Hemimegancephaly

Findings:

–       Salient feature is Cerebral hemisphere Asymmetry.

–       Abnormal sulcation, poor grey-white diff on right side with right cerebral enlargement. There are associated areas of dysmyelination / non myelinated white matter on right side which suggest that right side is abnormal.

DDs:

Left side hemi atrophy, unlikely as if there is left atrophy the ventricle on left side should be dilated owing to volume loss and not the right as in this case.

Rasmussen Encephalitis, also unlikely as it’s an after birth problem so poor development of left hemi cranium not expected as in this case. 

Hemimegancephaly

Def : Hamartomatous overgrowth of part/all of a hemisphere
Defect of cellular organization, neuronal migration

Best diagnostic clue enlarged dysplastic hemisphere
Dysplastic cortex, abnormal gyri
Displaced posterior falx
Large lateral ventricle with abnormally shaped frontal horn

Location: Occipital common (any lobe may be involved)
Size: Subtle or grossly enlarged
Morphology: Normal sulci or pachygyria,or polygyria. 

Clinical Presentation
• Most common signs/symptoms
o Seizures
o Macrocrania
• Clinical profile
Early seizures (infantile spasms, focal and later generalized)
Severe developmental delay and contralateral hemiparesis common
Systemic involvement with overgrowth syndromes common.