What is dandy-walker syndrome (also known as dandy-walker malf)?

Congenital defect: Drs dandy and walker described a brain defect in children that caused a cystic enlargement of the fourth ventricle due to lack of development of drainage holes that normally drain spinal fluid out of the fourth ventricle. This often causes large head, problems with balance, problems with learning, and seizures. Surgery relieves pressure but does not cure the defect.