Development of the fetal spinal cord: time of ascendance of the normal conus medullaris as detected by sonography.

OBJECTIVE

The purpose of this study was to perform high-resolution sonographic examinations to determine the normal anatomic relationship of the conus medullaris (CM) of the spinal cord with the vertebral column during different stages of gestation.

METHODS

In this prospective study, fetal sonographic evaluations were performed between 13 and 40 weeks' gestation. Transvaginal probes (7.5-8 MHz) or abdominal probes (5-8 MHz) were used, depending on gestational age and position of the fetus. The CM was located in coronal longitudinal sections. The positions of the kidneys and lumbosacral junction and the origin of the ribs determined the location of the vertebrae. The locations of the CM were divided into 5 groups according to their positions relative to the vertebrae.

RESULTS

A total of 110 fetuses between 13 and 40 weeks' gestation were studied. Between 13 and 18 weeks' gestation, the CM was situated at the level of the L4 vertebra, or more caudally, in 100% of the fetuses. At term, all fetuses showed the CM above L2. A distinct ascent of the CM was detected between 13 and 40 weeks' gestation. The results were statistically significant (P < .0001).

CONCLUSIONS

A distinguishable ascent of the CM in relation to the vertebral column during fetal life was detected.