I. Applied anatomy
1.Applied anatomy of the male urethra
The male urethra starts from the internal urethral opening of the bladder and goes down to the external urethral opening of the head of the penis. According to foreign statistics, the male urethra can pass through F10 at the age of 1, F15 at the age of 5, F18 at the age of 10, and F24 in adults, and the male urethra crosses the prostate gland from the inner orifice to the membrane, which is called the prostatic urethra, that is, the posterior urethral part, about 25 mm long, and is also a very wide part of the urethral internal diameter. It is also the part of the urethra with a wide internal diameter. In the posterior wall there is a longitudinal elevation called the urethral ridge. The central part of the ridge is the seminal caruncle, and the central part of the caruncle has a depression for the prostatic capsule, and on each side of the capsule there is a small ejaculatory duct opening, and on both sides of the seminal caruncle there are many prostatic duct openings, so the male urinary system and the reproductive system are connected here, and once the infection is easy to spread to each other here, the urethra has also become the gateway for bacteria to invade both systems.
The urethra passes downward through the urogenital diaphragm, a segment called the membranous urethra, which is surrounded by the external sphincter and is the most fixed and relatively narrow part of the lumen. There is also a small segment of the supra-membranous urethra, about 5 mm, between the tip of the prostate and the urogenital diaphragm that lacks surrounding supporting tissue. When the pelvis is fractured, the prostate is displaced posteriorly with the lateral ligaments of the pelvic wall and the rectum, forming a shearing force that tears the membranous urethra, so pelvic fractures occur in this area when complicated by posterior urethral rupture. In addition, when metal instruments are used in the urethra, injury is also likely to occur here, because the urethral membrane is the weakest, easy to penetrate the anterior wall of the membrane urethra and enter the bladder, forming a false channel.
The urethra continues forward into the anterior urethral section, which is surrounded by the urethral spongiosa, also known as the urethral spongiosa. The urethra located in the bulb is called the urethral bulb and is the widest section of the urethra where the urethral bulb gland opens. The membranous part of the urethra and the spongy part of the urethra migrate a few millimeters, only loose connective tissue wrapped spare, the wall of the tube is very thin, especially in the front wall, in the urethra ball gland excretory duct opening mucous membrane is of varying sizes of the fossa, so when the urethra metal instruments can be operated through this to the upper posterior penetration into the rectum. When the body falls from a height, a straddling injury can occur, and the urethral rupture occurs when an external force squeezes the urethral bulb at the inferior border of the pubic symphysis. In addition, there are many mucus glands under the mucosa of the anterior urethra, called urethral glands, which open in the anterior urethra and form fossae of varying sizes, which are easy to hide bacteria and infections, so inflammatory urethral strictures often occur in the anterior urethra. In addition, there is a mucosal fold in the anterior wall of the navicular fossa, so when applying metal instruments with lateral holes (such as cystoscopes), the lateral holes should be directed towards the ventral side of the penis, and then rotated forward in the body of the penis to prevent damage to the fold. At the same time, the external urethra is another narrow place, so do not be violent when inserting metal instruments or forceps to remove stones, and the narrowing of the external urethra is very likely to occur after injury.
The urethra has three wide places, three narrow places and two curves. Three wide places are located at the prostate, ball and navicular fossa; three strictures are at the urethral orifice, membrane and external orifice; two bends, one under the pubic bone, that is, the beginning of the membrane urethra and the ball urethra, and more curved and fixed, the other bend in the anterior urethra at the junction of the scrotal section and the free section, the bend concave surface downward, in order to lift the penis to the abdominal wall, the bend can be made to disappear, which is conducive to the operation of intracavitary instruments. When a long time to perform auditory catheterization patients, this concave surface is often due to a long period of time is easy to be pressed periurethritis, and even the formation of urinary leakage, so the auditory catheter can be fixed upward reverse abdominal wall, can achieve the role of preventing infection.
The urethral wall is composed of mucosal layer, submucosal layer and muscle layer, the mucosal layer is migrating epithelium in the prostate, the membrane, the ball and the body of the penis are compound columnar epithelium, the head of the penis is squamous epithelium; the submucosal layer is loose connective tissue, rich in blood vessels; the muscle layer includes 2 layers of internal longitudinal muscle and external circular muscle.
The blood supply to the posterior urethra comes from the inferior cystic artery and the branches of the internal pubic artery, while the anterior urethra is supplied by the internal pubic artery and the urethral artery, with anastomoses between them. The posterior urethral veins return to the prostatic venous plexus of the bladder, while the anterior urethra returns to the internal pubic veins. The urethral lymph is abundant and forms a lymphatic network in the submucosa, with the posterior urethra feeding into the external iliac lymph nodes, the foramen ovale lymph nodes and the pelvic lymph nodes, and the anterior urethra feeding into the inguinal lymph nodes. The urethral nerve comes from the pubic nerve, genitofemoral nerve and sympathetic nerve.
2.Applied anatomy of the female urethra
The female urethra is located behind the pubic symphysis and in front of the vagina, passing from the internal bladder opening to the lower part of the urogenital diaphragm and opening in the vestibule of the vagina, with a total length of about 30-50 mm and a diameter of 8-10 mm, and the thinnest at the external urethral opening.
The upper part of the female urethra is a circular smooth muscle, which is connected with the circular muscle of the bladder neck, and the muscle fibers are particularly thick, forming a strong internal urethral sphincter, which plays an important role in urinary control; the middle part of the urethra is surrounded by the urethral sphincter, which is a transverse muscle, playing the role of the external sphincter; the lower part of the urethra is surrounded by a small number of muscle fibers of the vaginal sphincter and anal sphincter, playing the role of the sphincter of the urethra. In addition, the levator muscle and the deep perineal muscle group play an auxiliary role in controlling urination. The upper part of the female urethral mucosa is migratory epithelium and the lower part is squamous epithelium; there are abundant urethral glands under the urethral mucosa, which open on the mucosal surface.
