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Articles » Central nervous system » Agenesis of the corpus callosum
1994-11-21-17 Corpus callosum, agenesis © Varma www.thefetus.net/
Corpus callosum, agenesis

Thangam R. Varma, PhD, FRCS, FRCOG, Robert Roger Lebel, MD, FACMG

Address correspondence to: Thangam R. Varma, PhD, FRCS, FRCOG, Senior Lecturer & Consultant OB &GYN, St. George"s Hospital & Medical School, Cranmer Terrace, London SW17 ORE, UK Ph: 081-672-9944 Fax: 081-767-9585. Genetics Services, 360 West Butterfield Road, Suite 245, Elmhurst, IL 60126 Ph:708-832-4363 Fax: 708-832-9580.

Synonym: Callosal agenesis, or dysgenesis.

Prevalence: 70-530:10,000 depending on the series reported.

Etiology: Probably often hereditary in isolation or as part of a syndrome, but often assumed to be sporadic and sometimes associated with aneuploidy.

Pathogenesis: Uncertain, midline developmental failure.

Associated anomalies: Hydrocephaly (dilatation of posterior horns of the lateral ventricles), various malformations involving other anatomic systems, trisomies 18 and 13.

Differential diagnosis: Arachnoid cyst, porencephaly, hydrocephaly, and prominent septum cavum pellucidum.

Prognosis: Variable, from asymptomatic to severe developmental delay (depending in large part on the underlying etiology and any associated abnormalities).

Recurrence risk: Dependent on etiology in the specific case, from 1% (if sporadic or chromosomal) to 25% (if autosomal recessive, as in the Charlevoix or Andermann syndrome; McKusick catalog number *218000) or even 50% in males (if X-linked recessive, as in McKusick catalog number 304100)1.

Management: Normal obstetric care with close serial fetal ultrasonographic follow-up, and amniocentesis.

MESH Corpus callosum BDE 0220 ICD9 742.2 CDC 742.210

Introduction

The diagnosis, symptoms, clinical spectrum, and prognosis of absence/agenesis of the corpus callosum have been extensively reviewed in the literature2-7.

The corpus callosum is a white matter structure connecting the cerebral hemispheres and is important in coordinating information and bilateral exchange of sensory stimuli. It is derived from the lamina terminalis in the portion of the neural tube cephalic to the rostral neuropore. Until the fourth month of gestation, only the most rostral part of the corpus callosum is formed; the caudal portion develops only after the fifth month8,9. Insults responsible for agenesis of the corpus callosum or varying degrees of hypoplasia of the corpus callosum are not identified. An early failure may lead to complete agenesis, whereas a later one will lead to hypoplasia10.

Case report

A 33-year-old primigravida was seen for ultrasonographic fetal examination, when her uterus was found to be larger than normal for gestation age 14 weeks (based on last normal menses), at first visit to the antenatal clinic. The ultrasonic examination confirmed the gestational age on the basis of fetal femur length and biparietal diameter. The uterus was larger than normal due to two large anterior wall fibroids (8 and 10 cm). At 20 weeks, repeat ultrasonic examination was performed to confirm dates and search for fetal anomalies. Measurements were compatible with dates and the fibroids were unchanged.

At 26 weeks, ultrasonic examination was indicated by uterine pain. The findings were again reported normal. The pain was thought to be due to the fibroids undergoing degeneration.

At 31 weeks, the ultrasonic examination was repeated to check fetal growth. The biparietal diameter and femur length were normal, but the abdominal area was at two standard deviations below the mean.

The biophysical profile and Doppler study were normal; however, dilatation of occipital horns of the lateral ventricles was noticed (fig. 1,2). No other abnormality was detected. A possible diagnosis of absence of corpus callosum was considered.

Figure 1: Transverse section of the cranium showing isolated dilated posterior horn of the lateral ventricle at 31 weeks.

Figure 2: Coronal section showing bilateral dilated posterior horns at 31 weeks gestation.

At 33, 35, and 37 weeks, the isolated dilatation of the occipital horns was seen but was not apparently progressive (fig. 3,4).

Figure 3: Transverse section of the cranium showing isolated dilated posterior horn of the lateral ventricle at 35 weeks.

