CONGENITAL BRAIN MALFORMATIONS ON MR IMAGES Report of

CONGENITAL BRAIN MALFORMATIONS ON MR IMAGES : Report of two cases of Polymicrogyria M. SAIDI, S. JERBI OMEZZINE, Z. KHADIMALLAH, S. BOUABIDI, S. YOUNES 1, MH. SFAR 1, HA. HAMZA Department of Medical Imaging, 1 Department of Internal Medicine, University Hospital Tahar Sfar, Mahdia, Tunisia NR 13

Introduction Polymicrogyria is a derangement of the lamination of the deep layers of the cerebral cortex, resulting in numerous small gyri with intervening sulci. Various causes include infections, genetic, hypoxia, and trauma. MRI is considered as a valuable imaging tool for confirmation and characterization of this congenital brain Malformation.

Patients and methods We report two cases of epilepsy patients, a 46 years old women and a 15 years old boy Brain MRI scans were performed looking for an eventual organic cause.

Case reports Case 1: B. K ; a 15 years-old epilepsy boy Coronal T 2 weighted MR Imaging: Cerebral cortex on the borders and in the depth of the sylvian fissures is bilaterally thickened and abnormally infolded.

Case reports Case 2: K. B ; a 46 years-old epilepsy women Coronal T 2 weighted MR Imaging: Absence of normal cortical ribbon with abnormal irregular cortex and shallow sulci in the right sylvian fissure

Results Ø MRI has shown in these two cases a focal absence of normal cortical ribbon with abnormal irregular cortex and shallow sulci Ø These Features were suggestive of Polymicrogyria.

Discussion Polymicrogyria is a relatively common malformation of cortical development, in which the brain surface is irregular and the normal gyral pattern is replaced by an excessive number of small and partly fused gyri separated by shallow sulci

(A) Gross appearance of brain surface in left perisylvian region. The gyri are small and excessive in number. (B) Coronal section through posterior thalamus. Polymicrogyria is evident throughout most visible regions of cerebral cortex, particularly in the perisylvian regions bilaterally

PATHOGENESIS OF POLYMICROGYRIA Polymicrogyria is causally and histologically heterogeneous and its pathogenesis remains poorly understood. Polymicrogyria results from a developmental disorder or injury that occurs toward the end of the period of neuronal migration and in the early phase of cortical organisation.

AETIOLOGY OF POLYMICROGYRIA Little is known about the factors that contribute to the development of Polymicrogyria. There is evidence that extrinsic factors, such as intrauterine cytomegalovirus infection, can be involved in the pathogenesis Fetal cerebral ischaemia from placental perfusion failure, twin–twin transfusion, loss of a twin in utero, and maternal drug ingestion have been described in association with polymicrogyria.

AETIOLOGY OF POLYMICROGYRIA The association of polymicrogyria with several genetically determined syndromes such as Zellweger, Aicardi and Walker-Warburg syndrome, the presence of Polymicrogyria in patients with chromosomal abnormalities, and the occurrence of familial cases of polymicrogyria all strongly indicate a genetic component in its development.

CLINICAL AND IMAGING FEATURES OF POLYMICROGYRIA Polymicrogyria can appear as either a focal lesion or a more widespread cortical abnormality and is often seen in association with other developmental brain malformations such as schizencephaly. the spectrum of clinical manifestations ranges from normal individuals with only selective impairment of cognitive function and no or easily controlled epilepsy to patients with severe encephalopathies and intractable epilepsy.

CLINICAL AND IMAGING FEATURES OF POLYMICROGYRIA MRI sequences to characterise polymicrogyria include axial spin echo T 2 weighted images and spin echo T 1 weighted images with 4 mm section thickness. Thin section (1. 5 mm) coronal images obtained either by T 1 weighted, three dimensional Fourier transformed, gradient recalled echo or by T 2 weighted fast spin echo sequences usually enable differentiation between polymicrogyria and pachygyria.

CLINICAL AND IMAGING FEATURES OF POLYMICROGYRIA The topographic distribution of polymicrogyria does not always appear to be completely at random. The perisylvian regions are affected most often. Barkovich et al classified polymicrogyrias and schizencephalies into four categories. They further sub classified these four categories into 15 subgroups, 5 of them applying to the Polymicrogyria syndromes Øbilatéral diffuse Polymicrogyria Øbilateral fronto-parietal polymicrogyria Øbilateral perisylvian polymicrogyria Øbilateral parieto-occipital polymicrogyria Øbilatéral mesial occipital Polymicrogyria

CLINICAL AND IMAGING FEATURES OF POLYMICROGYRIA Polymicrogyria syndromes : Bilateral perisylvian polymicrogyria BPP The first bilateral polymicrogyria syndrome to be described and the most common form of polymicrogyria cerebral cortex on the borders and in the depth of the sylvian fissures is thickened and abnormally infolded The sylvian fissures are often more vertically oriented and extend more posteriorly up to the parietal lobes. The abnormality is usually symmetrical but varies in extent among patients

CLINICAL AND IMAGING FEATURES OF POLYMICROGYRIA Polymicrogyria syndromes : Bilateral perisylvian polymicrogyria (BPP) Clinical manifestations of BPP include pseudobulbar palsy with diplegia of the facial, pharyngeal, and masticatory muscles (facio-pharyngoglosso-masticatory paresis), pyramidal signs, and seizures

CLINICAL AND IMAGING FEATURES OF POLYMICROGYRIA Polymicrogyria syndromes : BPP Axial (A) and sagittal T 1 weighted (B) magnetic resonance images showing bilateral perisylvian polymicrogyria. The axial slice displays bilateral inward folding of abnormal cortex in the posterior segments of the sylvian fissure bilaterally. The multiple small gyri are better demonstrated in the sagittal plane. Genetics of the polymicrogyria syndromes A Jansen, E Andermann

Conclusion Polymicrogyria is one of the developmental brain anomalies that give rise to cortical disorganization in the late fetal period. Since the advent of high resolution magnetic resonance imaging, various forms of diffuse or focal Polymicrogyria have been reported. The role of MRI is not only to confirm or exclude possible lesions but also to define their full extent, aiding in their characterization, and to demonstrate associated abnormalities.