Renal · Obstructive Uropathy
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Most common cause is outflow obstruction from benign prostatic hyperplasia (BPH) in older men; also consider neurologic impairment, pelvic surgery, and anticholinergic medications.
Acute retention presents with severe suprapubic pain and a tense, palpable bladder; chronic retention is painless with overflow incontinence.
Diagnosis is by bladder ultrasound showing a postvoid residual (PVR) >300 mL, whereas a PVR <50 mL is normal.
First-line intervention is immediate Foley (urethral) catheterization for rapid bladder decompression.
If catheterization fails or there is urethral trauma (blood at the meatus), a suprapubic catheter is required.
For BPH-induced retention, start an alpha-1 blocker (e.g., tamsulosin) before a trial without catheter, and discontinue offending anticholinergic and sympathomimetic drugs.
Always check for saddle anesthesia and loss of anal sphincter tone to exclude cauda equina syndrome; untreated retention causes AKI and hydronephrosis.
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A 72-year-old man presents with 8 hours of inability to urinate and severe lower abdominal pain. He reports months of urinary hesitancy and a weak stream. On exam there is a tender, palpable, distended bladder above the pubic symphysis and an enlarged, smooth prostate on rectal exam with normal sphincter tone. Bladder ultrasound shows a postvoid residual of 700 mL.
Which of the following is the most appropriate immediate intervention?
Urethral (Foley) catheterization for bladder decompression.
Acute urinary retention from BPH presents with suprapubic pain, a palpable bladder, and a high postvoid residual. Immediate urethral catheterization relieves obstruction and prevents postrenal AKI and hydronephrosis; an alpha-1 blocker such as tamsulosin is then started before a trial without catheter.
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Etiology / Epidemiology
Most commonly caused by outflow obstruction secondary to benign prostatic hyperplasia (BPH) in older men. Other key triggers include neurologic impairment, recent pelvic surgery, and anticholinergic medications.
Clinical Manifestations
Acute presentation features severe suprapubic pain and a tense, palpable bladder, while chronic cases manifest with painless overflow incontinence.
Diagnosis
Diagnosed via bladder ultrasound demonstrating a postvoid residual (PVR) >300 mL.
Treatment
Immediate management requires urethral catheterization for rapid decompression. Treat the underlying cause with alpha-1 blockers (e.g., tamsulosin) and immediately discontinue any offending drugs.
Prognosis
Failure to decompress the bladder can lead to acute kidney injury (AKI), hydronephrosis, and recurrent urinary tract infections.
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Epidemiology & Etiology
The most common etiology of acute urinary retention in males is benign prostatic hyperplasia (BPH). Neurologic triggers include multiple sclerosis, spinal cord injury, and cauda equina syndrome. Iatrogenic retention is frequently precipitated by anticholinergic medications, sympathomimetics, or recent regional anesthesia. It is overwhelmingly more prevalent in males >60 years old.
Pertinent Anatomy
The detrusor muscle contracts via parasympathetic stimulation from the nervi erigentes (S2-S4) to empty the bladder. Normal micturition requires simultaneous relaxation of the internal urethral sphincter (sympathetic control) and the external urethral sphincter (somatic control via the pudendal nerve). Mechanical obstruction most frequently occurs anatomically at the bladder neck or prostatic urethra.
Pathophysiology
Retention results from either increased outflow resistance or decreased detrusor contractility (detrusor areflexia). Mechanical obstruction physically blocks the urethra, leading to a compensatory but ultimately failing increase in intravesical pressure. Neurologic impairment disrupts the parasympathetic reflex arc, preventing detrusor contraction entirely. Chronically elevated bladder pressures transmit retrograde, resulting in hydronephrosis and irreversible renal parenchymal damage.
Clinical Manifestations
Acute retention presents with severe suprapubic pain, an inability to void, and a prominently palpable bladder. Chronic retention is often painless, presenting insidiously with overflow incontinence, hesitancy, and a weak stream. A digital rectal exam may reveal an enlarged prostate or decreased rectal tone. Always assess for saddle anesthesia or lower extremity weakness, which are catastrophic red flags for cauda equina syndrome.
Diagnosis
The gold standard initial, non-invasive test is a bladder ultrasound to measure retained volume. A postvoid residual (PVR) >300 mL strongly confirms retention, whereas a PVR <50 mL is normal. Serum creatinine and BUN must be drawn to evaluate for postrenal acute kidney injury (postrenal azotemia). A urinalysis is required to rule out concomitant infection, as stagnant urine is a nidus for bacteria.
Treatment
The first-line intervention is immediate Foley catheterization for rapid bladder decompression. If urethral catheterization fails or is contraindicated by urethral trauma (e.g., blood at the meatus), a suprapubic catheter is urgently required. For BPH-induced retention, initiate an alpha-1 blocker (e.g., tamsulosin) before attempting a trial without catheter (TWOC). Discontinue all offending anticholinergic and sympathomimetic drugs immediately.
Prognosis
Prompt decompression usually leads to full recovery, but patients must be strictly monitored for post-obstructive diuresis, which can cause profound hypovolemia and electrolyte derangements. Chronic retention carries a high risk of recurrent urinary tract infections and irreversible detrusor myopathy. Long-term unrelieved obstruction culminates in end-stage renal disease.
Differential Diagnosis
Anuria/Oliguria: Differentiated by a low PVR (<50 mL), indicating poor renal output rather than outflow obstruction.
Urinary Tract Infection: Presents with dysuria and suprapubic pain, but patients are able to void and lack a massive postvoid residual.
Cauda Equina Syndrome: A neurologic emergency presenting with retention, saddle anesthesia, and loss of anal sphincter tone.
Urethral Stricture: Often features a history of prior STIs or urethral instrumentation, presenting with a chronically diminished stream rather than sudden acute obstruction.