PSAグレーゾーン症例における前立腺針生検前MRI撮影の有用性に関する検討

Abstract

To evaluate the diagnostic accuracy of prostate magnetic resonance imaging (MRI), we compared MRI findings with the results of biopsy as well as findings from specimens following total prostatectomy. The subjects consisted of 260 males who showed a prostate specific antigen (PSA) level in the gray zone (4 ng/ml ≤PSA <10 ng/ml) and also underwent digital rectal examination (DRE), transrectal ultrasound (TRUS), and MRI prior to prostate biopsy between April 2005 and December 2009. In Evaluation 1, the results of DRE/TRUS/MRI were compared with those of prostate biopsy. The biopsy-positive rate was higher in males positive in each examination. However, 24.8% of males negative in all examinations were biopsypositive. Thus, these examinations were considered to be inappropriate for secondary screening. In evaluation 2, the prostate was divided into 4 regions, and the findings from specimens following total prostatectomy were compared with MRI findings in each region. For the region containing prostate cancer, MRI showed a sensitivity of 26.0%, specificity of 98.3%, positive predictive value of 96.2%, and negative predictive value of 44. 4%. In patients with a Gleason score ≥7, cancer foci were more frequently detectable using MRI. MRI prior to prostate biopsy in patients in the PSA gray zone is inappropriate for secondary screening due to its low sensitivity. However, by virtue of its high positive predictive value, MRI is useful for determining patients indicated for biopsy, as well as DRE and TRUS. Accurate evaluation of the localization of all cancer lesions is difficult using MRI. However, when MRI findings are present, they frequently indicate the cancer lesion, which may be useful information for treatment.