Bladder, urethra and prostate
Bladder, Urethra and Prostate: Anatomy, Injuries and Clinical Links
Bladder, urethra and prostate for FCPS Part 1: bladder position, trigone, nerve control, parts of the male urethra, prostate zones and venous drainage. Explains bladder rupture, urine extravasation, incontinence, fistula, TURP syndrome and prostate disease.
One of the most tested topics in past papers
Urinary bladder: position and structure
- Empty, it lies in the true pelvis behind the symphysis. Filling, it rises into the abdomen and strips the peritoneum off the anterior abdominal wall, so a suprapubic catheter or needle just above the symphysis enters without crossing the peritoneum.
- Between the bladder and pubis is the retropubic (prevesical) space of Retzius, filled with fat and the vesical venous plexus.
- Capacity about 400–600 mL; first urge at about 150–300 mL.
- Trigone: smooth triangle between the two ureteric orifices and the internal urethral orifice; formed from incorporated mesonephric ducts (mesoderm), later overgrown by endoderm. It does not stretch.
- The rest of the bladder and its transitional epithelium come from the urogenital sinus (endoderm) after the urorectal septum divides the cloaca.
- Ureters run obliquely through the wall, forming a flap valve against reflux; a short intramural ureter in children allows vesicoureteric reflux.
- Posterior relations in men: the ureters enter the posterolateral angles; the seminal vesicles lie lateral to the ampullae of the vas, with the rectum behind them, separated by Denonvilliers fascia (rectovesical septum). A vesicocolic fistula from diverticulitis causes faecaluria and pneumaturia.
- Arteries: superior and inferior vesical (internal iliac); in women the vaginal artery replaces the inferior vesical. Lymph: external and internal iliac nodes.
Nerve control of micturition
| Supply | Origin | Action |
|---|---|---|
| Parasympathetic (pelvic splanchnic) | S2–S4 | Contracts detrusor (M3), relaxes bladder neck: voiding |
| Sympathetic (hypogastric) | T11–L2 | Relaxes detrusor (β3); contracts bladder neck and internal urethral sphincter (α1): storage, prevents retrograde ejaculation |
| Somatic (pudendal) | S2–S4 | Contracts external urethral sphincter (voluntary) |
- The pontine micturition centre coordinates detrusor contraction with sphincter relaxation; the frontal cortex inhibits it until voiding is convenient.
Incontinence and fistula
- Stress incontinence: leakage on coughing or laughing, stable detrusor; caused by weak pelvic floor support of the bladder neck and urethra after childbirth. Pelvic floor training or surgery helps; anticholinergics do not.
- Urge incontinence: detrusor overactivity; anticholinergics or β3 agonists.
- Vesicovaginal fistula: prolonged obstructed labour compresses the bladder base against the pubis, causing ischaemic necrosis; continuous leakage of urine from the vagina appears days later. Also follows hysterectomy.
Bladder rupture, diverticula and exstrophy
| Type | Cause | Urine collects | Management |
|---|---|---|---|
| Intraperitoneal | Blow to a full bladder; dome ruptures | Peritoneal cavity; contrast outlines bowel loops | Surgical repair |
| Extraperitoneal | Pelvic fracture, bony spike | Retropubic (prevesical) space: flame-shaped contrast around the bladder base, confined to the pelvis | Catheter drainage usually |
- Bladder diverticulum from chronic outflow obstruction is a pulsion (false) diverticulum: mucosa herniating between hypertrophied detrusor bundles, with no muscle in its wall. Carcinoma in it spreads early.
- Bladder exstrophy: failure of the infraumbilical body wall; exposed bladder mucosa, widely separated pubic bones and epispadias.
- Bladder cancer: commonest is urothelial (transitional cell) carcinoma, linked to smoking and aromatic amines (aniline dyes, benzidine, 2-naphthylamine); schistosomiasis and chronic stones or catheters cause squamous cell carcinoma. Carcinoma in situ is flat with the basement membrane intact.
