Callosal Dysgenesis

KEY FACTS

TERMINOLOGY

• Partial or complete absence of corpus callosum (CC),

hippocampal commissure, or anterior commissure (AC); can

be isolated or associated with additional cerebral

malformations

• Spectrum of congenital CC structural abnormalities

○ Total agenesis (absence from birth of all anatomically

defined regions of CC)

○ Partial agenesis (absence from birth of at least 1, but not

all, regions of CC)

○ Hypoplasia (thinner CC with normal anteroposterior

extent)

○ Hyperplasia (thick CC resulting from decreased postnatal

axonal pruning)

○ Dysgenesis (CC present but malformed in some way,

including partial AC and hypoplasia of CC)

IMAGING

• Absent corpus callosum on sagittal, coronal views

• Atrium/occipital horns often dilated (colpocephaly)

• DTI: Callosal fiber tracts form Probst bundles instead of

crossing, where corpus callosum is absent

• Vertical/posterior course of anterior cerebral artery

CLINICAL ISSUES

• Any age; classically identified in early childhood, most

common malformation found in fetuses

• Seizures, developmental delay, cranial

deformity/hypertelorism

• Sporadic/isolated agenesis/dysgenesis corpus callosum:

Normal/near normal at 3 years (75%), but subtle cognitive

defects apparent with increasing complexity of school tasks

• Agenesis/dysgenesis CC with associated/syndromic

anomalies = worst

DIAGNOSTIC CHECKLIST

• Look for absent/incomplete CC rather than indirect signs

• Fully assess for associated lesions

(Left) Coronal graphic shows a

lack of transverse corpus

callosum and separate lateral

ventricles. The

interhemispheric fissure

extends to the 3rd ventricle.

The bundles of Probst ﬈

contain the parasagittally

rerouted callosal fibers.

(Right) Coronal T2WI with

callosal dysgenesis shows

Viking helmet or moose head

appearance of widely

separated lateral ventricles

﬇. The very hypointense

white matter tracts medial to

the lateral ventricles are the

Probst bundles ſt. Note the

heterotopic GM st.

(Left) Sagittal T2WI in the

same patient shows absence

of the corpus callosum,

radially oriented gyri

converging on a high-riding

3rd ventricle. Note the

azygous anterior cerebral

artery ﬈. The anterior

commissure is also absent.

(Right) Axial T2WI in the same

case shows the characteristic

parallel, nonconverging lateral

ventricles ﬇ seen in corpus

callosum agenesis. Heavily

myelinated Probst bundles ſt

are seen just medial to the

lateral ventricles.

Trauma, and Stroke

Brain: Pathology-Based Diagnoses: Malformations,

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