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Imagery contribution in a rare case of agenesis of corpus callosum

Autor: Miron Popescu Axinia Corcheș
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SUMMARY
The case of a 7 months old patient is presented; the patient has debut tonic-clonic seizures while feverless. Th e successive cerebral imaging examinations (ultrasounds, computer tomography) have oriented and ultimately (the magnetic resonance) have set the diagnostic of pronounced partial sub-total agenesis of corpus callosum (CC/DAP-RFDAP: 9.8%). We can notice that there are several cumulated partial ageneses (of rostrum, splenium and of the corpus callosum), in this case, respectively a rare aspect of partial agenesis of corpus callosum. Th e indirect signs of corpus callosum agenesis have been in high number, more relevant in the magnetic resonance: the lateral ventricles are parallel and distant, colpocephaly, the frontal horns have aspect of ”bull horns” the third ventricle is ascended, the Probst Bundles, the cingulated gyrus is absent having radial aspect gyrus (on the inter-hemispheric sides), ”key-like” temporal horns. Key words: corpus callosum, partial, subtotal agenesi

BACKGROUND The corpus callosum is a bundle of nerve fibers interconnecting the two cerebral hemispheres [1]. The corpus callosum agenesis is a rare congenital anomaly that can be total or partial [2, 3]. The partial agenesis is also known as hypogenesis [3]. The corpus callosum agenesis can be isolated or associated with other malformations [2, 4]. It is considered a partial agenesis of corpus callosum when at least a segment of the corpus callosum is incontestably absent and the undisputable presence of a part of corpus callosum (minimum 5 mm) [2].
The Corpus callosum agenesis is quite rare. J. L. Grogono has presented in 1968 an incidence of 0.05% up to 0.7% of the general population [6]. The prevalence is difficult cu establish due to the asymptomatic cases that are not detected (and declared). The possible causes of the corpus callosum agenesis are very numerous and variable: infectious, toxic, metabolic, genetic, environmental factors [7].
The computer tomography is revealing the parallelism of the lateral ventricles, the colpocephaly and the inter-hemispheric fissure and the third ventricle [8]. The magnetic resonance is the imaging procedure to choose for new-born and children [8]. Within the differential diagnostic of the isolated, partial agenesis of corpus callosum, we have to discuss the hypoplasia of the corpus callosum and the cases of partial agenesis having associated another anomaly: inter-hemispheric cyst, lipoma, malformations of the cerebral cortex (heterotopy, lissencephaly), the Arnold– Chiari malformation. Hypoplasia, the corpus callosum is present, but abnormally thin [10]. It is difficult to make the prognostic of an isolated agenesis of corpus callosum. The patients having such pathology may present a high number of epilepsies, mental development retard, psychotic manifestations, but some of the children have normal development. The prognostic of partial agenesis is delicate; it depends on the location and the extent of the agenesis [10].
PRESENTATION OF THE CASE A 7 months old patient is admitted due to debut tonic-clonic seizures while feverless. The EEG exam is revealing medium voltage delta transients with multiple motion artifacts. The posterior part of the corpus callosum is not visible by the tranfontanelle ultrasounds, and the radial aspect of gyrus on the internal sides of hemispheres. Several indirect signs are observed by the computer tomography: 1. the lateral ventricles are parallel and distant (fig. 1). 2. the enlargement of the posterior horns (colpocephaly) (Fig. 2). 3. presence of radially oriented gyri towards the third ventricle is ascended. 4. the moderately enlarged inter-hemispheric fissure and the ascendant position of the third ventricle. As the CT exam cannot singularize the corpus callosum, a total agenesis of corpus callosum is suspected, therefore MRI exam is recommended.

Only the presence of the corpus callosum genu is observed, presented as hypoplasic. In fact only the posterior part of the genu is present. The patient is registered in the Pediatric Neuropsychiatry Department Timisoara with the diagnostic of partial agenesis of the corpus callosum and epilepsy with generalized tonic-clonic seizures while feverless. Treatment with anticonvulsant drugs with Deparkine is decided and rehabilitation treatment according to protocols.

