[Usefulness and limitation of digital rectal examination and imaging studies in staging prostate cancer]

The diagnostic usefulness of digital rectal examination (DRE), transrectal ultrasonography (TRUS), magnetic resonance imaging (MRI) and computed tomography (CT) was compared in the differentiation of stage B from stage C prostate cancer. Eighteen patients who had undergone radical retropubic prostatectomy were included in this study. Overall, the positive predictive values (PPV) for detecting extraprostatic disease (extracapsular extension, seminal vesicle invasion) were 100% for DRE, 88.9% for TRUS and 80.0% for MRI, respectively. Corresponding figures for accuracy in detecting extraprostatic spread were 55.6%, 66.7% and 61.1%, respectively. The PPV and accuracy for detecting extraprostatic disease in 13 patients with localized cancer (< stage B) were 75.0%, 53.8% for TRUS and 66.7%, 53.8% for MRI, respectively. Both of these examinations appeared to be superior to DRE alone. The PPV and accuracy increased when findings on TRUS and MRI coincided. Computed tomography was less accurate than MRI in diagnosing nodal involvement because of the higher incidence of false positives. Further efforts should be focused on enhancing preoperative diagnostic precision in staging prostate cancer because of the limited usefulness of the current imaging techniques. Development of more reliable diagnostic modalities or designing ideal combination of these studies are desperately needed.