Voiding cystourethrography with synchronous measurements of pressures and flow in the diagnosis of subvesical obstruction in men: a radiological view.

Cystourethrography with synchronous urodynamic monitoring was done in 90 men who were diagnosed radiologically as having normal function or bladder outlet obstruction. The separation was based on the caliber of the bladder outlet measured on spot roentgenograms at peak voiding: less than 4 mm. for obstructed and more than 6 mm for normal voiding. The radiological observations are discussed together with the measurements of bladder capacity, residual urine, intravesical pressures and voiding flow rate. The separation between normal men and those with obstruction according to radiologically determined calibers had a strong impact on the distribution of the maximum flow rates. Observations on the onset of micturition suggest that in normal voiding the contracting detrusor meets a simultaneously relaxing bladder neck without interposition of an isometric phase. The patients with subvesical obstruction presented with 2 forms of isometric overload, either as uninhibited contractions or as a variable isometric time lag between the onset of detrusor contraction and opening of the bladder neck. The pre-voiding isometric pressure increase is believed to be an abnormal finding that distinguishes the normal state from obstruction and other disorders. A characteristic decrease in subtracted intravesical pressure at the opening of the bladder neck in patients with uninhibited contractions conceivably indicates that bladder instability is caused by an abnormal reflex originating in the tightened bladder neck. Voiding cystourethrography was an accurate means of diagnosis of subvesical obstruction, especially owing to its ability to quantitate the caliber of a narrowed zone.