From the Guidelines
Evan's criteria for Normal Pressure Hydrocephalus (NPH) are primarily based on imaging features, particularly the Evan's index.
Key Criteria
- The Evan's index, which is the ratio of the maximal width of the frontal horns to the maximal width of the inner skull, should be greater than 0.3 1.
- Other supportive imaging features include: + Enlargement of the temporal horns + Callosal angle of less than 90 degrees + Evidence of altered brain water content + Aqueductal or fourth ventricle flow void on MRI 1 ### Imaging Recommendations
- A noncontrast MRI is optimal for visualizing these findings, and MRI with IV contrast is not needed 1.
- Additional supportive findings may include an MRI performed before the onset of symptoms showing smaller ventricular size, and a cine MRI study showing increased ventricular flow rate 1.
From the Research
Evans' Criteria for Normal Pressure Hydrocephalus (NPH)
- Evans' index is used to assess ventriculomegaly in NPH patients, with an index > 0.3 indicating ventricular enlargement 2
- The cella media index is also used, with a value < 4 indicating disproportionately enlarged subarachnoid space hydrocephalus (DESH) pattern 3
- Key features of NPH include: + Ventriculomegaly + Gait disturbances + Urinary incontinence + Cognitive changes
- Radiological findings should be differentiated from ventriculomegaly in atrophy combined with enlarged convexity sulci 3
- Clinical and invasive diagnostic tests, such as repeated spinal tap or lumbar drainage, can help confirm the diagnosis and select patients for CSF diversion 3, 4