Is it common to have hydrocephalus but have no other symptoms other than an enlarged head?

Yes: Depending upon the exact cause of the hydrocephalus, hydrocephalus in a neonate/infant may present purely with an enlarging head circumference without any other apparent neurological issues. If left untreated, however, a child will likely develop significant neurological symptoms related to brain dysfunction - mental delay, vision loss, psychomotor difficulties, etc.