Corpus Callosum

This photo gallery presents the anatomy of corpus callosum by means of MRI (T1-weighted sagittal, axial and coronal views).

The corpus callosum, meaning “calloused body” in Latin, is a thick bundle of nerves that bridges the brain’s two cerebral hemispheres or sides⁽¹⁾.

The rapid development of the corpus callosum starting from infancy continues until an individual reaches four⁽²⁾.  Following that, the corpus callosum’s growth continues at a much slower pace until the person’s third decade of life.

Anatomy of the Corpus Callosum

A sagittal (longitudinal or lengthwise) cross-sectional view of the brain reveals a sizable curved structure in the middle. This structure is the corpus callosum⁽³⁾.

The corpus callosum is composed of almost 200 million nerve fibers⁽⁴⁾. These nerve fibers have a white appearance due to the myelin covering the neurons’ axons.

Axons are the tail ends of neurons that carry electrical impulses away from the cell body. Meanwhile, myelin is a fatty protective substance that sheaths the axons and gives white brain matter its distinctive color.

The corpus callosum’s nerve fibers are arranged in an orderly way and connect to the mirror or corresponding cortical patch of each hemisphere⁽⁵⁾.

This arrangement means that the occipital area (back and lower end) of the left hemisphere is connected to the occipital area of the right hemisphere⁽⁶⁾. Similarly, nerve fibers on the frontal lobe of the left hemisphere symmetrically connect to the frontal lobe of the right hemisphere.

The corpus callosum has four parts, with each part connecting to different areas of the cerebral cortex or outer layer.

The sections going from the anterior to posterior (front to back) are the following:

• The rostrum is often the thinnest part of the corpus callosum⁽⁷⁾. The nerve fibers in this area connect the frontal lobes of the brain⁽⁸⁾. 
• The genu or knee is the bend or corner immediately behind the rostrum. The nerve fibers in this part of the corpus callosum also connect the frontal lobes⁽⁹⁾.  
• The body or trunk is the posterior part or back end of the genu. The nerve fibers of the body form large white matter tracts or pathways, such as the corona radiata⁽¹⁰⁾. 
• The splenium is the bulbous part of the corpus callosum that connects the occipital lobes. The splenium’s nerve fibers also form the forceps major, a bulging mass found on the middle wall of the atrium⁽¹¹⁾.  

Additionally, between the body and the splenium towards the back of the corpus callosum is a narrow area called the isthmus⁽¹²⁾. 

Blood supply to the corpus callosum primarily comes from the internal carotid artery network, particularly the pericallosal artery (a branch of the front or anterior cerebral artery)⁽¹³⁾. 

Functions of the Corpus Callosum

The primary function of the corpus callosum is to enable communication or send information signals between the brain’s left and right hemispheres⁽¹⁴⁾.

The information that travels through the corpus callosum allows the brain to process motor, sensory, and high-level cognitive signals. These signals are continually being sent between the hemispheres⁽¹⁵⁾.

Findings indicated that the different locations of the corpus callosum’s nerve fibers transfer specific information⁽¹⁶⁾:

• Motor information – transferred through the anterior callosal fibers or nerve fibers in the rostrum
• Somatosensory signals – transferred through the posterior fibers
• Auditory information – sent through the nerve fibers in the isthmus
• Visual cues – communicated through the nerve fibers in the splenium

Moreover, researchers noted that the corpus callosum may play a vital role in improving motor movements and cognitive functions as the individual grows and the brain matures⁽¹⁷⁾.

Clinical Significance of the Corpus Callosum

Damage to the corpus callosum may result in the two brain hemispheres losing their sole method of communication⁽¹⁸⁾.

Severing the corpus callosum would cause the loss of a range of functions, including speech, visual perception, and memory⁽¹⁹⁾.

Agenesis or the imperfect development of the corpus callosum may result in intellectual impairment and seizures⁽²⁰⁾.

Additionally, researchers noted that demyelinating lesions or lesions that damage the myelin sheath (protective covering nerve fibers in the corpus callosum) may result in multiple sclerosis⁽²¹⁾.

