Investigation On The Secondary Degeneration Of Pyramidal Tract After Cerebral Hemorrhage With Magnetic Resonance Imaging

Background: Animal experiments demonstrate that a focal cerebral infarct can cause secondary damage of center never system (CNS) in regions remote from the primary lesion. Computed Tomography (CT) and conventional magnetic resonance imaging (MRI) reveal the secondary neural fiber degeneration in pyramidal tract (PT) (peduncle of cerebrum, pons, medulla and spinal cord) distal to a supratentorial cerebral infarct, which was confirmed by postmortem. Besides infarct, focal cerebral damage including hemorrhage, tumor, trauma, postoperative and multiple sclerosis can cause secondary damage of CNS. Therefore, the damage in CNS resulted from a focal cerebral infarct involved not only in the focal site but in regions far away from the initial lesion. The diffusion tensor imaging (DTI) is a new MRI technique based on diffusion-weighted imaging (DWI), which applied to study the molecular displacement (diffusion) in biologic tissue. DTI can detect the cerebral damage by using to observe the diffusion of free water protons on the orientation of white matter fiber tracts. Contrast with conventional MRI, DTI can determine the diffusivity of every voxel and fully depict tissue diffusion characteristics. Therefore DTI takes the advantage in detecting the secondary impairments. PT is the maximal nerve fiber bundle in human body, the secondary degeneration of PT may be the most easily happen and to be detected. Studies with DTI demonstrate that the secondary degeneration in PT after a cerebral infarct advances with time course, and its progressive process correlates with neurological deficit in acute stage and motor outcome same months later, and hemorrhage can also cause CNS focal lesion and degeneration of PT. As a result, future study with DTI may be useful to elucidate the mechanism on how and what an extent a focal cerebral hemorrhage to impair the CNS. However, the prospective report on the secondary degeneration of PT after cerebral hemorrhage haven't seen in reports, the mechanism and the dynamic process of the secondary degeneration of the PT isn't elucidated. Whether the secondary degeneration would impact the neurological recovery and how to effect is unknown, so study on the secondary degeneration of the PT after cerebral hemorrhage is significance in clinical instruction besides theory in somewhat.Objective: to apply the conventional MRI and DTI techniques, retrospectively study the signal intensity change at MRI and prospectively study the DTI parameter change on the PT respectively, which are upper and lower to the primary lesion on the basal district with hemorrhage, to analyze the correlation between the DTI parameter and the neurological recovery, and to explore the development rule of the secondary degeneration of PT after cerebral hemorrhage and its clinical significance.Methods: Section one: The data of MRI from the patients, with first cerebral hemorrhage, admitted to our hospital from Jan 2007 to Dec 2007, were reviewed retrospectively. Patients underwent MRI examinations in the acute stage (7days) and subacute or chronical stage (after 21d) respectively. On T2-weight/ FLAIR images, abnormal signal intensity remote to initial lesion were observed on the ipsilateral cerebral peduncle,pons or medulla slices from the secondary MRI examinations.Section two: Twelve patients with a recent unilateral basal hemorrhage admitted to our hospital from Jan 2007 to Jun 2008, and the hematoma seriously press or through the posterior limber of internal capsule. All the patients underwent conventional MRI, DTI and evaluation with the National Institutes of Health Stroke Scale (NIHSS), the Fugl-Meyer motor scale (FMS) and the Barthel Index (BI) in the second week (W2), at the second month (M2) and at the end of the sixth month (M6) respectively. Twelve age and gender matched volunteers underwent DTI one time as controls, Mean diffusivity (MD) and fractional anisotropy (FA) were measured at the region of interest (ROI): centrum semiovale levels, peduncle of cerebrum and pons. FA values use T test between the ipsilateral cerebrum and the control group. Repeat measure was established to reveal the time course of clinical scores and DTI quantitative data obtained at W2, M2 and M6. Spearman correlation analysis was used to assess the association between the FA values and the clinical scores.Results: Section one: 11 cases were enrolled, 10 man and 1 women. Hyperintense signal of 9 cases and hypointense signal of 2 cases appeared on T2-weight/ FLAIR images of the ipsilateral cerebral peduncles,pons or bulbus in subacute or chronical stage, but no visible signal intensity change in the acute stage.Section two: In conventional MRI, there are invisible intensive signal changes in the PT of the ipsilateral cerebrum on W2 in all cases, Hyperintense signal on T2-weight/ FLAIR images of the ipsilateral cerebral peduncles,pons or bulbus ,which only 3 cases on M2 and 5 cases on M6 can be seen respectively. However, on the map of FA, intensive signal decrease in the PT at W2, M2and M6, which contrast to the opposite site and controls. The FA values of lesion site, the ipsilateral proximal (centrum semiovale levels) and distal portion of PT (peduncle of cerebrum and pons) in patients significantly decreased at W2, M2and M6 (P < 0.01 respectively). The MD of the ipsilateral proximal and distal portion of pyramidal tract in patients was not significantly different at any time points (P > 0.05, respectively). The FA value of the ipsilateral proximal and distal portion of PT associated negatively with the NIHSS scores(rup=0.825 and rdown=0.803, P <0.01), but which associated positively with the FMS scores (rup=0.795 and rdown=0.768, P <0.01), and B I scores respectively (rup=0.804 and rdown=0.775, P <0.01).Conclusion:1. The secondary degeneration of PT after cerebral hemorrhage can be detectable with MRI, and this secondary degeneration should not be misinterpreted as a newly developed infarction or other disease.2. Cerebral hemorrhage involved internal capsule can cause the anterograde and retrograde secondary degeneration of PT, which can be detected by conventional MRI sometime, but DTI not only demonstrate it clearly with the map of FA, but which can identify and quantify the secondary degeneration with the precise data of the FA value.3. Our finding indicated that the secondary degeneration will last in half of a year and be serious as the time course, which may hamper the neurological recovery.