Accuracy of transrectal ultrasonography to evaluate pathologic prostate weight: correlation with various prostate size groups.

OBJECTIVE

To report the accuracy of transrectal ultrasonography (TRUS) to measure prostate size before robotic-assisted radical prostatectomy using the prolate ellipsoid formula and its correlation to the weight of the postoperative prostate specimen, for different prostate size groups.

METHODS

Preoperative prostate size estimated by TRUS and the weight of postoperative prostate specimens were collected from 440 men undergoing robotic-assisted radical prostatectomy. Patients were grouped according to preoperative prostate size: <30, 30-60, 60-80, and ≥80 g. To evaluate accuracy, the mean absolute percentage of error was used. The mean percentage of error was used to indicate whether the estimation of TRUS had a tendency to overestimate or underestimate prostate size. The correlation between both measurements was analyzed for each size group.

RESULTS

Accuracy of TRUS estimation was associated with increased prostate size. TRUS estimation was more accurate for larger prostates. The mean absolute percentage of error of each group was 38.64% (<30 g), 21.33% (30-60 g), 13.23% (60-80 g), and 14.96% (≥80 g). Correlation followed a similar size-dependent trend, with a stronger r coefficient for larger prostates: 0.174 (<30 g), 0.327 (30-60 g), 0.457 (60-80 g), and 0.839 (≥80 g). Interestingly, smaller prostates were underestimated, whereas larger glands (≥80 g) had a tendency to be overestimated by TRUS.

CONCLUSION

This study demonstrates that the accuracy of the prolate ellipsoid formula for TRUS varies according to prostate size. Although this formula is fairly accurate for assessing larger prostates, it shows some limitations for smaller prostates. This must be taken into account when evaluating treatment modalities such as transurethral incision of the prostate and brachytherapy.