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Bladder outlet obstruction is impedance to urine flow at the level of the bladder neck or urethra, leading to increased intravesical pressure and secondary changes in the bladder, ureters, and kidneys.

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Etiology

Adults Pediatric
• Benign prostatic hyperplasia (most common)
• Prostate carcinoma
• Bladder neck contracture
• Urethral stricture (post-infective/iatrogenic/traumatic)
• Neurogenic bladder (functional BOO)
• Bladder calculi or tumors at bladder neck • Posterior urethral valves (most common)
• Urethral atresia/stricture
• Anterior urethral valves (rare)

Clinical Significance

Radiology

Imaging-pathology correlate:

  1. ↑ Detrusor pressure → bladder wall hypertrophy
  2. Chronic obstruction → trabeculation, sacculation, diverticula
  3. Vesicoureteric reflux → hydroureteronephrosis
  4. Prolonged obstruction → obstructive uropathy → renal insufficiency

Imaging features:

Feature Acute BOO Chronic BOO
Bladder wall Mild thickening Marked trabeculation
Diverticula Absent Common
Upper tracts Mild / none Bilateral HUN
Renal cortex Normal Thinned
PVR Increased Markedly increased

Differentials