[Growing septum pellucidum cyst in infancy].

We report a baby's development with expanding cyst of the septum pellucidum. It was detected accidentally during diagnostic evaluation of epileptic convulsions and psychomotoric retardation. The dramatic increasing of the cyst was followed by cranial ultrasonography for ten months. The progression of clinical symptoms couldn't be explained because after drainage of the cyst, no improvement took place. MRT with Spectroscopy lead to the tentative diagnosis, Morbus Alexander. This couldn't be proved because no biopsy of the brain was performed against the decision of the child's mother, nor postmortal (the child died at 20 months).