Posterior callosal section in a non-epileptic patient.

The major studies of the effects of callosal section in humans have been conducted in severe epileptic patients in whom commissurotomy has been performed for management of intractable seizures. In spite of the evidence which has been amassed it is possible to criticise the results, on the grounds that all patients had seizures for many years prior to surgery and hence it is conceivable that some adaptive reorganisation of the epileptic brain might account for the different behaviour of the two hemispheres. Specifically, since the primary epileptic focus and its possible underlying focal damage are often asymmetric, one hemisphere might have had to adapt to the functional deficit of the other and thereby produce the basis for the unusually striking hemispheric differences. The answer to these reservations must come from the study of non-epileptic subjects who undergo some form of commissurotomy for reasons other than treatment of seizures, particularly if the intervention involves the posterior third of the corpus callosum, the sector considered responsible for the more remarkable "disconnection" signs. Only seven such cases have been reported. Here we report findings in a non-epileptic and previously normal 16-year-old boy who underwent section of the splenium for exploration of a pineal tumour. Our results indicate that surgical section of the splenium produced visual disconnection signs comparable to those seen in epileptic patients with complete commissurotomy.