[Visual evoked potentials as an indicator of supratentorial and infratentorial herniation]

The VEP was investigated in 172 patients with infratentorial and in 100 patients with supratentorial space occupying lesions. In each group 65% of the patients showed marked or even extensive changes in VEP. An immediate relation of the lesion to the optochiasmatic system or a hydrocephalus was noted in a few cases only. In contrast the VEP of patients with a clear transtentorial herniation showed severely pathological changes, occasionally up to complete loss of the potential. The VEP changes were reversible on removal of the space occupying lesions in all patients. The constellation of VEP changes in subgroups of patients with different types of the space occupying lesions, as well as the observed symmetry of the VEP changes, allow the assumption that the functional inhibition of the optic pathway occurs in the perimesencephalic part via their compression or stretching. The assumption is supported by pathoanatomical MRT findings in some cases. It seems, therefore, that VEP investigations enable the registration of a compression or torsion of the cranial mesencephalon (mesencephalo-diencephalic mechanical irritation) or the presence of a clinical silent transtentorial herniation in space occupying lesions. The loss of the VEP appears to yield an early and certain signal of the progressing mid-brain syndrome.