The correlation between prostate volume, transition zone volume, transition zone index and clinical and urodynamic investigations in patients with lower urinary tract symptoms

Objective To determine if, in patients with lower urinary tract symptoms (LUTS), measurement of the transition zone (TZ) of the prostate by transrectal ultrasonography (TRUS) and the ratio between the TZ volume and total prostate volume (TZ index) correlates better with clinical and urodynamic investigations than total prostate volume alone. Patients and methods In total, 150 consecutive patients with LUTS underwent a standardized screening programme including the International Prostate Symptom Sore (IPSS), a physical examination, TRUS of the prostate and urodynamic investigations with pressure‐flow studies. The total prostate volume and TZ volume were assessed from TRUS using the ellipsoid formula. Spearman’s rank correlation coefficients were calculated between different prostate volume measurements and specific symptomatic and urodynamic variables. Results The relationships between specific IPSS symptoms, symptom scores and the prostate volume measurements were not statistically significant except for one domain, nocturia, that appeared to be statistically significantly correlated with the TZ index (r=0.25). The correlations for free flow, pressure‐flow variables and prostate volume measurements were stronger, but only moderate at best. The highest correlations were between TZ volume and the linear passive urethral resistance obstruction category, urethral resistance factor and detrusor pressure at maximum flow (r=0.43, 0.44 and 0.40, respectively). The differences between the correlations of prostate volume and TZ index and these variables were small (r=0.39, 0.38 and 0.37, respectively for prostate volume and r=0.38, 0.40 and 0.33 respectively for TZ index). Conclusions There were very small differences between the correlations of total prostate volume, TZ volume and TZ index, and clinical and pressure‐flow variables. In the assessment of the last two, the estimation of the total prostate volume by TRUS was a reasonable way to obtain the required information about prostate size and measuring TZ volume and calculating TZ index was of limited additional value. Symptoms and bladder outlet obstruction were mainly determined by other factors than the prostate and, specifically, TZ volume. As earlier studies have indicated that including pressure‐flow data in the pre‐operative evaluation and selection of patients for interventional therapies may improve the overall clinical results, we think that prostate volume, TZ volume or symptoms alone should not b