Functional variability of sacral roots in bladder control

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Sacral roots are involved in sensory, autonomic, and motor innervation of the lower limbs and perineum. Theoretically, it can be assumed that the S-3 root level innervates the bladder; however, clinical practice shows that this distribution can vary. Few researchers have studied this variability.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>The authors conducted a retrospective study involving 40 patients who underwent surgery requiring an electrophysiological exploration of the sacral roots. They performed stimulations for the monitoring of muscular (3 Hz, 1 V) and bladder responses under cystomanometry (30 Hz, 10 V).</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Although the S-3 roots were involved in bladder innervation in all cases, they were exclusively involved (i.e., the only nerve roots involved) in only 8 of 40 cases. In the remaining 32 cases, other sacral nerve roots were involved. The most common association was S-3+S-4 (12 cases), followed by S-2+S-3 (6 cases), S-2+S-3+S-4 (5 cases), and S-3+S-4+S-5 (2 cases). Stimulation of S-2 could sometimes induce bladder contraction (15 cases, 40%); however, the amplitude was often low. S-4 nerve roots were involved in 24 of 40 cases (60%) in the bladder motor function, whereas S-5 roots were only involved 7 times (17%). Occasionally, we noticed a horizontal asymmetry in the response, with a predominant response from the right side in 6 of 7 cases, always with a major S-3 response.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>This is the first study showing a significant horizontal and vertical variability in the functional distribution of sacral roots in bladder innervation. These results show the variability of cauda equina syndromes and their forensic implications. These data should help with the monitoring of sacral roots and the performance of several tasks during surgery, including neurostimulation and neuromodulation.</jats:p></jats:sec>

International Continence Society best practice statement for use of sacral neuromodulation

“…A direct ventral sacral root electrical stimulation study measuring bladder contraction by means of intravesical pressure showed that in 100% of the patients, bladder pressure increase was measured upon stimulation of the S3 anterior sacral root, but also in 60%, upon stimulation of S4, 40% on S2 and around 15% at S5. There is an individual difference in distribution of bladder efferent fibers . It is unknown if the distribution of motor nerves activated directly by neurostimulation is similar to the distribution of the rootlets stimulated for the indirect neuromodulation effect.…”

“…There is an individual difference in distribution of bladder efferent fibers. 127 It is unknown if the distribution of motor nerves activated directly by neurostimulation is similar to the distribution of the rootlets stimulated for the indirect neuromodulation effect.…”

Sacral neuromodulation using the standardized tined lead implantation technique with a curved vs a straight stylet: 2‐year clinical outcomes and sensory responses to lead stimulation

“…A lead is implanted in S4, instead of S3, when the best bellows response upon lead stimulation is elicited at this location. This could be explained by the fact that sacral spinal nerves are mixed nerves and show great variability in their functional distribution . The foraminal level, therefore, seems less important than placement inside a foramen leading to an adequate bellows response upon stimulation.…”

The Filum Terminale Revisited: A Histological Study in Human Fetuses

“…Carlucci et al [14] found a significant horizontal and vertical variability in the functional distribution of sacral roots in bladder innervation. These findings help us to understand the variability in cauda equina syndrome.…”