Objectives To assess the value of endorectal magnetic resonance imaging (MRI) for detecting the tumor site, tumor size, and disease extent in patients with localized prostate cancer. Methods The MRI findings were compared with the histopathologic findings of radical prostatectomy specimens in 95 patients. Results The histologic examination revealed 186 cancer foci. Endorectal MRI detected 109 cancer foci. The accuracy, sensitivity, and positive predictive value of endorectal MRI for detecting tumor foci greater than 1.0 cm in diameter was 79.8%, 85.3%, and 92.6%, respectively; the corresponding value for detecting tumor foci smaller than 1.0 cm was 24.2%, 26.2%, and 75.9%, respectively. The maximal tumor diameter on endorectal MRI correlated with that shown by histologic examination for tumors larger than 1.0 cm in diameter. However, it did not correlate significantly with the histologic diameter of tumors smaller than 1.0 cm. The accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of endorectal MRI was 74.7%, 57.1%, 82.1%, 57.1%, and 82.1%, respectively, for the detection of extracapsular extension and was 75.8%, 62.1%, 81.8%, 60.0%, and 83.1%, respectively, for local staging. Conclusions The results of the present study suggest that endorectal MRI is useful for predicting local extension, as well as tumor site and tumor size, of cancer foci greater than 1.0 cm in diameter.
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