Depends. The term hydrocephalus is generally used to describe any condition producing an excess of fluid within the brain. The more common form is due to a blockage of the spinal fluid plumbing system with a buildup of pressure that can expand the infant skull. Another cause is the loss of brain substance due to injury (stroke, infection) & fluid fills is the empty space under little or no pressure.
Can it be possible that there is no visible head enlargement for a 1-yr-old child diagnosed with hydrocephalus?
Its possible. This would depend on the cause of the hydrocephalus. If the cause is blockage of CSF flow (by a blood clot or tumor) there should be a back pressure that will cause the head enlargement. If the cause of the hydrocephalus is an ex vacuo phenomenon from a problem with development (ie. There is not as much brain tissue), the ventricles can dilate out to fill the space. There is not the back pressure.