Agenesis of the corpus callosum is the congenital absence of the corpus callosum or part of it. The anomaly is caused by genetic disorders, vascular malformations, teratogenic factors. The main signs of the disease: motor disorders, delayed speech development, convulsive seizures. With a non-rough (partial) variant of pathology, a low-symptomatic course is possible. To diagnose the condition, cerebral CT or MRI, neurosonography in newborns, genetic studies are prescribed. Symptomatic treatment: drug correction of complications, rehabilitation programs.
Q04.0 Congenital anomaly of the corpus callosum
Agenesis of the corpus callosum (ACC) is one of the most common defects of the nervous system. The prevalence of the disease in the population ranges from 0.05% to 7% among newborns, and in the group of children with delayed mental development, agenesis occurs in 2.3%. The California Program for the Study of Congenital Malformations provides other data on the frequency of agenesis – 1.4 per 10,000 live newborns. For the first time, the condition was described in 1812 during an autopsy conducted by the German anatomist I. Reil, and called “a natural model of a dissected brain.”
Reasons of agenesis of the corpus callosum
The exact etiological factors of the disease have not been established. In modern neurology, the multifactorial theory prevails, according to which a combination of unfavorable exogenous and endogenous causes is required for the formation of a congenital defect of the central nervous system. Scientists identify several of the most likely prerequisites for the development of agenesis:
- Genetic anomalies. Damage to the corpus callosum is noted in various hereditary syndromes: Miller-Dicker, Rubinstein-Taubi, Donnai-Coogan. The condition is part of at least 7 autosomal dominant, 23 autosomal recessive, 12 X-linked congenital diseases.
- Vascular disorders. The cause of underdevelopment of the corpus callosum may be arteriovenous malformations or aneurysms, which are characterized by the absence of a normal capillary network. At the same time, the phenomenon of theft occurs, CC cells do not receive the proper amount of oxygen and nutrients.
- Toxic effects. The disease is associated with the action of teratogenic chemical factors: drugs, heavy metal salts, pesticides and household chemicals. Inhaling tobacco smoke (active or passive smoking) or taking alcohol during gestation has a negative effect on the formation of the fetal central nervous system.
- Intrauterine infections. Anomalies in the formation of neurological structures, including agenesis of the corpus callosum, occur when pathogens enter the fetus at 2-3 months of pregnancy. Neurotropic properties are demonstrated by herpetic infections, toxoplasmosis, cytomegalovirus.
The main risk factor is prematurity. In newborns born before the 27-week gestation period, CC is thinned in the posterior parts, between 28 and 30 weeks – only in the area of the roller. In those born after 30 weeks in the neonatal period, no changes are detected, although neuropsychological examination of schoolchildren often reveals a deficit in the interhemispheric transmission of cognitive information.
The corpus callosum (CC) is a large bundle of commissural nerve fibers. This is an important axonal pathway that connects the corresponding zones of the cortex of the right and left hemispheres. The anatomical structure has a length of 7-9 cm, consists of more than 300 million axons. The formation of C begins at the stage of late neuroontogenesis (8-9 weeks of embryogenesis). Its maturation normally lasts up to 20-25 years.
Agenesis occurs when there is a violation of the differentiation of the neural tube in the period from 2 to 5 months of intrauterine development. In the complete absence of CC, the third cerebral ventricle remains open, the pillars of the brain vault do not form, there are no transparent partitions. In 60% of cases with ACC, there is no anterior commissariat at all. It is increased by 10% and takes over part of the functions of the corpus callosum in newborns, as well as in the following stages of the postnatal period.
A characteristic anatomical change is colpocephaly, in which the posterior sections of the lateral cerebral ventricles are expanded. The condition does not relate to true hydrocephalus of newborns, but is due to a decrease in cortical associative pathways. Another typical sign of a defect is the Probst bundles, which are incorrectly oriented axons located parallel to the interhemispheric gap.
In practical neurology, the condition is divided into total, when the organ is completely absent, and partial (partial), in which visualization methods do not detect individual areas of CC. This is crucial for the severity of the clinical picture, possible complications. In accordance with the pathogenetic features of the formation of congenital malformations, the following 3 forms of the disease are distinguished:
- Agenesis. The laying of the embryonic germ of CC is completely absent.
- Aplasia. There is an embryonic rudiment of the corpus callosum, but it does not develop.
