Assessment of in vivo calculation with ultrasonography compared to physical sections in vitro: a stereological study of prostate volumes

We compared three methods for the determination of prostate volume: prostate volume measured via transrectal ultrasonography (TRUS); the Cavalieri method for measuring physical sections; and volume by displacement. TRUS volumes were calculated by the prolate ellipsoid volume formula. Five patients underwent TRUS examination of the prostate prior to radical prostatectomy; specimens were measured when freshly excised. Mean prostate volume by fluid displacement, before formalin fixation was 52.8 +/- 21.5 cm(3), and after formalin fixation 50.4 +/- 20.9 cm(3). Volumes determined by the Cavalieri principle (point-counting and planimetry) were 47.8 +/- 19.3 and 49.1 +/- 20.5 cm(3); volume measured by TRUS was 42.9 +/- 21.9 cm(3). Thus TRUS underestimated prostate volume by 21.4%, but excellent agreement was found between actual volume and point counting techniques. We believe that the classic ellipsoid formula is inadequate for determining prostate volume. We compared three methods for the determination of prostate volume: prostate volume measured via transrectal ultrasonography (TRUS); the Cavalieri method for measuring physical sections; and volume by displacement. TRUS volumes were calculated by the prolate ellipsoid volume formula. Five patients underwent TRUS examination of the prostate prior to radical prostatectomy; specimens were measured when freshly excised. Mean prostate volume by fluid displacement, before formalin fixation was 52.8 ± 21.5 cm(3), and after formalin fixation 50.4 ± 20.9 cm(3). Volumes determined by the Cavalieri principle (point-counting and planimetry) were 47.8 ± 19.3 and 49.1 ± 20.5 cm(3); volume measured by TRUS was 42.9 ± 21.9 cm(3). Thus TRUS underestimated prostate volume by 21.4%, but excellent agreement was found between actual volume and point counting techniques. We believe that the classic ellipsoid formula is inadequate for determining prostate volume.