Prenatal assessment and pregnancy outcomes of foetal low-lying conus medullaris using 3D ultrasound

Abstract

Objectives This study aims to follow up on low-lying conus medullaris (CM) cases and explore the correlation between the CM location and the final prognosis. Methods We retrospectively collected 37 cases diagnosed with low-lying CM during pregnancy in the Peking University First Hospital from January 2019 to December 2020. The location of CM was confirmed by 3D ultrasonography, and clinical data, including postnatal outcomes, were recorded. When the conus medullaris was below L3 (excluding L3), it was diagnosed as low-lying conus medullaris, regardless of gestational age. The short-term postnatal outcome included assessment of symptoms and signs of motor and sensory neuron dysfunction. Results The average gestational weeks of low-lying diagnosis was between 23 and 24 weeks. Among 37 cases, nine (24.3%) were complicated with spine dysraphism (3 cases of open spina bifida, 6 cases of tethered cord syndrome). Apart from 7 cases of pregnancy termination, the remaining 30 live births had a good prognosis in the short term, though 5 out of 6 cases of tethered cord syndrome underwent surgical release. The mean location of cases of open spinal dysraphism (n = 3) and those of closed dysraphism/tethered cord syndrome (n = 6) was at Lumber vertebra 5 (L5) and between L5 and Sacral vertebra 1 (S1), respectively, which showed statistical significance compared with the postnatally normal group. When we set Lumber 4.25 as the cut-off value to predict the diagnosis of spine dysraphism (mainly involving open spinal dysraphism and closed spinal dysraphism/tethered cord syndrome), the sensitivity was 66.7. At the same time, the specificity was 96%, along with the area under the curve (AUC) at 0.877. Conclusion The second trimester finding of low CM is associated with spinal defects, mainly open spinal dysraphism and closed spinal dysraphism/tethered cord syndrome. Careful assessment of the fetal spine should be considered especially when the location of CM is lower than L4.

Tethered cord syndrome from pediatric and adult perspectives: a comprehensive systematic review of 6135 cases

“…52,53 Ultrasound can also assist in early TCS diagnosis, especially during pregnancy, due to its rapid and noninvasive nature. 54,55 However, after closure of the spinal canal, ultrasound becomes less effective in accurately detecting the conus position given its limited ability to penetrate bone. Ultrasound can be used intraoperatively to assess the re- traction and mobility of the spinal cord conus after spinal column shortening to confirm surgical success.…”

Ultrasound-based horizontal ranging in the localization of fetal conus medullaris

“…The low position of the conus medullaris is closely related to the tethered cord. Advancements in ultrasound technology and the improvement in machine resolution have enabled the visualization of the vertebral canal and internal spinal cord echoes [ 4 ]. According to the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) Practice Guidelines (updated), during the second and third trimesters of pregnancy, the conus medullaris is usually located at the level of the second/third lumbar vertebra (L2-L3) in ultrasound examination of the fetal central nervous system [ 5 ].…”

Quantifying tethered spinal cord tension: Ultrasound elastography results from computational, cadaveric, and intraoperative first-in-human studies

“…Increased length is used as a surrogate for tension 4,26 . However, the normal anatomical variability of spinal cord lengths adds uncertainty to this metric [27][28][29] . A more direct evaluation of suspected tension involves invasively stretching the filum terminale to gauge elasticity and, thus, tension 30 .…”