Male urethra (about 20 cm)
| Part | Length | Features |
|---|---|---|
| Preprostatic (bladder neck) | 1–1.5 cm | Internal sphincter (smooth, sympathetic) |
| Prostatic | 3–4 cm | Widest, most dilatable; urethral crest, verumontanum with prostatic utricle and ejaculatory duct openings; prostatic ducts open in sinuses beside the crest |
| Membranous | 1–2 cm | Narrowest (apart from the meatus), least distensible; surrounded by the external urethral sphincter in the deep perineal pouch; torn in pelvic fracture |
| Spongy (penile) | About 15 cm | In corpus spongiosum; bulbourethral gland ducts open into its bulbar part (the glands sit in the deep pouch); bulbar part torn in straddle injury; navicular fossa |
Urethral injury and extravasation
| Injury | Urine and blood go |
|---|---|
| Membranous (pelvic fracture) | Extraperitoneal pelvic space above the urogenital diaphragm; blood at meatus, retention, high-riding prostate |
| Bulbar (fall astride) | Superficial perineal pouch under Colles' fascia: scrotum, penis, anterior abdominal wall; not the thighs (fascia lata attachment) |
| Penile with Buck's fascia intact | Confined to the penile shaft |
| Penile with Buck's fascia torn | Same as bulbar spread |
- Blood at the meatus with a pelvic fracture means urethral injury: do not pass a catheter blindly. A catheter that passes easily with bloodstained urine suggests bladder rather than urethral injury.
- The female urethra is about 4 cm, runs in front of the vagina, has paraurethral (Skene) glands; its shortness explains frequent cystitis.
Prostate
- Fibromuscular gland around the prostatic urethra; weight about 20 g; base against the bladder neck, apex on the urogenital diaphragm; Denonvilliers fascia behind, separating it from the rectum.
| Zone (McNeal) | Proportion | Disease |
|---|---|---|
| Peripheral (posterior, felt on DRE) | About 70% | Carcinoma (about 70%) |
| Transition (around the urethra) | About 5%, enlarges with age | Benign prostatic hyperplasia: outflow obstruction |
| Central | About 25% | Surrounds the ejaculatory ducts |
| Anterior fibromuscular stroma | Non-glandular |
- In the older lobar description, the median lobe enlarges in BPH and carcinoma favours the posterior lobe.
- BPH is driven by dihydrotestosterone (5α-reductase): α1 blockers relax smooth muscle; 5α-reductase inhibitors shrink the gland and halve PSA. An enlarged, smooth, firm gland with modest PSA (e.g. 3.5 ng/mL) suggests BPH; a hard irregular nodule suggests cancer.
- PSA is organ-specific, not cancer-specific: acute prostatitis disrupts acini so PSA leaks into blood; repeat it weeks after treatment before considering biopsy.
Prostate vessels and nerves
- Arterial supply from the inferior vesical artery: the main prostatic branches enter at the bladder neck at about 5 and 7 o'clock, the vessels that bleed in TURP.
- Dorsal venous complex (Santorini plexus) lies in front of the prostate under the pubic arch; the source of heavy bleeding in radical prostatectomy.
- The prostatic plexus communicates with the vertebral venous plexus (Batson): osteoblastic metastases to the lumbar spine and pelvis.
- Cavernous nerves (neurovascular bundles, parasympathetic) run posterolaterally; damage causes erectile dysfunction.
TURP complications
- TUR syndrome: hypotonic 1.5% glycine irrigant at high pressure enters opened prostatic venous sinuses, causing dilutional hyponatraemia and fluid overload: confusion, nausea, visual disturbance (glycine), hypertension with bradycardia. Spinal anaesthesia lets early confusion be noticed.
- Others: bleeding, retrograde ejaculation (bladder neck resected), incontinence if the external sphincter is damaged, urethral stricture.
