Venous compression syndromes can cause generalised pelvic venous congestion. The most common mechanism is the combined effect of left renal vein compression and left common iliac vein compression.

While compression of the left common iliac vein obstructs normal drainage of the pelvis, compression of the left renal vein forces large volumes of collateral blood flow into the left hemisphere of the pelvis via the left ovarian vein, the psoas veins and the veins accompanying the left ureter.

The well-known consequences are aching and postural pain in the genitals, in the deep pelvis, radiating to the left groin and left leg, accompanied by swelling of the left leg, a tendency to left leg thrombosis, pain during sexual intercourse, menstrual pain and painful bowel movements.

It is less well known that urethral obstruction may be responsible for urination difficulties.

PixelFlux measurements allow precise quantification of the degree of congestion. In this patient, the urethra was the epicentre of the pelvic congestion.

The urethra is surrounded by large veins, similar to the haemorrhoidal veins that cover the veins of the rectum. They both help to close these tubal structures to prevent urine or faeces from leaking out.

As the urethra and rectum are both part of the collateral circulation within the left pelvic hemisphere, the filling of these veins increases as a result of the compression syndromes mentioned above.

This can lead to an increasing counter-pressure against the constricting force of the bladder itself, which is required to empty the bladder completely.

Initially, the patient feels the need to urinate frequently with only small amounts of urine. Later, the patient, usually a woman, will need to exert additional pressure to get rid of the urine. The most common mechanism is to bend forward during voiding, which increases the abdominal pressure and thus the intravesical pressure to overcome the counterpressure of the venous cuff of the urethra.

In more severe cases, manual pressure may be applied to the bladder to assist voiding. If the venous pressure within the venous cuff around the urethra continues to increase, urinary retention may occur, requiring emergency catheterisation.

Once other important causes of urinary retention, mainly mechanical and neurological, have been ruled out, self-catheterisation is usually recommended, as the inability to void completely remains a problem.

It is therefore important to understand that increased venous pressure in the cuff-like venous sheath surrounding the urethra may be the cause of the symptoms. Medical or surgical treatment of the vascular compression syndrome then helps to restore bladder control.