Estimation of prostate gland volume with transrectal ultrasound may provide important information in the evaluation of benign and malignant prostatic diseases. To determine the most accurate means of volume estimation 150 patients underwent transrectal ultrasound with 15 separate methods of volume estimation. All patients underwent subsequent radical prostatectomy or cystoprostatectomy. Prostate specimen weights were compared with the results of each volume estimation method. Step-section planimetry, previously assumed to be the most accurate means of volume measurement, exhibited a Pearson correlation coefficient of 0.93. The elliptical volume, widely used as an alternative to planimetry, demonstrated a correlation coefficient of 0.90. The most accurate method to estimate prostate weight (r = 0.94) was a variation of the prolate spheroid formula, expressed as π/6 (transverse dimension)2 (anteroposterior dimension). When different volume ranges were considered, this prolate spheroid formula provided the closest estimate of weight in glands of less than 40 gm. and those in the 40 to 80 gm. range. The most accurate method to estimate prostates weighing greater than 80 gm. was the formula π/6 (transverse dimension)3.
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