Transition Zone Index as a Method of Assessing Benign Prostatic Hyperplasia: Correlation with Symptoms, Urine Flow and Detrusor Pressure

Purpose: Prostate volume has been poorly correlated to various parameters used to assess benign prostatic hyperplasia (BPH), including symptoms, peak urine flow and detrusor pressure at peak urine flow. The purpose of this study was 2-fold: 1) to determine it transrectal ultrasound measurement of the transition zone of the prostate served as a better proxy for determining prostate size and correlated better with American Urological Association symptom score, peak urine flow and detrusor pressure, and 2) if the parameter transition zone index (the ratio between transition zone volume and prostate volume) was useful in evaluating clinical prostatism. Materials and Methods: We prospectively evaluated 61 men with symptomatic BPH (age 64.6 plus/minus 9.7 years) according to symptoms, peak urine flow, pressure/flow analysis, transrectal ultrasound volume of the entire prostate and the transition zone, and calculation of the transition zone index. Results: Age correlated with symptoms (r = 0.31, p = 0.01) and peak urine flow correlated negatively with symptoms and age (p = 0.002). Age also correlated with prostate volume (r = 0.54 and p = 0.03) and transition zone (r = 0.31, p = 0.05). There was a weak correlation between prostate volume and symptoms, peak urine flow and detrusor pressure at peak urine flow; a stronger correlation between transition zone and symptoms (r = 0.48, p = 0.03), and peak urine flow (r = -0.34, p = 0.05), and a significant correlation (p = 0.001) between transition zone index and symptoms (r = 0.75), peak urine flow (r = -0.71) and detrusor pressure at peak urine flow (r = 0.43). A transition zone index of greater than 0.50 was a useful cutoff point and highly significant (p = 0.002) for delineating patients with more severe abnormalities of symptoms, peak urine flow and detrusor pressure at peak urine flow. Conclusions: Transition zone index is a parameter that correlates significantly with evaluated parameters of BPH and may serve as a useful proxy for evaluating worsening obstruction. Studies are underway to determine if transition zone index can be used prospectively to predict and correlates response with therapies designed to ablate prostatic tissue medically or surgically.