EXPERIMENTAL SYRINGOMYELIA - LATE ULTRASTRUCTURAL-CHANGES OF SPINAL-CORD TISSUE AND MAGNETIC-RESONANCE-IMAGING EVALUATION

BACKGROUND In human hydrosyringomyelia and in the late stage of experi mental syringomyelia, the spinal cord tissue adjacent to the syrinx is exposed to a similar pathophysiologic condition. We investigated the ultrastructural changes in the late stages of kaolin-induced syringomy elia, and in addition, we presented magnetic resonance imaging (MRT) f indings of the cervicomedullary junction and syrinx, and the nature of edema in the spinal cord of this experimental model. METHODS Syringom yelia was induced in rabbits by intracisternal injection of kaolin. MR I was performed at 6 weeks, and 6 and 12 months following injection, a nd the animals were killed by transcardial perfusion of formaldehyde s olution and examined by transmission electron microscopy. Evans blue w as injected intravenously in six rabbits, 6 weeks and 12 months follow ing kaolin injection and was examined by confocal laser scanning micro scopy. RESULTS MRI showed that the syrinx communicated with the fourth ventricle in most animals. Demyelination of varying degrees and sligh t edematous change were seen in the perisyrinx white matter. No extrav asation of Evans blue was seen by confocal microscopy. Abundant astroc ytic proliferation with a large number of glial filaments was seen at the margin of the syrinx and between the axons in the perisyringeal re gion. The perivascular space enlargement occurred in both the gray and white matter. The endothelial junctions appeared intact, Regenerating axons and remyelination by oligodendrocytes were seen occasionally. C ONCLUSIONS The MRI confirmed the communication fourth ventricle and th e syrinx. The changes were almost identical to those of the early stag e syrinx, but the astrocytic proliferation was more severe, and the ed ema was less in the late stage. The perisyrinx edema appeared to be of the interstitial type, as in hydrocephalus. Axonal degeneration and d emyelination continued with abortive attempt at regeneration and remye lination in the less edematous late stage, which might be the cellular basis for the persistence or worsening of clinical symptoms and signs in the chronic stage of syringomyelia even after surgical treatment. (C) 1997 by Elsevier Science Inc.