Evaluation of the Conus Medullaris with 2D and 3D Ultrasonography in Fetal Neural Tube Defect Anomalies

INTRODUCTION: This study aimed to evaluate the fetal conus medullaris (CM) using 3D ultrasonography in fetuses with central nervous system (CNS) anomalies and in healthy fetuses. The aim was to evaluate the vertebral ending levels of CM and its utility as a biomarker in prenatal diagnosis.
METHODS: This prospective study, conducted at the Obstetrics and Perinatology Clinic of Van Yüzüncü Yýl University, Faculty of Medicine, included 80 pregnant women between 11 and 22 weeks of gestation with a singleton pregnancy, aged 18 to 45, and with a body mass index (BMI) <30. 40 women with fetal CNS anomalies were included in the patient group, while 40 healthy pregnant women were included in the control group. All pregnant women underwent 2D ultrasonography followed by 3D ultrasonography. The ending level of the CM relative to the vertebral column and various biometric measurements were recorded. Data were analyzed using SPSS 27.0.
RESULTS: When demographic data were analyzed, no significant difference was found between the two groups in terms of age, height, weight, and gestational age (p>0.05). The distances between the CM and the lower end of the sacrum (CM–Os Sacrum) and the anterior abdominal wall (CM–Abdomen) were also similar (p=0.279 and p=0.299). When the ending levels of the CM relative to the lumbar vertebrae were evaluated, it was observed that the CM most frequently ended at the L4 level in 23 patients (53.5%) in the patient group, at the L3 level in 15 patients (37.5%), and at the L2 level in 2 patients (5%). In the control group, it was observed that the CM ended at the L3 level in 23 patients (57.5%) and at the L2 level in 17 patients (42.5%). While it was found that the CM extended to the L4 level in the patient group, this ending was not observed in the control group. Ending at the L2 level was more frequently observed in the control group (5% vs. 42.5%). In subgroup analyses, it was determined that the CM ending was more caudal in cases with anomalies such as spina bifida and anencephaly.
DISCUSSION AND CONCLUSION: The ending level of the CM at the vertebral end, particularly its extension to the L4 level, may be a powerful biomarker for identifying CNS anomalies prenatally. This study demonstrates the utility of prenatal 3D ultrasound assessment of the CM ending level in the early diagnosis of CNS anomalies.

Keywords: conus medullaris, neural tube defect, 3D ultrasonography, central nervous system abnormalities.