On account of the median location of tumours of the corpus callosum, serial angiography reveals displacements only at an advanced stage. In many cases there is no lateral displacement of the anterior cerebral artery and a lateral angiogram of the pericallosal artery does not reveal tumours of the corpus callosum, especially if they are associated with a vascular pattern characteristic of arteriosclerosis or hydrocephalus. The deep mid-line veins are not consistently displaced. A differentiation of the vascular pattern associated with small tumours of the corpus callosum from normal variations may be problematic. The inner veins cannot be visualised sometimes on account of increased intracranial pressure and a slowing of the circulation.