Figure 4: Transverse section of the cranium showing dilated posterior horn of the lateral ventricle at 37 weeks gestation.

No other abnormality was noticed. Measurements confirmed asymmetrical growth retardation (fig. 5-7).

Figure 5: Mean fetal head area and + 2 standard deviations from 26 to 40 weeks gestation and the growth curve of the fetus.

Figure 6: Mean fetal abdominal area and + 2 standard deviations from 26 to 40 weeks gestation and the growth curve of the fetus.

Figure 7: Mean fetal head/abdomen ratio and + 2 standard deviations from 26 to 40 weeks gestation and the ratio of the fetus.

Estimated fetal weight at 37 weeks was 2.5 kg. The biophysical profile, Doppler study, and the cardiotocographic tracings remained normal. The third ventricle appeared normal. The findings were discussed with the mother, and it was decided to manage the pregnancy conservatively, monitor the fetus in utero carefully, and check the infant at birth using ultrasound and CT scan or MR subsequently.

At 38 weeks, elective cesarean section produced a female infant weighing 2.6 kg, with Apgar scores of 7 at 1 minute and 10 at 5 minutes. The baby looked normal at general inspection. Ultrasonic examination confirmed dilatation of the occipital horns of the lateral ventricles. There was difficulty in visualizing the corpus callosum; CT of the head confirmed agenesis of the corpus callosum.

Post-natal development

The post-natal development was assessed on a regular basis. Chromosomal analysis revealed 46,XX. Isolated upper limb amyoplasia was discovered (elbows in the position of extension with pronation of the hands and ulnar deviation). Electrophysiological studies of nerve and muscle have been normal. Radiological studies showed no evidence of bony abnormalities in the upper and lower limbs. At 3 years of age, the child can eat, play and write, can hear and see, and has normal intelligence. However, she is still slow in power movement of the upper limbs, with some muscle atrophy. Her weight and height have followed the tenth centiles. There was some delay in walking.

The pattern of amyoplasia in this child is very unusual, and the pediatrician and the geneticist who have seen her believe that the condition is consistent with deformation rather than a malformation. They have not determined a syndromic diagnosis that might unite the amyoplasia with the agenesis of the corpus callosum. However, the differential diagnostic effort should include a number of different possibilities, as discussed below.

This child illustrates the difficulty in identifying agenesis of the corpus callosum antenatally, though it was suspected because of the finding of an isolated dilatation of occipital horns of the lateral ventricles without any other structural anomalies being identified.

Discussion

Incidence

There is a discrepancy in the reported incidence between autopsy series and those based on pneumoencephalographic studies. The incidence ranges from 0.7% to 5.3%11,12. Lacey13 stated that the incidence of agenesis of the corpus callosum was only 0.0005% in an unselected random autopsy population; this seems to be lower than one would expect for a malformation which is so well known in the dysmorphology literature and community of specialists.

Etiology

The corpus callosum develops between the 10th and 20th weeks of gestation, from the lamina reuniens, which is the thickened dorsal aspect of the lamina terminalis. The fibers of the corpus callosum develop medially and longitudinally in the fetal brain. They converge medially and grow across a commissural plate; longitudinally, they grow in bands in an anterior-to-posterior direction. If the commissural plate fails to develop or is damaged, the uncrossed callosal fibers run parallel to the medial walls of the lateral ventricles, forming the bundles of Probst. These bundles do not cross the midline. This is the basis for the congenital form of agenesis of the corpus callosum. Acquired absence of the corpus callosum may occur due to destruction, usually as a result of intrauterine insults which produce infarction in the distribution of the anterior cerebral artery.

Agenesis of the corpus callosum may be part of the holoprosencephaly spectrum or may occur later as a separate neuroembryonic malformation. Associated central nervous system anomalies may include gyral abnormalities, heterotopias, pyramidal tract abnormalities, hypoplastic olfactory tracts and bulbs, and cerebellar hypoplasia15.

Agenesis of the corpus callosum can occur in chromosomal abnormalities, such as trisomy 13 and trisomy 18, as a part of the holoprosencephalic sequence12, and also may be found in chromosomal translocation syndromes13. Familial recurrence suggests a genetic heterogeneity with autosomal dominant, autosomal recessive, and X-linked recessive inheritance8,16-19. It also has been described in the median cleft face syndrome 19-20, Andermann syndrome21, F.G. syndrome, and acrocallosal syndrome22. An association with maternal rubella and toxoplasmosis has been reported23,24.

