Polymicrogyria-Teaching Points

14 year old girl with history of seizures, shows on MRI marked cortical malformations symmetrically and bilaterally in the perisylvian regions with scalloping / inversion of the bodies of the lateral ventricles consistent with bilateral symmetrical perisylvian polymicrogyria.  Case Submitted by Dr MGK Murthy.

Teaching points :

·         Also known as bilateral perisylvian syndrome / bilateral opercular syndrome. Defined as malformation of the cortical development characterized by abnormal arrangement and excessive folding of cerebral cortex cell layers often with fusion of gyral surfaces.

·         Exact etiopathogenesis not known. However results from abnormal organization of neurons within the cortical lamina after completion of neuroblast migration from germinal zone and through intermediate zone of developing brain possibly in 5^th / 6^th months of fetal life. Though ischaemic factors play definite role in few cases, genetic factors are also known to contribute (familial cases are known to occur).

·         Differential vulnerability in different regions in different stages of development probably explain the neuronal insult in selected regions without restriction to vascular territories (28% of neonates who suffer cerebral infarctions do not show any deficit by 5 years of age)

·         Neuronal function in the regions of involvement on spectroscopy and FDG scan are unremarkable.

·         Clinical presentation varies from delayed milestones (proportionate the severity of involvement), seizures in posterior parieto-occipital involvement to quadriparesis, mental retardation (frontal involvement) and problems of phonation and delayed speech (perisylvian involvement).

·         Sagittal imaging (thin sections of 3 – 4 mm) is more valuable than other planes.

·         Imaging features including abnormal gyral pattern / increased cortical thickness / irregular cortical – white matter junctions / scalloping or inversion of the bodies of the lateral ventricles (unlike pachy gyria which has no scalloping). Associated conditions include arthrogryposis multiplex / infantile spasms etc.