Bilateral symmetrical perisylvian polymicrogyria.

Clinical History

A 31-year-old woman with seizures. The clinical examination revealed mental retardation, dysarthria, diminished tongue side-movements and mild hyperreflexia. The electroencephalogram showed waveforms compatible with idiopathic generalized epilepsy.

Imaging Findings

A brain MRI with T1 and T2 weighted images was performed revealing bilateral thickening of the Sylvian cortex along with irregularity of the cortical-white matter junction and enlargement of the Sylvian fissures. These findings were compatible with polymicrogyria (Fig. 1, 2).

Discussion

Polymicrogyria (PMG) is one of the most common malformations of cortical development. PMG is thought to result from both genetic mutations and prenatal cytomegalovirus infection occurring during late neuronal migration and early cortical organization. Early fetal brain ischaemia is another aetiology of bilateral PMG, especially in monochorionic twins. The cortex is characterized by multiple small adjacent gyri, with fusion of the superficial layers and obliteration of the intervening sulci. Microscopically there is cortical thinning owing to reduction of the neuronal population. Histologically two major forms of PMG exist: 1) unlayered PMG with disorganized cortex without lamination and 2) four-layered PMG caused by cortical laminar necrosis which involves the 5th cortical layer and arises later. Imaging is unable to distinguish the two forms [1]. PMG can be unilateral or bilateral.
Bilateral, symmetric PMG is typically found in genetic syndromes, and the perisylvian regions are most commonly involved. In these cases, there is a failure of the Sylvian opercularization with abnormally shallow Sylvian fissures, which extend posteriorly into the parietal regions. The cortical surface has an irregular flattened appearance as a result of fusion of the superficial layers of the gyri. The grey-white matter interface is typically corrugated, reflecting the multiple subcortical white matter interdigitations in the depth of the microgyri. Volumetric MRI techniques with thin partition size and curvilinear and surface reconstructions are especially useful to fully depict the cortical abnormality. CT plays an important role in detecting associated cerebral calcification, suggesting underlying congenital cytomegalovirus infection [2-4]. In bilateral perisylvian PMG, the most common of PMG syndromes, the affected patients display a typical clinical syndrome consisting of facial, lingual, and masticatory diplegia (developmental Foix-Chavany-Marie syndrome), associated with mental retardation and seizures [5-6]. Bilateral perisylvian PMG is genetically heterogeneous. However, a locus for bilateral perisylvian PMG has been mapped in Xq28 [1]. Prenatal diagnosis using fetal ultrasound and MRI may be particularly difficult, as the regions of the brain that are involved may not have reached the final folding until birth. However, there have been studies in which patients with bilateral polymicrogyria were identified with prenatal MR imaging and genetic analysis was performed [7].

Differential Diagnosis List

Final Diagnosis

Bilateral symmetrical perisylvian polymicrogyria.

URL:	https://www.eurorad.org/case/12888
DOI:	10.1594/EURORAD/CASE.12888
ISSN:	1563-4086