Because they develop embryonically in close proximity, agenesis of the corpus callosum is commonly associated with malformations of local limbic structures, particularly the septum and hippocampal formations25. Impairment of memory, cognitive function, behavior, and personality has been reported with extensive malformations or damage to the limbic structures26,27. Studies of patients with agenesis of the corpus callosum unrelated to holoprosencephaly show that some have normal intelligence and others are developmentally delayed14,28.

Pathology

Agenesis of the corpus callosum is an uncommon cerebral malformation that has been reported in 1 in 19,000 unselected autopsies and 2.3% of children with mental retardation11,29. The defect may be complete or partial, depending on the stage at which callosal development is arrested. In partial agenesis of the corpus callosum, the posterior portion is missing30. Consequently, the two lateral ventricles are set apart, and the third ventricle may sometimes be displaced upwards (fig. 8).

Figure 8: Schematic representations of a normal brain (left) and agenesis of the corpus callosum (right). In the absence of the corpus callosum, the lateral ventricles are set apart, and the third ventricle is displaced upwards.

Complete agenesis of the corpus callosum usually occurs as a primary process before 12 menstrual weeks, but less often may be secondary to the destructive process of an already formed corpus callosum after 20 weeks31,32.

Agenesis of the corpus callosum produces characteristic pathologic changes of the cerebral hemispheres and the ventricular system4,31,33,34. Dilatation and superior displacement of the third ventricle (interhemispheric "cyst") is the most characteristic finding of agenesis of the corpus callosum, but it is also the most variable finding8,9,35. The lateral cerebral ventricles are displaced laterally and superiorly. In most cases, there is a stable, non-progressive dilatation of the caudal portion of the lateral ventricles (atria and occipital horns)8,9,10. The reason for this enlargement is not known. There is no evidence of obstruction along the CSF pathways. There is neither increased intraventricular pressure nor progressive ventriculomegaly.

Diagnosis

In the newborn, agenesis of the corpus callosum can be diagnosed using magnetic resonance (MR), computed tomography (CT), or sonography. Characteristic changes of the ventricular system and cerebral hemispheres were first described by Davidoff and Dyke in 1934 from observations made on pneumoencephalography4. They noticed:

  • lateral separation of the frontal horns and bodies of the lateral ventricles,
  • angled lateral peaks of the frontal horns and bodies of the lateral ventricles,
  • elevation and variable dilatation of the third ventricle,
  • dilatation of the occipital horns,
  • concave medial wall of the lateral ventricles related to the bundles of Probst, and
  • abnormal radial orientation of medial cerebral gyri extending from the roof of the third ventricle.

Similar findings have been identified on sonography — most often on postnatal sonograms performed in coronal and sagittal planes33,36,37. Few cases of agenesis of the corpus callosum have been diagnosed on prenatal sonography35,36,38-42. The diagnosis is most evident when an interhemispheric cyst, representing a dilated and elevated third ventricle is present. The diagnosis may be very difficult in the absence of an interhemispheric cyst (fig.9).

Figure 9: Schematic diagram of agenesis of the corpus callosum without interhemispheric cyst. A coronal view (top left) shows that the lateral ventricles point superiorly. At the superior scan level (top right), both walls of the lateral ventricles are identified where only periventricular lines are normally present. The lower section (bottom right) shows dilatation of the occipital horns and separation of the frontal horns. The third ventricle may or may not be dilated.

A specific diagnosis of agenesis of the corpus callosum has seldom been made before the third trimester, probably because the corpus callosum is not normally formed until 18 to 20 weeks43. Most authors agree that detection of agenesis of the corpus callosum is difficult prenatally, depending as it does on postnatal sonograms or CT or MR scans. In a series of seven fetuses with agenesis of the corpus callosum, Bertino et al35 reported that only three demonstrated a characteristic midline cyst. They described three findings that might lead one to suspect agenesis of the corpus callosum on routine transverse views:

  • disproportionate enlargement of the occipital horn,
  • demonstration of both medial and lateral ventricular walls at a level where the single periventricular line is normally demonstrated, and
  • a more parallel course of both ventricular walls than normal.

