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.