Development Outcome of Isolated Fetal Macrocephaly and Microcephaly
Abstract & Commentary
By John C. Hobbins, MD, Professor, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert.
Dr. Hobbins reports no financial relationship to this field of study.
Synopsis: Once other abnormalities were excluded, children diagnosed to have macrocephaly and microcephaly in utero generally performed as well on developmental testing at age 2-6 as matched control children with fetal head circumferences within normal range.
Sources: Biran-Gol Y, et al. Developmental outcome of isolated fetal macrocephaly. Ultrasound Obstet Gynecol 2010;36:147-153; Stoler-Poria S, et al. Developmental outcome of isolated fetal microcephaly. Ultrasound Obstet Gynecol 2010;36:154-158.
Virtually every pregnant woman in the united states will have at least one ultrasound examination, and, by simple arithmetic, one-tenth of these women will have fetuses whose head circumferences (HCs) are defined as being too big (above the 95th percentile) or too small (below the 5th percentile). Until now, counseling these patients has been more difficult than performing a number on Dancing with the Stars.
A group of investigators from Israel have addressed this dilemma by studying neural-psychological behavior in children who were noted as fetuses to have "isolated" macrocephaly or microcephaly. The two studies were presented back-to-back in the August issue of Ultrasound in Obstetrics and Gynecology. In the first study, the authors identified 45 fetuses whose HCs in the third trimester were 2-3 SDs above the mean for gestation. Seventeen of these children were available for sophisticated developmental testing at 2-6 years of age. A control group of 17 children with in utero HCs that were within normal range underwent the same testing procedures.
First, 11 of the 17 (65%) diagnosed with fetal macrosomia did have neonatal head circumferences above 2 SDs at birth. The 35% who did not have macrocephaly at birth by neonatal standards represent a rather high false-positive rate. Eight fathers and 2 mothers had large heads, leaving less than half of the macrocephalic fetuses without a possible familial tendency for their in utero findings. None of the control parents had large heads. Most importantly, there were no major differences between groups in their neuropsychological evaluations (cognition, language, and motor function). However, 3 children in the study group were evaluated at some point for behavioral/attention deficit disorders, compared with none in the control group of children. It is ironic that cognitive performance seemed to be inversely proportional to the size of the father's head. The authors concluded that "a large head circumference does not appear to be a significant risk factor for abnormal long-term neuropsychological development."
The second study dealt with children whose heads were smaller than expected before birth. Forty-five patients were identified whose fetuses had HC values < 2 SDs below the mean. After employing exclusions, 20 children were available for the same neuropsychological testing used in the first study. The results were compared with 20 control children with normal HCs in utero. Only 1 child in the study had an HC < 3 SDs.
No significant differences were noted between groups regarding cognitive, language, and motor function. However, there was a higher rate of emotional and behavioral problems in the microcephalic group. Surprisingly, those in the study group who also were growth restricted tested no differently than those whose estimated fetal weight was above the 10th percentile. Also, although only 5 of the 20 in the study group had parents with small heads, there was no relationship between testing performance and the parents' head size. Of the 20 with HCs < 2 SD below the mean, only 2 were diagnosed as being microcephalic at birth but, interestingly, another 3 children became microcephalic at the time of their later behavioral testing.
Commentary
Dealing with large fetal heads has been easier than small ones because, with the exception of a few very rare conditions, one can easily rule out pathological causes for macrocephaly. These findings would almost always include ventriculomegaly or a mega cisterna magna. If these areas are normal, and spurious dating has been ruled out, the most common cause of macrocephaly is a familial tendency towards "bigheadedness," with the father of the baby being the usual culprit. This study provides further support for our being up-beat regarding the outcome of truly "isolated" macrocephaly.
One cannot be so cavalier regarding isolated microcephaly, since signs of cortical dysgenesis, frontal lobe shortening, or intrauterine infection, are sometimes subtle. However, the study shows the prognosis is still reasonably good in isolated microcephaly regarding cognitive, language, and motor performance. To explain the poorer behavioral scores, the authors conjure up the idea that maternal anxiety during pregnancy, fueled by mothers being told that their fetuses have a very small head, may have indirectly affected the fetus/child.
We had noticed in our center fetal HCs popped up on reports as being less than the 5th percentile far more often than 5% of the time, simply because our mixture of fetuses at 5000 feet above sea level have smaller heads than the fetuses of Texans incorporated into the Hadlock nomogram used in the report software of most of today's ultrasound machines. The point here is for clinicians to use a nomogram that more appropriately reflects their populations. Also, to be truly concerned about the possibility of microcephaly, one should use a more stringent definition, like the one used by the above authors. Their definition of < 2 SDs would be analogous to about the 2nd percentile, and would represent an HC that would be more than 3 weeks discrepant with dates at 28-30 weeks gestation and about four weeks thereafter.
In the microcephaly study, only one out of four fetuses had parents with small heads. However, in our experience, small fetal heads often reflect parents of small stature, in general, even if these parents do not have head circumferences that are strikingly small. The study's growth-restricted fetuses did not show any difference in neurological testing compared with fetuses of normal weight. However, by definition, this group could have included genetically small fetuses that were simply constitutionally small, and not deprived.
Both studies provide useful information with which to better counsel patients. If the author's hypothesis is right (and this does represent a real stretch), armed with more reassuring information about outcome, we can temper maternal anxiety to a point where the behavioral fallout can be avoided.
Virtually every pregnant woman in the united states will have at least one ultrasound examination, and, by simple arithmetic, one-tenth of these women will have fetuses whose head circumferences (HCs) are defined as being too big (above the 95th percentile) or too small (below the 5th percentile).You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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