[Endorectal magnetic resonance imaging for staging of prostatic cancer]

We retrospectively studied the staging accuracy of endorectal magnetic resonance imaging (MRI) using a surface coil for 14 localized prostatic cancers resected by retropubic radical prostatectomy. The prostatic tumor in the peripheral zone was mostly demonstrated as a low signal intensity on the T2 weighted image, and prostatic capsular invasion was indicated as an interruption of prostatic capsule, irregularity of glandular margins, and a low signal intensity of periprostatic venous plexus on the T2 weighted image. The seminal vesicular invasion was seen as a high signal intensity on the enhanced T1 weighted image, and a low signal intensity on the T2 weighted image. The clear prostatic zonal anatomy was demonstrated on the T2 weighted image. The accuracies of clinical staging in endorectal MRI and transrectal ultrasound examination (TRUS) were 79% and 57%, respectively. Also, the accuracies of seminal vesicular invasion in endorectal MRI and TRUS were 93% and 57%, respectively. The endorectal MRI revealed more accurately the seminal vesicular invasion than TRUS (p = 0.038), but there was no significant difference in the accuracy of detecting prostatic capsular invasion between endorectal MRI (79%) and TRUS (71%). The reduction of prostatic volume after 4 months of endocrine neoadjuvant therapy (LH-RH agonist) was compared in each prostatic intraglandular zone with the T2 weighted image. The total prostatic reduction rate was 43.2%. The reduction rate in the peripheral zone (64.8%) was more than two-fold that (29.7%) in the central gland (transition zone + central zone). The endorectal MRI may greatly contribute to the local staging of prostatic cancer, especially to the diagnosis of seminal vesicular invasion.