TRANSRECTAL ULTRASOUND VERSUS MAGNETIC-RESONANCE-IMAGING IN THE ESTIMATION OF PROSTATIC VOLUME

Objective To establish which method of determining prostatic volume (t ransrectal ultrasound [TRUS] or magnetic resonance imaging [MRI]) and which calculation formula give the most exact and least variable resul ts; to determine the size and the source of the variability; and to es tablish which method is the more sensitive to drug-induced changes in prostate volume. Patients and methods Prostatic size was estimated by TRUS and MRT in 21 patients treated medically (either active treatment or placebo) for benign prostatic hyperplasia. Each patient was examin ed at baseline, and after 3 months and 6 months of treatment. Prostati c volume was calculated at every visit using different formulae propos ed in the literature. Results With some of these formulae, including t he classical ellipsoid formula, there was a strong correlation (r>0.8) between TRUS and MRI volume estimates. For others the correlation was much weaker, suggesting unreliability. MRI gave a significantly large r volume than TRUS because of larger values for the cephalocaudal and anteroposterior diameters. For patients on placebo the visit-to-visit variability of the prostate volume was 10-12% of the mean volume, whet her calculated by TRUS or MRI. Part of this variability was apparently due to natural variation of prostate size. Conclusion The classical e llipsoid formula is adequate for determining prostate volume. MRI and TRUS give different volumes. Visit-to-visit variability is similar for both methods and is partly due to real, natural variation. MRI is bet ter able than TRUS to detect drug-induced changes in prostate volume.