Defining the degree of intravesical prostatic protrusion in association with bladder outlet obstruction

Purpose: The present study was done to define the degree of intravesical prostatic protrusion (IPP) causing bladder outlet obstruction (BOO) in patients with benign prostatic hyperplasia (BPH)/lower urinary tract symptoms. Materials and Methods: We retrospectively evaluated 239 patients with BPH, analyzing age, IPP, prostate volume, International Prostate Symptom Score (IPSS), and the results from a pressure-flow study. Urethral resistance was quantified by using the BOO index (BOOI), according to the formula BOOI=PdetQmax-2×Qmax (where Pdet is detrusor pressure at the peak flow rate and Qmax is peak flow rate). BOO was defined by a BOOI above 40. Patients with a BOOI below 20 were excluded. Patients were classified into two groups (obstructed and unobstructed groups) by the BOOI. Correlations were determined by logistic regression analysis, and receiver operating characteristic curves were plotted to estimate the optimal cutoff for IPP. Results: There were significant differences in total prostate volume, postvoiding residual urine (PVR), IPP, and Qmax (p<0.001, p<0.001, p<0.001, and p=0.026, respectively) between the obstructed and unobstructed groups, but there were no significant differences in age (p=0.653), IPSS total score (p=0.624), or quality of life score (p=0.138). IPP had a significant prognosis (p<0.001) but was weakly correlated with prostate volume (p=0.026). The correlation coefficients between IPP and Qmax, PVR, prostate volume, and BOO were 0.551, -0.159, 0.225, and 0.391, respectively. For IPP, the area under the curve was 0.759 (95% confidence interval, 0.657 to 0.861) and the cutoff to indicate BOO was 5.5 mm with 66.7% sensitivity and 80.5% specificity. Conclusions: An IPP exceeding 5.5 mm was significantly associated with BOO.