Obstructive hydrocephalus, also known as non-communicating hydrocephalus, occurs when the cerebrospinal fluid is blocked along a passage which connects the cavities within the brain (ventricles). This type of hydrocephalus is usually caused by the narrowing of the small passage in between the third and fourth ventricles. This then leads to the buildup of fluid, increased size of brain ventricles, and increase of pressure on the brain. The triad symptoms are impaired bladder control, difficulty walking or gait disturbance, and mild dementia. The treatment is surgery which drains excess fluid.