Corpus Callosum (Splenium)

The splenium of the corpus callosum is the thick, rounded posterior portion of the corpus callosum, the largest commissural fiber bundle connecting the right and left cerebral hemispheres. It forms the posterior end of the corpus callosum and is continuous anteriorly with the body.

Fibers passing through the splenium connect posterior cortical regions of the two hemispheres, including portions of the parietal, temporal, and occipital lobes. A prominent group of splenial fibers curves posteriorly into the occipital lobes as the forceps major.

Through these connections, the splenium contributes to interhemispheric transfer of visual, visuospatial, sensory association, language-related, and higher-order information. Its posterior location and extensive connections make it especially important for integration between visual cortical areas and posterior association networks.

Corpus Callosum

The corpus callosum is the principal commissural pathway of the cerebral hemispheres. It contains a massive collection of myelinated axons crossing the midline between corresponding and functionally related cortical territories.

On midsagittal examination, the corpus callosum forms a curved white matter structure above the ventricular system and diencephalon.

Parts of the Corpus Callosum

Part	Position	General Fiber Distribution
Rostrum	Thin inferior anterior portion	Inferior and orbital frontal regions
Genu	Anterior bend	Frontal and prefrontal regions
Body	Long central portion	Posterior frontal and parietal regions
Splenium	Thick rounded posterior portion	Posterior parietal, temporal and occipital regions

Location

The splenium lies at the posterior end of the corpus callosum in the cerebral midline. It is positioned posterior to the callosal body and superior to structures of the posterior diencephalic and ventricular regions.

On midsagittal sections and MRI, it is readily recognized by its characteristic thick, rounded appearance.

Shape

The splenium is typically the thickest and most bulbous portion of the corpus callosum. Its rounded contour distinguishes it from the relatively elongated body and the anterior curvature of the genu.

Relationship to the Body

Anteriorly, the splenium is continuous with the body of the corpus callosum. The transition is gradual, and subdivisions of the corpus callosum are descriptive rather than sharply separated histological compartments.

Relationship to the Lateral Ventricles

The splenium is closely related to the posterior parts of the lateral ventricles. Fibers radiating from the posterior corpus callosum contribute to the white matter surrounding the atrium and occipital horn.

This relationship is particularly important in sectional neuroanatomy and neuroimaging.

Relationship to the Third Ventricle

The splenium lies superior and posterior to the third ventricular region. Its position provides an important landmark for identifying neighboring midline structures on sagittal imaging.

Relationship to the Pineal Region

The pineal gland lies inferior to the posterior corpus callosum and posterior to the third ventricle. The splenium therefore forms an important superior anatomical relationship of the pineal region.

Relationship to the Cingulate Gyrus

The cingulate gyrus follows the superior contour of the corpus callosum. Posteriorly, the cingulate region curves around the splenium and continues toward the parahippocampal region through the isthmus of the cingulate gyrus.

The cingulum within this region is an association tract and is anatomically distinct from the commissural fibers of the splenium.

Fiber Classification

Fibers of the splenium are commissural fibers. They cross the cerebral midline to connect cortical regions of the right and left hemispheres.

Fiber Type	Connection	Example
Commissural	Between cerebral hemispheres	Corpus callosum
Association	Between cortical regions within one hemisphere	Cingulum
Projection	Between cortex and subcortical structures	Internal capsule

Callosal Radiations

After crossing through the splenium, callosal fibers spread laterally and posteriorly through the cerebral white matter as part of the callosal radiations.

These fibers intermingle with other white matter pathways while traveling toward posterior parietal, temporal, and occipital cortical territories.

Forceps Major

A major group of fibers arising from the splenium curves posteriorly into the occipital lobes to form the forceps major.

On horizontal sections, fibers from the two sides create a forceps-like configuration around the posterior ventricular region.

The forceps major provides important commissural connections between posterior cortical regions, particularly the occipital lobes.

Occipital Connections

The splenium contains extensive fibers connecting the occipital lobes. These connections permit visual information processed in one hemisphere to interact with visual and association networks in the opposite hemisphere.

This is particularly important because each cerebral hemisphere initially receives visual information predominantly from the contralateral visual hemifield.

Visual Cortical Integration

Normal visual perception requires integration across cortical regions in both hemispheres. Splenial fibers allow posterior visual and association areas to exchange information across the midline.

This communication contributes to unified processing of objects, scenes, spatial relationships, and visually presented information.

