Urinary retention

Urinary retention is the inability to voluntarily empty the bladder. The causes can be either mechanical (e.g., benign prostatic hyperplasia, tumors, urethral strictures) or functional (e.g., detrusor underactivity due to peripheral neuropathy, anticholinergic drugs). Patients with acute urinary retention (AUR) present with a sudden, painful inability to void and a tender, distended bladder on palpation. Patients with chronic urinary retention (CUR) are typically unable to void completely but do not experience pain. AUR is usually diagnosed clinically and is considered a urological emergency. Therefore, urgent bladder catheterization should precede diagnostics. These include renal function tests to assess for renal damage (obstructive nephropathy) and ultrasound of the kidneys, ureter, and bladder to identify the underlying cause and possible complications (e.g., hydroureteronephrosis). Further evaluation depends on the patient history and physical examination. Treating the underlying cause (e.g., alpha adrenergics and/or TURP for BPH) is essential to prevent recurrence and complications due to urinary retention, such as UTI, nephrolithiasis, and renal failure.

• Brief overview of bladder control
  • The frontal lobe cortex has an inhibitory effect on the pontine micturition center and an excitatory effect on the urethral sphincter (voluntary control of micturition).
  • The central micturition center lies in the pons (brain stem) and controls the sympathetic and parasympathetic nerve supply of the bladder and urethra.
  • T12–L2: sympathetic bladder innervation (via the hypogastric nerve; α and β adrenergic receptors) → detrusor relaxation and increased urethral sphincter tone (bladder filling phase)
  • S2–S4: parasympathetic innervation (via the pelvic splanchnic nerves; muscarinic receptors) → detrusor contraction and relaxation of the urethral sphincter (voiding phase)
  • The pudendal nerve (S2–S4) send afferent impulses from the bladder to the brain during bladder filling/voiding.

Mechanical obstruction

Functional obstruction

Enlarged prostate gland Benign prostatic hyperplasia (most common) Prostate cancer Acute prostatitis (rare) Urethral narrowing Urethral stricture (see below) Urethral carcinoma Posterior urethral valves Urethritis (inflamed, edematous urethra) Meatal stenosis (rare) Bladder neck obstruction Bladder calculi Urothelial cancer Urinary bladder tamponade Phimosis and paraphimosis Extrinsic obstruction (rare) Anterior vaginal wall prolapse Pelvic masses (e.g., benign/malignant ovarian tumor) Rectal mass or fecal impaction

Detrusor underactivity and/or sphincter overactivity Neurological causes (neurogenic bladder) Central nervous system Spinal cord compression or trauma Congenital anomalies of the spinal cord (e.g., meningomyelocele, spina bifida) Stroke Multiple sclerosis, Parkinson's disease Peripheral nervous system Damage to pelvic splanchnic nerves (bladder denervation) → causes ↓ bladder sensation and detrusor contractility → infrequent, incomplete urination → overflow incontinence Diabetic autonomic neuropathy Trauma (e.g., pelvic fracture, surgery/radiation of the pelvis) Drug-induced urinary retention Due to detrusor underactivity : anticholinergics, tricyclic antidepressants, antipsychotics, calcium channel blockers, antiparkinson agents Due to increased urethral sphincter tone : sympathomimetic agents, nonselective beta blockers, opioids) Detrusor-sphincter dyssynergia Urethral/bladder trauma (e.g., urethral transection) Bladder neck dysfunction Postoperative urinary retention

References:^{[1][2][3][3][4][5][6][7]}

Urethral stricture

• Definition: narrowing of the urethra with possible restriction of urinary flow
• Etiology
  • Traumatic or iatrogenic (instrumentation/catheterization)
  • Post-infectious (e.g., urethritis)
  • Congenital
  • Idiopathic
• Clinical findings
  • Features of bladder outlet obstruction (straining to micturate, weak stream, dribbling)
  • Pollakiuria
  • Feeling of incomplete urination
  • Urinary retention
• Diagnostics
  • Uroflowmetry: plateau-shaped uroflow curve
  • Retrograde urethrography/voiding cystourethrography: visualizes urethral strictures
• Treatment
  • Urethral dilation: intermittent dilation of the urethra; can be curative in some cases
  • Internal urethrotomy: endoscopic transurethral approach; incision at 12 o'clock position to release strictures/scar tissue
  • Urethroplasty: open reconstruction with excision of the fibrotic urethra and reanastomosis ; indicated if urethrotomy fails
  • Permanent urethral stents: placed endoscopically; indicated in patients with short-length strictures

References:^[12]

AUR is a urological emergency and urgent bladder catheterization should precede any further investigations. In doubtful cases, abdominal ultrasound should be performed first. In patients with postoperative AUR, diagnostic tests are usually not needed.

Laboratory studies

• Urinalysis and culture: indicated in all patients with urinary retention; evaluate for UTI, hematuria, glycosuria, and crystals
• Renal function tests (BUN, creatinine levels, electrolytes): in all patients to evaluate for renal failure (obstructive nephropathy)
• Blood sugars: glucose control in known diabetics or if diabetic neuropathy is suspected
• Serum prostate-specific antigen levels (PSA): indicated in men with ≥ 10-year life expectancy to identify co-existent prostate cancer, if suspected
• Coagulation profile and hemoglobin levels: indicated in patients with urinary bladder tamponade

Imaging

• Ultrasound of the kidney, ureter, and bladder: indicated in all patients with urinary retention
  • AUR: bladder distended with > 400 mL of urine
  • CUR: post-void residue > 300 mL; bladder wall thickening (in chronic obstructive urinary retention)
  • In both: evaluate for hydroureteronephrosis (due to BOO); diagnose bladder calculi or BPH, if present
  • In bladder tamponade: blood clot visualized as an echogenic, mobile mass; often seen at the base of the bladder

Further investigations

• Transrectal ultrasound (and prostate biopsy): suspected prostate cancer
• Cystoscopy, CT urography: suspected bladder cancer (gross hematuria)
• Retrograde urethrogram or voiding cystourethrogram: suspected urethral trauma, strictures, or tumors
• Pelvic ultrasound: suspected pelvic mass
• MRI brain or spinal cord: if urinary retention is due to a neurological cause
• Uroflowmetry: preceding history of lower urinary tract symptoms
• Urodynamic studies: patients with neurogenic bladder

AUR is an urological emergency and requires urgent bladder catheterization before any further investigations are performed!
References:^{[13][1][14][15][16][17][18]}

Urgent complete bladder catheterization

In all patients with acute or acute on chronic urinary retention (before further diagnostics)

• Transurethral Foley catheterization
• Suprapubic catheterization (SPC) if transurethral catheterization is not possible (e.g., urethral stricture, large prostate) or contraindicated (e.g., suspected urethral trauma, recent urethral surgery, acute bacterial prostatitis)

Treatment of the underlying cause

In all patients with acute or chronic urinary retention:

• Precipitating drugs: discontinue or substitute
• Benign prostatic hyperplasia
  • Alpha adrenergic drugs (e.g., tamsulosin) and trial void without catheter
  • TURP
• Prostatitis: antibiotics (fluoroquinolones or trimethoprim-sulfamethoxazole)
• Prostate cancer: treatment depends on the stage (see “Treatment” of prostate cancer)
• Bladder tamponade: clot removal and continuous bladder irrigation with sterile water/saline
• Neurogenic bladder : clean intermittent catheterization or indwelling catheter , parasympathomimetic drugs (bethanecol)

See posterior urethral valves, urethral trauma, and treatment of lower urinary tract obstruction in urinary tract obstruction for information on the management of other causative factors.

References:^{[1][8][19][20][2][21][22]}