Evaluated anatomical variations in children by sacrococcygeal ultrasonography as a new tool: a report from a Chinese tertiary hospital

Abstract

Objective: Anatomical variations in the sacrococcygeal region can lead to complications such as accidental dural puncture during caudal block. This study aimed to determine the prevalence of sacrococcygeal anatomical variations using ultrasonography and to evaluate the necessity of ultrasound guidance in sacral block procedures.

Methods: Ultrasound findings of sacrococcygeal anatomy were validated against magnetic resonance imaging (MRI). A detailed ultrasound protocol was subsequently applied to assess sacrococcygeal anatomy in pediatric patients.

Results: Ultrasound and MRI demonstrated strong concordance in evaluating sacrococcygeal anatomy. The most common anatomical variation was a low-lying dural sac (16.2%), followed by incomplete sacral cornua (4.9%). The dural sac termination level was inversely associated with age (odds ratio: 0.996, 95% CI: 0.945-0.987; p < 0.001). Other variations included abnormal coccyx curvature (4.3%), sacral skewness (3.8%), and sacral hiatus atresia (1.1%), with no pathological abnormalities detected.

Conclusion: Comprehensive ultrasound scanning effectively identifies anatomical variations in the sacrococcygeal region of pediatric patients, which are highly prevalent. Routine preprocedural ultrasound examinations and ultrasound guidance during caudal block procedures are strongly recommended to enhance safety and accuracy.

Keywords: Caudal block; magnetic resonance imaging; sacrococcygeal anatomical variations; ultrasound.

Figure 1.

Location and movement of the ultrasound probe for sacral imaging. (A) Schematic diagram of short-axis scanning: the probe is placed horizontally at the sacral hiatus and slid continuously from S5 to L5 along the arrow. (B) Schematic of longitudinal scanning: the probe is rotated 90 degrees and moved cephalad from S5 to S1. (C) Schematic of paracentral scanning: the probe is positioned 0.5–1 cm to the left/right of the midline and tilted towards the midline for paracentral imaging. L5, the fifth lumbar vertebra; S1, the first sacral vertebra; S5, the fifth sacral vertebra.

Figure 2.

Representative MRI and ultrasound images. Normal spinal MRI (A) and ultrasonography (B–D) in a 2-year-old child. The termination of the dural sac is marked by a red arrow. S1, the first sacral vertebra; S2, the second sacral vertebra; S3, the third sacral vertebra; S4, the fourth sacral vertebra; S5, the fifth sacral vertebra.

Figure 3.

Ultrasound images showing measurement indicators. (A) Transverse plane: a, distance between skin and sacral cornu; b, height of sacral cornu; c, distance between bilateral sacral cornua; d, diameter of the sacral canal at the apex of the hiatus. (B) Longitudinal plane: e, angle of the sacral hiatus. S3, the third sacral vertebra; S4, the fourth sacral vertebra; S5, the fifth sacral vertebra.

Figure 4.

Bland-Altman plots demonstrating agreement between MRI and ultrasound. (A) Diameter of the sacral canal. (B) Optimal angle of the sacral hiatus.