AJR 2000; 175:900-901
© American Roentgen Ray Society
Sonography Case of the Day |
Case 3
Corpus Callosal Agenesis
Kuldeep Vaswani,
William F. Bennett and
James G. Bova
The largest commissure in the central nervous system is the corpus callosum
connecting the cerebral hemispheres. Its absence may be partial or complete,
and it may not have functional abnormalities. Corpus callosal agenesis may be
an isolated abnormality or may have associated central nervous system or other
abnormalities [1,
2].
The corpus callosum starts to develop at about 12 weeks' gestation from the
lamina terminalis near the anterior end of the third ventricle. Development
occurs in anterior—posterior fashion, beginning with the rostrum,
followed by the genu, body, and splenium, with formation of cavum septum
pellucidum as it grows. Development is usually complete by 20 weeks'
gestation. Development disturbance usually affects the posterior part;
however, previously formed parts can also be affected
[3]. Associated anomalies
include gyral dysplasias, heterotopias, and hypoplasias, including cerebral
vermis. Non—central nervous system anomalies include abnormalities of
the face, limbs, and genitourinary tract. High association with other
anomalies indicate that corpus callosal agenesis is part of widespread
developmental disturbance. Over-all prognosis depends on associated anomalies
and their severity [4]. Because
the development of corpus callosum is not complete until 20 weeks of
gestation, diagnosis may be difficult before that time
[5]. Development of cavum
septum pellucidum occurs by 17 weeks of gestation and is associated with
corpus callosum development. Therefore, corpus callosal agenesis should be
suspected if no cavum is present by 17-20 weeks
[5].
Sonographic findings (Fig.
3A,3B)
include disproportionate enlargement of occipital horns (colpocephaly),
lateral displacement of both walls (medial and lateral) of lateral ventricles,
angular pointing of anterior ends of lateral ventricles, absent cavum septum
pellucidi, and multiple sulci perpendicular to interhemispheric fissure during
the later part of gestation. On coronal images, the third ventricle is
elevated and lateral ventricles are almost horizontal ("steer
horns"). On parasagittal images, there is no corpus callosum and a
"sunburst" appearance of interhemispheric brain is noted.
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Fig. 3A. —Premature male infant with respiratory distress and possible
intracranial hemorrhage. Coronal echoencephaologram of cranium shows
high-riding third ventricle (arrow), horizontal ventricles
("steer horn" appearance), lateral ventricles (frontal horns), and
falx cerebri approaching lateral ventricles.
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Fig. 3B. —Premature male infant with respiratory distress and possible
intracranial hemorrhage. Saggittal echoencephalogram of cranium shows absence
of corpus callosum (arrowheads) and slightly prominent
ventricles.
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The other diagnoses are incorrect for various reasons. Arachnoid cysts are
usually midline, raising and deforming the third ventricle, resulting in
hydrocephalus. Heterotopia is usually seen in 3% of the healthy population.
Heterotopia is caused by the arrested migration of neuroblasts between 7 and
24 weeks of gestation. There are two forms: nodular heterotopia, which
manifests itself as subependymal and periventricular nodules; and laminar
heterotopia (also known as band heterotopia), which occurs as bands in deep
subcortical regions. Hydrocephalus is caused by an excess production of
cerebrospinal fluid or blockage of arachnoid villi or lymphatic channels of
the cranial nerves. Hydrocephalus can be communicating or noncommunicating,
with dilatation of all or some of the ventricule. Sonography in premature
infants or intrauterine fetuses (approximately 20 weeks of gestation and
older) shows dilated atria (>1 cm), dangling choroid plexus, biparietal
diameter greater than the 95th percentile, and polyhydroamnios in 30% of
cases.
References
-
Byrd SE, Harwood-Nash DC, Fitz CR. Absence of corpus callosum:
computed tomographic evaluation in infants and children. J Can
Assoc Radiol 1978;29:108
-112[Medline]
-
Blum A, Andre M, Droulle P, et al. Prenatal echographic diagnosis
of corpus callosum agenesis: the Nancy experience 1982-1989. Genet
Consul 1990;38:115
-126
-
Pilu G, Bovicelli L. Sonography of the fetal cranium.
Clin Diag Ultrasound
1989;25:221
-229
-
Vergani P, Ghidini A, Mariani S, et al. Prognostic indicators in
the prenatal diagnosis of agenesis of corpus callosum. Am J Obstet
Gyenecol 1994;170:753
-758
-
Bennett GL, Bromley B, Benacerraf BR. Agenesis of the corpus
callosum: prenatal detection usually is not possible before 22 weeks of
gestation. Radiology
1996;199:447
-450[Abstract/Free Full Text]
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