Cranial Index & Cranial Vault Asymmetry Index Calculator Pro

Anatomical Reference & Landmarks (CI)

Formula & Definition

$$\text{Cranial Index (CI)} = \frac{\text{Line A: Biparietal Diameter (BPD)}}{\text{Line B: Occipitofrontal Diameter (OFD)}}$$

Expressed as a ratio (and percentage) formatted strictly to two decimal places.

Clinical Cut-off Thresholds

CI < 0.75 (< 75.00%) Dolichocephaly / Scaphocephaly (Sagittal Synostosis)
0.75 - 0.85 (75 - 85%) Mesocephaly (Normal Cranial Vault Ratio)
CI > 0.85 (> 85.00%) Brachycephaly (Coronal / Lambdoid Synostosis)
CI > 0.90 (> 90.00%) Severe Brachycephaly / Oxycephaly

Clinical Note: Diagnosis is clinical. Threshold values provided can vary depending on the age, sex, and race/ethnicity of the child.

Longitudinal Cranial Index Measurements

Total Scans: 5

Scan #	Date	Context (Meta)	Biparietal Diameter (BPD)	Occipitofrontal Diameter (OFD)	Cranial Index (CI)	Classification	Action

Total Scans Computed 0

Baseline Cranial Index --

Latest Cranial Index --

Total Change (Δ CI) --

Longitudinal Cranial Index Bar Graph

Visualizing cranial ratio evolution over time & treatment

Enter measurements into at least 1 time point row to generate the Cranial Index Bar Graph.

Diagonal Landmarks & Obliques (CVAI)

CVAI Denominator Convention:

Formula & Definition

$$\text{CVAI (\%)} = \frac{|\text{Longer} - \text{Shorter}|}{\text{Shorter Diagonal}} \times 100$$

Diagonals taken at 30° to the midline (crossing at vault center). CVA is the absolute difference ($|A - B|$) in mm/cm.

Clinical Cut-off Thresholds (CVAI)

CVAI < 3.5% Normal Symmetry
3.5% - 6.25% Mild Plagiocephaly
6.25% - 8.75% Moderate Plagiocephaly
CVAI > 8.75% Severe Plagiocephaly

Threshold Note: The cut-off thresholds above were derived using the shorter diagonal diameter as the denominator. Diagnosis is clinical; values can vary depending on age, sex, and race/ethnicity.

Literature & Denominator Reference

Regardless of whether the shorter or longer diagonal diameter is chosen as the denominator, research demonstrates little practical clinical difference in threshold values.

Reference Citation:
Miyabayashi H, Saito K, Kato R, Noto T, Nagano N, Morioka I. Denominator of Cranial Vault Asymmetry Index: Choosing Between Longer and Shorter Diagonal Lengths. J Craniofac Surg. 2023;33(5):e369. doi:10.1097/SCS.0000000000009263

Critical Clinical Points

Scaphocephaly Alert: A normal CVAI does not reassure in scaphocephaly. Sagittal synostosis is symmetric, so CVAI remains normal while CI falls.
Morphology Differentiation: CVAI cannot distinguish deformational plagiocephaly (parallelogram deformation) from synostotic plagiocephaly (trapezoid deformation). Morphological clinical examination is required.

Longitudinal CVAI & Asymmetry Measurements

Total Scans: 5

Scan #	Date	Context (Meta)	Shorter diagonal diameter	Longer diagonal diameter	CVA (\|B-A\|)	CVAI (%)	Classification	Action

Total Scans Computed 0

Baseline CVAI (%) --

Latest CVAI (%) --

Total Change (Δ CVAI) --

Longitudinal CVAI Asymmetry Bar Graph

Visualizing plagiocephaly vault asymmetry index over time & treatment

Enter measurements into at least 1 time point row to generate the CVAI Bar Graph.