Corpus callosum

● Lesion manifestations

▪ Posterior corpus callosum (splenium):

◦ Visual-language disconnection syndromes:

Alexia without agraphia (classically due to left occipital cortex infarction with splenial involvement, often in the territory of the left posterior cerebral artery)

Left visual field anomia (inability to name objects presented in the left visual field because visual information cannot reach dominant language regions)

▪ Body of the corpus callosum:

◦ Tactile anomia (inability to name objects placed in the left hand with the eyes closed, despite preserved recognition of the object through vision, due to failure of somatosensory information to reach dominant language networks)

◦ Difficulty with bimanual coordination requiring integration of information from both hands

▪ Diffuse callosal injury:

◦ Cognitive slowing and reduced processing speed

◦ Executive dysfunction

◦ Increased emotional reactivity (e.g., irritability, reduced frustration tolerance)

● Clinical pearls

▪ The corpus callosum is the brain’s major interhemispheric communication pathway; lesions can produce symptoms through disconnection, even when the cortical regions themselves remain structurally intact.

▪ Alexia without agraphia is the classic splenial disconnection syndrome. A left occipital lesion disrupts visual processing in the dominant visual cortex, while splenial damage prevents visual information from the intact right visual cortex from reaching dominant left occipitotemporal reading networks.

▪ Patients with ‘alexia without agraphia’ can:

◦ write normally;

◦ understand spoken language;

◦ recognise objects;

◦ but cannot read because visual information cannot access the dominant reading network.