Contrary to popular belief, not every case of fetal macrocephaly requires a referral to genetic counselling. In fact, a large head circumference is a relatively common symptom, without medical significance.
As long as the head circumference is within normal range or slightly above the upper limit, all that is necessary is making sure there are no other congenital defects (such as a ventricular enlargement in the brain) and that the fetal development rate is constant and there is no accelerated circumference growth from a certain stage.
It is worth noting that in many cases of macrocephaly, one of the parents also has a larger than usual head circumference.
What is macrocephaly?
Unlike cases in which head circumference is in the normal range or slightly above its upper limit, macrocephaly is a condition in which the head circumference is mora than two SDs larger than average for the specific gestational age.
This finding is detected in three percent of fetuses and is usually no cause for concern. This is especially true when one of the parents has a larger head circumference. However, when this condition is diagnosed, it is important to rule out other conditions that may have caused macrocephaly.
What should parents do after macrocephaly is diagnosed?
After diagnosis of a head circumference more than two SDs than the average for gestational age, a fetal anomaly scan must be performed to rule out conditions such as intracranial hemorrhage, brain ventricular enlargement, hydrocephaly, and other factors that could cause macrocephaly. When the rest of the body is found to be enlarged, like the head, further investigation is required to find the cause for this condition.
If neither of the parents have a larger head circumference, amniocentesis may be required, in addition to further inquiry. When the femur is found to be shorter than average for gestational age in addition to a larger head circumference, inquiry is necessary since this condition may indicate a higher risk for achondroplasia.
What genetic disorders are associated with macrocephaly?
As stated above, not every case of a large head circumference is evidence of a genetic disorder. However, macrocephaly is indeed a symptom of various genetic diseases and syndromes, such as:
- Microdeletions or microduplications in the short arm of chromosome 1.
- MLC1 disease – megalencephalic vacuolating leukoencephalopathy.
- Sotos syndrome.
- Klinefelter’s syndrome.
- Alexander disease (fibrinoid leukodystrophy).
