Localization of the fetal conus medullaris by oblique view extended imaging.

Abstract

To evaluate the accuracy of oblique view extended imaging (OVEI) in locating the position of the fetal conus medullaris. One hundred and twenty-two normal fetuses and five counterparts with spinal bifida received prenatal ultrasound examination. The vertebral body at the terminal of the conus medullaris and the coronal section of over five vertebral bodies were reconstructed using OVEI. Development of the nervous system of normal fetuses was assessed at postnatal day 28. For spinal bifida cases, pathological examination was performed. Among 127 fetuses, the conus medullaris was accurately positioned in 120 (94.0%) cases according to OVEI. OVEI failed to locate the conus medullaris in three healthy fetuses due to obesity of the mother and four cases with spinal bifida due to abnormal fetal position. The conus medullaris was located at L3 or above in 115 healthy fetuses. The conus medullaris was positioned below L4 in five fetuses with spinal bifida, including L5 in two, S1 in two, and S3 in one, which was consistent with the findings of pathological examination. OVEI can display the 12th rib, T12, and conus medullaris simultaneously. OVEI is applicable to precisely locate the position of the conus medullaris and useful for prenatal evaluation of spinal bifida.