Correlation of fetal frontal lobe and transcerebellar diameter measurements: the utility of a new prenatal sonographic technique.

Several authors have reported the value of the sonographic assessment of both the fetal frontal lobe and the cerebellum. Both frontal lobe shortening and cerebellar hypoplasia have been associated with fetal aneuploidy. We anecdotally observed that the distance between the calvarium and the posterior cavum septum pellucidum (frontal lobe) closely approximated the transcerebellar diameter. This study was undertaken to investigate this relationship. Between 1 July 1994 and 1 January 1996, the frontal lobe (posterior cavum septum pellucidum to the inner calvarium) and transcerebellar diameter were measured in patients referred to two prenatal ultrasound laboratories in Denver, Colorado, USA. All pregnancies had certain dates and were uncomplicated. Statistical comparison was completed using interval polynomial regression analysis. During the study period, we performed 221 detailed ultrasound examinations in which the frontal lobe and the transcerebellar diameter were measured. We found a correlation coefficient of 0.950 when comparing the two variables (p < 0.0001). Some conditions (Down's syndrome, lethal trisomies and pathological microcephaly) have differential effects on the frontal lobe and the transcerebellar diameter. Our preliminary judgement is that this new technique may prove to be a useful tool in assessing the relative effect of these conditions on structural neuroanatomy.