This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The perineum is involved in extravasations of blood and urine in cases of rupture of the urethra; also in operations on the deep urethra and bladder for the retention of urine from stricture; also in operations for vesical calculus, enlarged prostate, and disease of the seminal vesicles.
Urinary extravasation results most often from stricture and occurs almost always in front of the anterior layer of the triangular ligament. The urine enters the superficial perineal space and is confined superficially by Colles's fascia and beneath by the triangular ligament. It is prevented from going back into the ischiorectal space by the union of Colles's fascia and the triangular ligament posterior to the superficial transverse perineal muscles; it is prevented from extending laterally by the attachment of Colles's fascia to the ischiopubic rami; hence it works its way forward, distends the scrotum, and follows the spermatic cord up over the crest of the pubis between the spine of the pubis and the median line. Reaching the surface of the abdomen it is prevented from descending on the thigh by the attachment of the deep layer of the superficial fascia (Scarpa's fascia) just below Poupart's ligament, so it flows laterally and makes a collection in the flank of each side above the iliac crests. It may also infiltrate the penis as far forward as the glans. The septum in the median line of the abdomen, perineum, and scrotum hinders but does not prevent the passage of the urine from one side to the other. In treating it, numerous free incisions are made down to the deep fascia.
This is produced by falling astride a hard object and jamming the urethra against the subpubic arch, or it results from stricture. The rupture almost always involves the urethra just in front of the triangular ligament and sometimes a part of the membranous urethra. The superficial perineal space becomes infiltrated with blood, and if urine is passed it follows the blood, collecting between Colles's fascia and the triangular ligament.
If the membranous urethra is ruptured the blood and especially the urine may escape into the deep perineal space between the layers of the triangular ligament. It may break or leak through the anterior layer and enter the superficial perineal space; it may work backward into the ischiorectal regions; it may work up and back between the prostate and rectum or breaking through the deep layer of the triangular ligament it may work up and anterior behind the symphysis pubis, in the prevesical space (of Retzius) between the peritoneum and transversalis fascia (see Fig. 476). Ruptured urethra is treated by perineal section or by a retained catheter.
In these operations the bladder is entered through an incision in the median line into the bulbomembranous urethra. They are done to divide deep strictures, to allow the urine to escape in extravasation and rupture of the urethra, to remove foreign bodies and calculi from the bladder, and to remove enlargements of the prostate gland. The incision is to be made through the raphe in the median line; ordinarily it does not begin farther forward than 3 cm. (1 1/4 in.) in front of the anus. As the central point of the perineum is 2 cm. in front of the anus the incision passes through it and divides the posterior fibres of the bulbocavernosus muscle but involves little if at all the erectile tissue of the bulb. There is little bleeding if the incision is kept in the median line. The urethra is entered about 2.5 cm. (1 in.) from the surface, and the knife passed upward and back through the membranous and prostatic urethra into the bladder, a distance of 6.25 to 7.5 cm. (2 1/2 to 3 in.) from the surface. In fat people or those with enlarged prostates one may be unable to reach the interior of the bladder with the finger. The membranous and prostatic urethra is distensible, so that when the former is opened the finger can be introduced and pushed into the bladder. In children the urethra may be too small to permit the entrance of the finger and a blunt guide is introduced, along which forceps may be passed to extract any foreign body. In Cock' s operation for retention of urine the index finger of one hand is introduced through the rectum and its tip placed at the apex of the prostate. A straight knife is then inserted 2.5 cm. (1 in.) in front of the anus and pushed up and inward into the urethra, being guided by the finger in the rectum. (For removal of enlarged prostate see page 450).