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08: Nerve density assessment of urethra, paraurethral tissue, and anterior vaginal wall using immunohistochemistry and automated neuronal axon detection

      Objectives

      To examine nerve density of the urethra, paraurethral tissue, and anterior vaginal wall within regions of clinical interest and to correlate findings to surgery in the anterior pelvic compartment.

      Materials and Methods

      Microscopic examination at three levels of interest along the length of the urethra and at the level of the upper trigone was performed in nulliparous female cadavers. Axial tissue sections were procured at the levels of the ureteral orifices (upper trigone), urethrovesical junction, 1 cm distal to urethrovesical junction, and at the distal urethra, just as it passed under the pubic symphysis. At each level, adjacent tissue sections, approximately 4 microns apart, were stained with Gomori Trichrome for structural identification and antibodies against beta III tubulin, a specific marker of neuronal axons. Antibody staining was performed using standard colorimetric immunostaining protocols (Figure). Digital images were analyzed using Aperio Imagescope (Leica) for automated nerve density analysis of anatomic subregions of clinical interest. Statistical analysis was performed using mixed effects repeated measures design with pairwise contrasts among regions of interest.

      Results

      Two adult nulliparous (ages 47 and 52 years) and 1 infant cadaver (age 12 weeks) were examined. The highest nerve density, at the level 1 cm distal to the urethrovesical junction, was noted in the sub region that included the posterior aspect of the urethra and mid portion of anterior vaginal wall (p = 0.009). At this level, no distinct plane was seen between the urethra and the vaginal wall. The next highest nerve density was found on the lateral portions of anterior vaginal wall at this same level (p = 0.026, p = 0.044). At the levels of the urethrovesical junction and at 1 cm distal, albeit not statistically significant, the paraurethral tissue exhibited increased nerve density in the medial regions, those closest to the urethra, as compared to the more lateral regions, near the pelvic sidewall. At the upper trigone level, the lowest nerve density was found at the mid segment of the vesicovaginal space in all specimens.

      Conclusion

      The higher nerve density found within the medial, relative to the lateral, aspect of the paraurethral tissue may contribute to higher rates of postoperative voiding dysfunction if trocars, sutures or graft material are placed in close proximity to the urethral wall. The higher nerve density noted in the posterior urethra, compared to the anterior, highlights importance of avoiding deep dissection through an anterior midline vaginal wall incision. The lower nerve density found at the mid portion of the vesicovaginal space at the upper trigone level emphasizes importance of avoiding excessive lateral dissection during anterior colporrhaphy or with distal exposure of the vesicovaginal space during sacrocolpopexy. Avoiding these regions of high nerve density during pelvic surgical procedures may also help reduce rates of postoperative pain and sexual dysfunction.
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