[Changes in visually evoked potentials in space-occupying processes of the posterior fossa--on the problem of ascending transtentorial herniation].

Through the use of VEP investigations in 82 patients with space occupying lesions in the infratentorial region this study attempts to find the cause and location of dysfunctions of optical signal pathways. The majority of such expandatory processes involved tumours exterior to the brainstem of inhomogeneous histomorphology (n = 65). The rest involved metastases of the cerebellum (n = 5) and expanding infarcts of one cerebellar hemisphere (n = 12). Besides a shifting of the 4th ventricle (n = 64) an accompanying hydrocephalus (n = 40) and an ascending transtentorial herniation (n = 29) was indicated radiologically. A pathological VEP was found in just over half of the patients (n = 43). Usually, the VEP change involved a latency increase of the cortical potential (P2). In 6 of these patients a complete loss of this potential was noted. Furthermore, ten more of these patients did not have the P1-following negative potential (N2). In 32 patients with a pathological VEP a hydrocephalus was proven to be present. On the other hand, there were 8 patients with accompanying hydrocephalus but with a normal VEP. All 29 patients, though, with a radiological ascending herniation had changed VEP. Three of these patients had no accompanying hydrocephalus. Following surgical decompression a complete normalization of the VEP set within 2 to 3 weeks, while it reappeared in tumour recurrence. These findings indicate that dysfunctions of VEP, that is the visual pathways in infratentorial occupying lesions are not only dependent on the existence of accompanying hydrocephalus.(ABSTRACT TRUNCATED AT 250 WORDS)