History: must include:

1. insidious onset (vs. acute)

2. onset age ≥ 40 years

3. duration ≥ 3–6 months

4. no antecedent head trauma, ICH, meningitis, or other known cause of secondary hydrocephalus

5. progression over time

6. no other neurological, psychiatric, or general medical conditions that are sufficient to explain the presenting symptoms

Brain imaging: CT or MRI after the onset of symptoms must show:

ventricular enlargement not attributable to cerebral atrophy or congenital enlargement (Evan’s index > 0.3 or comparable measure)

no macroscopic obstruction to CSF flow

≥ 1 of the following supportive features

a) enlarged temporal horns not entirely attributable to hippocampal atrophy

b) callosal angled ≥ 40°

c) evidence of altered brain water content, including periventricular changes not attributable to microvascular ischemic changes or demyelination

d) aqueductal or 4th ventricle flow void on MRI

Other imaging findings that may support Probable designation but are not required:

1. pre-morbid study showing smaller or nonhydrocephalic ventricles

2. radionuclide cisternogram showing delayed clearance of radiotracer over the convexities after 48–72 hours

3. cine-MRI or other technique showing increased ventricular flow rate

4. SPECT showing decreased periventricular perfusion that is not altered by acetazolamide challenge