Head – Brain

BRAIN

Describe the anatomy of the corpus callosum (30 marks)

DESCRIPTION

• Largest white myelinated tract allowing electrical communication between two brain hemispheres
• Approximately 10cm anterior to posterior
• Inverted U shape

4 PARTS:

1. Rostrum
2. Genu (frontal forceps)
3. Body + tapetum
4. Splenium (occipital forceps)

Rostrum

• anteroinferior tip of genu
• connects frontal lobes – orbital parts (i.e. inferior)

Genu & frontal forceps (minor)

• most anterior section
• curved (knee-like)
• fibres curve forward as forceps minor
• connects lateral / medial frontal lobes

Body

• Central section
• fibres pass laterally to intersect with projection fibres of corona radiata to connect wider areas of hemispheres
• located superior to thalamus, lateral ventricles and septum pellucidum
• indusium griseum = thin grey matter which covers superior surface of corpus callosum and continuous laterally with grey matter of cingulate cortex
• + Tapetum
  • formed by body + some splenium fibres
  • forms the roof of the posterior horn of the lateral ventricle

Splenium & occipital forceps (major)

• Posterior tail
• superior to quadrigeminal cistern
• fibres curve into occipital lobes as forceps major

WHITE MATTER COURSE

• Midline/body of corpus callosum: CC fibres left to right
• Laterally: fibres fan out and intermingle with projection and association tracts

ARTERY

• Pericallosal arteries (immediately superior) + callosomarginal artery from ACA
• Subcallosal artery 50% (from ACA)
• Medial callosal artery30%

VEIN

• callosal vein / posterior vein of corpus callosum -> great cerebral vein / Galen -> straight sinus
• septal veins of internal cerebral vein -> great cerebral vein of Galen

RELATIONS

• Anterior: frontal lobe
• Posterior: falx, straight sinus, inferior sagittal sinus, occipital lobes
• Lateral: corona radiata, cortex superficial surface
• Superior:
  • indusium griseum = grey matter directly above corpus callosum
  • cingulum = cingulate gyrus,
  • superior longitudinal fasciculus
  • short arcuate fibres
  • longitudinal cerebral fissure and falx
  • corona radiata
• Inferior:
  • septum pellucidum,
  • fornix,
  • 3rd ventricle, lateral ventricle
  • thalamus
  • pituitary gland,
  • anterior commissure,
  • basal ganglia (caudate, putamen, globus pallidus)

VARIANTS

• Dysgenesis of corpus callosum
• Absent splenium