The upper segment of the female urethra is supplied by the inferior cystic artery, the middle segment by a branch of the vaginal artery, and the lower segment by the internal pubic artery. Venous return flows to the paravaginal and internal pubic venous plexus of the bladder. The submucosa of the urethra is rich in lymphatic vessels that converge into the inguinal lymph nodes and the internal iliac lymph nodes.
In women, the urethra is wide, short and straight, with the opening exposed to the vestibule, close to the vagina and near the anus, and easily contaminated. Therefore, women are more likely to cause urethral infection, but are less likely to be injured.
Second, the relationship between urethral injury and stricture formation
Singh has conducted animal experiments and concluded that there are three points: 1) the distribution of urethral glands is consistent with the site of gonococcal urethral stricture; 2) the chance of stricture is greater in penetrating urethral injury than in non-penetrating injury, and the chance of stricture is higher in urethral rupture without suprapubic osteotomy than in suprapubic osteotomy; 3) because of the different components of the scar, it can be soft, hard or elastic. 3. Scars can be soft, hard or elastic due to the different cellular components that make up the scar.
This experiment is a good guide for us in the early management of urethral injury and the prevention of stricture and scars of different nature.
III. Etiology
(A) Trauma: It is the main cause of urethral stricture, and there are several common causes as follows
1, traffic accidents: about 70% or more of traumatic urethral strictures, mostly located in the posterior urethra.
2.Jumping injuries: all occur in the bulbous urethra.
(3) Medical origin: It can occur in the anterior or posterior urethra due to improper operation of instruments in the urethra, such as cystoscopy, electrosurgery, urethral dilatation, etc.
(ii) Infection: It is the second most common cause of urethral stricture after trauma.
1. Pathogenic bacteria: non-specific bacteria, tuberculosis, viruses, gonorrhea, etc.
2. Characteristics: ① Most of them occur in the anterior urethra, ② The strictures are mostly long and multifocal.
(iii) Congenital: see hypospadias, duplicate urethra, prepuce, etc.
(iv) Medical origin: Injuries caused by improper operation of urethral instruments, inflammatory strictures including improper care and other causes.
IV. Diagnosis.
1. History and signs: patients with urinary difficulty and lower urinary tract obstruction or urinary retention, history of trauma or urethral infection and indwelling catheter, etc. Patients who have undergone surgery should be asked in detail about previous surgeries, and in long-term obstruction cases, attention should be paid to the examination of the upper urinary tract, such as renal function and whether there is pelvic ureteral effusion and other manifestations. Male patients should pay attention to the examination of the scrotum, and note whether there are abnormal changes such as inflammation of the spermatic cord and epididymis.
2.Urethral dilation: For patients suspected of having urethral stricture, doing trial urinary dilation is an effective means of diagnosis and treatment. The choice of urethral probe should start with a medium-thick probe strip, such as F18 or F16. The site and extent of the stricture can be understood.
3.Imaging.
(1) Urography: It is the most common method of examination. In order to obtain satisfactory imaging results, the following points should be noted: (1) Take an oblique position (left anterior oblique or right anterior oblique) with the torso at an angle of 30 degrees to the X-ray bed plate, with the lower thigh flexed forward and the upper thigh extended posteriorly to avoid cross-over of the urethra and femur. ②, one film each of retrograde urethrography and voiding urethrography should be taken. In cases where suprapubic cystostomy has been performed, a metal urethral probe can be used to introduce the posterior urethra from the fistula to the stricture when voiding is not possible, and then a combination of retrograde urethrography and urethrography can help to understand the site and extent of the stricture and the condition of the posterior urethra. (We do not recommend the use of metal urethral probes for both anterior and posterior urethra because of the large error).
(2) The use of ultrasound in urethrograms (see separate chapter)
(3) KUB and IVU are used in some patients with long-term severe obstruction to find out whether there are stones and whether there are functional and morphological changes in the upper urinary tract.
(4) MRU can be used when iodine allergy is present and the upper urinary tract must be understood.
V. Differential diagnosis.
It should be differentiated from the following common conditions: benign prostatic hyperplasia, bladder neck contracture (fibrosis), neurogenic bladder, urethral calculi, urethral foreign body and posterior urethral valves, etc.
VI. Prevention.
(i) Medically induced urethral strictures: Most of the causes of this category can be prevented by paying attention to the following aspects.
1. Urethral instruments should be operated gently and without violence. When instruments and urethra do not match in caliber, external urethrotomy or urethrotomy should be performed instead of forcing through; in addition, good anesthesia is very important.
In addition, it is important to prevent infection. In particular, attention should be paid to the following when indwelling catheter is performed in the urethra: ①, choose a catheter with good material and good tissue compatibility; ②, the diameter of the catheter should be slightly smaller than the internal diameter of the urethra and be fixed by turning upward toward the abdominal wall to facilitate drainage of secretions and reduce the occurrence of pressure sores at the junction of the penis and scrotum; ③, strengthen the daily catheter care work.
(ii) Traumatic urethral stricture: If the following aspects are paid attention to, it will reduce the chance of urethral stricture complications
1.Prevent further expansion of the injury. (e.g. repeated trial of the catheter, etc.)
2.Preventing urinary extravasation: temporary diversion of urinary flow is very important.
3.Preventing infection