The normal neonatal head circumference (frontal and occipital) is 33-35 cm, the average head circumference is about 46 cm at the age of 1 year, reaches 50 cm at the age of 5 years, and approaches the adult head circumference at the age of 15 years, about 54-58 cm. 2.CT and MRI CT and MRI are the main and reliable methods for diagnosing hydrocephalus. In particular, Cine-MRI can not only make accurate qualitative and quantitative measurements of the flow rate and flow of cerebrospinal fluid, but also distinguish the type of hydrocephalus, the site and degree of hydrocephalic obstruction, which is the gold standard for the diagnosis and differential diagnosis of hydrocephalus. 3.Brain pool imaging Through lumbar puncture, radionuclide is injected into the subarachnoid space, and brain scans are performed at 4, 24, 48 and 72 hours respectively. Under normal conditions, the isotope flows on the convex surface of the brain without entering the ventricles, and the isotope disappears completely from the surface of the brain after 48 hours. In patients with primary normal pressure hydrocephalus, isotopes enter the ventricles and remain there for up to 72 hours without accumulation on the convex surface of the brain. Or the isotope enters the ventricles and also accumulates on the convex surface of the brain.