Remember Sympathetic stores urine, parasympathetic passes it, pudendal holds it voluntarily.
Exam trap BPH arises in the transition zone; carcinoma in the peripheral zone.
Exam trap Pelvic fracture tears the membranous urethra; straddle injury tears the bulbar urethra.
How FCPS asks about this
- Urine around the bladder base after pelvic fracture with an easy catheter: extraperitoneal rupture into the retropubic space.
- Continuous vaginal leakage after obstructed labour: vesicovaginal fistula from pressure necrosis.
- Confusion, bradycardia and Na 118 during TURP: absorption of hypotonic glycine irrigant.
- Wall of a bladder diverticulum in BPH: mucosa only, herniating between muscle bundles.
- Nerve supply of internal and external urethral sphincters: sympathetic T11–L2; pudendal S2–S4.
- Zone of prostate cancer: peripheral zone, felt on rectal examination.
- Bleeding veins in radical prostatectomy: dorsal venous complex in front of the prostate.
Test yourself on this topic
5 of the 77 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
After radical prostatectomy with removal of the bladder neck, continence depends mainly on which of the following structures?
Answer: External urethral sphincter
In men the internal sphincter is smooth muscle at the bladder neck, supplied by sympathetic fibres; it is removed with the prostate in radical prostatectomy. Continence afterwards depends on the external urethral sphincter (rhabdosphincter), striated muscle around the membranous urethra in the deep perineal pouch, supplied by the pudendal nerve (S2–S4). Surgeons preserve as much membranous urethral length as possible, and pelvic floor exercises strengthen the sphincter. Bulbospongiosus empties the urethra after voiding but does not maintain continence.
Urethral sphincters in men
- Internal: smooth muscle, bladder neck, sympathetic
- External: striated, membranous urethra
- External nerve: pudendal (S2–S4)
- After prostatectomy: external sphincter only
Remember Without the bladder neck, the rhabdosphincter does the work.
Exam trap Injury to the external sphincter or its pudendal supply, not the bladder neck, causes lasting incontinence.
Why the other options are wrong
- Internal urethral sphincter Removed with the bladder neck.
- Detrusor muscle Contracts to void; it does not hold urine in.
- Bulbospongiosus Clears the urethra after voiding and in ejaculation.
- Ischiocavernosus Maintains erection.
A 4-year-old girl has had three febrile urinary infections. A micturating cystourethrogram shows contrast refluxing up both ureters into dilated calyces during voiding. Spine and urethra are normal. Which of the following is the most likely underlying cause?
Answer: Short intramural course of the ureters
The ureters pass obliquely through the bladder wall for about 1.5–2 cm. As the bladder fills and contracts, pressure on this intramural segment flattens it and acts as a flap valve that stops urine going back up. In primary vesicoureteric reflux, the intramural tunnel is congenitally short and the orifice lies laterally, so the valve fails. Reflux carries infected urine to the kidney, causing pyelonephritis and scarring. Many cases improve as the tunnel lengthens with growth.
Vesicoureteric junction
- Oblique intramural course
- Acts as a flap valve
- Short tunnel: primary reflux
- Risk: pyelonephritis and scarring
Remember Short tunnel, leaky valve.
Exam trap Posterior urethral valves cause secondary reflux in boys; primary reflux is a ureteric valve problem.
Why the other options are wrong
- Posterior urethral valves Occur only in boys.
- Neurogenic bladder from spina bifida The spine is normal.
- Pelviureteric junction obstruction Causes hydronephrosis without reflux.
- Ectopic ureter opening into the vagina Causes constant dribbling, not reflux on voiding.
After a blow to the lower abdomen with a full bladder, a man has suprapubic pain, inability to void and peritonism. Cystogram shows contrast outlining bowel loops. What type of injury is this and how is it managed?
