M. SAIDI, S. JERBI OMEZZINE, Z. KHADIMALLAH, S. BOUABIDI, S. YOUNES1, MH. SFAR1, HA. HAMZA

Department of Medical Imaging, 1Department of Internal Medicine, University Hospital Tahar Sfar, Mahdia, Tunisia

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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.

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.

Coronal T2 weighted MR Imaging: Cerebral cortex on the borders and in the depth of the sylvian fissures is

bilaterally thickened and abnormally infolded.

Case 1: B.K ; a 15 years-old epilepsy boy

Case 2: K.B ; a 46 years-old epilepsy women

Coronal T2 weighted MR Imaging: Absence of normal cortical ribbon with abnormal irregular cortex and shallow

sulci in the right sylvian fissure

MRI has shown in these two cases a focal absence of normal cortical ribbon with abnormal irregular cortex and shallow sulci

These Features were suggestive of Polymicrogyria.

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

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.

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.

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.

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.

MRI sequences to characterise polymicrogyria include axial spin echo T2 weighted images and spin echo T1 weighted images with 4 mm section thickness.

Thin section (1.5 mm) coronal images obtained either by T1 weighted, three dimensional Fourier transformed, gradient recalled echo or by T2 weighted fast spin echo sequences usually enable differentiation between polymicrogyria and pachygyria.

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

bilatéral diffuse Polymicrogyriabilateral fronto-parietal polymicrogyriabilateral perisylvian polymicrogyriabilateral parieto-occipital polymicrogyriabilatéral mesial occipital Polymicrogyria

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

Polymicrogyria syndromes : Bilateral perisylvian polymicrogyria BPP

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

Axial (A) and sagittal T1 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 syndromesA Jansen, E Andermann

Polymicrogyria syndromes : BPP

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.