Parietal Connections

Fibers passing through the splenium also connect posterior parietal association cortex. These regions participate in visuospatial processing, attention, sensory integration, and representation of the body and surrounding environment.

Interhemispheric communication allows bilateral parietal networks to coordinate these functions.

Temporal Connections

The splenium contains commissural fibers associated with posterior temporal cortical regions. These connections contribute to bilateral communication among networks involved in visual recognition, semantic processing, auditory association, and multimodal integration.

Posterior Association Cortex

The posterior parietal, temporal, and occipital lobes contain extensive association cortex. These areas integrate information from multiple sensory systems and contribute to perception, language, spatial cognition, recognition, and memory-related processing.

Splenial fibers provide an important structural route connecting these distributed networks across the hemispheres.

Interhemispheric Visual Transfer

Visual information reaching one hemisphere can be transferred to the opposite hemisphere through posterior commissural connections, particularly the splenium.

This becomes clinically important when visual information reaches the nondominant hemisphere but must be transferred to dominant hemisphere language networks for naming or reading.

Language-Related Functions

The splenium is not itself a language center, but its fibers can be essential for transferring visually processed information to language-dominant cortical networks.

Disruption of posterior callosal connections can therefore contribute to specific disconnection syndromes involving reading and naming.

Reading

Reading requires visual information to reach cortical networks capable of linguistic interpretation. In most individuals, language networks are predominantly left lateralized.

Visual information initially processed in the right occipital cortex may need to cross through posterior callosal fibers to reach left hemisphere language-related regions.

Damage to this transfer pathway can contribute to characteristic reading disorders when associated posterior cortical pathways are also affected.

Interhemispheric Integration

The fundamental role of the splenium is interhemispheric communication between posterior cerebral regions.

It allows visual, spatial, sensory association, and higher-order information represented in one hemisphere to influence processing in the other.

Topographic Organization

The corpus callosum has broad topographic organization. Anterior portions predominantly contain frontal connections, the body carries many posterior frontal and parietal fibers, and the splenium contains many fibers connecting posterior parietal, temporal, and occipital territories.

These divisions overlap, and modern tractography demonstrates that callosal fiber organization is more complex than rigid anatomical compartments.

Splenium Compared with Other Callosal Parts

Part	Major Connections
Rostrum	Inferior and orbital frontal regions
Genu	Frontal and prefrontal regions
Body	Posterior frontal, motor, somatosensory and parietal regions
Splenium	Posterior parietal, temporal and occipital regions

Forceps Major and Forceps Minor

Feature	Forceps Major	Forceps Minor
Callosal origin	Splenium	Genu
Direction	Posterior	Anterior
Primary lobe	Occipital	Frontal
Major role	Posterior and visual interhemispheric connectivity	Frontal interhemispheric connectivity

Tapetum

Some callosal fibers extend laterally and inferiorly along the walls of the posterior and inferior portions of the lateral ventricles, contributing to the tapetum.

The tapetum forms a thin sheet of commissural fibers associated with the lateral ventricular wall and is related particularly to posterior callosal fiber systems.

Development

The corpus callosum develops during fetal life as commissural axons cross specialized midline structures and establish connections with the opposite cerebral hemisphere.

Development of posterior callosal regions requires appropriate growth and guidance of axons connecting posterior cortical territories.

Myelination

Splenial axons are myelinated by oligodendrocytes. Myelination increases conduction speed and efficiency across the cerebral midline.

The corpus callosum continues to mature after birth as axonal organization and myelination develop through childhood and adolescence.

Blood Supply

The splenium has a relatively rich vascular supply. It receives contributions from the posterior pericallosal arteries, which arise from the posterior cerebral circulation, as well as anastomotic contributions from anterior pericallosal vessels.

This overlapping arterial supply helps explain why isolated callosal infarction is less common than infarction in many other cerebral territories.

MRI Appearance

The splenium is readily identified on magnetic resonance imaging because of its thick, rounded appearance at the posterior end of the corpus callosum.

Its size, shape, signal characteristics, and relationship to neighboring structures can provide useful information in evaluating developmental, inflammatory, metabolic, vascular, traumatic, and neoplastic disorders.

Diffusion MRI and Tractography

Diffusion-weighted MRI and tractography can demonstrate the transverse and posteriorly curving orientation of splenial fibers.

