Monitoring Ischemic Cerebral Injury in Spontaneously Hypertensive Rats by Diffusion Tensor Imaging.

AIM: We have applied diffusion tensor imaging (DTI) to interrogate microstructural changes in white matter integrity in a widely used middle cerebral artery occlusion (MCAO) model of cerebral ischemia. MATERIAL AND METHODS: We performed ex vivo DTI 35 days after 60 minutes transient focal ischemia in male spontaneously hypertensive rats and generated fractional anisotropy (FA), mean, axial and radial diffusivity maps. Regions of interest corresponding to external capsule (EC), corpus callosum (CC) and internal capsule (IC) were compared among sham and stroked rats. We compared tractographic projections of white matter fiber patterns and examined white matter integrity by Luxol fast blue histological analysis. We also determined infarct lesion volumes at 24 hours post-ischemia by T2-weighted magnetic resonance imaging (MRI) or at 35 days by histological staining with cresyl violet. RESULTS: We found alterations in EC and IC, but not CC, as represented by decreased FA and increased mean, axial and radial diffusivities. The size of the ischemic lesion detected subacutely by T2-weighted MRI or at 35 days by histological staining correlated with the decline in FA in the affected structures. Tractography revealed disruption of fiber trajectories through the EC and reorientation of fibers within the caudate/putamen of rats subjected to MCAO. Similarly, loss of white matter integrity in the EC and increased white matter density in the caudate/putamen along the infarct border zone was evidenced by Luxol fast blue staining. CONCLUSION: Diffusion tensor imaging therefore allows for monitoring of white matter injury and reorganization in hypertensive rats.

Microsurgical anatomy of the dorsal thoracic rootlets and dorsal root entry zones.

BACKGROUND: For successful DREZ (dorsal root entry zone) surgery, optimal neuroanatomical orientation and precise microsurgical dissection are required. Although cervical, lumbar, and sacral spinal segments have been studied in detail, such information is not available for thoracic segments. The objective of this anatomical study is to comprehensively illustrate the microanatomical features of the thoracic DREZs and their variations. METHODS: Fifteen formalin-fixed adult cadaveric spinal cords from T1 to T12 were used. The dorsal rootlet numbers, distance between the posteromedial and posterolateral sulcus, length of each DREZ, length of each segment, and mean length of the dorsal rootlets were measured under a surgical microscope. RESULTS: The longest DREZs were observed at the T6, T7, and T8 segments with mean values of 15.3 mm, 15.6 mm, and 15.4 mm, respectively. The longest segment was observed at the T10 segment with a mean value of 21.0 mm, and the shortest segment was observed at the T1 segment with a mean value of 13.5 mm. CONCLUSIONS: The highest dorsal rootlet density is at the T1 segment of the spinal cord, can be easily distinguished visually, and may be a useful surgical landmark. The DREZs in T6-7 segments are longest, while these two segments have the least number of rootlets. Because the dorsolateral tract is remarkably narrow and the dorsal horn is exceedingly deep, DREZ surgery at the thoracic level may be difficult and risky for the dorsal column and corticospinal tract. Acquaintance with the microanatomy of the DREZ in the thoracic spinal cord is crucial to DREZ surgery.