Another disorder that may affect the corpus callosum is the Marchiafava-Bignami disease. This condition is characterized by accelerating or continuous demyelination of the corpus callosum’s cells or nerve fibers⁽²²⁾.

Traumatic brain injury, metabolic dysfunction, and exposure to specific viruses may trigger demyelination and cause corpus callosum lesions⁽²³⁾.

Ischemia of the corpus callosum is rare, though still a possibility. Ruptured aneurysms in the cerebral and pericallosal artery (end part of the anterior cerebral artery) usually results in hemorrhage in the corpus callosum⁽²⁴⁾.

Computed tomography (CT) angiograms and three-dimensional or 3D time of flight magnetic resonance (MR) angiography are recommended for locating hematomas (collection or pool of blood) in the corpus callosum⁽²⁵⁾.

Reference:

• Harnsberger HR, Osborn AG, Ross JS, Moore KR, Salzman KL, Carrasco CR, Halmiton BE, Davidson HC, Wiggins RH. Diagnostic and Surgical Imaging Anatomy: Brain, Head and Neck, Spine. 3rd ed. Salt Lake City, Utah. Amirsys. 2007.
• Bourjat P, Veillon F. Imagerie radiologique tête et cou. Paris, Vigot. 1995.
• Gouazé A, Baumann JA, Dhem A. Sobota. Atlas d’Anatomie humaine. Tome 3. Système nerveux central, système nerveux autonome, organe des sens et peau, vaisseaux et nerfs périphériques. 1er éd. Paris, Maloine. 1977.
• Kahle W, Cabrol C. Anatomie. Tome 3: Système nerveux et organe des sens. 1er éd. Paris, Flammarion. 1979.

1. Elsevier, Incorporated. (2013). The brain. In Fundamentals of cognitive neuroscience (pp.98-108). Academic Press. Retrieved from https://www.sciencedirect.com/topics/medicine-and-dentistry/hemisphere
2. Goldstein, A., Covington, B. P., Mahabadi, N., & Mesfin, F. B. (2020). Neuroanatomy, Corpus Callosum. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK448209/
3. Baynes, K. (2002). Corpus Callosum. In K. Baynes (ed.), Encyclopedia of the brain (pp.51-64). Academic Press, Elsevier Science Ltd. https://www.sciencedirect.com/topics/neuroscience/corpus-callosum 
4. Goldstein, A., et al. (2020). Op. cit.
5. Elsevier, Incorporated. (2013). The brain. Op. cit.
6. Ibid.
7. De Melo Mussi, A. C. & da Luz de Oliveira, E. P. (2019). Chapter 5 – Ventricular Anatomy, In Comprehensive overview of modern surgical approaches to intrinsic brain tumors (pp.107-118). Academic Press, Elsevier Science Ltd. https://www.sciencedirect.com/topics/neuroscience/corpus-callosum
8. Goldstein, A., et al. (2020). Op. cit.
9. De Melo Mussi, A. C. & da Luz de Oliveira, E. P. (2019). Op. cit.
10. Goldstein, A., et al. (2020). Op. cit.
11. De Melo Mussi, A. C. & da Luz de Oliveira, E. P. (2019). Op. cit.
12. Goldstein, A., et al. (2020). Op. cit.
13. Ibid.
14. Ibid.
15. The University of Queensland. (n.d.). Corpus callosum. Retrieved from https://qbi.uq.edu.au/brain/brain-anatomy/corpus-callosum
16. Goldstein, A., et al. (2020). Op. cit.
17. Ibid.
18. The University of Queensland. (n.d.). Op. cit.
19. Ibid.
20. Britannica, T. Editors of Encyclopaedia. (2009, April 9). Corpus callosum. In Encyclopedia Britannica. https://www.britannica.com/science/corpus-callosum
21. Goldstein, A., et al. (2020). Op. cit.
22. Britannica, T. Editors of Encyclopaedia. (2009, April 9). Op. cit.
23. Goldstein, A., et al. (2020). Op. cit.
24. Ibid.
25. Ibid.