Bladder outflow obstruction - Disorders of the bladder and prostate

Disorders of the bladder and prostate

Bladder outflow obstruction

Definition

Obstruction to urinary flow from the bladder to the urethral meatus.

Incidence/prevalence

Common in men.

Age

Increases with age

Sex

M > F

Aetiology

The causes of bladder outflow obstruction are shown in Table 6.13.

Pathophysiology

A reduction of >70% in the urethral lumen or vesicourethral junction (VUJ) causes obstruction, leading to reduced flow, increased voiding pressure and compensatory bladder hypertrophy. Over time, the bladder distends, then the ureters (causing hydroureters) and finally the renal pelvises. Often there may be an underlying chronic obstruction for example an enlarged prostate. Another factor may then cause acute urinary retention, e.g. constipation, bed rest (e.g. after surgery).

Clinical features

The symptoms depend on the speed of onset and degree of obstruction.

·        Acute obstruction (acute urinary retention) causes severe discomfort, due to a wish to void urine, without the ability to do so. The bladder is tender, palpably enlarged. There is complete anuria, although there may be small amounts of urine voided due to overflow incontinence.

·        Chronic obstruction causes three features: hesitancy, poor urinary stream (<10 mL/second) and terminal dribbling. Frequency and nocturia are not symptoms of obstruction. The symptoms usually develop over years, and if left untreated patients may present with renal failure. However, polyuria and/or nocturia may be symptoms of the loss of concentrating ability of the tubules, which can occur in long-standing obstruction.

Macroscopy

Dilation above the obstruction. Bladder trabeculation.

Complications

As a result of chronic obstruction, the bladder dilates and fails to empty fully, defined as >50 mL residual urine (normally 5–10 mL in young, fit person). Renal failure can be caused by both acute and chronic obstruction. Chronic urinary retention leads to:

·        Reduced functional bladder capacity and therefore increased frequency.

·        Recurrent UTI’s.

·        Stone formation can be caused by urinary stasis, UTI’s predispose to stone formation, and also stones may predispose to infection.

Management

Relief of the obstruction is usually by insertion of a urinary catheter, followed by treatment of the underlying cause.