They suggested that demonstration of these findings on axial views should stimulate additional coronal and sagittal views for evaluation of agenesis of the corpus callosum.

The increased separation of the normal-sized bodies and the enlargement of the atria and occipital horns of the lateral ventricle result in a typical ultrasound image. Upward displacement of the third ventricle is a very specific sign36 but presents only in 40% of fetuses. Hilpert et al44 used transvaginal ultrasound and reported that the technique may be useful in identifying the intracranial structures and anomalies, especially in the late second and third trimester when the fetal head is presenting.

Recently, Byrd et al45 reported that MR is the best technique to evaluate the child or newborn with suspected agenesis of the corpus callosum and associated brain anomalies. They stated that CT and/or MR scans demonstrated the characteristic findings in agenesis of the corpus callosum with a slightly enlarged high-riding third ventricle interposed between the lateral ventricles. They could demonstrate Probst"s bundles in children with true agenesis, on a sagittal MR midline scan, which is the definitive radiological modality for evaluating agenesis of the corpus callosum.

The classic findings of agenesis of the corpus callosum on MR consist of lack of demonstration of the corpus callosum in all three anatomic planes with a third ventricle which is elevated and interposed between the lateral ventricles. The complete outline of the normal corpus callosum is always visible on the sagittal MR in infants and children, and a mistake in the diagnosis is seldom made.

Byrd et al45 found that ultrasound is a good screening modality of the neonatal head and can be used to demonstrate agenesis of the corpus callosum. When the findings are subtle on the ultrasound, or when agenesis of the corpus callosum is demonstrated on the ultrasonic examination, a CT or preferably an MR should be obtained to evaluate the brain for a complete outline of the corpus callosum and associated structures.

Pilu et al42 identified agenesis of the corpus callosum by prenatal ultrasound in 35 fetuses between 19 and 37 weeks. Findings included absent corpus callosum and cavum pellucidum, "teardrop" configuration of lateral ventricles, distended interhemispheric fissure, upward displacement of third ventricle, radiate arrangement of medial cerebral gyri, and abnormal branching of anterior cerebral artery. They identified associated anomalies in 20 fetuses, including anatomic defects and chromosomal abnormalities.

Differential diagnosis

Other midline cystic masses such as arachnoid cyst, porencephaly, prominent cavum septum pellucidum31,33,36 may be mistaken for agenesis of the corpus callosum. All types of holoprosencephaly include agenesis of the corpus callosum as part of the underlying malformation, although alobar and semilobar holoprosencephaly should not be mistaken for agenesis of the corpus callosum alone. If a midline cyst is absent and dilatation of the atria and occipital horns is demonstrated, it may be mistaken for hydrocephalus. However, agenesis of the corpus callosum typically demonstrates greater enlargement of the occipital horns compared to the remaining ventricular system.

Associated anomalies

In an autopsy series of 47 cases of agenesis of the corpus callosum, Parrish et al14 reported that 85% of patients had other CNS anomalies, and 62% had extra-CNS anomalies. Associated CNS anomalies may include gyral anomalies, heterotopia, midline intracerebral lipomas, encephalocele, interhemispheric arachnoid cyst, microcephaly, Dandy-Walker malformation, Arnold-Chiari malformation, holoprosencephaly, hydrocephalus and aqueductal stenosis14,32.

Extra-CNS malformations may include anomalies of the face, musculoskeletal system, gastrointestinal tract, genitourinary tract, cardiovascular system, and respiratory system14.

The London Dysmorphology Database lists 108 syndromes in which agenesis of the corpus callosum is a feature46. Agenesis of the corpus callosum may be associated with a variety of other abnormalities in syndromes of Mendelian or unknown etiology, which are listed in Table 1. Others which are exceedingly rare or involve teratogen exposures are not included in this table.

