Urinary Retention

Urinary retention refers to the inability to micturate of which there may be three different types:

  • Acute
    • sudden and painful
  • Chronic
    • insidious onset and painless
  • Acute-on-chronic
    • Suddenly painful on the back of chronic retention

The major causes of urinary retention are down to three aetiological factors which include:

  • Benign prostatic hypertrophy
  • Prostatic malignancy
  • Urethral strictures

One of the best ways to think about the causes of urinary retention is as follows:

  • Luminal causes (Pathology within the lumen): clot retention/stone
  • Mural causes (Pathology within the wall): Strictures
  • Extramural causes (Pathology outside the wall): BPH, malignancy, constipation, uterine fibroid, ovarian mass

As well as local causes of urinary retention, it is important to think about the more systemic causes, which generally refer to drugs or neurological deficits, although surgery can also be an option. When thinking about any neurological deficit it is important to talk about UMNL and LMNL –

  • LMNs cause an overflow incontinence
  • UMNs cause a reflex or urge incontinence

Before we talk about acute and chronic urinary retention it is important to understand some basic facts involving bladder physiology:

  • The bladder will usually hold between 300 and 400ml of urine of which there needs to be about 150ml for us to urinate.
  • In acute retention it is thought that the bladder will generally hold over 500mls of urine leading to the sudden onset of pain
  • In chronic retention the bladder can hold a much larger volume or urine without any pain - up to 2 litres!


Acute retention:

  • As we described above, acute retention results in sudden pain and the inability to pass urine.
  • There is usually a suprapubic mass that is dull to percussion on abdominal examination.
  • The dullness should occur when the bladder is over 150mls full, however, with more extensive filling the dullness will extend into the abdomen.
  • In any patient presenting with a acute retention it is important to assess the state of the prostate.

The investigations needed for acute retention will generally come after the treatment and are usually used for identifying the underlying cause.

The treatment itself is very simple and requires the insertion of a urinary folly catheter using an aseptic technique. If this fails, there are two further methods of treatment:

  • Urethral dilatation
  • Suprapubic catheterisation

Investigation into the condition then requires:

  • Urine dipstick + urine MC&S
  • Bloods for U&Es and PSA need to be taken
  • Imaging for acute retention requires a radiograph and an ultrasound if a likely stone is suspected
  • Cystoscopy can be used alongside urodynamics to assess the flow of the urine through the urinary system.


Chronic retention:

Chronic urinary retention can be divided again into two different categories, which include:

  • High Pressure
    • Disruption of the vesico-ureteric junction
      • This leads to back pressure on the upper urinary system and kidneys leading to hydronephrosis and if this is left untreated it can lead to renal failure
        • Hydronephrosis is essentially an expansion of the calyces around the kidneys leading to increased pressure on the renal parenchyma and possible damage and scarring
  • Low Pressure
    • This is generally due to an atonic bladder – a bladder with no tone
      • This is usually because of nerve pathology, but essentially it means there is no disruption of the vesico-ureteric junction and therefore no back pressure to the ureters and kidneys and thus no hydronephrosis


  • The overall clinical features of chronic urinary retention are obstructive symptoms with overflow incontinence.
  • This leads to a non-tender, non-tense suprapubic mass that is dull to percussion.
  • Remember the salient feature of chronic retention, unless it is acute-on-chronic, is that it is painless!!
  • Just like with an acute urinary retention, the investigation into the cause of the problem is exactly the same and it requires catheterisation
    • If the problem is neurological then catheterisation may need to be intermittent if the problem is neurological.