Diffusion tensor imaging in detection of Wallerian degeneration of pyramidal tract after cerebral infarction

Abstract

Objective To investigate the evolution of diffusion indices in the pyramidal tract with Wallerian degeneration(WD)due to cerebral infarction using diffusion tensor imaging(DTI),and to study the relationship between early changes of diffusion indices and motor deficit.Methods Fifteen patients (13 males and 2 females)with acute cerebral infarction(within 7 days)were recruited from the Neurology Department from Mar 2006 to Jan 2007.A11 patients were assessed with DTI.National Institutes of Health Stroke Scale(NIHSS),Bathel Index(BI),modified Rankin Scale(mRS)and Motricity Index(MI)within 7 days from onset,and at the second week.DTI was performed with SIEMENS Trio 3.0 T MR scanner.The placement of region of interest(ROI),measurement of diffusion indices were performed by DTI Studio software.The mean diffusivity(MD),the fractional anisotropy(FA),the first eigenvalue (λ1),the second eigenvalue(λ2),and the third eigenvalue(λ3)were computed.Results At the second week.NIHSS was 6.93±3.39.BI 45.33±26.01,mRS 4.33±0.90.and MI 69.47± 60.71.At the second week from onset.MD of the pyramidal tract at the levels of the middle slice of pons and the superior slice of medulla oblongata showed no significant differences between both the two sides at second week from onset. Other ROI showed significant differences between both sides.MD.FA and λ1 of affected side were lower than the unaffected side.λ2 and λ3 of the affected side were higher than the unaffected side.Positive correlations were found between FA and BI(r=0.530,P=0.042),FA and MI(r=0.543,P=0.036)at the second week.Negative correlations were found between FA and NIHSS(r=-0.613,P=0.015)at the second week.Conclusions DTI can detect the changes in the pyramidal tract due to WD within 7-14 days after ischemic stroke.including a decrease of the fractional anisotropy.the first eigenvalue and increased the second and the third eigenvalues.The fractional anisotropy of the second week from onset is related to the outcome of the motor function. Key words: Brain infarction; Pyramidal tracts; Wallerian degeneration; Diffusion magnetic resonance imaging; Movement disorders