Sonographic determination of normal Conus Medullaris level and ascent in early infancy

Controversial reports exist in the literature regarding both the spinal level of the conus medullaris (CM) in normal infants and the age at which the CM achieves its adult level. Autopsy studies have demonstrated ascent continuing into early infancy while more recent imaging study series' suggest the adult conus level is attained by the 40th postmenstrual week.

The authors conducted a retrospective review of 1,273 screening lumbar ultrasound studies performed over 5 years at a pediatric tertiary referral center. All patients were infants referred for initial imaging to rule out the presence of a tethered spinal cord. Referral sources included urban academic, urban private practice, and rural private practice pediatricians. After excluding studies lacking sufficient documentation (n = 90) and those reported as abnormal (n = 106), 1,077 remained for review. The CM level and patient age in days were recorded from each study. Statistical analysis was performed using unpaired t testing and ANOVA for continuous variables; chi-square for categorical data.

The mean CM level for infants in group I (ages 0-30 days) was compared to those in groups II (31-60 days) and group III (61-100 days). Group I had a mean CM level of 0.125 and 0.2 vertebral segments lower than groups II and III (p = 0.0005 and <0.0001, respectively). ANOVA comparison of all three groups confirmed a rostral migratory trend (p < 0.001). The prevalence of CM level caudal to L2 in group I was 13 %, group II 11.4 %, and group III 4.7 %; also indicating a significant rostral trend (p = 0.004).

Rostral migration of CM level continues through the first few months of post-natal life, albeit of limited extent. Documentation of continued ascent in a neonate may obviate the need for magnetic resonance imaging.