The normal location of the fetal conus medullaris.

In vivo studies of the location of the normal conus medullaris in infancy and childhood have been extended to the fetus utilizing sonography. This prospective study of 33 fetuses showed that the fetal conus medullaris can be visualized in the prone fetus as early as 19 menstrual weeks. By the time the conus medullaris was observed sonographically, its location was within the normal adult range, thus refuting the commonly held notion that the conus medullaris ascends to adult levels sometime in childhood. Our results suggest that a fetal spinal cord termination level of L2-L3 or higher should be considered within normal limits. A termination level of L3 is indeterminate and requires neonatal evaluation. A termination level of L3-L4 or lower is abnormal and should instigate a careful sonographic search for associated abnormalities.