Bladder height to width ratio as a surrogate marker for non-physiological storage pressures in children with spinal dysraphism

Abstract

Introduction: Spinal dysraphism is the most frequent cause of neurogenic bladder. Urodynamic study (UDS) is an important component of the follow-up of a child with neurogenic bladder. However, it suffers from a lack of widespread availability and is further hampered by technical difficulties and difficulty in its interpretation in children. A neurogenic bladder often appears vertically elongated; only limited and sparse literature is available regarding objectively defining the bladder shape and the urodynamic parameters in the cohort.

Objectives: This study aimed to investigate the usefulness of the bladder's height-to-width ratio (HWR) on cystogram as a screening tool for identifying "non-physiological" bladder pressures in children with spinal dysraphism. A prospective study was undertaken to evaluate children operated for spinal dysraphism. Cystogram, ultrasonography and UDS evaluation were performed. HWR was calculated by the ratio of the maximum height to the maximum bladder width at maximum cystometric capacity (MCC), where MCC was calculated using standard Koff's formula, given by (age in years + 2) *30 ml in children more than one year and weight *7 ml for infants. The children were categorised into groups based on maximum detrusor pressure (MDP) into two groups (MDP ≥ 30 cmH₂O and MDP < 30 cmH₂O). A receiver-operative characteristic curve was constructed to analyse the sensitivity and specificity of HWR in predicting the MDP.

Results: A total of 53 children, operated for spinal dysraphism, met the study criteria during the study period, from March 2021 to September 2022. The median age of children was 4 years (IQR-3-5.5 years). The HWR ratio was compared between the two groups and was significantly higher for the non-physiological pressure bladders than for physiological pressure bladders (mean of 1.55 vs 1.26, p = 0.001). On evaluating the sensitivity and specificity of HWR for discerning children with non-physiological bladder pressures were 87.5% and 48.28%, respectively. The area under the curve (AUC) was 0.781, with a cut-off value of 1.3.

Discussion: We attempted to evaluate the HWR based on bladder shape objectively. We demonstrated a moderate correlation between the bladder shape and the bladder pressures. An HWR of 1.3 or higher could be significant for identifying a non-physiological bladder storage pressure.

Conclusion: The height to width ratio of the bladder on cystogram is a useful tool as a surrogate marker for non-physiological storage pressures in bladders of children with spinal dysraphism.

Keywords: HWR; Hydronephrosis; Neurogenic bladder; Spinal dysraphism; height to width ratio.