Answer: Intraperitoneal; surgical repair
When full, the bladder rises out of the pelvis, and its dome is covered by peritoneum. A blow to a distended bladder (often in drunk patients) ruptures the dome, leaking urine into the peritoneal cavity (contrast outlines bowel loops, urinary ascites, raised creatinine from peritoneal reabsorption); it requires laparotomy and repair. Extraperitoneal rupture, usually with pelvic fractures, leaks urine into the perivesical space (flame-shaped contrast) and is usually managed with catheter drainage for about 2 weeks unless complicated. Urethral injury is suspected with blood at the meatus and should be excluded before catheterisation.
Bladder rupture
- Intraperitoneal: full bladder, dome tears; contrast outlines bowel → surgical repair
- Extraperitoneal: pelvic fracture; flame-shaped contrast → catheter
- Blood at meatus → exclude urethral injury before catheter
Remember Contrast around bowel: the dome burst; repair it.
Why the other options are wrong
- Extraperitoneal; catheter alone Contrast stays around the bladder base.
- Urethral; suprapubic catheter Blood at meatus; different injury.
- Renal pelvis; stent Not this picture.
- Ureteric; nephrostomy Not this picture.
A para 4 woman leaks urine when she coughs or laughs, without urgency. Urodynamics show a stable detrusor. What is the main cause?
Answer: Weak pelvic floor support of the bladder neck
Normally the bladder neck and proximal urethra sit above a firm hammock of levator ani and endopelvic fascia, so a rise in abdominal pressure compresses the urethra as well as the bladder and continence is kept. Childbirth can stretch and damage these supports and the pudendal nerve, so the bladder neck descends and the urethra can no longer be compressed. A cough then pushes urine out: stress incontinence. Pelvic floor muscle training is first-line. Urge incontinence is from detrusor overactivity, and a fistula gives continuous leakage.
Stress incontinence
- Leak with cough, laugh, lift
- Bladder neck descends below the pelvic floor
- Risk: childbirth, menopause, obesity
- First line: pelvic floor exercises
Remember Cough leak with a stable bladder: weak support.
Exam trap Anticholinergic drugs treat urge incontinence, not stress incontinence.
Why the other options are wrong
- Uninhibited detrusor contractions Excluded by urodynamics; causes urge incontinence.
- A vesicovaginal fistula Gives continuous leakage day and night.
- Overflow from bladder outlet obstruction Gives dribbling with a large residual, mainly in men.
- Loss of pelvic splanchnic supply to the detrusor Causes a large atonic bladder with overflow.
A 68-year-old man with long-standing outflow obstruction from BPH has a thick, trabeculated bladder with a large diverticulum on CT. What does the wall of this diverticulum consist of?
Answer: Mucosa herniating between muscle
To overcome outflow obstruction the detrusor hypertrophies into thick, criss-crossing bundles (trabeculation). High pressure during voiding pushes the mucosa out through weak gaps between bundles, first forming saccules and then diverticula. These acquired (pulsion) diverticula are false: their wall is mucosa and connective tissue without muscle, so they empty poorly, causing stasis, infection and stones. A congenital diverticulum near the ureteric orifice (Hutch) and a urachal diverticulum are different.
Bladder diverticulum
- Cause: outflow obstruction
- Detrusor trabeculation
- Mucosa herniates: false diverticulum
- Poor emptying: stasis, stones, infection
Remember High pressure pushes mucosa out between muscle.
Exam trap Carcinoma in a diverticulum spreads early because there is no muscle layer to cross.
Why the other options are wrong
- All layers of the bladder wall This describes a true diverticulum, which is rare here.
- A persistent urachal remnant A urachal diverticulum lies at the dome and is congenital.
- Ureteric mucosa that has ballooned A ureterocele involves the ureter, not the bladder wall.
- Granulation tissue after infection Not how pulsion diverticula form.
Where this sits in the CPSP syllabus
- Paper 1: Pelvis and perineum, Bladder, urethra and prostate
- Surgery & Allied, Paper 2: Pelvis and perineum, Bladder, urethra and prostate