Corpus callosum agenesis: a review

The corpus callosum (CC) connects the two brain hemispheres through axonal fiber tissues, being important for the functional integration of sensory, motor, visuomotor and cognitive processes, in addition to processing and management of social and emotional stimuli. Agenesis of the corpus callosum (ACC) is a congenital brain malformation defined by anatomy (complete or partial absence of the corpus callosum), rarely occurring in isolation and is a specific and relatively easy to detect phenotypic marker for developmental disorders. The prevalence of ACC in the general population is extremely variable and probably underestimated due to the asymptomatic course, the usual range is 0.020–0.025%, in individuals with neurodevelopmental impairment this defect has a prevalence of 1 to 3%. Etiology that varies, from maternal alcohol consumption, to prenatal infections, chromosomal errors or genetic mutations. Fetal alcohol syndrome (FAS) is the most important non-genetic congenital cause of ACC, with an incidence of approximately 7% in FAS cases, but the most frequent cause of ACC are genetic mutations related to axonal guidance pathways, ciliary development, cell adhesion, proliferation, differentiation and migration. Patients with ACC can be divided into three groups: the first including individuals with “syndromic” ACC who commonly present severe neurocognitive deficiency that obscures the deficiencies directly caused by the absence of CC generally associating cerebral malformations, non-cerebral structural defects, altered patterns of growth and development, in addition to progressive neurological symptoms and sensory impairment; the second presents with neurodevelopmental diseases in which ACC has been suggested to play a role; and the final includes patients with isolated complete or partial ACC who remain neurologically asymptomatic and have normal intelligence, however, in-depth neuropsychological screening can often reveal mild behavioral and cognitive deficits. In recent decades, magnetic resonance imaging (MRI) has been implemented, a tool that has increased the recognition of fetal diagnosis, which is performed in three planes and is useful in identifying associated anomalies. The use of MRI is essential and must be done together with a complementary fetal ultrasound exam, with the midsagittal plane parallel to the CC being ideal for evaluation. Multiplanar fetal neurosonography is the best imaging test to evaluate the fetus from the 20th week of gestation onwards. Most brain abnormalities remain undiagnosed until midway through the first trimester, and may go undetected due to small fetal brain structures. Between the 11th and 13th weeks, ultrasound can highlight changes that are incompatible with life. Multiplanar neurosonography is indicated in the middle of the first trimester of pregnancy, including non-axial plane scanning. The sonographer's knowledge of fetal anatomy and sonoembryology results in early diagnosis.