An Experimental Study on the Effect of Differential Ventriculomegaly on the Somatosensory Evoked Potential

Abstract

Differential ventriculomegaly is encountered after head injury, craniectomy or in some congenital hydrocephalic patients. The evoked potential studies have been widely used for the functional evaluation of the neural tissue. To evaluate the effect of ventriculomegaly on the somatosensory evoked potentials (SEP's) and the effect of increased intracranial pressure (lCP) on SEP in ventriculomegaly, the authors had recorded SEP in a differential ventriculomegaly model. To make a differential ventriculomegaly model, twenty-eight cats had kaolin-injections with cisternal puncture and hemicraniectomy. With the SEP studies of the cats in pre-hydrocephalic phase, in post-hydrocephalic phase 4-8 weeks after kaolin-injection, and in increased ICP phase, the effects of differential ventriculomegaly on the electrophysiologic function of the brain were evaluated. The size of the ventricles were evaluated with brain CT scan in 7 cats and with autopsy specimen in all 28 cats. Intracranial kaolin-injection and hemicraniectomy produced asymmetrical ventriculomegaly with the larger one on the hemicraniectomy side in 68%. In pre-hydrocephalic and post-hydrocephalic phase studies with left-sided hemicraniectomy, there were no significant side differences in the latencies. With the increased ICP, there was a significant increase in the PI-Nl interpeak latency on the left side (p<O.Ol). Comparing pre- and post-hydrocephalic phases, the latencies of wave II increased significantly in both sides (p<O.Ol), but there was no significant difference between the increases of both sides. There was no significant influence of the differential ventriculomegaly on the central conduction time (II-PI) of the SEP's with or without increased ICP. The differential ventriculomegaly with increased ICP did prolong the early cortical transmission (PI-Nl) of the SEP's on the left side (p<O.Ol), which suggested greater vulnerability of cerebral cortex compared with that of the right side.