Definition Painful inability to void, with relief of pain following drainage of the bladder by catheterisation.

The combination of reduced or absent urine output with lower abdominal pain is not in itself enough to make a diagnosis of acute retention. Many acute surgical conditions cause abdominal pain and .uid depletion, the latter leading to reduced urine output, and this reduced urine output can give the erroneous impression that the patient is in retention, when in fact they are not. Thus, central to the diagnosis is the presence of a large volume of urine, which when drained by catheterisation, leads to resolution of the pain. What represents ‘large’ has not been strictly de.ned, but volumes of 500 to 800 mL are typical. Volumes <500mL should lead one to question the diagnosis. Volumes >800mL are de.ned as acute-on-chronic retention (see Is It Acute or Chronic Retention? below).

Pathophysiology

There are three broad mechanisms: _ increased urethral resistance, i.e., bladder outlet obstruction (BOO) _ low bladder pressure, i.e., impaired bladder contractility _ interruption of sensory or motor innervation of the Bladder

Causes in Men

The commonest cause is benign prostatic enlargement (BPE) due to benign prostatic hyperplasia (BPH) leading to BOO; less common causes include malignant enlargement of the prostate, urethral stricture, and, rarely, prostatic abscess.

Urinary retention in men is either spontaneous or precipitated by an event. Precipitated retention is less likely to recur once the event that caused it has been removed. Spontaneous retention is more likely to recur after a trial of catheter removal, and therefore is more likely to require de.nitive treatment, e.g., transurethral resection of the prostate (TURP). Precipitating events include anaesthetics and other drugs (anticholinergics, sympathomimetic agents such as ephedrine in nasal decongestants); nonprostatic abdominal or perineal surgery; and immobility following surgical procedures, e.g., total hip replacement.

Causes in Women

There are more possible causes in women, but acute urinary retention is less common than it is in men. The causes include pelvic prolapse (cystocoele, rectocoele, uterine), the prolapsing organ directly compressing the urethra; urethral stricture; urethral diverticulum; postsurgery for ‘stress’ incontinence; Fowler’s syndrome (impaired relaxation of external sphincter occurring in premenopausal women, often in association with polycystic ovaries); and pelvic masses (e.g., ovarian masses) (Fowler 2003).

Causes in Either Sex

A wide variety of pathologies can cause urinary retention in both men and women: haematuria leading to clot retention; drugs (as above); pain (adrenergic stimulation of the bladder neck); postoperative retention; sacral (S2–S4) nerve compression or damage—so-called cauda equina compression (due to prolapsed L2–L3 disc or L3–L4 intervertebral disc, trauma to the vertebrae, benign or metastatic tumours); radical pelvic surgery damaging the parasympathetic plexus (radical hysterectomy, abdominoperineal resection); pelvic fracture rupturing the urethra (more likely in men than women); neurotropic viruses involving the sensory dorsal root ganglia of S2–S4 (herpes simplex or zoster); multiple sclerosis; transverse myelitis; diabetic cystopathy; damage to dorsal columns of spinal cord causing loss of bladder sensation (tabes dorsalis, pernicious anaemia).

Neurological Causes of Retention—A Word of Warning!

It is all too easy to assume that urinary retention in a man is due to BPH. Of course this is by far the commonest cause in elderly men, but in the younger man (below the age of 60, but even in some men older than 60), spend a few moments considering whether there might be some other cause. Similarly, in women, where retention is much less common than in men, think why the patient went into retention.

Be wary of the patient with a history of constipation and be particularly wary where there is associated back pain. We all get back pain from time to time, but pain of neurological origin, such as that due to a spinal tumour or due to cauda equina compression from a prolapsed intervertebral disc (pressing on S2–S4 nerve roots, thereby impairing bladder contraction) may be severe, relentless, and progressive. The patient may say that the pain has become severe in the weeks before the episode of retention. Nighttime back pain and sciatica (pain shooting down the back of the thigh and legs), which are relieved by sitting in a chair or by pacing around the bedroom at night, are typical of the pain caused by a neuro.broma or ependymoma affecting the cauda equina. Interscapular back pain is typically caused by tumours that have metastasized to the thoracic spine.

Altered sensation due to a cauda equina compression can manifest as the inability to tell whether the bladder is full, inability to feel urine passing down their urethra while voiding, and dif.culty in knowing whether one is going to pass faeces or .atus. Male patients with a neurological cause for their retention (such as spinal tumour) may report symptoms of sexual dysfunction that may appear bizarre (and may therefore be dismissed). They might have lost the ability to get an erection or have lost the sensation of orgasm. They might complain of odd burning or tingling sensations in the perineum or penis. It doesn’t take more than a minute or two to ask a few relevant questions (Are you constipated? Have you had back pain? Do your legs feel funny or weak?), to establish whether the patient has a sensory-level sign (the cardinal sign of a cord compression) and other neurological signs and to test the integrity of the sacral nerve roots that subserve bladder function—S2 to S4. In the male patient, this can be done by squeezing the glans of the penis while performing a digital rectal examination (DRE). Contraction of the anus, felt by the physician’s palpating .nger, indicates that the afferent and efferent sacral nerves and the sacral cord are intact. This is the bulbocavernosus re.ex (BCR). In women, once catheterised, the ‘same’ re.ex can be elicited by gently tugging the catheter onto the bladder neck, again while doing a DRE. Again, contraction of the anus indicates that the afferent and efferent sacral nerves and the sacral cord are intact. If you don’t know about these rare causes of retention, you won’t think to ask the relevant questions. Missing the diagnosis in such cases can have profound implications for the patient (and for you!). One should have a low threshold for arranging an urgent magnetic resonance imaging (MRI) scan of the thoracic, lumbar, and sacral cord, and of the cauda equina in patients who present in urinary retention with these additional symptoms or signs.

Risk Factors for Postoperative Retention

Postoperative retention may be precipitated by instrumentation of the lower urinary tract; surgery to the perineum or anorectum; gynaecological surgery; bladder overdistention; reduced sensation of bladder fullness; preexisting prostatic obstruction; and epidural anaesthesia. Postpartum urinary retention is not uncommon, particularly with epidural anaesthesia and instrumental delivery.

Urinary Retention: Initial Management

Urethral catheterisation is the mainstay of initial management of urinary retention. This relieves the pain of the overdistended bladder. If it is not possible to pass a catheter urethrally, then a suprapubic catheter will be required. Record the volume drained—this con.rms the diagnosis, determines subsequent management, and provides prognostic information with regard to outcome from this treatment.