Prenatal Assessment and pregnancy outcomes of foetal low-lying conus medullaris using 3D Ultrasound

Abstract Objectives This study aimed to follow up cases with low conus medullaris (CM) using three dimensional (3D) ultrasonography and analyze and explore the correlation between the CM location and the final prognosis. Methods 39 cases of low CM diagnosed prenatally in the Peking University First Hospital was collected retrospectively from January, 2019 to December, 2020. The location of CM was confirmed by 3D ultrasonography and clinical data including postnatal outcomes were collected. Results The average gestational weeks when low CM was diagnosed was between 23 and 24 weeks. Among 39 cases, there are 9 cases (23.1%) which were complicated with spine abnormality (3 cases of open spina bifida, 6 cases of tethered cord syndrome). Apart from 9 cases of pregnancy termination, the remaining 30 cases of live births had good prognosis, though 5 of 6 cases of tethered cord syndrome underwent the surgical release. The mean location of cases of open spinal dysraphism and cases of closed dysraphism/tethered cord syndrome was at L5 and between Lumber vertebra (L)5 and Sacral vertebra (S) 1 respectively, which showed statistically significance compared with the postnatally normal group. When we set Lumber 4.25 as the cut-off value to predict the diagnosis of spine abnormality (mainly open spina dysraphism and closed spinal dysraphism/tethered cord syndrome, the sensitivity was 66.7 and the specificity was 96% with the area under curve (AUC) at 0.877. Conclusion Low CM was related with spinal defects (mainly open spinal dysraphism and closed spinal dysraphism/tethered cord syndrome). Clinicians should be cautious especially when the location of CM was lower than L4. In cases of tethered cord syndrome, release surgery was needed according to the postnatal condition. Otherwise, the prognosis of low CM was good.