Introduction: Hemimegalencephaly is a disorder of neurone proliferation and migration, associated with excessive growth of all or part of one cerebral hemisphere, and variable degrees of pachygyria, polymicrogyria, neuronal heterotopy and gliosis of white matter. It is considered to be a rare malformation with severe encephalopathy, epilepsy resistant to treatment started early, contralateral hemiparesia and severe retardation of development. However, there may also be milder forms. The syndrome of pathological left handedness is associated with disorders of language, visuo-spatial changes and weakness and hypertrophy of the right limbs, with no family history of left handedness. It occurs in lesions predominantly of the left hemisphere which have occurred in the first six years of life.
Clinical case: A 12 year old girl presented with a syndrome of pathological left-handedness and craniofacial asymmetry of the left hemisphere. MR showed the left ventricle and hemisphere to be of increased size and with focal hyperintensity in the white matter, and at the level of the left parietotemporoccipital region there was a thick cortex with little interdigitation of white and grey matter.
Conclusions: Minor forms of hemimegalencephaly are probably more frequent than is generally believed. A high index of suspicion is necessary to identify them. They should be considered in cases of left handedness, craniofacial or bodily asymmetry, cutaneous hamartomas, persistent electroencephalographic asymmetry and asymmetry on neuroimaging with an enlarged ventricle and homolateral hemisphere. Study of this may give information which is useful for understanding plasticity and mechanisms of recovery and functional compensation of immature nerve tissue.