Corpus callosum

The corpus callosum is the largest and principal commissural white-matter fibre bundle of the cerebrum, containing numerous heavily myelinated axons that connect the left and right cerebral hemispheres.

Subparts of corpus callosum

Anatomically, the corpus callosum is divided from anterior to posterior into the rostrum, genu, body (trunk) and splenium.

• The isthmus is the relatively narrow region between the posterior body and splenium. Rostral fibres connect orbital frontal regions. Fibres of the genu curve anteriorly into the frontal lobes as the forceps minor, while fibres of the body pass transversely and radiate into the white matter of the cerebral hemispheres. Fibres of the splenium curve posteriorly into the occipital lobes as the forceps major. Some callosal fibres also sweep posteriorly and inferiorly along the lateral ventricle as the tapetum.

Relationship with nearby structures

The corpus callosum lies deep within the longitudinal cerebral fissure and has close anatomical relationships with the lateral ventricles and fornix. Its body contributes to the roof of the lateral ventricles, while the septum pellucidum extends between the corpus callosum and fornix anteriorly. Superiorly, the corpus callosum is related to the callosal sulcus and cingulate gyrus, with the pericallosal vessels coursing close to its surface.

Functional correlates

Functionally, the corpus callosum enables the integration and transfer of sensory, motor and higher cognitive information between the cerebral hemispheres. Its organisation is broadly topographic: anterior callosal regions are particularly involved in frontal, motor and higher cognitive interhemispheric communication, whereas more posterior regions participate in somatosensory transfer through the posterior midbody, auditory transfer through the isthmus, and visual transfer through the splenium.

Blood supply

The arterial supply is predominantly derived from the pericallosal branches of the anterior cerebral arterial circulation. The splenium additionally receives supply from branches of the posterior cerebral artery, contributing to the relatively rich vascularisation of the corpus callosum.

Clinical correlates

Acquired callosal lesions can produce interhemispheric disconnection syndromes, while surgical corpus callosotomy may be performed in selected patients with medically refractory epilepsy, particularly disabling drop attacks. The corpus callosum may also be affected by demyelinating disease, especially multiple sclerosis, as well as tumours, trauma and, less commonly, infarction.

Important distinction

The corpus callosum contains commissural fibres, which cross the midline to connect the two hemispheres. This distinguishes them from association fibres, which connect cortical regions within the same hemisphere, and projection fibres, which connect the cerebral cortex with subcortical structures, brainstem and spinal cord.