Dysgenesis of the corpus callosum may be complete (agenesis) or partial and represents an in utero developmental anomaly.
It can be divided into:
- primary agenesis: the corpus callosum never forms
- secondary dysgenesis: the corpus callosum forms normally and is subsequently destroyed
A true estimate of incidence is difficult to establish as many isolated cases are asymptomatic. It may be as uncommon as 1:20,000 according to autopsy series 6. It should be noted however that in paediatric neuroradiology practice it may be seen in as many as 1% of referrals, clearly representing a significant selection bias, attributable to the large number of symptomatic associated abnormalities.
There appears to be a male predilection (M:F ~2:1) 6. Maternal alcohol consumption during pregnancy has been recognised as an other risk factor 6.
Associated anomalies can be frequent and broad which includes:
- aneuploidy syndrome
- non-aneuploidy syndrome
- other CNS associations: often multiple present
- inborn errors of metabolism 6
Isolated partial dysgenesis of the corpus callosum is often asymptomatic. The clinical picture in other cases is dictated by the associated abnormalities that are frequently found, especially in agenesis 4.
Children with agenesis may have dysmorphic facies, most commonly demonstrating hypertelorism 6.
Agenesis is a result of an insult occurring at approximately 8-12 weeks gestation 2,4 resulting in failure to form the corpus callosum. The white matter tracts which usually cross the midline, instead are oriented vertically, separating the lateral ventricles widely, in a racing car sign configuration. These bundles of white matter are known as Probst bundles.
Dysgenesis (which may be complete or partial) is a result of encephalomalacia secondary to toxic, ischaemic or traumatic events 2.
The development of the corpus callosum occurs between the 12th and 16-20th weeks of gestation 2,4. It begins with the genu and then continues posteriorly along the body to the splenium. The rostrum is the last part to be formed. In primary agenesis parts of the corpus callosum which form before the insult will be present whereas later parts will be absent. Presence of the rostrum essentially excludes primary agenesis.
Myelination of the corpus callosum occurs in the opposite direction, from the splenium forwards.
As with other structural anomalies, all modalities reflect the underlying morphology, with a greater lesser degree of sensitivity.
- third ventricle 5
- can be elevated or dorsally displaced 8
- may communicate with the interhemispheric cistern
- may project superiorly as a dorsal cyst
- choroid may be seen as echogenic structure in the roof of the cyst
- lateral ventricles
- septum pellucidum: absent
- interhemispheric fissures: widened
- gyri: may be seen in a "sunray appearance" on the sagittal plane
- colour Doppler study may show an abnormal course of pericallosal arteries
MRI is the modality of choice in evaluating both the corpus callosum and the frequently associated anomalies. Features include:
- ventricles run parallel rather than the normal "bow-tie" configuration giving a racing car appearance on axial imaging
- colpocephaly (dilatation of the trigones and occipital horns) gives a characteristic "longhorn"/moose head/viking helmet appearance on coronal imaging
- dilated high-riding 3rd ventricle communicating with the interhemispheric cistern or projecting superiorly as a dorsal cyst
- bundles of Probst
- radial gyri (absent cingulate gyrus)
- everted cingulate gyrus 10
- limbic system 4
Angiography no longer has a role in diagnosis, however if performed for other reasons may demonstrate an abnormal course of the anterior cerebral artery, passing directly postero-superiorly with widely spaced pericallosal arteries, and absent pericallosal moustache.
Treatment and prognosis
The overall prognosis can be highly variable dependent on the presence of other associated anomalies.
High quality MRI essentially eliminates differentials due to the exquisite imaging of the corpus callosum.
In the setting of an antenatal ultrasound demonstrating an interhemispheric cyst then the following should be considered 5:
The key in distinguishing these entities from a dilated third ventricle with dorsal cyst is identifying the choroid plexus, which demarcates the roof of the the third ventricle 5.
- 1. Loevner LA. Case review, brain imaging. Mosby Inc. (1999) ISBN:032300430X. Read it at Google Books - Find it at Amazon
- 2. Kornienko VN, Pronin IN. Diagnostic Neuroradiology. Springer Verlag. (2009) ISBN:3540756523. Read it at Google Books - Find it at Amazon
- 3. Tang PH, Bartha AI, Norton ME et-al. Agenesis of the corpus callosum: an MR imaging analysis of associated abnormalities in the fetus. AJNR Am J Neuroradiol. 2009;30 (2): 257-63. doi:10.3174/ajnr.A1331 - Pubmed citation
- 4. Ketonen L, Hiwatashi A, Sidhu R. Pediatric brain and spine, an atlas of MRI and spectroscopy. Springer Verlag. (2005) ISBN:3540213406. Read it at Google Books - Find it at Amazon
- 5. Gebarski SS, Gebarski KS, Bowerman RA et-al. Agenesis of the corpus callosum: sonographic features. Radiology. 1984;151 (2): 443-8. Radiology (abstract) - Pubmed citation
- 6. Kumar P, Burton BK. Congenital malformations, evidence-based evaluation and management. McGraw-Hill Professional. (2007) ISBN:0071471898. Read it at Google Books - Find it at Amazon
- 7. Oba H, Barkovich AJ. Holoprosencephaly: an analysis of callosal formation and its relation to development of the interhemispheric fissure. AJNR Am J Neuroradiol. 1995;16 (3): 453-60. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 8. Warren ME, Cook JV. Agenesis of the corpus callosum. Br J Radiol. 1993;66 (781): 81-5. doi:10.1259/0007-1285-66-781-81 - Pubmed citation
- 9. Bertino RE, Nyberg DA, Cyr DR et-al. Prenatal diagnosis of agenesis of the corpus callosum. J Ultrasound Med. 1988;7 (5): 251-60. J Ultrasound Med (abstract) - Pubmed citation
- 10. Barkovich AJ, Norman D. Anomalies of the corpus callosum: correlation with further anomalies of the brain. AJR Am J Roentgenol. 1988;151 (1): 171-9. AJR Am J Roentgenol (abstract) - Pubmed citation
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Agenesis of the corpus callosum||✗|
|Corpus callosum agenesis||✓|
|Corpus callosum dysgenesis||✗|
|Agenesis of the corpus callosum (AGCC)||✗|
|Corpus callosal dysgenesis||✗|