What are the causes of bladder outlet obstruction?

Causes of Bladder Outlet Obstruction

Bladder outlet obstruction (BOO) is primarily caused by benign prostatic hyperplasia (BPH) in men, but can result from multiple other structural and functional abnormalities affecting the bladder neck, prostate, distal sphincter mechanism, and urethra.

Common Causes in Men

• Benign Prostatic Hyperplasia (BPH): The most common cause of BOO in men, with prevalence increasing with age, reaching 60% by age 60 and 80% by age 80 1

  • Causes obstruction through two mechanisms:
    • Static component: Direct physical obstruction from enlarged prostatic tissue
    • Dynamic component: Increased smooth muscle tone within the enlarged gland 1

• Prostate Cancer: Can cause obstruction through enlargement of the gland similar to BPH 2

• Urethral Stricture: Narrowing of the urethra due to scar tissue, trauma, or inflammation 2

• Posterior Urethral Valves: Most common cause of neonatal bladder outlet obstruction, occurring in 0.2% to 1% of cases of mild antenatal hydronephrosis and up to 6% in more severe cases 2

Common Causes in Women

• Pelvic Organ Prolapse: Cystocele, uterine prolapse, and rectocele can all cause anatomic obstruction 3, 4

• Primary Bladder Neck Obstruction: Functional obstruction at the level of the bladder neck 3, 4

• Dysfunctional Voiding: Functional obstruction due to inappropriate contraction of the urethral sphincter during voiding 3, 4

• Iatrogenic Obstruction: Often resulting from prior incontinence surgery 4

• Urethral Stricture: Less common in women than men, but can occur 4

• Periurethral Masses: Including urethral diverticulum 3, 4

Neurological Causes

• Detrusor-Sphincter Dyssynergia: Lack of coordination between bladder contraction and sphincter relaxation, often due to neurological conditions 2

• Fowler's Syndrome: A functional obstruction in women characterized by urinary retention due to failure of the urethral sphincter to relax 3

Pediatric Causes

• Posterior Urethral Valves: The most common cause of congenital bladder outlet obstruction in male infants 2

• Ureterocele: Cystic dilation of the distal ureter that can obstruct the bladder outlet 2

• Ectopic Ureter: Abnormal insertion of the ureter that can cause obstruction 2

Functional/Dynamic Causes

• Detrusor Underactivity: While not a direct cause of obstruction, it can coexist with BOO and contribute to voiding symptoms 2

• Detrusor Overactivity: Often associated with BOO, particularly in men with BPH 2

Traumatic/Iatrogenic Causes

• Post-surgical Complications: Including bladder neck contracture after prostate surgery 5

• Radiation-induced Fibrosis: Following radiation therapy for pelvic malignancies 5

Diagnostic Considerations

• Urodynamic studies are essential for confirming BOO, particularly in women where the diagnosis can be challenging 4

• Video urodynamics with simultaneous imaging of the bladder outlet during voiding greatly facilitates diagnosis in women 4

• Pressure-flow studies alone may fail to diagnose obstruction in women, who typically have lower voiding pressures compared to men with BOO 4

Clinical Implications

• BOO can lead to significant lower urinary tract symptoms (LUTS) that affect quality of life 1, 6

• If left untreated, BOO can lead to complications including:

  • Acute urinary retention (AUR), which increases in incidence with age 7
  • Bladder remodeling and dysfunction 8, 6
  • Upper urinary tract damage in severe cases 2

• Early recognition and appropriate management are crucial to prevent irreversible bladder damage and the "point of no return" in bladder function 8