Pathology of subcortical visual centres in relation to cortical degeneration in Alzheimer's disease

Subcortical visual centres such as the lateral geniculate nucleus, the lateral inferior pulvinar and the superior colliculus, together with the primary visual cortex and its adjacent white matter, were studied in 12 Alzheimer brains and five age-matched controls. The periodic acid methenamine technique was used for the demonstration of senile plaques and the Gallyas technique for neurofibrillary tangles and neuritic threads in the neuropil. In the lateral geniculate nucleus and inferior pulvinar, the presence of periodic acid methenamine-positive senile plaques was observed in variable numbers in all Alzheimer cases. In the lateral geniculate nucleus, senile plaques were encountered more often in parvocellular than in magnocellular layers, in the interlaminar zones, in the optic radiation and in the adjacent pre-geniculate nucleus. Gallyas staining did not reveal any neurofibrillary tangles, neuritic threads or neuritic plaques, meaning that in this thalamic region there are mainly amyloid deposits without neuritic degeneration. In the superior colliculus both amyloid and neuritic plaques, as well as neurofibrillary tangles and neuritic threads were encountered in the superficial and deep layers. In the primary visual cortex, all types of senile plaques were observed as well as a rather high number of neurofibrillary lesions in pyramidal neurons, mainly in layers 5 and 6, but also in several types of non-pyramidal neurons. In the underlying white matter there was a morphologically heterogeneous population of neurofibrillary tangle-bearing neurons and a considerable number of threads representing degenerating axons, suggesting that degeneration could follow corticosubcortical connections. These data demonstrate that lesions in the primary visual structures and pathways are more prevalent than previously observed and could partly explain the visual disturbances in Alzheimer's disease.