Evaluation of the fetal conus medullaris in central nervous system anomalies using 3D ultrasound

Objective: This study aimed to evaluate the conus medullaris (CM) in fetuses with central nervous system (CNS) anomalies and in healthy pregnancies using three- dimensional (3D) ultrasonography, and to compare vertebral termination levels and associated biometric parameters. It was also investigated whether the vertebral level of CM termination could serve as a diagnostic biomarker in the prenatal period. Materials and Methods: This prospective observational case- kontrol study was conducted at the Department of Obstetrics and Perinatology, Van Yüzüncü Yıl University Faculty of Medicine. A total of 100 singleton pregnant women aged between 18 and 45 years and with a body mass index (BMI) <30, in their 11th to 22nd weeks of gestation, were included. The patient group consisted of 50 fetuses with prenatally diagnosed CNS anomalies, while the control group included 50 fetuses from healthy pregnancies. Fetal CM evaluation was performed in all participants using a Voluson E8 (GE Healthcare, USA) 3D ultrasonography device. The CM termination level was determined based on vertebral column anatomy, and the distances between the CM and the sacral endpoint and the anterior abdominal wall were measured. Biometric parameters such as abdominal circumference (AC), femur length (FL), and estimated fetal weight (EFW) were also recorded. Data were analyzed using SPSS 27.0 (IBM Corp., Chicago, IL, USA). Normality was assessed using the Kolmogorov–Smirnov test. Continuous variables were presented as mean ± standard deviation, and categorical variables as number (percentage). Independent samples t-test, Mann–Whitney U, and Chi- square tests were used for comparisons. Results: Of the 100 cases, 50 were in the CNS anomaly group and 50 in the control group. There was no significant difference in stillbirth, postnatal neonatal death, ectopic pregnancy, or molar pregnancy between the groups. Demographic variables such as age, height, weight, and gestational age were similar. However, the number of pregnancies (gravida) and living children were significantly higher in the anomaly group. Biometric measurements (AC, FL, EFW) were lower in the anomaly group but not significantly. CM termination was most commonly observed at L4 (52%) and L3 (42%) in the anomaly group, whereas in the control group, it was seen at L3 (52%) and L2 (48%). Termination at L4 occurred exclusively in the anomaly group, and L2 exclusively in the control group (p<0.001). Subgroup analyses revealed that all fetuses with L4 termination had CNS anomalies, particularly spina bifida and anencephaly. Conclusion: In this study, CM termination at the L4 level was observed only in fetuses with CNS anomalies. This finding suggests that vertebral-level CM localization may serve as a reliable prenatal marker for spinal dysraphism. 3D ultrasonography appears to be a valuable tool in the early detection of fetal spinal anomalies. Key Words: Central Nervous System Anomaly, Conus Medullaris, Fetal Spine, Prenatal Diagnosis, Three-Dimensional Ultrasonography.