Reminder: the Corpus Callosum is a bundle of white fibers connecting the two cerebral hemispheres (each part of a lobe with his counterpart in the other hemisphere). It allows the two hemispheres to communicate very quickly: the inter-hemispheric transfer of information lasts from 20 to 50 ms.

It is composed of 4 parts:

1.                the rostrum or isthmus, connecting essentially the 2 frontal lobes and part of the temporal lobes.

2.        the knee: the rounded part that makes essentially the link between the 2 frontal lobes; the posterior two-thirds consist inter-temporal fibers, and more posteriorly inter-parietal fibers.

3.        the trunk: the flattest part of the Corpus Callosum; its anterior part continues to connect the frontal lobes, but also the parietal lobes. Its posterior part connects the temporal lobes.

4. the splenium, connecting the occipital lobes.

On the other hand, the corpus callosum is composed of two types of fibers:

-        homotypic fibers (the majority of fibers) linking cortical areas of the same nature

-        heterotypic fibers linking non-homologous cortical areas (vision to speech area ,for example).

These fibers are transversal in the center of the corpus callosum but radiate to all parts to the cortex when they enter into the hemispheres.

Total or partial agenesis of the corpus callosum is found in many syndromes: it could be present in 0.05 to 0.7 % of the population and 2-3 % of patients suffering from mental disabilities.

One distinguishes:

-        isolated forms (50 %): no other brain anomaly is present; it can be a - or paucisymptomatic: disorders of cognitive functions (calculation, abstract reasoning) and social adjustment; intellectual impairment in 20 % of cases

-        associated forms : frequent developmental disabilities; other disorders are mainly related to other cerebral or extracerebral abnormalities .

Morphologically, there are the 'classic' agenesis and the total absence of corpus callosum: in the first case, the nerve fibers do not cross the midline but gather into longitudinal beams called Probst bundles.

Possible causes of agenesis of the corpus callosum:

-        chromosomal abnormalities: many trisomies (21, 13, 18, 11Q), mosaic tetrasomy 8 in mosaic, or abnormalities of structure (deletion 1 p 36, 6pter etc.).

-        syndromes with a known gene (< 300 !):

       - X-linked: Papillon-League, cranio-fronto-nasal dysplasia, X-linked hydrocephalus,
                   Opitz, FG, certain mutations in the ARX gene

       - autosomal recessive: Andermann, Donnai-Barrow, acrocallosal, Chudley-McCullough

       - autosomal dominant: Mowat-Wilson, Pitt-Hopkins, Greig cephalopolysyndactyly,
                                      genitopatellar syndrome

-        syndromes without a so far dentified gene: Aicardi, Fryns, Toriello-Carey

-        metabolic disease (2 % of cases): in some cases of pyruvate-dehydrogenase deficiency without ketosis, peroxisomal or mitochondrial diseases, disorders of the cholesterol synthesis disorders

-        environmental causes: in some cases of fetal alcohol syndrome (6.8 %),  in utero CMV infection, maternal phenylketonuria, antiepileptic drugs intake during pregnancy.

Anesthetic implications:

according to the associated brain malformations or metabolic disorders.

References :

-        Héron D, Mignot C, Burgien L.
Syndromes avec malformations cérébrales,
in Syndromes dysmorphiques, D Lacombe er N Philip, Doin 2013, p 231-49

Updated: December 2019