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%
- 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.
- 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.
- 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
- 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.
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