The conus medullaris ratio: A new way to identify tethered cord on MRI

Gestational age-specific reference standards of low-lying conus medullaris level in fetuses: a prospective cohort study

PURPOSE

To explore the position change of fetal conus medullaris by ultrasound, and to propose gestational age-specific references for the lower limits of fetal conus medullaris level.

METHODS

We prospectively collected the imaging and clinical data of fetuses whose mothers accepted routine prenatal ultrasonic follow-ups in the Department of Medical Ultrasonics, Chinese PLA General Hospital, between November 2020 and April 2021. By assigning to the conus medullaris levels, calculating statistical data, and performing linear regression analysis, we determined the correlation between the conus medullaris level and gestational week, as well as between the 95th percentile of the conus medullaris level, i.e., the lower limit of the conus medullaris level, and gestational week.

RESULTS

We included 1202 different fetuses at 17-40 gestational weeks in the study. Both the conus medullaris level and the 95th percentile of the conus medullaris level were linearly correlated with gestational week. We calculated the adjusted values of the lower limits of fetal conus medullaris levels, that is, the theoretical references of the lower limits, according to the linear regression equation, and composed a comparison table.

CONCLUSION

The fetal conus medullaris position continues changing cranially with gestational weeks during the whole pregnancy. The conus medullaris of a term fetus should not lie below the L2 vertebra level at birth. We proposed reference criteria of fetal low-lying conus medullaris for each gestational week from 17 to 40 weeks of gestational age, which potentially help prompt diagnosis and improve prognosis of fetal tethered cord syndrome.

Predictive value of spinal bone anomalies for spinal cord abnormalities in patients with anorectal malformations

AIM

To evaluate the correlation between sacral/vertebral anomalies and spinal cord anomalies (SCA) on MRI, in patients with anorectal malformation (ARM).

METHODS

Patients with ARM consecutively treated between January 1999 and August 2019 were included. Radiological imaging of sacrum and spine were retrospectively analyzed and correlated to the presence of SCA at MRI. Fisher's exact test and X² test were used as appropriate; p<0.05 was considered statistically significant.

RESULTS

348 patients with ARM were enrolled in the study, 147 presented SCA at MRI. 144 patients showed spinal bone anomalies, isolated vertebral and sacral anomalies were found in 17,6% and 35% respectively. Higher level of ARM was associated with a significant higher prevalence of sacral and vertebral anomalies. A significant correlation was found between the "level" of ARM and the presence of SCA (p<0.05). Sacral anomalies were significantly correlated with the presence of SCA at MRI (p<0.05). SCA were found in 70% of patients with vertebral anomalies (VA) and in 76% of patients with sacral anomalies. The presence of multiple malformations (vertebral and sacral anomalies) are strictly related to the presence of SCA. However, the absence of spinal bone anomalies does not exclude the presence of SCA. SD was the most represented type of SCA (n=94/147), of those 96% had fatty filum. Neurological or neurourological symptoms were detected in 11,5% patients (n=17) with SCA and required neurosurgical intervention.

CONCLUSIONS

Our data confirm the strong relation between sacral or vertebral anomalies and SCA. However, in our series also patients without sacral/vertebral anomalies had SCA at MRI. Our results suggest that, despite the presence or absence of spinal anomalies, spinal cord MRI should be performed in all children with ARM, to allow a correct multidisciplinary follow-up and treatment. In fact, most patients with spinal bone and SCA are asymptomatic, but could develop clinical manifestations during their growth.