Cephalic Index – What do the numbers mean?

When a baby is diagnosed with Deformational Plagiocephaly, it is important to determine whether or not the baby will benefit from Cranial Remodel Band or Helmet.  

So what is the Cephalic Index?  The Cephalic Index, also referred to as cranial ratio or cephalic ratio is the measurement that will be used to categorize your infants head shape.

CI = width ÷ length x 100    or    CI = (Left/Right) ÷ (Front/Back) x 100

Scale for Cephalic Index (CI)

Normal: 75 – 90 mm

Mild: 91 – 93 mm

Moderate: 94 – 97 mm

Severe: >97 mm

Normocephaly or plagiocephaly = CI >76%-<90%

Brachycephaly = CI >90%

Dolichocephaly = CI <76%

Scale for Measuring Plagiocephaly

Normal head shape: 0 – 4 mm

Mild Plagiocephaly: 5 – 9 mm

Moderate Plagiocephaly: 10 – 15 mm

Severe Plagiocephaly: >15 mm

Head symmetry is measured using cranial anthropometric landmarks, calipers (slide or spreading), and a head circumference tape. Head circumference is an important parameter; however, it is not an indicator of plagiocephaly, either synostotic or nonsynostotic, because in both types the absolute head circumference may be normal despite the skull being misshapen.  Clinicians should consider screening for head shape at the same time head circumference is measured at every well-child visit.

There are 5 primary measurement parameters included in this report for head shape determination:

1. Head circumference: measure from glabella (prominent point between eyebrows where supraorbital ridges join) around the opisthocranion (most prominent posterior point on the occiput).

2. Head width: side-to-side measurement; use sliding caliper across top of skull from eurion (most lateral point on parietal region) to opposite eurion.

3. Head length: anterior-posterior measurement; use sliding caliper across top of skull from glabella to opisthocranion.

4. Cranial Index (CI): also referred to as cephalic index, cranial ratio, or cephalic ratio; a measurement to categorize head shapes in populations. CI = width ÷ length x 100. We use the following ranges:

▪ Normocephaly or plagiocephaly = CI >76%-<90%[51]▪ Brachycephaly = CI >90%
▪ Dolichocephaly = CI <76%

5. Cranial vault asymmetry (CVA): also referred to as diagonal difference, oblique diagonal difference, or transcranial difference. CVA is the difference between 2 diagonal measurements (frontozygomaticus to opposite eurion). Note that CVA will be symmetric in symmetric brachy-, and dolichocephaly.

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Plagiocephaly Diagnosis:

  • CI >76% to <90%, asymmetric head shape, occipitoparietal flattening, ear misalignment
  • May affect temporal, parietal, and/or frontal bones and facial symmetry
  • May occur alone or in combination with brachycephaly or dolichocephaly
  • May result from premature fusion of one or both coronal sutures or rarely the lambdoid sutures.

Brachycephaly Diagnosis:

  • CI >90%, short skull, occiput flattened, widened
  • May affect parietal, temporal, and/or frontal bones and facial symmetry
  • May occur alone or in combination with plagiocephaly
  • May result from the premature fusion of the coronal or lambdoid sutures

Dolichocephaly Diagnosis:

  • CI <76%, long, narrow skull, affects occiput, temporal, parietal and frontal bones, may affect facial bones
  • May be familial, often noted in premature babies, uterine breech position
  • May result from premature fusion of the sagittal suture

These numbers may seem confusing but this has proven to greatly assist in the monitoring of children with any skull shape concerns.

If you would like help determining if your child would benefit from a Cranial Band- contact us at info@cappskids.org or find a provider and get a free evaluation here.