These methods can reconstruct the forceps major and estimate connections between posterior cortical territories, although tractography remains an indirect representation of underlying axonal anatomy.

Clinical Significance

Splenial Lesions

Lesions of the splenium can disrupt interhemispheric transfer between posterior cortical regions. Manifestations depend on lesion laterality, extent, associated cortical injury, and the specific callosal fibers affected.

Disconnection Syndromes

Posterior callosal damage can produce disconnection syndromes in which visual or other sensory information processed by one hemisphere cannot be efficiently transferred to specialized cortical networks in the opposite hemisphere.

Alexia Without Agraphia

Alexia without agraphia, also called pure alexia, is classically associated with a lesion involving the dominant occipital cortex together with posterior callosal fibers, often affecting the splenium.

In the classic left-sided lesion, visual information from the right visual field cannot be processed by the damaged left occipital cortex, while information from the left visual field reaches the right occipital cortex but cannot efficiently cross the damaged splenium to reach left hemisphere language networks.

The patient may therefore lose the ability to read while retaining the ability to write.

Visual Naming Deficits

Disruption of posterior callosal transfer can interfere with the ability to verbally identify visual information initially processed in the hemisphere opposite the dominant language cortex.

Such findings demonstrate the importance of splenial fibers in transferring visual information between hemispheres.

Traumatic Brain Injury

The corpus callosum is vulnerable to shearing forces during rapid acceleration, deceleration, and rotational head injury. The splenium is a recognized site of involvement in diffuse axonal injury.

Clinical consequences usually reflect widespread brain injury rather than an isolated splenial lesion.

Demyelinating Disease

The splenium can be affected by disorders of central nervous system myelin, including multiple sclerosis. Callosal lesions may disrupt posterior interhemispheric communication and are readily evaluated with MRI.

Ischemic Lesions

Infarction of the splenium can occur with compromise of posterior callosal arterial supply. Because splenial functions involve posterior interhemispheric transfer, deficits may include disturbances of visual, cognitive, or language-related integration depending on associated lesions.

Transient and Reversible Splenial Lesions

Restricted diffusion and signal abnormalities can occasionally appear within the splenium in association with a variety of neurological and systemic conditions.

Some of these lesions are transient and may resolve on follow-up imaging. Their clinical significance depends on the underlying disorder and broader neurological context.

Brain Tumors

Infiltrative tumors can involve the splenium and may extend across the posterior corpus callosum between the cerebral hemispheres.

The continuous white matter of the corpus callosum provides a potential route for spread of infiltrative processes.

Agenesis and Dysgenesis

Developmental abnormalities of the corpus callosum may involve complete absence, partial absence, or abnormal formation of posterior callosal structures.

The clinical presentation varies widely and depends strongly on associated cerebral malformations and developmental reorganization.

Splenium Compared with the Anterior Commissure

Feature	Splenium	Anterior Commissure
Fiber type	Commissural	Commissural
Parent structure	Corpus callosum	Independent commissure
Major connections	Posterior parietal, temporal and occipital regions	Temporal and olfactory-associated regions
Characteristic fibers	Forceps major	Temporal and olfactory commissural fibers

Key Anatomical Features

Feature	Key Point
Structure	Thick posterior portion of corpus callosum
Fiber classification	Commissural fibers
Anterior continuation	Body of corpus callosum
Characteristic radiation	Forceps major
Major cortical connections	Posterior parietal, temporal and occipital cortex
Major functional association	Posterior interhemispheric integration
Visual role	Transfer of visual information between hemispheres
Ventricular relationship	Related to posterior lateral ventricular regions
Inferior relationship	Pineal and posterior diencephalic region
Important clinical association	Posterior disconnection syndromes

Anatomical Importance

The splenium forms the thick posterior end of the corpus callosum and contains extensive commissural fibers connecting posterior parietal, temporal, and occipital cortical regions. Its fibers include the forceps major, which curves posteriorly into the occipital lobes.

This anatomical arrangement makes the splenium particularly important for transferring visual and higher-order association information between the cerebral hemispheres. Posterior cortical networks can therefore operate as coordinated bilateral systems despite the lateralized organization of many sensory and cognitive functions.

The clinical importance of the splenium is especially apparent in posterior disconnection syndromes. Damage can prevent visual information processed in one hemisphere from reaching specialized networks in the other, illustrating how normal perception and cognition depend not only on intact cortical regions but also on the white matter pathways connecting them.