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Corpus Callosum Agenesis (ACC) is a congenital malformation characterized by partial or complete absence of the corpus callosum, the major commissural tract connecting the two cerebral hemispheres.

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https://www.youtube.com/watch?v=TBMCCqso8ag

It results from disruption in commissural axonal growth or midline patterning during embryonic development, typically between the 12th and 16th weeks of gestation.

Embryology

Corpus callosum develops from anterior to posterior (genu → body → splenium).
Disruption at any stage (genetic, metabolic, infectious, or toxic) can lead to agenesis or dysgenesis.
Associated with a variety of syndromes and CNS malformations.

Types of Agenesis:

Type	Description
Complete agenesis	Entire corpus callosum (rostrum, genu, body, splenium) is absent
Partial agenesis	Most commonly involves absence of splenium and body, with preservation of genu/rostrum
Hypoplasia	Corpus callosum is thin or underdeveloped
Dysgenesis	Abnormal development or malformation (e.g., thick, short, or irregular CC)

Clinical features

Isolated ACC may be asymptomatic or cause:
- Mild intellectual disability
- Language or learning delays
- Seizures (in some cases)
Syndromic ACC or associated with CNS anomalies:
- Global developmental delay
- Epilepsy
- Hydrocephalus
- Endocrinopathies (if hypothalamic involvement)

Radiology

Prenatal imaging:

Modality	Key Findings
US	- Absent cavum septum pellucidum (CSP)

Widely spaced lateral ventricles (“teardrop ventricles”)
High-riding 3rd ventricle | | MR | - Confirms absence of corpus callosum
Assesses associated malformations (e.g., cortical migration anomalies) |

![Neuroanatomical features of agenesis of the corpus callosum (AgCC) and callosal hypogenesis revealed by MRI and diffusion tensor imaging (DTI). Structural T1-weighted MRI (top 3 rows) and directionally encoded colour anisotropy dMRI (bottom row) are shown from a normal young adult male volunteer (left column), a young adult male with AgCC (middle column), and a young adult male with callosal hypogenesis (right column). The DTI images encode fibre orientation in white matter tracts using a three-colour scheme such that fibre pathways with predominantly left–right orientation are displayed as red, anteroposterior orientation as green, and craniocaudal orientation as purple.

AC, anterior commissure; ASB, anterior sigmoid bundle; C, colpocephaly; CB, cingulum bundle; CC, corpus callosum; CM, cortical malformation; PB, Probst bundle. Paul, L., Brown, W., Adolphs, R. et al. Agenesis of the corpus callosum: genetic, developmental and functional aspects of connectivity. Nat Rev Neurosci 8, 287–299 (2007). https://doi.org/10.1038/nrn2107](attachment:5323d6fe-cced-4610-9ed9-19866b141770:41583_2007_Article_BFnrn2107x_Fig2_HTML.webp)

Neuroanatomical features of agenesis of the corpus callosum (AgCC) and callosal hypogenesis revealed by MRI and diffusion tensor imaging (DTI). Structural T1-weighted MRI (top 3 rows) and directionally encoded colour anisotropy dMRI (bottom row) are shown from a normal young adult male volunteer (left column), a young adult male with AgCC (middle column), and a young adult male with callosal hypogenesis (right column). The DTI images encode fibre orientation in white matter tracts using a three-colour scheme such that fibre pathways with predominantly left–right orientation are displayed as red, anteroposterior orientation as green, and craniocaudal orientation as purple.

Postnatal MR (modality of choice):