When hydrocephalus is congenital (present at birth), it doesn’t usually develop until the third trimester of the mother’s pregnancy. Fetal ultrasound is used to diagnose hydrocephalus when a baby is still in the womb.

In infants and older children, hydrocephalus is diagnosed with one or more of the following tests:

1. An ultrasound a type of imaging that uses high-frequency sound waves to take pictures of the body's organs

2. 2. A computed tomography (CT) scan. a non-invasive procedure using x-ray equipment and powerful computers to create detailed images of particular parts of the body magnetic resonance imaging (MRI), a combination of electromagnets, radio frequency waves and computers that take two-dimensional and three-dimensional images of organs and other body structures

3. intracranial pressure monitoring. which measures the pressure in a child's skull by either: 1) placing a small, hollow tube into the brain's ventricle where the cerebrospinal fluid is produced or 2) inserting a small, hollow bolt or screw into the space just inside the brain's covering and using a monitor to take constant readings, sounding an alarm if the pressure begins to rise