External urethral sphincter dilation for the management of high risk myelomeningocele: 15-year experience

We investigate the long-term outcome using external urethral sphincter dilation for high risk myelomeningocele.

Since 1984 external urethral sphincter dilation was performed in 25 patients with myelomeningocele who demonstrated passive leak point pressure greater than 40 cm. H2O and/or poor bladder compliance. Mean followup from the first dilation was 8.4 years. Overall 2.4 dilations were performed per patient (range 1 to 8). Cystometrography, imaging study and continence status were evaluated retrospectively.

Overall external urethral sphincter dilation produced durable improvements in mean leak point pressure (60.9 versus 34.4 cm. H2O), capacity (119.8 versus 233.3 ml.), initial compliance (11.5 versus 28.4 ml./cm. H2O) and terminal compliance (1.1 versus 7.7 ml./cm. H2O). Categorical analysis revealed 3 groups in terms of outcome. Group 1 consisted of 11 patients (44%) who demonstrated durable improvements in urodynamic parameters as well as preservation of the upper tracts. These patients demonstrated a 2-step compliance pattern on pre-dilation cystometrography, in which elevated leak point pressure was associated with excellent initial compliance. Group 2 consisted of 5 patients (20%) who failed to maintain safe leak point pressure and whose upper tracts deteriorated, including 4 who eventually underwent augmentation cystoplasty. This group demonstrated a 1-step hypertonicity in which elevated leak point pressure was associated with a steep pressure increase during early filling. Group 3 consisted of 9 patients (36%) who responded minimally in terms of leak point pressure reduction but whose upper tracts remained well preserved. They demonstrated a high pressure instability pattern associated with excellent baseline compliance.

External urethral sphincter dilation provides an effective long-term solution for select high risk myelomeningocele cases. Those who demonstrate elevated leak point pressure and poor bladder compliance at the time of external urethral sphincter dilation are less likely to respond, suggesting that the bladder may have already undergone irreversible changes due to high outlet resistance. Patients who demonstrate instability patterns are less likely to respond to external urethral sphincter dilation in terms of leak point pressure reduction but the upper tracts appear to be well preserved.