Prenatal evaluation of the conus medullaris position in normal fetuses and fetuses with spina bifida occulta using three-dimensional ultrasonography.

OBJECTIVES

This study aimed to assess the fetal conus medullaris (CM) position with three-dimensional (3D) ultrasonography and its use in detecting and diagnosing spina bifida occulta (SBO).

METHODS

We examined 150 normal fetuses (gestational age, 20-38 weeks) and 14 fetuses with SBO. All fetuses underwent prenatal 3D ultrasonography, and the CM position in relation to the vertebral body was evaluated using volume contrast imaging. Intra- and inter-observer agreements were assessed using weighted kappa. The correlation between gestational age and CM level was determined by linear regression analysis.

RESULTS

Operators successfully located the CM position in 145 cases. The CM was at L3 or higher in all normal group cases. A linear relationship was noted between gestational age (X) and CM position (Y) (Y = 0.118X + 6.011, R(2)  = 0.679, P < 0.001). The weighted kappa values for intra- and inter-observer agreement were 1.0 and 0.788, respectively. The CM was located at L3 in one case and lower than L3 in 13 cases in the SBO group. All values were below the fifth percentile for the normal group.

CONCLUSIONS

Three-dimensional ultrasonography may accurately determine the CM vertebral level. Prenatal evaluation of the CM position may improve the detection and diagnosis of SBO.