Hemimegalencephaly with hemihypertrophy (Klippel-Trénaunay-Weber syndrome).

A 17-year-old Japanese girl had right hemihypertrophy, vascular nevus of the right side of the body, right hemimegalencephaly, multiple haemangiomatosis, varicosis and chronic proliferative glomerulonephritis. The hypertrophied side of the cerebrum showed no malformations. Quantitative studies showed no significant differences between the two cerebral hemispheres in size, form, density or DNA content of nerve and glial cells. The hemimegalencephaly seemed to be due to an increase in the absolute number of nerve and glial cells in the ipsilateral cerebral hemisphere. Eight cases of hemihypertrophy with hemimegalencephaly have been reported to date, in all of them hemihypertrophy and hemimegalencephaly were on the same side. This condition seems to be due to unilateral overproduction of neuroblasts and glioblasts or hindrance of the normal loss of excess neurons, which may be induced by hemihypertrophy of the mesenchyme surrounding the CNS.