Where is the apex of the sacral hiatus for caudal epidural block in the pediatric population? A radio-anatomic study

Caudal epidural block (CEB), administered through the sacral hiatus, is a regional anesthetic technique commonly used in children. To facilitate and optimize pediatric CEB, morphometric data that may be important for the sacral hiatus have been obtained using multidetector computed tomography (MDCT). This study is the first radio-anatomic study designed to address this topic in children. Images of 79 children (39 girls and 40 boys between 1 and 9 years old) were divided into three groups according to age [group I (ages 1-3), group II (ages 4-6), and group III (ages 7-9)] and were retrospectively examined. Data were gathered via 3D volume-rendered images. Measurements included the height and width of the sacral hiatus, S2-S4 (sacral vertebra) distance, the distances between the poles of the unfused spinous process of each sacral vertebra, and the dimensions of an imaginary triangle formed between the right and left posterior superior iliac spines (PSIS) and the apex of the sacral hiatus. The most frequently fused spinous process was at S2 level. The mean S2-S4 distance was 1.36 cm for group I, 1.78 cm for group II, and 2.17 cm for group III. There was not the imaginary equilateral triangle used in the method of finding the sacral hiatus for CEB, and the apex of this triangle did not occur at the standard level (S4) in most of the children. It was observed that the apex deriving from the most distal fused spinous process was at the level of S2 in one of two children. Dural puncture is inevitable for CEB applied at the S2 level. Consequently, CEB should be applied below this level (range, 1.36-2.17 cm) from the midpoint of the interspinous distance between the PSIS (at the same level with S2) in children aged 1-9 years.