An 11 month old baby boy is presenting for umbilical hernia repair. The medical student asks how spinal anesthesia is different in the infant when compared to the adult. You can confidently say all of the following EXCEPT:
a) The conus medularis terminates at L1 for most adults
b) The conus medularis terminates at L4 in most infants
c) The dural sac terminates at S1 in adults
d) The dural sac terminates at S3 in infants
Answer b. The conus medularis terminates at L2-L3 in most infants (1). Differential rates of growth for the developing human spinal cord and spinal column create changing relationships between these two structures. Spinal anesthesia (as with lumbar puncture) should target the dural puncture to be inferior to the conus medularis, yet superior to the termination of the dural sac. This position minimizes trauma to neural tissue, yet still provides access to the CSF spaces. In infants, the conus medularis terminates at the L2-L3 space; in adults the termination is usually at L1. The more cephalad position of the sacrum and the relatively smaller pelvis position the dural sac closer to S3 in infants. This increases the likelihood of a dural puncture when providing caudal anesthesia.