Purpose or Case Report: Abstract:
Sacral development is a key determinant of bowel and bladder function in children with anorectal malformations (ARM) and sacral agenesis. Accurate radiologic assessment of the sacrum provides essential prognostic information, guiding both surgical planning and long-term management. We aim to review the imaging-based metrics used to evaluate sacral development, highlighting their significance in predicting continence outcomes.
ARM result from abnormal development of the hindgut and cloacal membrane between weeks 6 and 9 of gestation. These malformations can vary significantly, ranging from minor anal displacement to complex defects that involve the rectum, vagina, and urethra. Both the anorectal structures and the sacrum develop from the caudal mesoderm during the same period, which means that sacral anomalies, such as hypoplasia or agenesis, often occur alongside ARM. Due to this close embryologic origin, the sacrum can provide important insights into the prognosis of ARM, and specific metrics can offer objective information for assessment.
The sacral ratio (SR), derived from anteroposterior (AP) and lateral pelvic radiographs, is the most widely used quantitative measure. It stratifies patients into prognostic categories, with SR ≥ 0.7 indicating good continence potential and SR < 0.4 associated with poor outcomes. However, SR is subject to variability due to patient positioning, pelvic tilt, and image quality.
Additional metrics such as the sacral index (SI) and sacral curvature (SC) offer complementary insights. SI reflects sacral width and height and has been correlated with ARM severity. SC provides a qualitative measure of sacral shape and is associated with continence outcomes. These measurements are often limited by the constraints of conventional radiography and the technical challenges of MRI, including non-isotropic data and restricted field of view.
This educational exhibit will provide a comprehensive review of sacral measurements in ARM and sacral agenesis. We encourage a standardized and multimodal approach to sacral assessment, and provide information for a deeper understanding of:
- Sacral and anorectal malformations embryology
- Key radiologic metrics (SR, SI, SC) and their interpretation
- Limitations and considerations in measurement techniques
- The prognostic significance of sacral development
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