The vast majority of congenital hydrocephalus patients develop it as of a bilateral symmetrical process, while in the less common type of obstructive hydrocephalus, as in this case, only one-sided lateral ventricular dilatation is seen.

Knowing basic anatomy of the ventricular system, one can tell that the obstruction of CSF flow is expected to be at the level of the foramen of Monro, and may include a web, or an intraventricular cyst (not visualized).