Objectives. In benign prostatic hyperplasia (BPH), bladder outlet obstruction is caused by mechanical blockage resulting from an enlarged prostate, and by the increased tone of prostatic smooth muscle. In patients with obstructive BPH, the prostatic urethra urodynamically corresponds to the flow-controlling zone (FCZ). We sought to investigate the relation between the obstruction and elastic properties of the FCZ and the histologic composition of the prostate in symptomatic patients with BPH.

Methods. The grade of infravesical obstruction was classified according to preoperative pressure-flow data from 30 men with symptomatic BPH, and the elastic properties of the FCZ were evaluated as the mean elastance, which was calculated using the three-parameter model. The area densities of smooth muscle, fibrous tissue, epithelium, and lumen were determined by quantitative morphometry, using BPH tissue obtained by transurethral resection.

Results. The area density of smooth muscle had a negative correlation with mean elastance (ρ = −0.50, P <0.01), the linear passive urethral resistance relation (ρ = −0.43, P<0.05), and the group-specific urethral resistance factor (ρ = −0.39, P <0.05). No other histologic element was correlated with these variables.

Conclusions. Our results suggest that urethral elasticity and bladder outlet obstruction grade are influenced by the relative content of smooth muscle within the prostate in patients with BPH.