- Hypoplasia. CC is insufficiently developed due to disorders at one of the stages of embryogenesis: the size and weight of the organ are reduced, its functional activity is reduced.
Symptoms of agenesis of the corpus callosum
The clinical picture of corpus callosum agenesis varies widely from practically asymptomatic forms (with hypoplasia) to critical neuropsychiatric disorders with its gross underdevelopment, accompanied by other congenital defects of the central nervous system. In newborns, signs of pathology may be completely absent and manifest as the baby grows up with a delay in psychomotor development.
Motor disorders are detected in 35-40% of patients. They are manifested by muscular hypotension or dystonia, hyper- or hyporeflexia, violation of swallowing and sucking reflexes. Children later begin to hold their heads, have difficulty learning to sit, crawl, walk. Coordination disorders, clumsy gait may be noted. Of the paroxysmal disorders in newborns and children of the first year of life, seizures predominate.
The corpus callosum maintains the connection between the cerebral zones, forms the interhemispheric organization of higher mental processes. With its agenesis or hypoplasia, cognitive disorders are detected in children. In newborn patients and in early childhood, there is a delay in speech, a decrease in the dynamic component of gaming activity. In preschool and school age, there are problems with concentration, memory disorders, with total ACC, the IQ is reduced.
About 65% of cases of the disease are accompanied by concomitant congenital pathologies, among which malformations of cortical development (22.8%), interhemispheric cysts (14.3%), holoprosencephaly (14.3%) predominate. More rare concomitant anomalies include cysts and cerebellar hypoplasia, Arnold-Chiari syndrome. Up to 20% of newborns, except for the structures of the central nervous system, have defects of several internal organs.
Symptomatic epilepsy of temporal-frontal localization is observed in 75% of patients with total lesion, cognitive impairment is expressed in 66% of cases. 16% of patients develop autism spectrum disorders. Occasionally there are pathologies of the visual organ in the form of chorioretinal lacunar foci, combined abnormalities of the optic nerves.
Obstetric ultrasound is performed as the primary method of examination in the prenatal period. In newborns, neurosonography is used for screening diagnostics, but this method does not always show good informativeness, especially with partial agenesis. To verify the diagnosis, the following research methods are prescribed:
- CT of the brain. Computed tomography determines the widely spaced anterior horns, the high standing of the third ventricle, the parallel course of the medial walls of the lateral ventricles. CT is performed as part of postnatal diagnostics.
- MRI of the brain. For the most accurate visualization of the degree of agenesis or hypoplasia of the corpus callosum, magnetic resonance imaging is performed in three planes in newborns. According to the indications, MRI can be recommended to pregnant women to exclude combined defects of the central nervous system incompatible with life.
- Neuropsychological examination. To study cognitive functions in children, the Wechsler intelligence scale (WISC-Revised), adapted reading and Spelling Tests (Schonnel Graded Reading and Spelling Tests), verbal fluency assessment, Controlled Oral Word Association Test (Controlled Oral Word Association Test) are used.
- Genetic analysis. To confirm or exclude hereditary diseases accompanied by agenesis of the corpus callosum, karyotyping, genome sequencing, performed both in newborns and children of other ages, are shown. Studies are also carried out in the antenatal period to make a decision about maintaining or terminating pregnancy.
Treatment of agenesis of the corpus callosum
There is no specific therapy. Medical treatment is prescribed by a neonatologist or pediatrician individually, taking into account the leading pathological syndromes: anticonvulsants, neurometabolic drugs, dehydration therapy are used in newborns and young children. The basis of medical care is comprehensive rehabilitation, which includes the following components:
- Neurologopedic programs. Classes with a children’s speech therapist are conducted to develop speech function, eliminate manifestations of dysarthria, and improve articulation.
- Defectological programs. The help of correctional teachers is required for children with intellectual disabilities who cannot attend regular classes.
- Neuroacoustic programs. The formation and harmonization of higher mental functions are carried out with the help of sound therapy, music therapy.
Prognosis and prevention
The prognosis is determined by the type of congenital anomaly of the corpus callosum, the presence of concomitant malformations of the central nervous system. A favorable outcome is observed with partial hypoplasia of MT, and in the case of combined cerebral malformations, newborns may have life-threatening complications. Preventive measures include medical and genetic counseling, exclusion of teratogenic effects in the gestational period.