Table 1: Differential syndromic diagnosis for agenesis of corpus callosum.
  Seen by ultrasound Not seen by ultrasound
Acrocallosal polydactyly anal atresia
Acrofacial short bones, oligodactyly midface
Adrenoleukodystrophy ventriculomegaly inborn error of metabolism
Aicardi holoprosencephaly colobomata
Al-Gazali microphthalmia Xp deletion
Apert syndactyly mental retardation
Basal cell nevus macrocephaly nevi
Beemer-Langer Ascites, clubfoot intestinal malrotation
Clefting/ectrodactyly facial cleft/claw hand ectodermal dysplasia
Frontonasal holoprosencephaly choanal atresia
Miller-Dieker cardiac malformation hand creases
Neu-Laxova Ascites, microcephaly cataract, ichthyosis
Opitz FG clubfoot, macrocephaly deafness, anal atresia
Oral-Facial-Digital hydronephrosis, polydactyly tongue lobules, oliogodontia
Rubenstein-Taybi cardiac malformations cryptorchidism
Shapiro ventriculomegaly hypothermia, hypoglycemia
Toriello-Carey clavicle malformations cryptorchidism
Tuberous sclerosis ventriculomegaly adenomata, retardation
Young-Madders facial cleft, anophthalmia cataract, cryptorchidism
Zellweger macrocephaly inborn error of metabolism

 

Agenesis of the corpus callosum has been associated with chromosome anomalies14,35,36,38 and translocations. In the largest prenatal series of fetuses with agenesis of the corpus callosum, Bertino et al35 reported a chromosome abnormality (trisomy 18) in one of seven fetuses (14%).

Prognosis

The corpus callosum is phylogenetically a recent structure, and its absence is not lethal. Isolated agenesis of the corpus callosum may be either a completely asymptomatic event (found incidentally) or revealed during the course of a neurologic examination by subtle deficits, such as inability to match stimuli using both hands or to discriminate differences in temperature, shape, and weight in objects placed in both hands16.

Persons with agenesis of the corpus callosum may have neurologic problems, such as seizures (60%), intellectual impairment (70%), and psychosis8,9,10. However, these conditions are believed to be caused by abnormalities in associated cerebral anomalies rather than in the corpus callosum per se. Hence, prognosis is determined primarily by the underlying or associated malformation(s)14. Studies of persons with isolated agenesis of the corpus callosum show that some have normal intelligence, while others are developmentally delayed28,48.

Grubben et al48 reported that three children they studied showed severe growth retardation of prenatal onset, hypotonia, and psychomotor retardation with notably impaired speech development. They also had hypotrophy of the distal extremities with small, puffy hands and feet.

Byrd et al45 studied a group of 105 children with a diagnosis of agenesis of the corpus callosum and reported that 26 (25%) had isolated agenesis of the corpus callosum with no associated brain anomalies. Eight of these presented with seizures which were controlled medically. Of the 105 children, 85% had symptoms and/or abnormal signs. The most common signs were macrocephaly with hydrocephalus and seizures. Postnatally, they found MR was the best radiological imaging modality for evaluating children with agenesis of the corpus callosum and associated brain anomalies. The most common associated brain anomalies (in decreasing frequency) were interhemispheric cyst with hydrocephalus, Dandy-Walker malformation, migrational disorder, absence of the inferior vermis, cephalocele, and lipoma of the interhemispheric fissure. The children who had the best prognosis without any significant neurologic sequelae were those with isolated agenesis of the corpus callosum.

The children with the worst prognosis and neurological sequelae were those with agenesis of the corpus callosum and migrational disorder with or without Dandy-Walker malformations45.

Pilu et al42 had follow-up data on 11 of the 20 patients they diagnosed prenatally. Two had IQ scores in the 70-85 range, while the other nine had scores above 85.

Obstetrical management

Identification of agenesis of the corpus callosum demands a careful search of fetal anatomy in its entirety. It is important to recognize that sonographic appearance of agenesis of the corpus callosum may be similar to that of uncomplicated hydrocephaly. A correct diagnosis is useful for guidance of appropriate and well-informed decision making. Diagnosis of isolated agenesis of the corpus callosum does not require any change in standard obstetrical management, but when multiple malformations are detected the optimum outcome may depend on special intervention. Amniocentesis is indicated.

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48. Grubben C, deCock P, Borghgraet M, et al. Severe pre- and postnatal growth retardation, developmental delay with hypotonia and marked hypotrophy of the distal extremities, dental anomalies, and exzematous skin. A new autosomal recessive entity. Clin Genet 1992;41:16-21.

Originally published in The Fetus in 1994, posted 6/1999

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