Evans' Index Plus Calculator

Patient Metadata & Measurement Units

Patient ID / MRN

Patient Initials / Name

Preferred Scan Modality

Measurement Unit

Longitudinal Evans' Index Time Points

Enter measurements across consecutive scan dates. The Evans' Index is calculated automatically as Bifrontal Horn / Maximal Internal Skull.

Unit: mm

# Time Point	Date *	Context	Bifrontal Horn Diameter (mm) *	Maximal Internal Skull Diameter (mm) *	Evans' Index	Clinical Status	Action

Longitudinal Evans' Index Bar Graph

Dates are automatically ordered chronologically in ascending sequence on the X-axis.

Chronological Tracking

Scans Evaluated 0

Baseline Index --

Latest Index --

Overall Delta (Δ) --

Bar Graph Requires ≥ 2 Time Points

Please fill in valid Date, Bifrontal Diameter, and Maximal Internal Skull Diameter for at least 2 time points to display the dynamic chronological bar graph.

Normal Evans' Index (< 0.30)

Elevated Ventriculomegaly (≥ 0.30)

Diagnostic Cut-Off Threshold (0.30)

Anatomical Reference & Clinical Guidance

Axial CT/MRI slice showing Bifrontal Horn Width (A) and Inner Skull Width (B).

Calculation Formula

\[\text{Evans' Index} = \frac{\text{Maximal Width of Frontal Horns (A)}}{\text{Maximal Internal Skull Diameter at Same Cut (B)}}\]

Diagnostic Cut-Off Thresholds

< 0.30
Normal Ventricular Size:
Ventricular system is within standard physiological limits for age.
0.30 - 0.33
Mild Ventriculomegaly:
Elevated ventricular ratio. Suggestive of early hydrocephalus or mild ex-vacuo enlargement.
> 0.33
Marked Ventriculomegaly:
High suspicion for Idiopathic Normal Pressure Hydrocephalus (iNPH) or Obstructive Hydrocephalus. Correlate with clinical triad (gait impairment, cognitive decline, urinary urgency).

Clinical Note: Measurements should be obtained on the axial slice showing the maximum frontal horn expansion and internal cranial diameter. When evaluating iNPH, combine Evans' Index with other DESH features (Sylvian fissure dilation, tight high-convexity sulci, and callosal angle).