DISCUSSIONS The parts of the corpus callosum are: rostrum, genu, corpus and splenium. The types of partial ageneses of the corpus callosum are: lack of rostrum (94%), of splenium (79%), of genu (24%), of corpus (9%) [5]. In this case, there is plurality of agenesis (of rostrum, of splenium, of corpus callosum), a rare aspect of partial agenesis
The antenatal diagnostic of corpus callosum agenesis is possible since the 20th week. The intrauterine characteristic aspects are: colpocephaly and the parallelism of the ventricular walls [7]. The total agenesis can be suspected in utero, but the diagnostic of partial agenesis is much more difficult [10]. The fetal cerebral magnetic resonance is necessary also to ascertain the diagnostic of corpus callous agenesis and to look for associated cerebral anomalies [11]. At the newborn, the ultrasound screening is clearly revealing the absence of the corpus callous before the closing of the anterior fontanelle [7]. In our case, the diagnostic of partial agenesis of corpus callosum has been set at the age of 7 months by successive imaging procedures (ultrasound, CT and MRI). The partial agenesis of the corpus callosum in children is categorized depending on the length ofthe corpus callosum/antero-posterior diameter of the brain (RFDAP), in two groups: subtotal agenesis and moderate agenesis [1, 8]. The subtotal agenesis corresponds to a RFDAP lower than 0.192, and the moderate agenesis to a RFDAF higher than 0.192.

In our case, RFDAP (CC/DAP) has been of 13.3/134.6, respectively -9.8% (indicating a pronounced subtotal agenesis) (Fig. 3). The size of the corpus callosum (length 13.3 mm and height – 2.9 mm) have been set on the sagittal section of the MRI examination (fig. 3, fig. 4). The indirect signs presented in the agenesis of the corpus callosum encountered in presented case are reported at the lateral ventricles, at the third ventricle, the Probst Bundles, on gyri and circumvolutions.
The inner concave aspect of the internal margin of the lateral ventricles, at the level of the frontal horns – on frontal sections, respectively “bull horns” (Fig. 5a and b), and colpocephaly, respectively the discordance between the thin frontal horns and the dilated occipital horns (approximately 20 mm) (Fig. 6) The presence of colpocephaly is explained by Raybaud as a lack of development of the white substance [1]. – the third ventricle seems ascended, located between the two lateral ventricles (Fig. 5b). – the Probst Bundles (bundles of white substance that unify the two cerebral hemispheres that run on longitudinal direction and are protruding on the upper inner edge of the lateral ventricle) [1,9] are present and enhanced on the axial cups (Fig. 7). – regarding the gyri and circumvolutions, the cingulated gyrus is absent and the radial aspect of the gyri on the inter-hemispheres sides is observed (oriented towards the third ventricle) (Fig. 8). – the temporal horns are deformed in “key”shape (Fig. 9). This aspect brings to discussion the hippocampal formations and the white substance on the inner side of the temporal lobes, respectively the presence of development anomalies [1].

CONCLUSIONS
The cerebral imagery investigations have facilitated the diagnostic of a pronounced partial sub-total agenesis of corpus callosum (CC/DAPRFDAP: 9.8%) in the case of a 7-month old patient. The magnetic resonance has set the diagnostic of pronounced subtotal agenesis of corpus callosum excluding the total agenesis of corpus callosum.
The size of the corpus callosum (length – 13.3 mm /height – 2.9 mm) have been set on the sagittal section of the MRI examination. The indirect signs have been present both at ultrasound examination and computer tomography, but more relevant in the resonance imaging. In cases of infant and pediatric epilepsy the cerebral imaging has an important role in establishing the nature of the epileptogenic lesion (malformation in our case) and in précising its extension. The malformation etiology is the most frequent cause of infant epilepsy [12].

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