Bladder consequences of prostatic obstruction.

The development of new imaging techniques has improved our knowledge of the cross-sectional anatomy of the pelvis and thereby our understanding of the bladder's response to prostatic obstruction. It is now known that changes in the bladder are intimately linked to the development of irritative and obstructive symptoms of BPH. This paper illustrates the anatomical changes within the pelvic region that can develop as a consequence of prostatic enlargement. The anatomical position of the prostate is such that its enlargement inevitably affects neighbouring organs. Enlargement of the median lobe can cause irritation of the trigone and the physical trapping of urine behind the lobe. The urethra may also become mechanically obstructed leading to an increase in the detrusor muscle mass as it struggles to overcome the restriction of the bladder outlet. In time, a change in the collagen to muscle ration in favour of collagen may develop, with the consequence that bladder compliance is reduced and the ability to increase volume without increasing pressure is diminished. Thereafter one of two scenarios may develop: the 'high pressure conflict' bladder or the 'distended low pressure' bladder. Urinary disturbance in BPH therefore results from an inadequate balance between bladder contractility and urethral resistance.