INVESTIGATIVE UROLOGY

The precise location and nature of the nerves to the male human urethra: histological and immunohistochemical studies with three-dimensional reconstruction
Karam I, Droupy S, Abd-Alsamad I, Korbage A, Uhl JF, Benoit G, Delmas V
Universite Rene Descartes -- Faculte de Medecine Paris V Institut d’Anatomie des Saints Peres, France
Eur Urol. 2005; 48: 858-64

• Objectives: The precise location, origin and nature of nerve fibers innervating the male urethral sphincter have not been clearly established. Classical anatomical studies based on cadaver dissections have provided conflicting results concerning the location of somatic and autonomic nerve fibers. This study was designed to identify nerve fibers innervating the male urethral sphincter and to provide a three-dimensional representation of their tissue relations in the human male fetus.
• Materials and Methods: Histology and immunohistochemistry (Hematein-Eosin-Safran, Luxol Fast Blue, Protein S 100 immunolabeling and smooth fibers actin immunolabeling) were performed in male external urethral sphincter of ten male fetuses (114-342 mm crown-rump length). Three-dimensional reconstruction of the urethral structure and innervation were obtained from serial sections using Surf Driver 3.5.3 software.
• Results: The three-dimensional reconstruction of the same section levels with different strains allowed to identify the precise structure of the muscular layers and the nature of nervous elements (myelinated and unmyelinated), their distributions and their relations with the urethral wall, the prostate and the seminal vesicles.
• Conclusion: Histological and immunohistochemical three-dimensional reconstruction of the nervous elements of the urethral sphincter gives a very didactical understanding of the three dimensional arrangement of the urethral nerves and their relationships with the urethral layers. It allows a better understanding of the origin, the course and the nature of the nervous elements participating in the urinary continence.
  
  
• Editorial Comment
  This is one more interesting applied anatomical study from Saint Peres, Paris, under the leadership of Vincent Delmas. The authors analyzed the innervation of the male urethral sphincter in 10 male fetuses of different CR lengths. After elegant and precise 3D reconstruction, the authors give an understanding of the origin and course of the nerves. They also confirmed the previous findings of Yucel and Baskin (1), that the majority of unmyelinated nerve fibers penetrates the male urethral smooth muscle layers at 5 o’clock and at 7 o’clock, where the majority of myelinated nerve fibers penetrates the striated muscles of the prostatic capsule and of the urethral sphincter at 9 o’clock and at 3 o’clock. This very intimate relations of somatic and autonomic nerve fibers place them at risk during any pelvic cancer surgery or urethral trauma. I strongly recommend all surgeons involved in pelvic surgery to read carefully this anatomical article.

Reference
1. Yucel S, Baskin LS: An anatomical description of the male and female urethral sphincter complex. J Urol. 2004; 171: 1890-7.

Dr. Francisco J.B. Sampaio
Full-Professor and Chair, Urogenital Research Unit
State University of Rio de Janeiro
Rio de Janeiro, Brazil