Figure 1, B and C correspond to a healthy 2-yr-old boy who underwent hypospadias repair during general anesthesia combined with ultrasound-guided continuous caudal block. Mid-sagittal plane lumbar ultrasound (Sonosite SII, FUJIFILM Sonosite, Inc., USA) showed the dural sac end at S4 vertebral level, significantly lower for the child’s age—usually at S1 to S2—and consistent with tethered spinal cord syndrome (fig. 1B).

Fig. 1.
(A) Normal spine. (B and C) Midsagittal plane lumbar ultrasound in a healthy 2-yr-old boy. Black arrows, needle tip; red dashed line, dural sac; yellow dashed line, distended epidural space. CS, caudal space; FTE, filum terminale externum; FTI, filum terminale internum; S, spinous process; SCM, sacrococcygeal membrane; VB, vertebral body.

(A) Normal spine. (B and C) Midsagittal plane lumbar ultrasound in a healthy 2-yr-old boy. Black arrows, needle tip; red dashed line, dural sac; yellow dashed line, distended epidural space. CS, caudal space; FTE, filum terminale externum; FTI, filum terminale internum; S, spinous process; SCM, sacrococcygeal membrane; VB, vertebral body.

Ultrasound-guided caudal anesthesia has proven superior to landmark technique in neonates/infants in terms of safety and effectiveness. However, this may not be the case in older children.  Despite its many benefits, ultrasound guidance is used in only about 3% of these blocks. Occult spinal dysraphism incidence in healthy children is about 0.1% but can reach up to 2% in those with simple urogenital anomalies (especially hypospadias). As compared to a normal spine (fig. 1A), sonographic features of tethered spinal cord syndrome include the lower level of the conus medullaris and dural sac tip and a thicker filum terminale, limiting the caudal epidural space to that immediately below the sacrococcygeal membrane and up to S4 vertebral level (fig. 1B).  Given the high risk of dural sac puncture and thus potential high spinal block related to accidental intrathecal injection of local anesthetics or postdural puncture headache, ultrasound-guided caudal block can be considered when the reduced caudal epidural space is well observed and the catheter placement must be conditional on a regular hydrodistension of the posterior epidural space with saline (avoiding local anesthetics). The in-plane approach is preferred, targeting the caudal space right under the sacrococcygeal membrane without advancing the epidural needle (20G × 50 mm PERIFIX ONE, Braun Medical Inc., USA) cranially. Subsequent saline injection for hydrodistension must be successful (fig. 1C) to ensure a safe and easy catheter insertion (24G × 711 mm PERIFIX ONE) up to S1 to S3 vertebral level—ours reached only to S3.

These images and accompanying video (https://links.lww.com/ALN/D437) support the added safety of using ultrasound guidance when performing caudal blocks in children with simple urogenital anomalies to potentially avoid complications where spinal dysraphism may be present.