restriction after vertical parasagittal hemispherotomy. Fifty-nine patients were included into this study, all of them having had one pre-operative and at least one post-operative MRI, including diffusion imaging at b‑values of 0and 1000 s/mm2 with acalculated ADC. Diffusion restriction occurred exclusively on the operated site in all patients. In the basal ganglia, diffusion restriction was present in 37of 38patients at the first postoperative day with aduration of 38days. In the midbrain, the posterior limb of the internal capsule and the thalamus, arestricted diffusion became postoperatively prominent at day9 in all three localizations, with aduration of 36, 34and 36days, respectively. The incidence of thalamic lesions was lower if apreoperative damage had occurred. The restricted diffusion in the basal ganglia resembles direct effects of the operation at its edges, whereas the later appearing diffusion restriction in the midbrain and the posterior limb of the internal capsule rather belong to adegeneration of the descending fibers being transected by the hemispherotomy in the sense of aWallerian degeneration. The presence of preoperative hemispheric lesions influences the development of diffusion restriction at subacute fiber degeneration.