How Should I Evaluate Small Head Size in Infants With Small Parents?

Marilyn W. Edmunds, PhD, NP


November 11, 2003


How do I determine if head growth/circumference is appropriate when small size may be in the family history? I have patients that begin to drop below the 5th percentile, but I suspect this may not be a problem because of the size of their petite parents. Is there a formula based on the circumference of parents' heads?

Shatzie Montellano, MSN, FNP-C


Laurie Scudder, MS, RN-C, PNP 

A child with growth that is trending downward on the growth curve is always a concern. Head circumference should never be measured and assessed in isolation but rather as part of the child's repeated growth measurements that include height and weight and an evaluation of parental and sibling stature. A child whose growth is decreasing, and crossing major centiles, should indicate that an investigation for growth failure is needed. (A report titled "Evaluating Pediatric Growth and Nutrition: Guidelines for the Primary Care Clinician," may provide guidance. In addition, the Centers for Disease Control (CDC) released new growth charts in 2000, which are available for download from their Web site.

It is important that growth be measured accurately and plotted at every well-child visit. The new growth charts, unlike the 1977 National Center for Growth Statistics (NCHS) charts used in the past, are based on a national sample of children of all major ethnic groups and include both bottle- and breast-fed infants. "The differences between the 1977 NCHS Growth Charts and the 2000 CDC Growth Charts are most pronounced in the head circumference-for-age charts. In general, the 2000 percentiles for head circumference are higher than the 1977 percentiles until age 4-6 months. At this point, a crossover occurs, and the 2000 curve becomes lower than the 1977 curve."[1] Microcephaly is rarely associated with overall growth failure.[2]

You describe a situation in which head growth is falling below the 5th percentile. However, your question does not note that this decline is accompanied by a corresponding decrease in height and weight. Microcephaly is defined as a head circumference that measures more than 3 standard deviations below the mean for age and sex.[3] It may also be suspected in full-term newborns and infants under the age of 6 months whose head circumference is smaller than that of their chest.[4]

Microcephaly is divided into primary and secondary categories. Primary microcephaly is usually evident at birth and associated with a brain insult that occurred early in fetal life. It is typically accompanied by severe mental retardation. It is often associated with skull deformities, such as backward sloping of the forehead and narrowing at the temples and fontanelles that close earlier than expected.

Secondary microcephaly occurs from an insult to the brain later in fetal life or in the perinatal period.[5] Brain injury after 2 years is not likely to be associated with severe microcephaly. Some causes of secondary microcephaly, such as Rett syndrome, may not be noted until 2-4 months of age when head growth begins to decelerate and are accompanied initially by a slowing in acquisition of developmental milestones and later a loss of milestones.[6]

It can be helpful to measure the head circumference of other family members and plot the measurements on an age-appropriate chart. For older children, the Nellhaus curves for the ages 0 to 18 years are widely used. These were developed by merging data from 14 studies of head growth published worldwide between 1948 and 1965.[7] They do have limitations, however, because the majority of those included in these studies were white Americans. A 1997 study conducted in Turkey on 408 adults computed male and female adult head circumference charts plotted against weight and height.

More important, though, is your overall assessment of the child. Is the small head size part of growth that is trending downward, or does the child have a small head and is staying at the same percentile with relation to a standardized growth curve chart? Serial head circumference measurements are more important than a single determination, particularly when the variation is small.

There are 2 major concerns that should be addressed when a child presents with microcephaly. The first is developmental delay and mental retardation, since microcephaly may be the presenting condition in a wide range of neurodevelopmental disorders. A child with a small head warrants ongoing, serial, developmental assessments to be sure that he or she is meeting age-appropriate developmental milestones. Thorough exams should be conducted at well-child visits to document that the child is developmentally appropriate, does not have unusual facies or other features, has open fontanelles at an age where they should be open, and appears to have normal vision and hearing.

The second concern is craniosynostosis, resulting from premature closure of the cranial sutures, as the cause of the suspected microcephaly. This may occur if many or all sutures close prematurely. Typically, however, craniosynostosis is not associated with microcephaly because the inhibited growth along the involved suture is compensated for by increased growth at open sutures and fontanelles.[5] Closure of only 1 suture will not cause impaired brain growth. The management of craniosynostosis is directed toward preserving skull shape.

The bottom line with this child is that an isolated measurement should be followed by repeated careful assessment of both growth and development. Yes, small parents may lead to small children, but before that conclusion is made, other causes must be ruled out.



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