Early Development of the Urethral Sphincter Muscle : Relationship of the Striated Muscle Fibres with the Prostate in Human Fetuses

Abstract

Purpose The urethral sphincter muscle has a major hole in the maintenance of urinary continence; its quick voluntary contraction especially during an abrupt interruption of micturition. Our purpose is to describe the arrangement of the striated muscle fibres of the urethral sphincter during gestation and to correlate these finds with those described in grown up prostates. Material and methods We analyzed 17 prostates of 17 human fetuses that died of causes unrelated to the urogenital tract. The fetuses were well preserved and none had any kind of detectable congenital malformations. Gestational age ranged between 10 and 31 weeks post conception (WPC) and was estimated according to foot length criteria. Transverse sections of the prostate were made and stained with Gomori's trichrome and immunolabeled with anti alpha-actin antibodies. Results We observed that the urethral sphincter muscle is located on the periphery of the smooth muscle and there wasn't a mixture between these two types of muscle fibres at any period. In the prostatic apex, the striated sphincter shows a circular arrangement and completely covers the urethra externally; adjacent to the verumontanum, it seems like a “horseshoe” and covers the anterior and lateral sides of the urethra, but not the posterior side. Near the neck of the bladder, we've found striated muscle fibres only at the anterior side of prostate, although they could be found at the lateral side of the prostate of the fetus from 20 WPC older. Conclusions The urethral sphincter muscle was present in all fetuses covering the anterior and lateral sides of the urethra. This muscular arrangement is very important in understanding the normal anatomy of the pelvic floor musculature and the alterations of this musculature in congenital anomalies of the genital tract.