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Hemispheric polymicrogyria and neonatal seizures: a potentially life-threatening combination Volume 19, numéro 1, March 2017

TEST YOURSELF

(1) Which distributions of polymicrogyria are usually associated with the most severe phenotypes?

 

(2) What should make one cautious in proceeding to hemispherectomy in a child with drug-resistant seizures secondary to unilateral PMG?

 

 

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Answers

(1) There are many factors that can influence the severity of the clinical phenotype associated with PMG. The underlying cause and any associated syndromic features involving other malformations in the brain or other organ systems will influence severity. The pattern of PMG on brain MRI is also relevant, with earlier age at seizure onset and a greater degree of developmental delay correlating with a greater extent of PMG. For example, generalized forms are usually the most severe, followed by bilateral focal forms, with the least severe being unilateral forms. The two neonates presented here highlight an extremely severe presentation of PMG, not generally expected given the unilateral nature of their malformation.


(2) The most important factor to exclude is independent seizure onset from the contralateral hemisphere. Whilst this can occasionally occur in young children with hemispheric lesions who ultimately have a favourable outcome to hemispherectomy, the presence of frequent and truly independent seizures from the apparently normal hemisphere warrant caution. Ascertaining this may require repeated or prolonged periods of video-EEG monitoring. Brain MRI should be scrutinized closely for subtle PMG in the apparently normal hemisphere. Bilateral perisylvian PMG may be highly asymmetric. The posterior perisylvian regions, in particular, may harbour very subtle areas of PMG. Repeated imaging, including high-field MRI and PET, may be required to demonstrate subtle contralateral abnormalities.

 

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